Hi
I'm new to this forum, so there may a post about this already, that I have not come across. This is the first Radio I have attempted to restore. Photocopier Tech by trade, so have electronics background, but no audio experience
I have an Electrohome console radio. Schematic says 1940 on it. My problem is the electro dynamic speaker is no good. Ohmeter test shows open, and upon further inspection, I can see the wiring on the coil of the speaker is broken (Rusted through) in several places. Thus I have no B+ (I think). Have replaced all caps, and performed meter checks on the chassis. Tubes light up etc. About 350 volts goes to the speaker, but stops there. Another place I measured shows around 1000 v. That seems like a lot to me...I seen some mention of replacing ED speakers with a PM type speaker, and using a power resistor and a choke.
This does not mean much to me at this point, since I just learning as I go. (copiers don't use chokes, and I'm not even sure how to wire the choke/resistor combo into my circuit). Anybody have any advice on where I start with this? I have a schematic, if someone needs to check it out. Thanks, and I look forward to hearing from you:)

:Hi
:I'm new to this forum, so there may a post about this already, that I have not come across. This is the first Radio I have attempted to restore. Photocopier Tech by trade, so have electronics background, but no audio experience
:I have an Electrohome console radio. Schematic says 1940 on it. My problem is the electro dynamic speaker is no good. Ohmeter test shows open, and upon further inspection, I can see the wiring on the coil of the speaker is broken (Rusted through) in several places. Thus I have no B+ (I think). Have replaced all caps, and performed meter checks on the chassis. Tubes light up etc. About 350 volts goes to the speaker, but stops there. Another place I measured shows around 1000 v. That seems like a lot to me...I seen some mention of replacing ED speakers with a PM type speaker, and using a power resistor and a choke.
:This does not mean much to me at this point, since I just learning as I go. (copiers don't use chokes, and I'm not even sure how to wire the choke/resistor combo into my circuit). Anybody have any advice on where I start with this? I have a schematic, if someone needs to check it out. Thanks, and I look forward to hearing from you:)
:
= = = = =

If you can post a model number, that would be very helpful.

Generally what you will need to know in order to replace your ED speaker with a PM one is the impedance of the original speaker's field coil. This varies from set maker to set maker but is usually in the range from 500 ohms to 2K ohms. You will also need to figure out the B+ current draw so that you can select the correct wattage for a dropping resistor to replace the field coil. (The resistor would electrically take the place of the field coil in the circuit.) A series inductor (choke) is really optional but may reduce the amount of background hum in the set. Recommend that you try the resistor alone, then decide if you need the inductor for additional DC smoothing.

Another consideration is the secondary impedance of the output transformer. Most modern PM speakers are 8 ohms but there are other values available, also (4 ohms, 16 ohms, etc.) Radio makers prior to the 1950's didn't use a standard voice coil impedance so you will find that various sets have "proprietary" impedances like 2.3 ohms, and so forth. It usually isn't a problem to drive a higher-impedance speaker with a low-impedance-output transformer, but it's possible that some loss of sound volume will be noted, with this getting more noticeable as the mismatch ratio increases.

Not sure what to make of the 1000 V reading. This is above any voltage that should be present in a tube radio. I suppose that you could get close to 900 VAC if you measured across the ends of a center-tapped B+ secondary, but even that is an extreme case. Most transformer sets had B+ in the sub-425 VDC range measured at the cathode of the rectifier tube. This usually was knocked back to ~325 VDC after the field coil, with around 100V being dropped in the speaker field. This of course varied quite a bit from set to set.

::Hi
::I'm new to this forum, so there may a post about this already, that I have not come across. This is the first Radio I have attempted to restore. Photocopier Tech by trade, so have electronics background, but no audio experience
::I have an Electrohome console radio. Schematic says 1940 on it. My problem is the electro dynamic speaker is no good. Ohmeter test shows open, and upon further inspection, I can see the wiring on the coil of the speaker is broken (Rusted through) in several places. Thus I have no B+ (I think). Have replaced all caps, and performed meter checks on the chassis. Tubes light up etc. About 350 volts goes to the speaker, but stops there. Another place I measured shows around 1000 v. That seems like a lot to me...I seen some mention of replacing ED speakers with a PM type speaker, and using a power resistor and a choke.
::This does not mean much to me at this point, since I just learning as I go. (copiers don't use chokes, and I'm not even sure how to wire the choke/resistor combo into my circuit). Anybody have any advice on where I start with this? I have a schematic, if someone needs to check it out. Thanks, and I look forward to hearing from you:)
::
:= = = = =
:
:If you can post a model number, that would be very helpful.
:
:Generally what you will need to know in order to replace your ED speaker with a PM one is the impedance of the original speaker's field coil. This varies from set maker to set maker but is usually in the range from 500 ohms to 2K ohms. You will also need to figure out the B+ current draw so that you can select the correct wattage for a dropping resistor to replace the field coil. (The resistor would electrically take the place of the field coil in the circuit.) A series inductor (choke) is really optional but may reduce the amount of background hum in the set. Recommend that you try the resistor alone, then decide if you need the inductor for additional DC smoothing.
:
:Another consideration is the secondary impedance of the output transformer. Most modern PM speakers are 8 ohms but there are other values available, also (4 ohms, 16 ohms, etc.) Radio makers prior to the 1950's didn't use a standard voice coil impedance so you will find that various sets have "proprietary" impedances like 2.3 ohms, and so forth. It usually isn't a problem to drive a higher-impedance speaker with a low-impedance-output transformer, but it's possible that some loss of sound volume will be noted, with this getting more noticeable as the mismatch ratio increases.
:
:
:Not sure what to make of the 1000 V reading. This is above any voltage that should be present in a tube radio. I suppose that you could get close to 900 VAC if you measured across the ends of a center-tapped B+ secondary, but even that is an extreme case. Most transformer sets had B+ in the sub-425 VDC range measured at the cathode of the rectifier tube. This usually was knocked back to ~325 VDC after the field coil, with around 100V being dropped in the speaker field. This of course varied quite a bit from set to set.
:
:
:
Thanks Tom

Yeah, forgot to give the model number, that would help:) Schematic says its a "Dominion Electrohome Industries" model 9A62-E-4. On the diagram it shows 1800 ohms across one of the coils on the speaker (L3).
The 1048 vac is from one of the tubes 5Y4-G pin (F) going to the speaker brown/black wire. If you need/ want to see a the schematic I could email or post it here somehow.Hope this is helpful. thanks for your input. Kinda over my head, but I am learning...

:::Hi
:::I'm new to this forum, so there may a post about this already, that I have not come across. This is the first Radio I have attempted to restore. Photocopier Tech by trade, so have electronics background, but no audio experience
:::I have an Electrohome console radio. Schematic says 1940 on it. My problem is the electro dynamic speaker is no good. Ohmeter test shows open, and upon further inspection, I can see the wiring on the coil of the speaker is broken (Rusted through) in several places. Thus I have no B+ (I think). Have replaced all caps, and performed meter checks on the chassis. Tubes light up etc. About 350 volts goes to the speaker, but stops there. Another place I measured shows around 1000 v. That seems like a lot to me...I seen some mention of replacing ED speakers with a PM type speaker, and using a power resistor and a choke.
:::This does not mean much to me at this point, since I just learning as I go. (copiers don't use chokes, and I'm not even sure how to wire the choke/resistor combo into my circuit). Anybody have any advice on where I start with this? I have a schematic, if someone needs to check it out. Thanks, and I look forward to hearing from you:)
:::
::= = = = =
::
::If you can post a model number, that would be very helpful.
::
::Generally what you will need to know in order to replace your ED speaker with a PM one is the impedance of the original speaker's field coil. This varies from set maker to set maker but is usually in the range from 500 ohms to 2K ohms. You will also need to figure out the B+ current draw so that you can select the correct wattage for a dropping resistor to replace the field coil. (The resistor would electrically take the place of the field coil in the circuit.) A series inductor (choke) is really optional but may reduce the amount of background hum in the set. Recommend that you try the resistor alone, then decide if you need the inductor for additional DC smoothing.
::
::Another consideration is the secondary impedance of the output transformer. Most modern PM speakers are 8 ohms but there are other values available, also (4 ohms, 16 ohms, etc.) Radio makers prior to the 1950's didn't use a standard voice coil impedance so you will find that various sets have "proprietary" impedances like 2.3 ohms, and so forth. It usually isn't a problem to drive a higher-impedance speaker with a low-impedance-output transformer, but it's possible that some loss of sound volume will be noted, with this getting more noticeable as the mismatch ratio increases.
::
::
::Not sure what to make of the 1000 V reading. This is above any voltage that should be present in a tube radio. I suppose that you could get close to 900 VAC if you measured across the ends of a center-tapped B+ secondary, but even that is an extreme case. Most transformer sets had B+ in the sub-425 VDC range measured at the cathode of the rectifier tube. This usually was knocked back to ~325 VDC after the field coil, with around 100V being dropped in the speaker field. This of course varied quite a bit from set to set.
::
::
::
:Thanks Tom
:
:Yeah, forgot to give the model number, that would help:) Schematic says its a "Dominion Electrohome Industries" model 9A62-E-4. On the diagram it shows 1800 ohms across one of the coils on the speaker (L3).
:The 1048 vac is from one of the tubes 5Y4-G pin (F) going to the speaker brown/black wire. If you need/ want to see a the schematic I could email or post it here somehow.Hope this is helpful. thanks for your input. Kinda over my head, but I am learning...
:
Hi Bruce, its too bad that its the field coil that is gone, the best way to go with a pm is to retain the feild coil as it acts as a choke, you willl need to retain the output transformer and if it is mounted on Your speaker that would be a good place to put it.If You do a bit of searching You should be able to find a choke that would be the best results, the resistor trick works but I did not get good results, was left with a hum that I could not get rid of.

