It's me again. I need a little help on this set. I had low volume, but now I have no volume. Years ago the 25vac filament voltage tap went out and someone replaced the rectifier tube and the output tube so they could use a 6.3vac tap.
I have restored the original configuration. But I haven't been able to find a transformer with a 25v tap. In order to get around that problem, I am using a 50vac secondary voltage and I have wired the two 25vac heaters in series with that 50v and I'm dropping 25vac on each. The 25Z has actually 28vac and the 25AC has 21.
My problem currently is I keep blowing out the 24z unless I drop my variac input voltage a little. I've been thinking about putting a resistor in line with my series connection to drop the voltage down a little on the 25Z. But even when I'm purring along at say maybe 105vac on the variac output, I have no signal to the speaker whatsoever. I lost my signal by accidentally hooking up my signal generator to the center tap on the center terminal without isolating it with a cap.
Any suggestions anyone?...Neal
Now, here you come on with a revival of the old, initial convoluted “6447” thread of yourself and Bill G and Rob, just when I had dee-ciphered all of the initial interchanges.
I have selectively picked out these excerpts out from that chronology in order to touch upon and pump you for more info.
I have 340 plate voltage, 25 vac on the 2 25 tubes heaters, and 6.8 on all the rest
That was among the very first comments of your series, so apparently that is the situation where you have the original transformer, with its HV secondary and 6.3 filament windings intact, but with its open 25VAC winding , so you are making the use of an outboard control transformer fill in for the 25VAC filamentary source for the rectifier and AF output tube. .
.
My existing transformer that no longer puts out 25vac is putting out to much voltage on my secondary high voltage. I'm getting early 450vdc on my speaker pins. I'm changing transformers. I have one on hand that has a 50vac bias tap
Now that next statement above is starting to confuse me, as that B+ is now up to 450VDC.
Sooooo. . . . apparently THIS info is relevant to having the original transformer, and you are then going to change to the new transformer with its HVAC, 6.3 VAC and an additional 50VAC bias winding.
Then on your comment at the DATE TIME GROUP of:
nom 11/07/2008 16:44
You are saying:
If you ground the 50v tap through 4meg resistance, it leaves you with 25v at the tap
O.K., now I see that we are dealing with the new transformer and I am perceiving two possible situations with the “4 Meg of resistor(s)” that you are possibly placing across the 50VAC bias winding to its adjunct center-tap of the high voltage winding.
If that is the case, no way is the loading of 4 megohms presented to that circuit going to pull that 50 VAC down to a 25VAC level.
HOW-SOME-EVER, if you were thinking of a resistive voltage divider, that could then be placed across the 50VAC tap to the HV center tap and then the common node between a pair of resistors ( be they 2meg + 2 meg or 4meg + 4 meg pair of units, as you were not specific of the “4” meg figure). At their common node, one would be finding 25VAC across them . . .BUT, and vewy, vewy heavy on the BUT, that high of series resistance is only going to be able to pass a mere microamperes of current capability, with you needing 300 milliamperes for that AF out and Power rectum-fire tubes’ filaments.
This is the point where I referenced:
Could my new transformer be drawing to much current through the tube? Its a 275-0-275 142VA, 150madc transformer. I got it from Antique electronic supply. The model number is 370FX. It's a universal input transformer
With a high degree of skepticism exhibited to the universal “ “ input “ “ transformer aspect thereof. Assuredly, a power transformer , instead.
Now to research that, and using The Mouse House, since they usually have manuf PDF referencing to the units data sheets.
Firstus, after checking the specs, then my eyes met with the units pricing, whereupon I nearly fell totally off from my hobby horse. . . . . hopefully your sourcing had a surplus priced version of that unit.
Here is the info on that unit:
The first a thing that I wanted to see was a confirmation of the location of that derived bias tap. . .NOW CONFIRMED. . .its just off center of HV windings center tap.
No possibility of there being a floating separate winding, its being placed on the HV winding. If used for its normal manner, there is no problem in that location, with the defined purpose of that winding going over and being fed into a rectifier and its following filtering to then supply bias and the emphasis on the BIAS aspect, with it not having to provide more than the microamperes or up into the sub milliamp level, at the most on its power consumption.