:Hi Bruce, its too bad that its the field coil that is gone, the best way to go with a pm is to retain the feild coil as it acts as a choke, you willl need to retain the output transformer and if it is mounted on Your speaker that would be a good place to put it.If You do a bit of searching You should be able to find a choke that would be the best results, the resistor trick works but I did not get good results, was left with a hum that I could not get rid of.

= = = = = = =

Yes, the field coil usually did "double duty" as an inductive-reactor filter element in the set's B+ power supply... later sets (post-WW2) which used permag speakers tended to have filter chokes in the pricier sets and dropping resistors in the budget range models- the latter achieved adequate smoothing by using relatively large capacitors (40-50 uf or so) in the post-rectifier filter network. ED-speaker sets got by with filter caps on the order of 8 to 16 uF.

Another trick that many radio manufacturers used in their ED speakers was to include a "hum bucking" winding on the voice coil bobbin. This was wired to oppose the current fluctuations coming from the power supply, and worked quite well to neutralize their effect on the speaker output. PM speakers did not have this feature so other means of achieving better DC smoothing were needed (generally, this meant bigger electrolytic caps).

I am surprised to hear that the resistor substitution for the field coil has resulted in hum. I did it a while back with a Zenith 5S127 and an Air Castle, without a trace of hum in either case.
This must depend on the radio.
On these, I mounted the resistor with the speaker, well away from the high impedance second detector circuits.

Best Regards,

Bill Grimm

::Hi Bruce, its too bad that its the field coil that is gone, the best way to go with a pm is to retain the feild coil as it acts as a choke, you willl need to retain the output transformer and if it is mounted on Your speaker that would be a good place to put it.If You do a bit of searching You should be able to find a choke that would be the best results, the resistor trick works but I did not get good results, was left with a hum that I could not get rid of.
:
:= = = = = = =
:
:Yes, the field coil usually did "double duty" as an inductive-reactor filter element in the set's B+ power supply... later sets (post-WW2) which used permag speakers tended to have filter chokes in the pricier sets and dropping resistors in the budget range models- the latter achieved adequate smoothing by using relatively large capacitors (40-50 uf or so) in the post-rectifier filter network. ED-speaker sets got by with filter caps on the order of 8 to 16 uF.
:
:Another trick that many radio manufacturers used in their ED speakers was to include a "hum bucking" winding on the voice coil bobbin. This was wired to oppose the current fluctuations coming from the power supply, and worked quite well to neutralize their effect on the speaker output. PM speakers did not have this feature so other means of achieving better DC smoothing were needed (generally, this meant bigger electrolytic caps).
:

:::Hi Bruce, its too bad that its the field coil that is gone, the best way to go with a pm is to retain the feild coil as it acts as a choke, you willl need to retain the output transformer and if it is mounted on Your speaker that would be a good place to put it.If You do a bit of searching You should be able to find a choke that would be the best results, the resistor trick works but I did not get good results, was left with a hum that I could not get rid of.
::
::= = = = = = =
::
::Yes, the field coil usually did "double duty" as an inductive-reactor filter element in the set's B+ power supply... later sets (post-WW2) which used permag speakers tended to have filter chokes in the pricier sets and dropping resistors in the budget range models- the latter achieved adequate smoothing by using relatively large capacitors (40-50 uf or so) in the post-rectifier filter network. ED-speaker sets got by with filter caps on the order of 8 to 16 uF.
::
::Another trick that many radio manufacturers used in their ED speakers was to include a "hum bucking" winding on the voice coil bobbin. This was wired to oppose the current fluctuations coming from the power supply, and worked quite well to neutralize their effect on the speaker output. PM speakers did not have this feature so other means of achieving better DC smoothing were needed (generally, this meant bigger electrolytic caps).
::
:Thanks All

The output transformer is inside the chassis.Labelled as T7. I looked at the schematic again, and in the section that shows the speaker connector it has L2, L3 and L4. Parts list says L2 is the bucking coil you mentioned. L3 is indeed the field coil and L4 is the voice coil.L2 and L4 are in series, and I measure about 2 ohms across them. Does that sound about right?So, I should get a power resistor around 1800 ohms to replace L3? I see people mention a 10-15 watt power resistor should be used. Keep in mind, I seem to have 1048 vac feeding into it. Am I going to set myself on fire?:)Schematic shows I should have around +200v after the L3 substitute resistor. My safety is a concern of my wife.:)
:

Just some advice on repairing these old sets. You should definitely be using a VariAC when working on any old radio, either AC or AC/DC type. The Variac will allow you to start up the radio gradually, so you can monitor AC & B+ voltages and stop before they get too high or take a component out.
AFA your radio, that 1000v seems way out of line. This is not an area to be fooling with, if you're not sure what you are doing. You must understand exactly what you are doing in a circuit of this voltage, or the results could wreck the radio or you.
Sorry for the lecture, but I thought it may be helpful for your safety (and your wife's nerves...)

The output transformer is inside the chassis.Labelled as T7. I looked at the schematic again, and in the section that shows the speaker connector it has L2, L3 and L4. Parts list says L2 is the bucking coil you mentioned. L3 is indeed the field coil and L4 is the voice coil.L2 and L4 are in series, and I measure about 2 ohms across them. Does that sound about right?So, I should get a power resistor around 1800 ohms to replace L3? I see people mention a 10-15 watt power resistor should be used. Keep in mind, I seem to have 1048 vac feeding into it. Am I going to set myself on fire?:)Schematic shows I should have around +200v after the L3 substitute resistor. My safety is a concern of my wife.:)

= = = = = =

2 ohms for the bucking coil/voice coil is typical for this vintage of set.

The power resistor that will replace the field coil will electrically install in place of L3 in the schematic. L2 will disappear as there will be no L2 in the PM speaker that you install. 2000 ohms is a good starting point for the power resistor value (2 K ohms or even 2.2 K will probably be easier to find than 1800).

To calculate its power rating, square the current through it and multiply by its ohmic value. For example, suppose that you have 90 mA current. Power dissipated by the resistor will be (0.09)(0.09)(2000)=16.7 watts. Derate by 70% for safety and you wind up with a 25 watt resistor. (Your resistor power rating is dependent upon actual B+ current draw. You may need to experiment with a "test" resistor in order to determine what ballpark your current draw is in before you settle on a final value, since you probably have no idea what the set B+ current draw actually is.)

Another way to calculate power is to take the schematic values on faith. If you are supposed to have 200 VDC after the 1800 ohm field coil, and you measure 325 going into it, that means that you need to drop 125 V in the coil. This is a pretty typical value. By Ohm's Law, that means that B+ current is 125/1800=0.70 mA. Running the numbers with that current and a 2K resistor, we have a 70%-derated power value of 14 watts. So a 15 watt resistor should
be fine.

Forget about the 1048 VAC. That is a red herring. All you care about is the voltage from the cathode of the rectifier tube to ground. This will be 325 VDC as you noted in your original posting. That voltage at the current level this radio or any similar radio is capable of generating is more than needed to be lethal- but it's like cleaning a pistol: follow a few simple rules and you'll be fine. The cardinal rule is: Never use both hands to take what could be a HV measurement (put one hand behind your back). This will prevent current flow through your heart which can be fatal if it happens. (Current flow through your fingers to your elbow will give you a nasty jolt but won't kill you outright.)

BTW- what your wife is really telling you is, "You need more life insurance." Bump up your premium to get a few million $ payout in the event of your demise and she'll come to accept your new hobby. :<)

... By Ohm's Law, that means that B+ current is 125/1800=0.70 mA....

Yeah, slipped a couple of decimal points on that number- should be 70 mA, or 0.070 amps. It's Sunday morning...