Now what you are encompassing is WANTING that 50 VAC portion of the secondary HV winding to suffice for the source of your 50VAC at 300 ma for that filament string. Check the secondary spec and you will see that the winding is made with wire sizing of the gauge to accommodate a permissible drain of 150 milliamperes.
That ‘soitanly shoots down your acquiring the power level needed for the filaments ALONG with ~ 75 ma drain for the B+ supply proper, not to mention the imbalance in loading that is being presented by the offset to one secondary winding only.
AND NOW. . . for your real killer. . . .(Hmmmm, no, make that 25Z6 killer) , is the fact that with that 50 VAC coming off one imbalanced leg of the HV winding, you are going to have yourself ANOTHER separate rectifier action being present between the ‘Z6’s cathode and filament on one polarity of the swinging AC node.
I’ll bet you have already found that out, and know the proximity of the critical voltage level threshold and the impending rising current level, ‘til that final point where things go. . . . . BOOM. . . . .Right ?
Most Honnable Confucius say. . . .Gonna hafta have an isolated supply for that needed filament supply.
For the time being, still got that 24VAC sprinklating system ? control transformer at hand, as it looks like it would be the right thing to do now in installing it again to take care of the present filamental supply crisis.
That would get the PS back to normal and I can walk you thru on the sets AF circuitry analysis. THEN one would be able to see how close the unit comes to pulling that specified 73 ma or so of B+ drain.
Additionally, I would want to confirm if the unit does have the two primary windings as the data sheet shows.
They are typically paralleled for 120 VAC use or series aided connected for operation at 220VAC.
If confirmed, and as I am looking at the power specs of that hefty transformer, I see it as having twice the power capability that you need. . . .so we may as well investigate the possibility of merely connecting one 120 VAC primary for the AC power input and thereby having an “isolation transformer” winding being created by the floating, unused primary winding, where one could then take the 20 VAC available across the BLUE and BRN/YEL wires and take one of them and route over to the unused 5VAC winding and connect it phased as series aiding such that the result will be that the two windings will then be making the equivalent of a hefty 25VAC winding. . . . . ISOLATED, no less.
I tried the tip that Rob suggested by putting a signal on the center tap of the volume control through a cap, but I forgot the cap and that produced more arcing in my 25z6.
We will save that for later, as it initially sounds like either a possibility of a hot chassis interconnect between equipment. . .BUT. . . the set you are working with is power transformer isolated.
The other retrospective was an upset in the biasing, at the volume control circuit by the resistors in the decde attenuator in the signal generator output being shunted into radio circuitry and I can’t see that
Yet another thought was a great blast of audio being created to load down the PS B+ circuitry, but you never had that great of an audio capability to begin with.
Here is a working schema of the sets points of interest highlighted, mainly the power supply definition enhanced a bit, along with a re-draw of the AF output circuit clutter associated with the AF output transformer plug connections.
[RED] Main B+ supply
[ORANGE] Sub B+ buss
And then, there is the pair of direct DC coupled AF output tubes.
In the interim there will be the need of an ~ 20 watt (10 watt---if you are a quick measurer-er-er) 3K resistive load, which you might be able to assemble up from multiple parallel-series-tandem-compounded -quasi-decaded values of different individual power resistor units. (That would be to use in order toload down that power supply after shedding all of its downstream circuitry loading)
73's de Edd
I've skimmed over your post and I am graciously in your debt over the amount of time you have taken to analyze my problem. I hope I can adequately respond to all your questions.
I never did use the 4meg resistance theory. I was suggested to put the 25v tubes heaters in series and that is how they are right now. I can certainly go back to my sprinkler system transformer with it's 25vac supply.
I don't know why B+ jumped to 450 but that was an integral part of my decision to change transformers.
I didn't pay as much for the transformer as MOUSER want's but it was somewhere around $70.
The power transformer has the capability of selecting multiple voltage inputs and the wires to do it with. It can be tapped for 100vac, 110vac, or 120vac on the primary side. I am not using any of them, but I am using the regular black and white 120vac 142VA. I don't know that it has two primary windings but I would expect that with all these wires.