:... By Ohm's Law, that means that B+ current is 125/1800=0.70 mA....
:
:Yeah, slipped a couple of decimal points on that number- should be 70 mA, or 0.070 amps. It's Sunday morning...
:

The electrolytic capacitors of today are so much smaller, better and cheaper than those of yesterday that you can get by just fin with eliminating the choke and increasing the capacitor values. Of course, if you can find a choke on Ebay or someplace, you will be better off, but I wouldn't go to a whole lot of trouble to find one. If you are going to keep the radio for personal use, you can put a resistor in and look for a choke later. If I had the radio working to suit me and found a choke, I would probably say its too much trouble and forget about it.
Lewis
PS, my brain doesn't work right on any morning of a day that ends in "Y", not just Sunday.
LL

:The output transformer is inside the chassis.Labelled as T7. I looked at the schematic again, and in the section that shows the speaker connector it has L2, L3 and L4. Parts list says L2 is the bucking coil you mentioned. L3 is indeed the field coil and L4 is the voice coil.L2 and L4 are in series, and I measure about 2 ohms across them. Does that sound about right?So, I should get a power resistor around 1800 ohms to replace L3? I see people mention a 10-15 watt power resistor should be used. Keep in mind, I seem to have 1048 vac feeding into it. Am I going to set myself on fire?:)Schematic shows I should have around +200v after the L3 substitute resistor. My safety is a concern of my wife.:)
:
:= = = = = =
:
:2 ohms for the bucking coil/voice coil is typical for this vintage of set.
:
:The power resistor that will replace the field coil will electrically install in place of L3 in the schematic. L2 will disappear as there will be no L2 in the PM speaker that you install. 2000 ohms is a good starting point for the power resistor value (2 K ohms or even 2.2 K will probably be easier to find than 1800).
:
:To calculate its power rating, square the current through it and multiply by its ohmic value. For example, suppose that you have 90 mA current. Power dissipated by the resistor will be (0.09)(0.09)(2000)=16.7 watts. Derate by 70% for safety and you wind up with a 25 watt resistor. (Your resistor power rating is dependent upon actual B+ current draw. You may need to experiment with a "test" resistor in order to determine what ballpark your current draw is in before you settle on a final value, since you probably have no idea what the set B+ current draw actually is.)
:
:Another way to calculate power is to take the schematic values on faith. If you are supposed to have 200 VDC after the 1800 ohm field coil, and you measure 325 going into it, that means that you need to drop 125 V in the coil. This is a pretty typical value. By Ohm's Law, that means that B+ current is 125/1800=0.70 mA. Running the numbers with that current and a 2K resistor, we have a 70%-derated power value of 14 watts. So a 15 watt resistor should
:be fine.
:
:Forget about the 1048 VAC. That is a red herring. All you care about is the voltage from the cathode of the rectifier tube to ground. This will be 325 VDC as you noted in your original posting. That voltage at the current level this radio or any similar radio is capable of generating is more than needed to be lethal- but it's like cleaning a pistol: follow a few simple rules and you'll be fine. The cardinal rule is: Never use both hands to take what could be a HV measurement (put one hand behind your back). This will prevent current flow through your heart which can be fatal if it happens. (Current flow through your fingers to your elbow will give you a nasty jolt but won't kill you outright.)
:
:BTW- what your wife is really telling you is, "You need more life insurance." Bump up your premium to get a few million $ payout in the event of your demise and she'll come to accept your new hobby. :<)
:
Thanks Tom and Brian for your helpful advice and concern for my welfare:) I'll see if I can locate a 2k-2.2k 15w resistor locally. The filter cap you mentioned earlier appears to be 20mfd 400v on my set. You suggest to increase? or wait to see how the resistor pans out? Also mentioned was the different speaker ratings 4 ohm, 8 ohm etc. What do people generally use for a replacement speaker? something from a car radio? I understand these sets do not put out a high wattage. I may try to tuck the smaller PM speaker"inside" the large OEM speaker for cosmetics.

:Thanks Tom and Brian for your helpful advice and concern for my welfare:) I'll see if I can locate a 2k-2.2k 15w resistor locally. The filter cap you mentioned earlier appears to be 20mfd 400v on my set. You suggest to increase? or wait to see how the resistor pans out? Also mentioned was the different speaker ratings 4 ohm, 8 ohm etc. What do people generally use for a replacement speaker? something from a car radio? I understand these sets do not put out a high wattage. I may try to tuck the smaller PM speaker"inside" the large OEM speaker for cosmetics.
:
= = = = = = = =

Since you will be replacing all of the electrolytic caps anyway, you can bump up the value of the one "downstream" of the dropping resistor to 40 uF with no ill effects. At 70 mA current draw this won't result in an unacceptable rise in B+ voltage but will give smoother DC (and therefore less hum).
These caps sell in the $3-4 dollar range.

You should be able to find an exact-size diameter replacement PM speaker. Replacing a larger-diameter speaker with a smaller one generally gives disappointing results. However, if necessary you can make an "adapter" out of thin plywood.

Impedance is a lesser consideration; even with a 2 ohm output transformer impedance, an 8 ohm speaker will work OK, but to couple maximum power into the speaker the closer you can get to 2 ohms, the better.
Because human hearing is logarithmic, not linear, this mismatch in practice doesn't make as big a difference as it seems it should on paper.

::Thanks Tom and Brian for your helpful advice and concern for my welfare:) I'll see if I can locate a 2k-2.2k 15w resistor locally. The filter cap you mentioned earlier appears to be 20mfd 400v on my set. You suggest to increase? or wait to see how the resistor pans out? Also mentioned was the different speaker ratings 4 ohm, 8 ohm etc. What do people generally use for a replacement speaker? something from a car radio? I understand these sets do not put out a high wattage. I may try to tuck the smaller PM speaker"inside" the large OEM speaker for cosmetics.
::
:= = = = = = = =
:
:Since you will be replacing all of the electrolytic caps anyway, you can bump up the value of the one "downstream" of the dropping resistor to 40 uF with no ill effects. At 70 mA current draw this won't result in an unacceptable rise in B+ voltage but will give smoother DC (and therefore less hum).
:These caps sell in the $3-4 dollar range.
:
:You should be able to find an exact-size diameter replacement PM speaker. Replacing a larger-diameter speaker with a smaller one generally gives disappointing results. However, if necessary you can make an "adapter" out of thin plywood.
:
:Impedance is a lesser consideration; even with a 2 ohm output transformer impedance, an 8 ohm speaker will work OK, but to couple maximum power into the speaker the closer you can get to 2 ohms, the better.
:Because human hearing is logarithmic, not linear, this mismatch in practice doesn't make as big a difference as it seems it should on paper.

I couldn't find the 2 Ohms reading for the output transformer, but if it is DC, then the AC impedance should be closer to 8. If true, a 4 or 8 should work equally well for a radio that plays at room volume. About mounting a speaker inside the original, you would have to put a piece of plywood under the original, and cut a hole to mount the smaller one, for unless the speaker is mounted on something, the air pushed out of the front will just run around the side of the speaker and fill in the vacuum at the back, and vice versa, giving a drastic reduction of bass response. As for the thousand Volts AC, you are only using half of the transformer secondary at a time, so that lowers you to 500 Volts, and various losses, starting with the rectifier tube itself, will lower the Voltage to reasonable values. I the edge of my hand once met the entire winding of such a transformer on the socket of a rectifier tube, I remember it well forty years later. Two bloody holes in my hand with smoke coming out of them. Nor recommended in the slightest.
Lewis
:

:::Thanks Tom and Brian for your helpful advice and concern for my welfare:) I'll see if I can locate a 2k-2.2k 15w resistor locally. The filter cap you mentioned earlier appears to be 20mfd 400v on my set. You suggest to increase? or wait to see how the resistor pans out? Also mentioned was the different speaker ratings 4 ohm, 8 ohm etc. What do people generally use for a replacement speaker? something from a car radio? I understand these sets do not put out a high wattage. I may try to tuck the smaller PM speaker"inside" the large OEM speaker for cosmetics.
:::
::= = = = = = = =
::
::Since you will be replacing all of the electrolytic caps anyway, you can bump up the value of the one "downstream" of the dropping resistor to 40 uF with no ill effects. At 70 mA current draw this won't result in an unacceptable rise in B+ voltage but will give smoother DC (and therefore less hum).
::These caps sell in the $3-4 dollar range.
::
::You should be able to find an exact-size diameter replacement PM speaker. Replacing a larger-diameter speaker with a smaller one generally gives disappointing results. However, if necessary you can make an "adapter" out of thin plywood.
::
::Impedance is a lesser consideration; even with a 2 ohm output transformer impedance, an 8 ohm speaker will work OK, but to couple maximum power into the speaker the closer you can get to 2 ohms, the better.
::Because human hearing is logarithmic, not linear, this mismatch in practice doesn't make as big a difference as it seems it should on paper.
:
:
:
:I couldn't find the 2 Ohms reading for the output transformer, but if it is DC, then the AC impedance should be closer to 8. If true, a 4 or 8 should work equally well for a radio that plays at room volume. About mounting a speaker inside the original, you would have to put a piece of plywood under the original, and cut a hole to mount the smaller one, for unless the speaker is mounted on something, the air pushed out of the front will just run around the side of the speaker and fill in the vacuum at the back, and vice versa, giving a drastic reduction of bass response. As for the thousand Volts AC, you are only using half of the transformer secondary at a time, so that lowers you to 500 Volts, and various losses, starting with the rectifier tube itself, will lower the Voltage to reasonable values. I the edge of my hand once met the entire winding of such a transformer on the socket of a rectifier tube, I remember it well forty years later. Two bloody holes in my hand with smoke coming out of them. Nor recommended in the slightest.
:Lewis
::
:Thanks guys, I will pick up a 40uf cap at the same time as the resistor then. I'll see what I can scare up for a OEM sized speaker. Radio will be for personal use and room volume will be fine. Feel better about Lewis's 1048 vac theory, and his cautionary tale is enough to keep me on my toes. I'll be extra careful now:)Thanks again everyone for the quick responses.
:

::::Thanks Tom and Brian for your helpful advice and concern for my welfare:) I'll see if I can locate a 2k-2.2k 15w resistor locally. The filter cap you mentioned earlier appears to be 20mfd 400v on my set. You suggest to increase? or wait to see how the resistor pans out? Also mentioned was the different speaker ratings 4 ohm, 8 ohm etc. What do people generally use for a replacement speaker? something from a car radio? I understand these sets do not put out a high wattage. I may try to tuck the smaller PM speaker"inside" the large OEM speaker for cosmetics.
::::
:::= = = = = = = =
:::
:::Since you will be replacing all of the electrolytic caps anyway, you can bump up the value of the one "downstream" of the dropping resistor to 40 uF with no ill effects. At 70 mA current draw this won't result in an unacceptable rise in B+ voltage but will give smoother DC (and therefore less hum).
:::These caps sell in the $3-4 dollar range.
:::
:::You should be able to find an exact-size diameter replacement PM speaker. Replacing a larger-diameter speaker with a smaller one generally gives disappointing results. However, if necessary you can make an "adapter" out of thin plywood.
:::
:::Impedance is a lesser consideration; even with a 2 ohm output transformer impedance, an 8 ohm speaker will work OK, but to couple maximum power into the speaker the closer you can get to 2 ohms, the better.
:::Because human hearing is logarithmic, not linear, this mismatch in practice doesn't make as big a difference as it seems it should on paper.
::
::
::
::I couldn't find the 2 Ohms reading for the output transformer, but if it is DC, then the AC impedance should be closer to 8. If true, a 4 or 8 should work equally well for a radio that plays at room volume. About mounting a speaker inside the original, you would have to put a piece of plywood under the original, and cut a hole to mount the smaller one, for unless the speaker is mounted on something, the air pushed out of the front will just run around the side of the speaker and fill in the vacuum at the back, and vice versa, giving a drastic reduction of bass response. As for the thousand Volts AC, you are only using half of the transformer secondary at a time, so that lowers you to 500 Volts, and various losses, starting with the rectifier tube itself, will lower the Voltage to reasonable values. I the edge of my hand once met the entire winding of such a transformer on the socket of a rectifier tube, I remember it well forty years later. Two bloody holes in my hand with smoke coming out of them. Nor recommended in the slightest.
::Lewis
:::
::Thanks guys, I will pick up a 40uf cap at the same time as the resistor then. I'll see what I can scare up for a OEM sized speaker. Radio will be for personal use and room volume will be fine. Feel better about Lewis's 1048 vac theory, and his cautionary tale is enough to keep me on my toes. I'll be extra careful now:)Thanks again everyone for the quick responses.
::
I guess using a resistor is cheaper that a choke coil, the radio I had tried this on was a Philco pt42-7 and it was an oval speaker, and I had mounted the resistor under the chassis, so that could be the difference, the cone was damaged beyond repair and was happy I hadn't trown it out yet, when the resistor did not work well, I harvested the field coil drilled the core out and mounted it on the basket of the pm speaker, and voila, good and nice sound.

:::::Thanks Tom and Brian for your helpful advice and concern for my welfare:) I'll see if I can locate a 2k-2.2k 15w resistor locally. The filter cap you mentioned earlier appears to be 20mfd 400v on my set. You suggest to increase? or wait to see how the resistor pans out? Also mentioned was the different speaker ratings 4 ohm, 8 ohm etc. What do people generally use for a replacement speaker? something from a car radio? I understand these sets do not put out a high wattage. I may try to tuck the smaller PM speaker"inside" the large OEM speaker for cosmetics.
:::::
::::= = = = = = = =
::::
::::Since you will be replacing all of the electrolytic caps anyway, you can bump up the value of the one "downstream" of the dropping resistor to 40 uF with no ill effects. At 70 mA current draw this won't result in an unacceptable rise in B+ voltage but will give smoother DC (and therefore less hum).
::::These caps sell in the $3-4 dollar range.
::::
::::You should be able to find an exact-size diameter replacement PM speaker. Replacing a larger-diameter speaker with a smaller one generally gives disappointing results. However, if necessary you can make an "adapter" out of thin plywood.
::::
::::Impedance is a lesser consideration; even with a 2 ohm output transformer impedance, an 8 ohm speaker will work OK, but to couple maximum power into the speaker the closer you can get to 2 ohms, the better.
::::Because human hearing is logarithmic, not linear, this mismatch in practice doesn't make as big a difference as it seems it should on paper.
:::
:::
:::
:::I couldn't find the 2 Ohms reading for the output transformer, but if it is DC, then the AC impedance should be closer to 8. If true, a 4 or 8 should work equally well for a radio that plays at room volume. About mounting a speaker inside the original, you would have to put a piece of plywood under the original, and cut a hole to mount the smaller one, for unless the speaker is mounted on something, the air pushed out of the front will just run around the side of the speaker and fill in the vacuum at the back, and vice versa, giving a drastic reduction of bass response. As for the thousand Volts AC, you are only using half of the transformer secondary at a time, so that lowers you to 500 Volts, and various losses, starting with the rectifier tube itself, will lower the Voltage to reasonable values. I the edge of my hand once met the entire winding of such a transformer on the socket of a rectifier tube, I remember it well forty years later. Two bloody holes in my hand with smoke coming out of them. Nor recommended in the slightest.
:::Lewis
::::
:::Thanks guys, I will pick up a 40uf cap at the same time as the resistor then. I'll see what I can scare up for a OEM sized speaker. Radio will be for personal use and room volume will be fine. Feel better about Lewis's 1048 vac theory, and his cautionary tale is enough to keep me on my toes. I'll be extra careful now:)Thanks again everyone for the quick responses.
:::
:I guess using a resistor is cheaper that a choke coil, the radio I had tried this on was a Philco pt42-7 and it was an oval speaker, and I had mounted the resistor under the chassis, so that could be the difference, the cone was damaged beyond repair and was happy I hadn't trown it out yet, when the resistor did not work well, I harvested the field coil drilled the core out and mounted it on the basket of the pm speaker, and voila, good and nice sound.
:

::::::Thanks Tom and Brian for your helpful advice and concern for my welfare:) I'll see if I can locate a 2k-2.2k 15w resistor locally. The filter cap you mentioned earlier appears to be 20mfd 400v on my set. You suggest to increase? or wait to see how the resistor pans out? Also mentioned was the different speaker ratings 4 ohm, 8 ohm etc. What do people generally use for a replacement speaker? something from a car radio? I understand these sets do not put out a high wattage. I may try to tuck the smaller PM speaker"inside" the large OEM speaker for cosmetics.
::::::
:::::= = = = = = = =
:::::
:::::Since you will be replacing all of the electrolytic caps anyway, you can bump up the value of the one "downstream" of the dropping resistor to 40 uF with no ill effects. At 70 mA current draw this won't result in an unacceptable rise in B+ voltage but will give smoother DC (and therefore less hum).
:::::These caps sell in the $3-4 dollar range.
:::::
:::::You should be able to find an exact-size diameter replacement PM speaker. Replacing a larger-diameter speaker with a smaller one generally gives disappointing results. However, if necessary you can make an "adapter" out of thin plywood.
:::::
:::::Impedance is a lesser consideration; even with a 2 ohm output transformer impedance, an 8 ohm speaker will work OK, but to couple maximum power into the speaker the closer you can get to 2 ohms, the better.
:::::Because human hearing is logarithmic, not linear, this mismatch in practice doesn't make as big a difference as it seems it should on paper.
::::
::::
::::
::::I couldn't find the 2 Ohms reading for the output transformer, but if it is DC, then the AC impedance should be closer to 8. If true, a 4 or 8 should work equally well for a radio that plays at room volume. About mounting a speaker inside the original, you would have to put a piece of plywood under the original, and cut a hole to mount the smaller one, for unless the speaker is mounted on something, the air pushed out of the front will just run around the side of the speaker and fill in the vacuum at the back, and vice versa, giving a drastic reduction of bass response. As for the thousand Volts AC, you are only using half of the transformer secondary at a time, so that lowers you to 500 Volts, and various losses, starting with the rectifier tube itself, will lower the Voltage to reasonable values. I the edge of my hand once met the entire winding of such a transformer on the socket of a rectifier tube, I remember it well forty years later. Two bloody holes in my hand with smoke coming out of them. Nor recommended in the slightest.
::::Lewis
:::::
::::Thanks guys, I will pick up a 40uf cap at the same time as the resistor then. I'll see what I can scare up for a OEM sized speaker. Radio will be for personal use and room volume will be fine. Feel better about Lewis's 1048 vac theory, and his cautionary tale is enough to keep me on my toes. I'll be extra careful now:)Thanks again everyone for the quick responses.
::::
::I guess using a resistor is cheaper that a choke coil, the radio I had tried this on was a Philco pt42-7 and it was an oval speaker, and I had mounted the resistor under the chassis, so that could be the difference, the cone was damaged beyond repair and was happy I hadn't trown it out yet, when the resistor did not work well, I harvested the field coil drilled the core out and mounted it on the basket of the pm speaker, and voila, good and nice sound.
::
:Hi All