I have the high wattage resistors you mentioned. I have a 2k 25W and a 1K 25W resistor but I didn't understand what you wanted me to do with them. We could go with 2k or series them for 3k.
I once again thank you for your time and interest in my problem. I'll put my two 25v tubes back in parallel and wire up the sprinkler system tranformer for the voltage source...Neal
:
:
:
:
:
:
:
:
:
:Now, here you come on with a revival of the old, initial convoluted “6447” thread of yourself and Bill G and Rob, just when I had dee-ciphered all of the initial interchanges.
:
:I have selectively picked out these excerpts out from that chronology in order to touch upon and pump you for more info.
:
:
:I have 340 plate voltage, 25 vac on the 2 25 tubes heaters, and 6.8 on all the rest
:
:
:That was among the very first comments of your series, so apparently that is the situation where you have the original transformer, with its HV secondary and 6.3 filament windings intact, but with its open 25VAC winding , so you are making the use of an outboard control transformer fill in for the 25VAC filamentary source for the rectifier and AF output tube. .
:.
:
:
:
:
:My existing transformer that no longer puts out 25vac is putting out to much voltage on my secondary high voltage. I'm getting early 450vdc on my speaker pins. I'm changing transformers. I have one on hand that has a 50vac bias tap
:
:
:Now that next statement above is starting to confuse me, as that B+ is now up to 450VDC.
:Sooooo. . . . apparently THIS info is relevant to having the original transformer, and you are then going to change to the new transformer with its HVAC, 6.3 VAC and an additional 50VAC bias winding.
:
:Then on your comment at the DATE TIME GROUP of:
:
:nom 11/07/2008 16:44
:
:You are saying:
:
:If you ground the 50v tap through 4meg resistance, it leaves you with 25v at the tap
:
:
:O.K., now I see that we are dealing with the new transformer and I am perceiving two possible situations with the “4 Meg of resistor(s)” that you are possibly placing across the 50VAC bias winding to its adjunct center-tap of the high voltage winding.
:If that is the case, no way is the loading of 4 megohms presented to that circuit going to pull that 50 VAC down to a 25VAC level.
:HOW-SOME-EVER, if you were thinking of a resistive voltage divider, that could then be placed across the 50VAC tap to the HV center tap and then the common node between a pair of resistors ( be they 2meg + 2 meg or 4meg + 4 meg pair of units, as you were not specific of the “4” meg figure). At their common node, one would be finding 25VAC across them . . .BUT, and vewy, vewy heavy on the BUT, that high of series resistance is only going to be able to pass a mere microamperes of current capability, with you needing 300 milliamperes for that AF out and Power rectum-fire tubes’ filaments.
:
:This is the point where I referenced:
:
:Could my new transformer be drawing to much current through the tube? Its a 275-0-275 142VA, 150madc transformer. I got it from Antique electronic supply. The model number is 370FX. It's a universal input transformer
:
:With a high degree of skepticism exhibited to the universal “ “ input “ “ transformer aspect thereof. Assuredly, a power transformer , instead.
:
:Now to research that, and using The Mouse House, since they usually have manuf PDF referencing to the units data sheets.
:
:Firstus, after checking the specs, then my eyes met with the units pricing, whereupon I nearly fell totally off from my hobby horse. . . . . hopefully your sourcing had a surplus priced version of that unit.
:
:
:
:Here is the info on that unit:
:
:
:
:
:
:The first a thing that I wanted to see was a confirmation of the location of that derived bias tap. . .NOW CONFIRMED. . .its just off center of HV windings center tap.
:
:No possibility of there being a floating separate winding, its being placed on the HV winding. If used for its normal manner, there is no problem in that location, with the defined purpose of that winding going over and being fed into a rectifier and its following filtering to then supply bias and the emphasis on the BIAS aspect, with it not having to provide more than the microamperes or up into the sub milliamp level, at the most on its power consumption.
:
:Now what you are encompassing is WANTING that 50 VAC portion of the secondary HV winding to suffice for the source of your 50VAC at 300 ma for that filament string. Check the secondary spec and you will see that the winding is made with wire sizing of the gauge to accommodate a permissible drain of 150 milliamperes.