I'm back. I was pleased to find my local electronics supplier had a 1.8k 15w resistor in stock. I am displeased that I'm not listening to music yet:)
I installed the resistor as suggested to replace the faulty Electro Mag Speaker, and connected a temporary smaller diameter PM speaker for testing purposes. I do get static here and there as I try to tune in stations, but nothing that that even vaguely sounds like voice or music. I am going to GOOGLE my problem to see if I can find what commonly is the fault behind this. If any of you fellas have suggestions, I'm open...
Hope to hear from you and my radio soon:)
Bruce
:

::Hi All
:
:I'm back. I was pleased to find my local electronics supplier had a 1.8k 15w resistor in stock. I am displeased that I'm not listening to music yet:)
:I installed the resistor as suggested to replace the faulty Electro Mag Speaker, and connected a temporary smaller diameter PM speaker for testing purposes. I do get static here and there as I try to tune in stations, but nothing that that even vaguely sounds like voice or music. I am going to GOOGLE my problem to see if I can find what commonly is the fault behind this. If any of you fellas have suggestions, I'm open...
:Hope to hear from you and my radio soon:)
:Bruce
::
:
:
= = = = = =

I presume that you have tested the tubes or have "known good" ones installed, and have a decent antenna or signal generator hooked up to the set. If there is a bandswitch, is it set on the BC band? (some of the older bands are pretty empty these days). From there, I'd check the B+ on all the tube plates. Missing B+ on a plate generally means a coil winding has opened up, or a dropping resistor has failed open. If all that's OK, chances are that you have a coupling cap that has opened up in the audio stage and is not conducting audio AC to the first or second amp grid.

:::Hi All
::
::I'm back. I was pleased to find my local electronics supplier had a 1.8k 15w resistor in stock. I am displeased that I'm not listening to music yet:)
::I installed the resistor as suggested to replace the faulty Electro Mag Speaker, and connected a temporary smaller diameter PM speaker for testing purposes. I do get static here and there as I try to tune in stations, but nothing that that even vaguely sounds like voice or music. I am going to GOOGLE my problem to see if I can find what commonly is the fault behind this. If any of you fellas have suggestions, I'm open...
::Hope to hear from you and my radio soon:)
::Bruce
:::
::
::
:= = = = = =
:
:I presume that you have tested the tubes or have "known good" ones installed, and have a decent antenna or signal generator hooked up to the set. If there is a bandswitch, is it set on the BC band? (some of the older bands are pretty empty these days). From there, I'd check the B+ on all the tube plates. Missing B+ on a plate generally means a coil winding has opened up, or a dropping resistor has failed open. If all that's OK, chances are that you have a coupling cap that has opened up in the audio stage and is not conducting audio AC to the first or second amp grid.
:
Hi Tom
I checked all the plate voltages as suggested. They all have readings, but vary. Some have close to my B+ of 232vdc, one reads 214v and another 108v. I forgot to mention in my last post that my 1000+ volts is not and issue anymore, as I'm getting around 234Vdc, where schematic indicates I should be reading 200vdc. So I figured that was in the range. All new caps. My radio does have a band selector, labelled "P" , "L", and "S". I'm guessing "P" is for my phono jack, and "L" is what I should be searching on. Correct me if I'm wrong. I'm using the OEM antenna, a big wire screen that covered up the bottom half of the back of the radio. All tubes lite up but I'm not 100% sure of anything:)
Don't think I picked the easiest radio to begin my new hobby with. Not a real confidence builder at this point:) My schematic and parts list show a "C" bias cell. what is that? what does it look like? also noticed an extra resistor on the radio that is not listed nor in the schematic. Looks newer than the Barbell shaped ones. Possibly a mod? I'll have to look into that a little closer...

:Hi Tom
:I checked all the plate voltages as suggested. They all have readings, but vary. Some have close to my B+ of 232vdc, one reads 214v and another 108v. I forgot to mention in my last post that my 1000+ volts is not and issue anymore, as I'm getting around 234Vdc, where schematic indicates I should be reading 200vdc. So I figured that was in the range. All new caps. My radio does have a band selector, labelled "P" , "L", and "S". I'm guessing "P" is for my phono jack, and "L" is what I should be searching on. Correct me if I'm wrong. I'm using the OEM antenna, a big wire screen that covered up the bottom half of the back of the radio. All tubes lite up but I'm not 100% sure of anything:)
:Don't think I picked the easiest radio to begin my new hobby with. Not a real confidence builder at this point:) My schematic and parts list show a "C" bias cell. what is that? what does it look like? also noticed an extra resistor on the radio that is not listed nor in the schematic. Looks newer than the Barbell shaped ones. Possibly a mod? I'll have to look into that a little closer...
:
= = = = = = =

Voltage on each plate is a good sign. It's reasonable for the values to differ somewhat. If a tube stage is working and drawing current, the voltage measured at the plate will be somewhat less than B+ measured at the last filter cap.

I think that your set is Canadian so they probably used different control nomenclature than USA sets.
This is where alignment instructions come in handy- the procedure can help decipher what the markings are on the bandswitch knob.

If you don't have a schematic for the set already, now is probably a good time to get one. You are going to have to dig into each stage and find out where the signal is getting dumped.

The bias cell is a small drycell battery that is used to apply a slight (1.5 v) negative bias to a tube. It is a small metal "top hat"-looking item usually installed in a clip holder for easy replacement. These haven't been made for decades, but you can replace it with a standard 1.5 V alkaline AAA cell in a Radio Shack single-cell holder. Current draw is infinitesimal so the battery will last a LONG time.

::Hi Tom
::I checked all the plate voltages as suggested. They all have readings, but vary. Some have close to my B+ of 232vdc, one reads 214v and another 108v. I forgot to mention in my last post that my 1000+ volts is not and issue anymore, as I'm getting around 234Vdc, where schematic indicates I should be reading 200vdc. So I figured that was in the range. All new caps. My radio does have a band selector, labelled "P" , "L", and "S". I'm guessing "P" is for my phono jack, and "L" is what I should be searching on. Correct me if I'm wrong. I'm using the OEM antenna, a big wire screen that covered up the bottom half of the back of the radio. All tubes lite up but I'm not 100% sure of anything:)
::Don't think I picked the easiest radio to begin my new hobby with. Not a real confidence builder at this point:) My schematic and parts list show a "C" bias cell. what is that? what does it look like? also noticed an extra resistor on the radio that is not listed nor in the schematic. Looks newer than the Barbell shaped ones. Possibly a mod? I'll have to look into that a little closer...
::
:= = = = = = =
:
:Voltage on each plate is a good sign. It's reasonable for the values to differ somewhat. If a tube stage is working and drawing current, the voltage measured at the plate will be somewhat less than B+ measured at the last filter cap.
:
:I think that your set is Canadian so they probably used different control nomenclature than USA sets.
:This is where alignment instructions come in handy- the procedure can help decipher what the markings are on the bandswitch knob.
:
:If you don't have a schematic for the set already, now is probably a good time to get one. You are going to have to dig into each stage and find out where the signal is getting dumped.
:
:The bias cell is a small drycell battery that is used to apply a slight (1.5 v) negative bias to a tube. It is a small metal "top hat"-looking item usually installed in a clip holder for easy replacement. These haven't been made for decades, but you can replace it with a standard 1.5 V alkaline AAA cell in a Radio Shack single-cell holder. Current draw is infinitesimal so the battery will last a LONG time.
:
:
:
Bruce:
You say you get static as you tune around...maybe sounds like everything is more or less working, but you have antenna problems. At least you have a speaker working, connected to the amplifier. so you have made alot of progress....I have looked around this post, but I have not found mention of a schematic. Has anyone found one? I really need one before I can go much farther, but I think the light at the end of the tunnel is faintly visible.
Lewis

Here is the schematic:

Well that was not the best way to do that... however it is there.