:That ‘soitanly shoots down your acquiring the power level needed for the filaments ALONG with ~ 75 ma drain for the B+ supply proper, not to mention the imbalance in loading that is being presented by the offset to one secondary winding only.
:AND NOW. . . for your real killer. . . .(Hmmmm, no, make that 25Z6 killer) , is the fact that with that 50 VAC coming off one imbalanced leg of the HV winding, you are going to have yourself ANOTHER separate rectifier action being present between the ‘Z6’s cathode and filament on one polarity of the swinging AC node.
:I’ll bet you have already found that out, and know the proximity of the critical voltage level threshold and the impending rising current level, ‘til that final point where things go. . . . . BOOM. . . . .Right ?
:
:
:Most Honnable Confucius say. . . .Gonna hafta have an isolated supply for that needed filament supply.
:
:
:
:For the time being, still got that 24VAC sprinklating system ? control transformer at hand, as it looks like it would be the right thing to do now in installing it again to take care of the present filamental supply crisis.
:That would get the PS back to normal and I can walk you thru on the sets AF circuitry analysis. THEN one would be able to see how close the unit comes to pulling that specified 73 ma or so of B+ drain.
:
:
:Additionally, I would want to confirm if the unit does have the two primary windings as the data sheet shows.
:
:They are typically paralleled for 120 VAC use or series aided connected for operation at 220VAC.
:
:If confirmed, and as I am looking at the power specs of that hefty transformer, I see it as having twice the power capability that you need. . . .so we may as well investigate the possibility of merely connecting one 120 VAC primary for the AC power input and thereby having an “isolation transformer” winding being created by the floating, unused primary winding, where one could then take the 20 VAC available across the BLUE and BRN/YEL wires and take one of them and route over to the unused 5VAC winding and connect it phased as series aiding such that the result will be that the two windings will then be making the equivalent of a hefty 25VAC winding. . . . . ISOLATED, no less.
:
:
:
:
:I tried the tip that Rob suggested by putting a signal on the center tap of the volume control through a cap, but I forgot the cap and that produced more arcing in my 25z6.
:
:
:We will save that for later, as it initially sounds like either a possibility of a hot chassis interconnect between equipment. . .BUT. . . the set you are working with is power transformer isolated.
:
:
:The other retrospective was an upset in the biasing, at the volume control circuit by the resistors in the decde attenuator in the signal generator output being shunted into radio circuitry and I can’t see that
:
:Yet another thought was a great blast of audio being created to load down the PS B+ circuitry, but you never had that great of an audio capability to begin with.
:
:
:Here is a working schema of the sets points of interest highlighted, mainly the power supply definition enhanced a bit, along with a re-draw of the AF output circuit clutter associated with the AF output transformer plug connections.
:
:[RED] Main B+ supply
:
:[ORANGE] Sub B+ buss
:
:
:
:And then, there is the pair of direct DC coupled AF output tubes.
:
:
:In the interim there will be the need of an ~ 20 watt (10 watt---if you are a quick measurer-er-er) 3K resistive load, which you might be able to assemble up from multiple parallel-series-tandem-compounded -quasi-decaded values of different individual power resistor units. (That would be to use in order toload down that power supply after shedding all of its downstream circuitry loading)
:
:
:
:
:
:73's de Edd
:
:
:
:
Ohhhh Taaaay. . . now then . . .upon reviewing:
I(t) was suggested to put the 25v tubes heaters in series and that is how they are right now.
I can certainly go back to my sprinkler system transformer with it's 25vac supply.
Then the first thing now would be to rewire to the initial parallel filament hook up of the two 25v tubes, with them then requiring 25VAC @ 600 ma, and for sure, that control transformer is going to be at least rated at 24V @ 1 amp. . . or may be marked on it somewhere with a cumulative rating of ~25 VA.
Those little valves. . . solenoid coils don't require much drive/ and/ sustaining current.
I don't know why B+ jumped to 450 but that was an integral part of my decision to change transformers.