:::Hi Tom
:::I checked all the plate voltages as suggested. They all have readings, but vary. Some have close to my B+ of 232vdc, one reads 214v and another 108v. I forgot to mention in my last post that my 1000+ volts is not and issue anymore, as I'm getting around 234Vdc, where schematic indicates I should be reading 200vdc. So I figured that was in the range. All new caps. My radio does have a band selector, labelled "P" , "L", and "S". I'm guessing "P" is for my phono jack, and "L" is what I should be searching on. Correct me if I'm wrong. I'm using the OEM antenna, a big wire screen that covered up the bottom half of the back of the radio. All tubes lite up but I'm not 100% sure of anything:)
:::Don't think I picked the easiest radio to begin my new hobby with. Not a real confidence builder at this point:) My schematic and parts list show a "C" bias cell. what is that? what does it look like? also noticed an extra resistor on the radio that is not listed nor in the schematic. Looks newer than the Barbell shaped ones. Possibly a mod? I'll have to look into that a little closer...
:::
::= = = = = = =
::
::Voltage on each plate is a good sign. It's reasonable for the values to differ somewhat. If a tube stage is working and drawing current, the voltage measured at the plate will be somewhat less than B+ measured at the last filter cap.
::
::I think that your set is Canadian so they probably used different control nomenclature than USA sets.
::This is where alignment instructions come in handy- the procedure can help decipher what the markings are on the bandswitch knob.
::
::If you don't have a schematic for the set already, now is probably a good time to get one. You are going to have to dig into each stage and find out where the signal is getting dumped.
::
::The bias cell is a small drycell battery that is used to apply a slight (1.5 v) negative bias to a tube. It is a small metal "top hat"-looking item usually installed in a clip holder for easy replacement. These haven't been made for decades, but you can replace it with a standard 1.5 V alkaline AAA cell in a Radio Shack single-cell holder. Current draw is infinitesimal so the battery will last a LONG time.
::
::
::
:Bruce:
:You say you get static as you tune around...maybe sounds like everything is more or less working, but you have antenna problems. At least you have a speaker working, connected to the amplifier. so you have made alot of progress....I have looked around this post, but I have not found mention of a schematic. Has anyone found one? I really need one before I can go much farther, but I think the light at the end of the tunnel is faintly visible.
:Lewis
:
Hi Guys
sorry for the delay. Life gets in the way sometimes:)
Thanks for posting the schematic, I had a copy also but didn't know how to post it here. Thanks for the encouraging words Lewis, I am starting to see the light also...
So, it definetly does not have the "top hat" Bias cell, but that may explain the extra resistor I mentioned earlier...looks like a 1 watt with green, black and silver bands. It went from "G" on 6SF5 to ground, along with a .006uf cap (which I failed to mention earlier)that went from "G" to the center lug of R8 (volume ). Do you suppose that was some sort of work around for the Bias cell. I had removed the resistor a few months ago when I first started re-capping the set, and set it aside and forgot to put it back in, because I was following the schematic only. I had taken digital pictures of the bottom side of the set, in case I did something stupid:) and noticed the missing resistor then. My reading on the resistor out of the circuit measure 9.5 megaohms... does that sound right? I assume it would be best to put the resistor back in the circuit...?

:Hi Guys
:sorry for the delay. Life gets in the way sometimes:)
:Thanks for posting the schematic, I had a copy also but didn't know how to post it here. Thanks for the encouraging words Lewis, I am starting to see the light also...
:So, it definetly does not have the "top hat" Bias cell, but that may explain the extra resistor I mentioned earlier...looks like a 1 watt with green, black and silver bands. It went from "G" on 6SF5 to ground, along with a .006uf cap (which I failed to mention earlier)that went from "G" to the center lug of R8 (volume ). Do you suppose that was some sort of work around for the Bias cell. I had removed the resistor a few months ago when I first started re-capping the set, and set it aside and forgot to put it back in, because I was following the schematic only. I had taken digital pictures of the bottom side of the set, in case I did something stupid:) and noticed the missing resistor then. My reading on the resistor out of the circuit measure 9.5 megaohms... does that sound right? I assume it would be best to put the resistor back in the circuit...?
:
= = = = = = =

There are only a couple of ways of generating a negative DC potential in a radio: a bias cell is one, and a "B+ transformer center tap resistor stack" is the other. The radio probably will work without the bias cell, but without the cell the first audio amp tube won't be on the "sweet spot" of its transfer curve so the sound quality or volume (maybe even tube life) could be compromised.

My suggestion would be to rip out the nonoriginal components and install a dry cell as described earlier in this thread. That way you can be sure that the set is operating as originally designed.

::Hi Guys
::sorry for the delay. Life gets in the way sometimes:)
::Thanks for posting the schematic, I had a copy also but didn't know how to post it here. Thanks for the encouraging words Lewis, I am starting to see the light also...
::So, it definetly does not have the "top hat" Bias cell, but that may explain the extra resistor I mentioned earlier...looks like a 1 watt with green, black and silver bands. It went from "G" on 6SF5 to ground, along with a .006uf cap (which I failed to mention earlier)that went from "G" to the center lug of R8 (volume ). Do you suppose that was some sort of work around for the Bias cell. I had removed the resistor a few months ago when I first started re-capping the set, and set it aside and forgot to put it back in, because I was following the schematic only. I had taken digital pictures of the bottom side of the set, in case I did something stupid:) and noticed the missing resistor then. My reading on the resistor out of the circuit measure 9.5 megaohms... does that sound right? I assume it would be best to put the resistor back in the circuit...?
::
:= = = = = = =
:
:There are only a couple of ways of generating a negative DC potential in a radio: a bias cell is one, and a "B+ transformer center tap resistor stack" is the other. The radio probably will work without the bias cell, but without the cell the first audio amp tube won't be on the "sweet spot" of its transfer curve so the sound quality or volume (maybe even tube life) could be compromised.
:
:My suggestion would be to rip out the nonoriginal components and install a dry cell as described earlier in this thread. That way you can be sure that the set is operating as originally designed.
:
Hi Tom
Ok, I took your advice and removed the resistor and cap that had been added, and hooked up a 1.5 AA battery and holder as suggested, so it looks more like the original schematic.....
then, just to see what would happen, I connected an MP3 player to the phono jack.....and.....:) :) :) I have music!!! and not too bad sounding either, considering I'm still only using a 2" speaker probably better suited for a walkie talkie:)
I have some "hum" when there is suppossed to be silence, like in between songs.... but we can always fine tune that later.
So I thought I'd let you all know that much anyway, so we can assume the AMP part of the radio works.
May be just something to do with the antenna or tuner? Or the fact that there is probably only one AM radio station in my area. Still would love to get the radio portion working, so today I'll drag it out of the basement and try it upstairs to see if I can get a signal. If anyone has any ideas what else it could be, please let me know. Your help and encouragement is greatly appreciated:)

:Ok, I took your advice and removed the resistor and cap that had been added, and hooked up a 1.5 AA battery and holder as suggested, so it looks more like the original schematic.....
:then, just to see what would happen, I connected an MP3 player to the phono jack.....and.....:) :) :) I have music!!! and not too bad sounding either, considering I'm still only using a 2" speaker probably better suited for a walkie talkie:)
:I have some "hum" when there is suppossed to be silence, like in between songs.... but we can always fine tune that later.
:So I thought I'd let you all know that much anyway, so we can assume the AMP part of the radio works.
:May be just something to do with the antenna or tuner? Or the fact that there is probably only one AM radio station in my area. Still would love to get the radio portion working, so today I'll drag it out of the basement and try it upstairs to see if I can get a signal. If anyone has any ideas what else it could be, please let me know. Your help and encouragement is greatly appreciated:)
:
= = = = = = = =

The background hum may be due to the loss of the filter inductive reactance that the speaker field coil originally provided as a "bonus" for its main job of creating a magnetic field. You can try a larger-capacity (say, 2X the original value) filter cap on the B+ side "downstream" of the resistor that you used to replace the field coil.

Sounds like you are in a poor radio reception area. You might try stringing a temporary antenna indoors (or, even better, outdoors if you can do so) to see if you can pick up anything at all on standard broadcast. With a good antenna you should be able to pick up AM stations from hundreds of miles away at night with your set, if it is working properly.

::Ok, I took your advice and removed the resistor and cap that had been added, and hooked up a 1.5 AA battery and holder as suggested, so it looks more like the original schematic.....
::then, just to see what would happen, I connected an MP3 player to the phono jack.....and.....:) :) :) I have music!!! and not too bad sounding either, considering I'm still only using a 2" speaker probably better suited for a walkie talkie:)
::I have some "hum" when there is suppossed to be silence, like in between songs.... but we can always fine tune that later.
::So I thought I'd let you all know that much anyway, so we can assume the AMP part of the radio works.
::May be just something to do with the antenna or tuner? Or the fact that there is probably only one AM radio station in my area. Still would love to get the radio portion working, so today I'll drag it out of the basement and try it upstairs to see if I can get a signal. If anyone has any ideas what else it could be, please let me know. Your help and encouragement is greatly appreciated:)
::
:= = = = = = = =
:
:The background hum may be due to the loss of the filter inductive reactance that the speaker field coil originally provided as a "bonus" for its main job of creating a magnetic field. You can try a larger-capacity (say, 2X the original value) filter cap on the B+ side "downstream" of the resistor that you used to replace the field coil.
:
:
:Sounds like you are in a poor radio reception area. You might try stringing a temporary antenna indoors (or, even better, outdoors if you can do so) to see if you can pick up anything at all on standard broadcast. With a good antenna you should be able to pick up AM stations from hundreds of miles away at night with your set, if it is working properly.
:
Thanks Tom.
I'll see what I can rig up for an antenna. I have a 1970s Sony AM radio that I was getting NY on the other night, but haven't been able since. I'm in NB, Canada.
For the filter cap you're talking about... do you mean C27 in the schematic? and replace it with at least a 30uf, 350v?