I couldn't confirm that without out my hands on. . . .normal cause of that is a circuit not pulling its normal load from the power supply and the power supply voltage being at a higher level by that relief of not being loaded down as much. In this case it would be the only current hog in the set, which is the AF output stage. . . .note on my markup that I stopped the leftward extension of the sub B+ [Orange] buss at the arrow, as anything on to the left down that buss is only minutely loading the power supply.
(With the 1 possible exception of fault with the plate winding area of the I.F. transformer.)
BUT that mentioned DC voltage is WAYYYY higher than one would expect experiencing. A fault in the transformer HV secondary winding would cause a decline in the voltage, not an increase. A fault in the primary. . . .shorted turns. . . could cause a rise in the HV secondary, but there is a finite transition where the number of turns causes transformer heating, drop of conversion efficiency, and then a drop in output. A good referencing for that situation is to monitor the 6.3 VAC supply line and see how its voltage reading is, as ratio metrically compared to the HV secondary's AC output voltage.
The power transformer has the capability of selecting multiple voltage inputs and the wires to do it with. It can be tapped for 100vac, 110vac, or 120vac on the primary side. I am not using any of them, but I am using the regular black and white 120vac 142VA. I don't know that it has two primary windings but I would expect that with all these wires.
It is then, same as the supplied schematic, with the wire color coding as I mentioned, should we want to later try what I mentioned earlier, after getting the AF circuitry percolating properly.
Initially get the violet 50vac wire disconnected and revert the filament circuitry to parallel 25VAC operation with the "sprankler" t-former running the then 25 VAc filaments pair.
Unplug the speaker connector plug so that the B+ loading of the PS is removed, connect 3k @ 20 watts of load with power resistors from a clip lead connection onto either cathode of the 25Z6, the other lead of the 3k load gets grounded.
Bring up the AC power and note that all is normal . . .with no flashee-flashee of the 25Z6 as was produced before....and then monitor the resultant B+ to see what the power supply will be producing with its simulated specified sets load level. Run for a time to see if T-former temp is O.K.. . ..it should probably now be as cool a cuke.
Evaluating AF output:
If all is OK in the PS. . .Power down. . .reinstall the speaker plug.
Confirm that the 25AC5 tubes adjunct components are O.K., specifically :
That there is no leakage on the two tone caps C-21, C-22 connected to the plate circuitry.
Confirm the 27K value of R16 grid resistor/6AF5 cathode resistor and then the 470K value of R17 6AF5 1st grid resistor.
No DC leakage tolerated in .01 C18. . .probably already replaced.
Then .. .slowly power up via Variac and take note of the voltages.
Ye olde Schema sez:
Plate...25AC5...............................165vdc
Grid...25AC5................................18vdc
1st Grid...6AF5...........................Not specified on schema...give us your reading. This biasing establishes the conductive ratio of the two DC cascaded tubes.
Plate...6AF5.................................Schema referencing original has blurred numbers, but I suspect ~ 175vdc of a sub B+ level after it has been established after having passing thru the speaker field coil winding and dropping down a bit.
All of your B+ readings may be up a bit due to, possibly, that old transformer being spec'd down at a at 225-0-225 and your new one is 275-0-275.
Let us know the B+ readings, and the associative AF tubes readings.
If all seems sort of near specs on the voltages, how about making an audio output stages test , but in a safer manner this time by initially avoiding the AF generator and instead getting a sample of 6.3VAC from the hot, ungrounded filament pin of the 6AF5.
Take an .001 ufd / 200v+ capacitor and one lead goes to a clip lead and the other end of the clip lead connecting to the 6.3VAC, then the free lead of the capacitor will be quickly touched to the 1st grid of the 25AC5 and you will be listening for a 60~ hum coming from the speaker. If that is present, move on forward to the 1st grid of the 6AF5 and see if it responds with quite a greater volume level.
If you then have some HUMMMMMM…chum being amplified by the AF portion,then move the volume control to its down , min position and this time use clip leads to connect the .001 between the plate of the 25AC5 and the high side of the sets volume control, (where you have once ventured before. . . .not to worry this time though), and then bring up the volume slowly and see if you have not now created yourself a variable freq audio oscillator, frequency varying with the volume control setting, with the arrangement driving the speaker quite healthily, hopefully, with you now taking particular note of the max volume that the whole audio system is capable of producing.
Stopping time for results and feed back. . . .
73's de Edd
I have the two 25vac filament tubes wired in parallel and powered up by my external transformer. I have 275vac plate voltage on the 25z.
I put in the resistive load. It turned out to be 3.2k at 75W which was 3 25watt resistors in series.
I powered up slowly and reached normal line voltage with no complaints from my 25Z.
I tried to take a reading of my B+ at the speaker plug but I got a big goose-egg zero. What the heck?
I measured the B+ at the cathodes of the 25Z and it was 310vdc.
I followed my wire from the cathode over to the speaker plug (with no speaker plugged in) and found my 310vdc. But it was hooked to the wrong side of the speaker plug. It wasn't hooked to the side that has the two pins jumpered together, but it was hooked to the side that has the outside pin going to pin3 on the 25AC5G. That matches my schematic but not the schematic you sent me.
I can't get any farther along in your outlined proceedure until I get this figured out.
Some additional information: The two speaker pins that are jumpered together go up to a "technican of old's" modification. They go to a High wattage 300 ohm resistor suspended like a spider's web. On the end where the speaker wire connects it has the 16uf electrolytic. On the other end it is wired through a resistor to pin4 of 6U7G. And also same electronic point is through a resistor to pin3 of 6B6G and other places that seem to be your orange B+ line...Neal
:
:
:
:
:
:
:Ohhhh Taaaay. . . now then . . .upon reviewing:
:
:
:
:I(t) was suggested to put the 25v tubes heaters in series and that is how they are right now.
:I can certainly go back to my sprinkler system transformer with it's 25vac supply.
:
:
:
:Then the first thing now would be to rewire to the initial parallel filament hook up of the two 25v tubes, with them then requiring 25VAC @ 600 ma, and for sure, that control transformer is going to be at least rated at 24V @ 1 amp. . . or may be marked on it somewhere with a cumulative rating of ~25 VA.
:
:Those little valves. . . solenoid coils don't require much drive/ and/ sustaining current.
:
:
:
:I don't know why B+ jumped to 450 but that was an integral part of my decision to change transformers.
:
:
:I couldn't confirm that without out my hands on. . . .normal cause of that is a circuit not pulling its normal load from the power supply and the power supply voltage being at a higher level by that relief of not being loaded down as much. In this case it would be the only current hog in the set, which is the AF output stage. . . .note on my markup that I stopped the leftward extension of the sub B+ [Orange] buss at the arrow, as anything on to the left down that buss is only minutely loading the power supply.
: (With the 1 possible exception of fault with the plate winding area of the I.F. transformer.)
:
:BUT that mentioned DC voltage is WAYYYY higher than one would expect experiencing. A fault in the transformer HV secondary winding would cause a decline in the voltage, not an increase. A fault in the primary. . . .shorted turns. . . could cause a rise in the HV secondary, but there is a finite transition where the number of turns causes transformer heating, drop of conversion efficiency, and then a drop in output. A good referencing for that situation is to monitor the 6.3 VAC supply line and see how its voltage reading is, as ratio metrically compared to the HV secondary's AC output voltage.
:
:
:
:The power transformer has the capability of selecting multiple voltage inputs and the wires to do it with. It can be tapped for 100vac, 110vac, or 120vac on the primary side. I am not using any of them, but I am using the regular black and white 120vac 142VA. I don't know that it has two primary windings but I would expect that with all these wires.
:
:
:
:It is then, same as the supplied schematic, with the wire color coding as I mentioned, should we want to later try what I mentioned earlier, after getting the AF circuitry percolating properly.
:
:
:
:Initially get the violet 50vac wire disconnected and revert the filament circuitry to parallel 25VAC operation with the "sprankler" t-former running the then 25 VAc filaments pair.
:
:Unplug the speaker connector plug so that the B+ loading of the PS is removed, connect 3k @ 20 watts of load with power resistors from a clip lead connection onto either cathode of the 25Z6, the other lead of the 3k load gets grounded.
:
:
:Bring up the AC power and note that all is normal . . .with no flashee-flashee of the 25Z6 as was produced before....and then monitor the resultant B+ to see what the power supply will be producing with its simulated specified sets load level. Run for a time to see if T-former temp is O.K.. . ..it should probably now be as cool a cuke.