:For the filter cap you're talking about... do you mean C27 in the schematic? and replace it with at least a 30uf, 350v?
:
= = = = = =

I don't have the schematic handy, but it's the second big electrolytic capacitor on the "output" side of the speaker field coil (which is now a resistor in your modified set); i.e. the side that gets distributed in the radio as the B+ bus. If it originally was 15uF, then 30 uf would be OK. The things limiting the max capacitance value are inrush current loads on the rectifier tube and the max voltage capable of being generated due to the holdup effect of the cap. However, doubling the cap size should create no problems. Use the same or higher voltage rating as the original cap (350 V is fine).

:For the filter cap you're talking about... do you mean C27 in the schematic? and replace it with at least a 30uf, 350v?
:
= = = = = =

I don't have the schematic handy, but it's the second big electrolytic capacitor on the "output" side of the speaker field coil (which is now a resistor in your modified set); i.e. the side that gets distributed in the radio as the B+ bus. If it originally was 15uF, then 30 uf would be OK. The things limiting the max capacitance value are inrush current loads on the rectifier tube and the max voltage capable of being generated due to the holdup effect of the cap. However, doubling the cap size should create no problems. Use the same or higher voltage rating as the original cap (350 V is fine).

:
::For the filter cap you're talking about... do you mean C27 in the schematic? and replace it with at least a 30uf, 350v?
::
:= = = = = =
:
:I don't have the schematic handy, but it's the second big electrolytic capacitor on the "output" side of the speaker field coil (which is now a resistor in your modified set); i.e. the side that gets distributed in the radio as the B+ bus. If it originally was 15uF, then 30 uf would be OK. The things limiting the max capacitance value are inrush current loads on the rectifier tube and the max voltage capable of being generated due to the holdup effect of the cap. However, doubling the cap size should create no problems. Use the same or higher voltage rating as the original cap (350 V is fine).
:
Thanks for the response Tom,
But since I don't want to mess things up too badly yet, I want to be sure about what you are trying to tell me.
Can you (or anyone) verify which Capacitor you mean.
There is a schematic posted a few steps back by Nostalgia Air. Just want to play it safe since I am new at this and not 100% confident in my skills. Thanks again for all the help and your patience:)

:Can you (or anyone) verify which Capacitor you mean.
:There is a schematic posted a few steps back by Nostalgia Air. Just want to play it safe since I am new at this and not 100% confident in my skills. Thanks again for all the help and your patience:)
:
= = = = = =

The capacitor is C27.

:Can you (or anyone) verify which Capacitor you mean.
:There is a schematic posted a few steps back by Nostalgia Air. Just want to play it safe since I am new at this and not 100% confident in my skills. Thanks again for all the help and your patience:)
:
= = = = = =

The capacitor is C27.

:
::Can you (or anyone) verify which Capacitor you mean.
::There is a schematic posted a few steps back by Nostalgia Air. Just want to play it safe since I am new at this and not 100% confident in my skills. Thanks again for all the help and your patience:)
::
:= = = = = =
::The capacitor is C27.
:thanks Tom, I'm going to pick one up this weekend. I also found some simple instuctions for building an AM radio antenna. All I need now is a decent speaker, which I'm on the hunt for....

::
:::Can you (or anyone) verify which Capacitor you mean.
:::There is a schematic posted a few steps back by Nostalgia Air. Just want to play it safe since I am new at this and not 100% confident in my skills. Thanks again for all the help and your patience:)
:::
::= = = = = =
:::The capacitor is C27.
::thanks Tom, I'm going to pick one up this weekend. I also found some simple instuctions for building an AM radio antenna. All I need now is a decent speaker, which I'm on the hunt for....
:
:Hi.
I replaced C27 with a 33uf, 450v Cap. Still hums.
I remember at the first of all this someone suggested I may have to put a choke in series with the resistor to quiet it down. I may do that.
I did build an antenna over the weekend... not getting AM stations... but I was listening to a station from Romania! So I think the shortwave side of things work somewhat when I have the Band selector set to "S". Not a peep on "L" which I am assuming is AM. Any theories on that?
:

:I replaced C27 with a 33uf, 450v Cap. Still hums.
:I remember at the first of all this someone suggested I may have to put a choke in series with the resistor to quiet it down. I may do that.
:I did build an antenna over the weekend... not getting AM stations... but I was listening to a station from Romania! So I think the shortwave side of things work somewhat when I have the Band selector set to "S". Not a peep on "L" which I am assuming is AM. Any theories on that?

= = = = = = = =

Since the radio works on SW, then you may have a dirty bandswitch or an open BC band coil. Try shooting the bandswitch with aerosol contact cleaner; if that doesn't activate the BC band, you will need to locate the BC band coils (antenna, oscillator) and ohm them for continuity.

::I replaced C27 with a 33uf, 450v Cap. Still hums.
::I remember at the first of all this someone suggested I may have to put a choke in series with the resistor to quiet it down. I may do that.
::I did build an antenna over the weekend... not getting AM stations... but I was listening to a station from Romania! So I think the shortwave side of things work somewhat when I have the Band selector set to "S". Not a peep on "L" which I am assuming is AM. Any theories on that?
:
:= = = = = = = =
:
:Since the radio works on SW, then you may have a dirty bandswitch or an open BC band coil. Try shooting the bandswitch with aerosol contact cleaner; if that doesn't activate the BC band, you will need to locate the BC band coils (antenna, oscillator) and ohm them for continuity.
:
:
Thanks Tom. Found the bandswitch badly tarnished and one "prong" not touching so I thought for sure that was the problem. Cleaned up all contacts and formed prong so that it makes contact, but sadly no improvement:( Working on the BC band coils now...

:Thanks Tom. Found the bandswitch badly tarnished and one "prong" not touching so I thought for sure that was the problem. Cleaned up all contacts and formed prong so that it makes contact, but sadly no improvement:( Working on the BC band coils now...
:
= = = = =

I don't mean to discourage you, but whenever I find an AM multiband set that works on one band but not another, the problem is usually a coil that has opened up due to a past lightning strike(antenna coils are especially vulnerable) or wire corrosion. If you find an open you will need to remove the coil and rewind it. Depending on the set, this is easily said but often difficult to accomplish.

::Thanks Tom. Found the bandswitch badly tarnished and one "prong" not touching so I thought for sure that was the problem. Cleaned up all contacts and formed prong so that it makes contact, but sadly no improvement:( Working on the BC band coils now...
::
:= = = = =
:
:I don't mean to discourage you, but whenever I find an AM multiband set that works on one band but not another, the problem is usually a coil that has opened up due to a past lightning strike(antenna coils are especially vulnerable) or wire corrosion. If you find an open you will need to remove the coil and rewind it. Depending on the set, this is easily said but often difficult to accomplish.
:
Not giving up yet:) I'll try to test those coils once I figure my way around them. From the schematic I've identified the antenna and band coils. May look into putting a choke into the circuit to quiet down the hum. I'll have to look back on earlier post to see what type/value/rating is suggested...

:::Thanks Tom. Found the bandswitch badly tarnished and one "prong" not touching so I thought for sure that was the problem. Cleaned up all contacts and formed prong so that it makes contact, but sadly no improvement:( Working on the BC band coils now...
:::
::= = = = =
::
::I don't mean to discourage you, but whenever I find an AM multiband set that works on one band but not another, the problem is usually a coil that has opened up due to a past lightning strike(antenna coils are especially vulnerable) or wire corrosion. If you find an open you will need to remove the coil and rewind it. Depending on the set, this is easily said but often difficult to accomplish.
::
:Not giving up yet:) I'll try to test those coils once I figure my way around them. From the schematic I've identified the antenna and band coils. May look into putting a choke into the circuit to quiet down the hum. I'll have to look back on earlier post to see what type/value/rating is suggested...
:
Hello again. So I went back and read all previous posts and we talked about choke, but never talked specifically about what I'd need to reduce the hum. Sadly, we don't have Radio Shack up here in Canada anymore, but I'm heading to the US this weekend and plan to stop into Radio Shack and pick up a choke when I'm down there. What should I be asking for? I'm sure they'll know less about this than me:)

Sadly, we don't have Radio Shack up here in Canada anymore, but I'm heading to the US this weekend and plan to stop into Radio Shack and pick up a choke when I'm down there. What should I be asking for? I'm sure they'll know less about this than me:)

Find out what choke you need, then I would check Radio Shack's online site first before going to a store. Here's their link to o chokes...http://www.radioshack.com/search/index.jsp?kwCatId=13384949&kw=choke&origkw=choke&sr=1Chances are their help will be a 21 year old, with his/her head buried in their smart phone..and will know nothing about a choke...Just sayin'...Also, RS has very limited choices in parts anymore, you make want to buy it elsewhere online once you know your specs.