:
:
:
:Evaluating AF output:
:
:
:If all is OK in the PS. . .Power down. . .reinstall the speaker plug.
:
:
:Confirm that the 25AC5 tubes adjunct components are O.K., specifically :
:
:
:
:That there is no leakage on the two tone caps C-21, C-22 connected to the plate circuitry.
:
:
:Confirm the 27K value of R16 grid resistor/6AF5 cathode resistor and then the 470K value of R17 6AF5 1st grid resistor.
:
:
:No DC leakage tolerated in .01 C18. . .probably already replaced.
:
:
:
:Then .. .slowly power up via Variac and take note of the voltages.
:
:Ye olde Schema sez:
:
:Plate...25AC5...............................165vdc
:
:Grid...25AC5................................18vdc
:
:1st Grid...6AF5...........................Not specified on schema...give us your reading. This biasing establishes the conductive ratio of the two DC cascaded tubes.
:
:Plate...6AF5.................................Schema referencing original has blurred numbers, but I suspect ~ 175vdc of a sub B+ level after it has been established after having passing thru the speaker field coil winding and dropping down a bit.
:
:
:All of your B+ readings may be up a bit due to, possibly, that old transformer being spec'd down at a at 225-0-225 and your new one is 275-0-275.
:
:Let us know the B+ readings, and the associative AF tubes readings.
:
:
:If all seems sort of near specs on the voltages, how about making an audio output stages test , but in a safer manner this time by initially avoiding the AF generator and instead getting a sample of 6.3VAC from the hot, ungrounded filament pin of the 6AF5.
:
:Take an .001 ufd / 200v+ capacitor and one lead goes to a clip lead and the other end of the clip lead connecting to the 6.3VAC, then the free lead of the capacitor will be quickly touched to the 1st grid of the 25AC5 and you will be listening for a 60~ hum coming from the speaker. If that is present, move on forward to the 1st grid of the 6AF5 and see if it responds with quite a greater volume level.
:
:If you then have some HUMMMMMM…chum being amplified by the AF portion,then move the volume control to its down , min position and this time use clip leads to connect the .001 between the plate of the 25AC5 and the high side of the sets volume control, (where you have once ventured before. . . .not to worry this time though), and then bring up the volume slowly and see if you have not now created yourself a variable freq audio oscillator, frequency varying with the volume control setting, with the arrangement driving the speaker quite healthily, hopefully, with you now taking particular note of the max volume that the whole audio system is capable of producing.
:
:
:Stopping time for results and feed back. . . .
:
:
:
:
:73's de Edd
:
:
:
:
Initially:
I followed my wire from the cathode over to the speaker plug (with no speaker plugged in) and found my 310vdc. But it was hooked to the wrong side of the speaker plug. It wasn't hooked to the side that has the two pins jumpered together, but it was hooked to the side that has the outside pin going to pin3 on the 25AC5G. That matches my schematic but not the schematic you sent me.
Sooooo, is the wiring such that the Main B+ [RED] is going to the bottom supply side of the AF output transformer, and is that 310 VDC the same B+ level that you were reading back when you had the supply loaded down with the 3K load?
Now, that description of the situation that you are finding the speaker plug connectors wiring situation certainly reeks of the person in its past servicing, having need to replace the sets speaker and not having a proper dynamic speaker to replace it with.
A dynamic speaker in its inherent design, includes a field coil which is serving dual duty, both as producing an electromagnet for the speaker propers magnetic field that the voice coil will attracted or repelled to, and also as a series filter choke in the power supply in its dropping the main B+ to the sub B+ level and inductively filtering it.
Assuredly the person had used a common (now-a-days) Permanent Magnet speaker for his replacement and the 600 0hm power resistor was necessary to complete the B+ loop where the “730 ohm spkr field” coil would initially have been in the set. That is a workable solution to the problem that was at hand..
The current wiring that you describe is sounding like it is fulfilling the circuit’s needs,
IF you are finding the sub B+ level being present, as is shown on my [ORANGE] buss markup.
My initial schema redraw in the combining of the speaker male and female plugs into one connection, thus letting me reposition that portion of the schematic that was otherwise stretching waaaay over to the right by the depicted wiring interconnecting as was originally shown.
It is not abnormal for speaker plugs to contain an interlocking jumper connection of the B+, the B+ can skyrocket up in value if not loaded down, thus taxing the filter condensers HV end specs.
Looking at that schema below yet again as referenced below, I have redrawn again without the plug connections at all. Just confirm that the existent wiring now is as shown. The resistor is shown in place of the field coil winding. Basically, in an ohmming out of that circuitry, the main B+ is feeding the low ( supply) side of the AF output transformer and one leg of the existent 600 ohm power dropping / filter resistor, with the other leg of that 600 ohm power resistor being the sourcing of the sub B+.
Standing by for sub B+ voltage readings, or any other feedback, if you can proceed on in accordance to the initial plan.
73's de Edd
Yes that 310vdc was with the 3k ohm load in.
There was a 300 ohm 25w resistor in the sub B+ (orange)line. It was wired in series off the speaker plug.It's not on the schematic so I considered it to be part of the modification we're dealing with. So I took it out. It gave me my audio back.
Also I have used the voltage differences on the second secondary of the power transformer and the 5vac filament winding to fullfill my 25vac requirement. I've had it running for a day now and the power transformer isn't heating up so all is well that way.
My problem now is that my volume isn't loud enough, but it's linear. It sounds ok when turned down to midrange but distorts at full volume. (Which is not high enough).
Forgive me for straying from the 'original plan'. I'm going back a couple of your posts and study it.
Both these fixes came from ideas that you gave me...Neal
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:Initially:
:
:
:
:I followed my wire from the cathode over to the speaker plug (with no speaker plugged in) and found my 310vdc. But it was hooked to the wrong side of the speaker plug. It wasn't hooked to the side that has the two pins jumpered together, but it was hooked to the side that has the outside pin going to pin3 on the 25AC5G. That matches my schematic but not the schematic you sent me.
:
:
:
:
:
:Sooooo, is the wiring such that the Main B+ [RED] is going to the bottom supply side of the AF output transformer, and is that 310 VDC the same B+ level that you were reading back when you had the supply loaded down with the 3K load?
:
:
:Now, that description of the situation that you are finding the speaker plug connectors wiring situation certainly reeks of the person in its past servicing, having need to replace the sets speaker and not having a proper dynamic speaker to replace it with.
:
:A dynamic speaker in its inherent design, includes a field coil which is serving dual duty, both as producing an electromagnet for the speaker propers magnetic field that the voice coil will attracted or repelled to, and also as a series filter choke in the power supply in its dropping the main B+ to the sub B+ level and inductively filtering it.
:
:
:
:Assuredly the person had used a common (now-a-days) Permanent Magnet speaker for his replacement and the 600 0hm power resistor was necessary to complete the B+ loop where the “730 ohm spkr field” coil would initially have been in the set. That is a workable solution to the problem that was at hand..
:
:The current wiring that you describe is sounding like it is fulfilling the circuit’s needs,
:IF you are finding the sub B+ level being present, as is shown on my [ORANGE] buss markup.
:
:My initial schema redraw in the combining of the speaker male and female plugs into one connection, thus letting me reposition that portion of the schematic that was otherwise stretching waaaay over to the right by the depicted wiring interconnecting as was originally shown.
:
:
:It is not abnormal for speaker plugs to contain an interlocking jumper connection of the B+, the B+ can skyrocket up in value if not loaded down, thus taxing the filter condensers HV end specs.
:
:
:
:Looking at that schema below yet again as referenced below, I have redrawn again without the plug connections at all. Just confirm that the existent wiring now is as shown. The resistor is shown in place of the field coil winding. Basically, in an ohmming out of that circuitry, the main B+ is feeding the low ( supply) side of the AF output transformer and one leg of the existent 600 ohm power dropping / filter resistor, with the other leg of that 600 ohm power resistor being the sourcing of the sub B+.
:
:
:
:
:Standing by for sub B+ voltage readings, or any other feedback, if you can proceed on in accordance to the initial plan.
:
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:73's de Edd
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