:Hello again. So I went back and read all previous posts and we talked about choke, but never talked specifically about what I'd need to reduce the hum. Sadly, we don't have Radio Shack up here in Canada anymore, but I'm heading to the US this weekend and plan to stop into Radio Shack and pick up a choke when I'm down there. What should I be asking for? I'm sure they'll know less about this than me:)
:
= = = = = =

You are unlikely to find what you want at Radio Shack. Most of their components nowadays are solid-state-centric, meaning that they don't support operation at the relatively high voltages used by tube equipment.

You might do a Google search on Hammond Mfg and peruse their filter choke offerings. They have distributors in Canada. These are likely to be somewhat pricey but you can get exactly what you need.

The parameters that you need to know to select a choke are maximum voltage (probably 400VDC or less), current (probably in the neighborhood of 150 mA) and inductance in Henries. If you bust out the Google search engine again and search on "pi filter" you will find guidance on how to optimize the inductor size to the size of caps that you already have, at the desired AC blocking frequency (which would be 120 Hz, or 2X line frequency). You may need to trade off the ideal inductance value against size, weight, and cost. My guess is that something in the 2H range would work OK and yet not be so massive or costly as to be impractical. That's strictly a guess.

::Hello again. So I went back and read all previous posts and we talked about choke, but never talked specifically about what I'd need to reduce the hum. Sadly, we don't have Radio Shack up here in Canada anymore, but I'm heading to the US this weekend and plan to stop into Radio Shack and pick up a choke when I'm down there. What should I be asking for? I'm sure they'll know less about this than me:)
::
:= = = = = =
:
:You are unlikely to find what you want at Radio Shack. Most of their components nowadays are solid-state-centric, meaning that they don't support operation at the relatively high voltages used by tube equipment.
:
:You might do a Google search on Hammond Mfg and peruse their filter choke offerings. They have distributors in Canada. These are likely to be somewhat pricey but you can get exactly what you need.
:
:The parameters that you need to know to select a choke are maximum voltage (probably 400VDC or less), current (probably in the neighborhood of 150 mA) and inductance in Henries. If you bust out the Google search engine again and search on "pi filter" you will find guidance on how to optimize the inductor size to the size of caps that you already have, at the desired AC blocking frequency (which would be 120 Hz, or 2X line frequency). You may need to trade off the ideal inductance value against size, weight, and cost. My guess is that something in the 2H range would work OK and yet not be so massive or costly as to be impractical. That's strictly a guess.
:
:
:
I don't believe that you are going to find aything close to what you need at a Radio Shack. They don't have much of anything for oddball repair anymore. I would suggest online searches, that may be the best aand quickest way to get a choke. Until then, HMMMmmmm.
Lewis
:

:::Hello again. So I went back and read all previous posts and we talked about choke, but never talked specifically about what I'd need to reduce the hum. Sadly, we don't have Radio Shack up here in Canada anymore, but I'm heading to the US this weekend and plan to stop into Radio Shack and pick up a choke when I'm down there. What should I be asking for? I'm sure they'll know less about this than me:)
:::
::= = = = = =
::
::You are unlikely to find what you want at Radio Shack. Most of their components nowadays are solid-state-centric, meaning that they don't support operation at the relatively high voltages used by tube equipment.
::
::You might do a Google search on Hammond Mfg and peruse their filter choke offerings. They have distributors in Canada. These are likely to be somewhat pricey but you can get exactly what you need.
::
::The parameters that you need to know to select a choke are maximum voltage (probably 400VDC or less), current (probably in the neighborhood of 150 mA) and inductance in Henries. If you bust out the Google search engine again and search on "pi filter" you will find guidance on how to optimize the inductor size to the size of caps that you already have, at the desired AC blocking frequency (which would be 120 Hz, or 2X line frequency). You may need to trade off the ideal inductance value against size, weight, and cost. My guess is that something in the 2H range would work OK and yet not be so massive or costly as to be impractical. That's strictly a guess.
::
::
::
:I don't believe that you are going to find aything close to what you need at a Radio Shack. They don't have much of anything for oddball repair anymore. I would suggest online searches, that may be the best aand quickest way to get a choke. Until then, HMMMmmmm.
:Lewis
::
:Thanks guys, appreciate the quick follow up and advice. I'll research online. Yeah Radio Shack up here in Canada started getting out of the component business and canged their name to "the Source" last time i was there the racks were almost empty and their main thrust now, as far as i can tell is remote contolled toys, cell phones and GPS...nothing for the hobbyist like back in the 80's..... remember back that far?:)
:

::::Hello again. So I went back and read all previous posts and we talked about choke, but never talked specifically about what I'd need to reduce the hum. Sadly, we don't have Radio Shack up here in Canada anymore, but I'm heading to the US this weekend and plan to stop into Radio Shack and pick up a choke when I'm down there. What should I be asking for? I'm sure they'll know less about this than me:)
::::
:::= = = = = =
:::
:::You are unlikely to find what you want at Radio Shack. Most of their components nowadays are solid-state-centric, meaning that they don't support operation at the relatively high voltages used by tube equipment.
:::
:::You might do a Google search on Hammond Mfg and peruse their filter choke offerings. They have distributors in Canada. These are likely to be somewhat pricey but you can get exactly what you need.
:::
:::The parameters that you need to know to select a choke are maximum voltage (probably 400VDC or less), current (probably in the neighborhood of 150 mA) and inductance in Henries. If you bust out the Google search engine again and search on "pi filter" you will find guidance on how to optimize the inductor size to the size of caps that you already have, at the desired AC blocking frequency (which would be 120 Hz, or 2X line frequency). You may need to trade off the ideal inductance value against size, weight, and cost. My guess is that something in the 2H range would work OK and yet not be so massive or costly as to be impractical. That's strictly a guess.
:::
:::
:::
::I don't believe that you are going to find aything close to what you need at a Radio Shack. They don't have much of anything for oddball repair anymore. I would suggest online searches, that may be the best aand quickest way to get a choke. Until then, HMMMmmmm.
::Lewis
:::
::Thanks guys, appreciate the quick follow up and advice. I'll research online. Yeah Radio Shack up here in Canada started getting out of the component business and canged their name to "the Source" last time i was there the racks were almost empty and their main thrust now, as far as i can tell is remote contolled toys, cell phones and GPS...nothing for the hobbyist like back in the 80's..... remember back that far?:)
::

I remember back before that...
Lewis
:
:

:::::Hello again. So I went back and read all previous posts and we talked about choke, but never talked specifically about what I'd need to reduce the hum. Sadly, we don't have Radio Shack up here in Canada anymore, but I'm heading to the US this weekend and plan to stop into Radio Shack and pick up a choke when I'm down there. What should I be asking for? I'm sure they'll know less about this than me:)
:::::
::::= = = = = =
::::
::::You are unlikely to find what you want at Radio Shack. Most of their components nowadays are solid-state-centric, meaning that they don't support operation at the relatively high voltages used by tube equipment.
::::
::::You might do a Google search on Hammond Mfg and peruse their filter choke offerings. They have distributors in Canada. These are likely to be somewhat pricey but you can get exactly what you need.
::::
::::The parameters that you need to know to select a choke are maximum voltage (probably 400VDC or less), current (probably in the neighborhood of 150 mA) and inductance in Henries. If you bust out the Google search engine again and search on "pi filter" you will find guidance on how to optimize the inductor size to the size of caps that you already have, at the desired AC blocking frequency (which would be 120 Hz, or 2X line frequency). You may need to trade off the ideal inductance value against size, weight, and cost. My guess is that something in the 2H range would work OK and yet not be so massive or costly as to be impractical. That's strictly a guess.
::::
::::
::::
:::I don't believe that you are going to find aything close to what you need at a Radio Shack. They don't have much of anything for oddball repair anymore. I would suggest online searches, that may be the best aand quickest way to get a choke. Until then, HMMMmmmm.
:::Lewis
::::
:::Thanks guys, appreciate the quick follow up and advice. I'll research online. Yeah Radio Shack up here in Canada started getting out of the component business and canged their name to "the Source" last time i was there the racks were almost empty and their main thrust now, as far as i can tell is remote contolled toys, cell phones and GPS...nothing for the hobbyist like back in the 80's..... remember back that far?:)
:::
:
:I remember back before that...
:Lewis
::
::
Hi Guys
Just a quick update, I cleaned the volume, tone pots and band select switch with DE-Oxit and surprisingly my AC hum has almost completely disappeared. I've found a little cicuit on the Internet that allows me to safely hook up my MP3 player through the phono jack and the sound coming out now is actually quite good, conidering I'm still using the 2" speaker mentioned previously. Once I find a reasonably priced 12" speaker I think my project will be complete.
Bruce
: