:Set has been re-capped as required, all resistors outside a 20% tolerance of stated value have been replaced, and NOS tubes installed. Riders Vol 1 pp 1-7 depicts schematic and voltages at tube pins. Set performs well, but all measured DC voltages (Ep) exceed the stated values by 35-45% as noted on Riders. All measurements are referenced to chassis (B-) Calculated plate currents don't seem to match tube data. What am I missing?
:marv
Several things cause higher B+ voltage. The first being high AC line voltage. My line voltage is 125 volts. This is 10% higher than when these radios were made. It will cause B+ to increase by a similar amount.
Output tubes could have low emission? If so they draw less current causing voltage to be high.
First filter cap after your rectifier may be a higher value than original? This reduces ripple but causes higher voltage.
None of these things are problems unless component ratings are exceeded. Be sure your power transformer doesn't overheat.
Norm
:Set has been re-capped as required, all resistors outside a 20% tolerance of stated value have been replaced, and NOS tubes installed. Riders Vol 1 pp 1-7 depicts schematic and voltages at tube pins. Set performs well, but all measured DC voltages (Ep) exceed the stated values by 35-45% as noted on Riders. All measurements are referenced to chassis (B-) Calculated plate currents don't seem to match tube data. What am I missing?
:marv
:Hi Marv
:
: Several things cause higher B+ voltage. The first being high AC line voltage. My line voltage is 125 volts. This is 10% higher than when these radios were made. It will cause B+ to increase by a similar amount.
:
: Output tubes could have low emission? If so they draw less current causing voltage to be high.
:
: First filter cap after your rectifier may be a higher value than original? This reduces ripple but causes higher voltage.
:
: None of these things are problems unless component ratings are exceeded. Be sure your power transformer doesn't overheat.
:
:Norm
:
::Set has been re-capped as required, all resistors outside a 20% tolerance of stated value have been replaced, and NOS tubes installed. Riders Vol 1 pp 1-7 depicts schematic and voltages at tube pins. Set performs well, but all measured DC voltages (Ep) exceed the stated values by 35-45% as noted on Riders. All measurements are referenced to chassis (B-) Calculated plate currents don't seem to match tube data. What am I missing?
::marv
:Hi Marv
:
: Several things cause higher B+ voltage. The first being high AC line voltage. My line voltage is 125 volts. This is 10% higher than when these radios were made. It will cause B+ to increase by a similar amount.
:
: Output tubes could have low emission? If so they draw less current causing voltage to be high.
:
: First filter cap after your rectifier may be a higher value than original? This reduces ripple but causes higher voltage.
:
: None of these things are problems unless component ratings are exceeded. Be sure your power transformer doesn't overheat.
:
:Norm
:
::Set has been re-capped as required, all resistors outside a 20% tolerance of stated value have been replaced, and NOS tubes installed. Riders Vol 1 pp 1-7 depicts schematic and voltages at tube pins. Set performs well, but all measured DC voltages (Ep) exceed the stated values by 35-45% as noted on Riders. All measurements are referenced to chassis (B-) Calculated plate currents don't seem to match tube data. What am I missing?
::marv
:OOPS!!
:marv
:
::Hi Marv
::
:: Several things cause higher B+ voltage. The first being high AC line voltage. My line voltage is 125 volts. This is 10% higher than when these radios were made. It will cause B+ to increase by a similar amount.
::
:: Output tubes could have low emission? If so they draw less current causing voltage to be high.
::
:: First filter cap after your rectifier may be a higher value than original? This reduces ripple but causes higher voltage.
::
:: None of these things are problems unless component ratings are exceeded. Be sure your power transformer doesn't overheat.
::
::Norm
::
:::Set has been re-capped as required, all resistors outside a 20% tolerance of stated value have been replaced, and NOS tubes installed. Riders Vol 1 pp 1-7 depicts schematic and voltages at tube pins. Set performs well, but all measured DC voltages (Ep) exceed the stated values by 35-45% as noted on Riders. All measurements are referenced to chassis (B-) Calculated plate currents don't seem to match tube data. What am I missing?
:::marv
Thomas
:I cannot see your schematic, but if your old speaker was an electro-dynamic type which had the field coil connected across the power supply, and you omitted this load when installing the new speaker, your voltages would all be much higher.
:
:Thomas
Marv
At the top of the voltage chart is this: "Meter readings with Jewell test plug in socket of set."
If I remember correctly, the Jewell tester allowed you to test voltages without removing the chassis from the cabinet. You removed a tube, plugged the socket into the set, then plugged the tube into the test socket. You then tested the voltages by switching between pins.
This was back when 4-pin tubes were either diodes or filamentary triodes and 5-pin tubes had cathodes connected to pin 4.
I think you're supposed to connect the low side directly to the tube you're checking -- the filaments of the 45s or the cathodes of the 27s. If you do this, you might find the voltages closer to those listed on the voltage chart.
Regarding what Norm said about higher line voltages, this radio has settings for three line voltages -- 105, 115 and 125. Before you turn it on again, you should make sure the radio is set to 125 volts. There are two versions of the power chassis. On one, shown on page 1-10, you move the line fuse to the proper setting. On the version shown on pages 1-7 (schematic) and 1-9 (chassis wiring), there are three screw terminals on the underside of the power transformer. The one farthest from the side of the chassis is the 125 volt terminal. (If you are keeping the exterior power plug, that should be moved there too.)
::Set has been re-capped as required, all resistors outside a 20% tolerance of stated value have been replaced, and NOS tubes installed. Riders Vol 1 pp 1-7 depicts schematic and voltages at tube pins. Set performs well, but all measured DC voltages (Ep) exceed the stated values by 35-45% as noted on Riders. All measurements are referenced to chassis (B-) Calculated plate currents don't seem to match tube data. What am I missing?
::marv
:
:
:Marv
:
:At the top of the voltage chart is this: "Meter readings with Jewell test plug in socket of set."
:
:If I remember correctly, the Jewell tester allowed you to test voltages without removing the chassis from the cabinet. You removed a tube, plugged the socket into the set, then plugged the tube into the test socket. You then tested the voltages by switching between pins.
:
:This was back when 4-pin tubes were either diodes or filamentary triodes and 5-pin tubes had cathodes connected to pin 4.
:
:I think you're supposed to connect the low side directly to the tube you're checking -- the filaments of the 45s or the cathodes of the 27s. If you do this, you might find the voltages closer to those listed on the voltage chart.
:
:Regarding what Norm said about higher line voltages, this radio has settings for three line voltages -- 105, 115 and 125. Before you turn it on again, you should make sure the radio is set to 125 volts. There are two versions of the power chassis. On one, shown on page 1-10, you move the line fuse to the proper setting. On the version shown on pages 1-7 (schematic) and 1-9 (chassis wiring), there are three screw terminals on the underside of the power transformer. The one farthest from the side of the chassis is the 125 volt terminal. (If you are keeping the exterior power plug, that should be moved there too.)
Second, I know that Norm already asked you this question, but did you replace your filter condensers (original units being small value paper units)? If so, did you replace them with original values or with higher more modern values? Higher value condensers (30 MFD for example) will raise the B voltage a bit, but will eliminate hum and smooth out bass response.
Thomas
:First off I'd like to say that had I looked under Thomas A. Edison instead of simply Edison, I would have found your schematic. Sometimes my brain works and sometimes it doesn't.
:
:Second, I know that Norm already asked you this question, but did you replace your filter condensers (original units being small value paper units)? If so, did you replace them with original values or with higher more modern values? Higher value condensers (30 MFD for example) will raise the B voltage a bit, but will eliminate hum and smooth out bass response.
:
:Thomas
:Thomas,
:This was all done several months ago. Three caps were in a can (C27, 28, 29) in the power supply chassis. 2ea 2uf, and 1ea 1uf. Even though only one tested bad during initial power up, I sweated the pitch/caps out of the can and replaced all 3 with Riders values @400wvdc/1000ac metalized polyester from DigiKey. Initial measurements prior to first power up, indicated all 3 were within 20% of their original stated values, but B&K DMM/cap tester uses low voltage. Applying operational voltages though, started their immediate demise. After reading Steve of Oregon message, repeated tests cathode to plate, but voltages still exceeded a 20% margin. Maybe I should just be happy with his conclusion, and accept +20 or +30% margin for a radio of this age. I'm still concerned with what seems to be higher than spec'd tube currents, and their probable early demise.
:marv
:
::First off I'd like to say that had I looked under Thomas A. Edison instead of simply Edison, I would have found your schematic. Sometimes my brain works and sometimes it doesn't.
::
::Second, I know that Norm already asked you this question, but did you replace your filter condensers (original units being small value paper units)? If so, did you replace them with original values or with higher more modern values? Higher value condensers (30 MFD for example) will raise the B voltage a bit, but will eliminate hum and smooth out bass response.
::
::Thomas
I can't even begin to imagine what it is that is causing this. Since I found your schematic, I have realized that the field coil is in series with part of the radio, and so if it was failing, the radio would not work. I had an idea that maybe the power transformer had a shorted primary, which might raise the secondary voltage, but would also overheat the transformer and would boost the filament voltage as well. One other thing came to mind. That would be if one of the two phases of push-pull had gone out (open output primary half), but if you've found voltages at every tube, this can't be so, as something is feeding B+ to both plates, so the transformer must be fine.
Thomas
:Well, if the tubes are operating above their rated cathode to plate values, that is bad, but otherwise I guess more power would be a good thing, as you'd have more volume.
:
:I can't even begin to imagine what it is that is causing this. Since I found your schematic, I have realized that the field coil is in series with part of the radio, and so if it was failing, the radio would not work. I had an idea that maybe the power transformer had a shorted primary, which might raise the secondary voltage, but would also overheat the transformer and would boost the filament voltage as well. One other thing came to mind. That would be if one of the two phases of push-pull had gone out (open output primary half), but if you've found voltages at every tube, this can't be so, as something is feeding B+ to both plates, so the transformer must be fine.
:
:Thomas
345 volts at each plate of the #80 tube is fine as long as the amperage is not too high. This tube was commonly used in radios that utilized 350 volt transformers (as is the 5Y3, which is even commonly found in smaller guitar amplifiers--the tube is electrically identical to the #80). Actually, for a real mind blower, here's a weird one for you! My Heathkit model O2 oscilloscope (produced in about 1947 or 1948) uses a 5Y3 in the high voltage section! Both plates are tied in parallel for half wave rectification. Obviously the amperage here is not great, but 1,500 volts are on the tube! If I don't select a good properly working tube, sometimes sparks fly within the tube. If the tube is good, it works just fine. Bits of miscellaneous material within the tube, gaseous condition (even if slight and not a problem in ordinary radios), or poorly placed filaments cause trouble.
I find it odd that the voltage from each plate to the center tap is lower than what you would think it would be if you took the voltage from plate to plate and divided it in half. I assume that in all cases you are measuring these voltages either with the radio in operation or with the tubes removed, as altering this situation between tests would throw off standardization of readings. However, if you are measuring the voltage at the rectifier cathode to the chassis (DC voltage) with the radio loaded (all tubes in place and lit), this will likely be lower than half of the full AC voltage available across the entire H-V winding, due to voltage drop through the rectifier.
Does your power transformer get hot? If not, then you can be pretty sure that the primary is not shorted. If it was, it would more likely affect the high voltage than the low voltage, as the low voltage is under a heavy load. In that case it is somewhat possible to have high B voltage and normal filament voltage, though normally all voltages are affected. I'm sure that someone else asked this question, but is it possible that the transformer is not the original transformer?
At any rate, if none of your voltages exceed the ratings of the tubes or other components, and you absolutely cannot find an improper component (whether it be a failing one or a resistor value that you misread), and the set performs well, leave it alone for now. Perhaps install a 1 or 2 ampere fuse on the line.
Another thing to keep in mind is your meter setting. I'm sure that you would have caught this mistake by now if you made it, but if not, I'll mention it. With my Simpson 260 meter (or perhaps it's a different number...I forgot), if you take DC readings with the meter accidently set for AC, the DC readings will be significantly higher than they are supposed to be. With some meters you may actually damage the meter. Evidently mine is not damaged by this, but erroneous readings result.
Finally, you did not mention whether both halves of the push-pull output section were found in proper working order, so I will assume that they are working properly. If one half was out, this would cause higher B voltages within the set.
Thomas
:Thomas,
:Thanks for the quick reply. Honestly, hadn't thought about the primary having shorted turns, which would indeed raise the secondary HV. As you said, the filament voltage would also rise, which I didn't find to be the case. I reconfirmed the Ep using the cathode(s) as reference, but it still exceeds 20% as stated in Riders. Obviously with fixed bias resistors, an elevated Ep would raise the Ip, which I've calculated several times, with the same results. For the sake of longevity, may have to add a series dropping R, to bring these voltages into reality. Is 345vac referenced to B- (chassis) a reasonable voltage at the 80 plates? Forgot the formula for this simple calculation. Actually measured PP, and came up with 715vac. Could this be a clue or is my DMM going south with HV problems? 345vac x 2 = 690vac. I think its a true RMS meter, but a linear power supply wouldn't introduce a severe power factor anyway. I have an old mirrored scale VOM, and maybe I'll compare measurements of the two.
:marv
:
::Well, if the tubes are operating above their rated cathode to plate values, that is bad, but otherwise I guess more power would be a good thing, as you'd have more volume.
::
::I can't even begin to imagine what it is that is causing this. Since I found your schematic, I have realized that the field coil is in series with part of the radio, and so if it was failing, the radio would not work. I had an idea that maybe the power transformer had a shorted primary, which might raise the secondary voltage, but would also overheat the transformer and would boost the filament voltage as well. One other thing came to mind. That would be if one of the two phases of push-pull had gone out (open output primary half), but if you've found voltages at every tube, this can't be so, as something is feeding B+ to both plates, so the transformer must be fine.
::
::Thomas
Note: A short in the choke would not cause it to get hotter like a transformer, since it is passing DC, not AC. Therefore no extra current would be induced within the shorted turns, since there is no alternating current here to induce such a current.
Thomas
:Also, is it possible that the first part of the choke has shorted out somewhat or completely (perhaps even the entire choke has shorts)? If the voltage at the center tap of the output transformer is rather close to that at the cathode of the rectifier, then this may be so. Proper resistance of the entire choke winding is listed in your parts list (I think it was like 375 ohms or so). The voltage drop across this choke should be anywhere from 20 to 50 volts, depending on the load imposed upon it.
:
:Note: A short in the choke would not cause it to get hotter like a transformer, since it is passing DC, not AC. Therefore no extra current would be induced within the shorted turns, since there is no alternating current here to induce such a current.
:
:Thomas
Thomas
:Both halves of the push-pull circuit are working properly? Is the power transformer original?
:
:Thomas
:Thomas,
:This is long, but read all of it. No distortion, which would be the first indicator of PP output problems. Both tubes drawing current as reflected by filament/grid (-50.8vdc) voltage measurements. New output xformer installed (AES 125H), but with 8 ohm vs 16 ohm secondary. Pwr xformer is the original, although early operational tests revealed an intermittent short 45's filaments to 80 filament. Removed the phenolic xformer bottom, after documenting the internal connections to the outside solder lugs. A slight glint of copper revealed a break in the cloth insulation and the enamel coatings to allow the 2 windings to come together under the weight of all that copper, and when mounted in its upright position on the chassis. Initial DCR tests of the xformer setting upside down didn't reveal this problem. Also found that separate detector winding (L26) and R12 didn't exist. Detector shares filaments with all tubes in the TRF chassis. A serviceman of yesteryear had misdiagnosed this problem, disconnected the 80 filament section, butchered the chassis, added an outboard 5 volt filament xformer for the 80 only. I Patched the chassis with copper sheet and JB Weld. The original chassis was copper plated mild steel, although the copper had turned into green oxide in many places. I didn't re-plate it, but did re-paint close to the orig. moss green. The original problem applied the rectifier output to R13/14, but only R13 was damaged. I was able to restore it. I believe this short also wiped out the split secondary interstage xformer L16/17/18, because a simple open frame non-split unit had been installed and the bal. control R13 removed from the circuit. A new interstage unit (AES 124E) is being used now. Built a new can (orig missing)to contain the open frame 124E, which mounts in the same position, and looks much like all other cans on the chassis. Quite a bit of work over several months, but the final problem of abnormally high Ep is bothersome after all my effort, and the recent occurrence of the lightly buzzing choke inside a can.
:marv
:
::Both halves of the push-pull circuit are working properly? Is the power transformer original?
::
::Thomas
Thomas
:Well, if Riders told what the DC voltage should be from the 80 cathode to the transformer center tap, this would be a help. Perhaps it does, but I didn't see it. Sounds sort of like a transformer problem, though I don't know what kind. If the set works well, especially with that resistor you added, and the transformer doesn't hum, then I guess all is well if left alone. Just enjoy it and put a fuse on the line. I had another idea that is really far out, and is probably not electrically possible, so I'll let it go for now.
:
:Thomas
If the voltage to the amplifier plates is accurate now, with the addition of that B+ resistor, then all of your current readings within the amplifier should be correct, assuming that the amplifier is functioning properly.
Thomas
Thomas
:Measuring the voltage across the cathode bias resistor will give you the current being drawn from both tubes (not directly, but through mathematical calculation). It would be easier to simply wire your multi-meter in series with the cathode bias resistor and the tubes (as opposed to doing the math, though perhaps the math is easier), if your meter has a miliamperage setting that will take the current that the tubes draw. Be sure that your meter is hooked up appropriately (positive to cathode and negative to the resistor), and be absolutely sure that your meter is set to the right settings before turning on the set. If not, you will either blow the fuse in your meter, if it has one, or blow the meter, or both, though usually the fuse protects the meter.
:
:If the voltage to the amplifier plates is accurate now, with the addition of that B+ resistor, then all of your current readings within the amplifier should be correct, assuming that the amplifier is functioning properly.
:
:Thomas
:
:Thomas
Thomas
:Thomas,
:I chose to do the math, after neasuring across the cathode resistor, but shouldn't the value be x 2 compared to the calculation of individual tube current(s) via bias? None of the above compares closely with plate curves of tube data sheet.
:marv
:
::Measuring the voltage across the cathode bias resistor will give you the current being drawn from both tubes (not directly, but through mathematical calculation). It would be easier to simply wire your multi-meter in series with the cathode bias resistor and the tubes (as opposed to doing the math, though perhaps the math is easier), if your meter has a miliamperage setting that will take the current that the tubes draw. Be sure that your meter is hooked up appropriately (positive to cathode and negative to the resistor), and be absolutely sure that your meter is set to the right settings before turning on the set. If not, you will either blow the fuse in your meter, if it has one, or blow the meter, or both, though usually the fuse protects the meter.
::
::If the voltage to the amplifier plates is accurate now, with the addition of that B+ resistor, then all of your current readings within the amplifier should be correct, assuming that the amplifier is functioning properly.
::
::Thomas
::
::Thomas
:The current across the resistor is double that of each tube, so divide it in half. If a data sheet gives certain current values, they are for a given plate voltage and a given negative grid bias. If these are different than those found within your set, then the current readings will not be the same. What are your current readings? Are they higher or lower? If they're lower, perhaps this is why the power is so high within the radio. If they're higher, then I don't know what to say since you put in that extra resistor.
:
:Thomas
:
::Thomas,
::I chose to do the math, after neasuring across the cathode resistor, but shouldn't the value be x 2 compared to the calculation of individual tube current(s) via bias? None of the above compares closely with plate curves of tube data sheet.
::marv
::
:::Measuring the voltage across the cathode bias resistor will give you the current being drawn from both tubes (not directly, but through mathematical calculation). It would be easier to simply wire your multi-meter in series with the cathode bias resistor and the tubes (as opposed to doing the math, though perhaps the math is easier), if your meter has a miliamperage setting that will take the current that the tubes draw. Be sure that your meter is hooked up appropriately (positive to cathode and negative to the resistor), and be absolutely sure that your meter is set to the right settings before turning on the set. If not, you will either blow the fuse in your meter, if it has one, or blow the meter, or both, though usually the fuse protects the meter.
:::
:::If the voltage to the amplifier plates is accurate now, with the addition of that B+ resistor, then all of your current readings within the amplifier should be correct, assuming that the amplifier is functioning properly.
:::
:::Thomas
:::
:::Thomas
:Thomas,
:This is long, hope your eyes are open wide. Lotsa data. Assuming you have a schem of this set , here goes. Trying to read my notes, but maybe some small errors. The self bias R14 in the 45's filament ckt measures 760 ohms, in series with the balance control of 100 ohms to B-. Three measurements were made from B- to top of R14 with the bal. control at different positions. ie center 0 ohms; midway 50 ohms; stop 100 ohms. #1 -43vdc (calc. 56.5ma);#2 -45.2vdc (calc. 55.6ma);#3 -49.2vdc (calc 57.2ma) for both tubes. V6 Ep to B-, 281.5vdc; Ep to K, 236.8vdc. V7 Ep to B- 283.8vdc; Ep to K 239.1vdc. V6 bias -45.2vdc, V7 bias -44.7vdc, with bal set at midway (0 ohms) Output xformer pri. Z =10k CT. DCR 94 ohms @1/2 (meas. 50.8vdc drop; calc. 54ma Ip), DCR 102 ohms@1/2 (meas. 51.9vdc drop; calc 50.8ma Ip) Using bias volts to calculate, Kp closely agrees with Ip, but not with tube data sheet. The tube data sheet addresses a plate load line of 3900 ohms, but my xformer has a Z=5k load line, which I didn't convert yet, but I would expect Ep to rise and Ip to go down under these conditions.
:marv
:
::The current across the resistor is double that of each tube, so divide it in half. If a data sheet gives certain current values, they are for a given plate voltage and a given negative grid bias. If these are different than those found within your set, then the current readings will not be the same. What are your current readings? Are they higher or lower? If they're lower, perhaps this is why the power is so high within the radio. If they're higher, then I don't know what to say since you put in that extra resistor.
::
::Thomas
::
:::Thomas,
:::I chose to do the math, after neasuring across the cathode resistor, but shouldn't the value be x 2 compared to the calculation of individual tube current(s) via bias? None of the above compares closely with plate curves of tube data sheet.
:::marv
:::
::::Measuring the voltage across the cathode bias resistor will give you the current being drawn from both tubes (not directly, but through mathematical calculation). It would be easier to simply wire your multi-meter in series with the cathode bias resistor and the tubes (as opposed to doing the math, though perhaps the math is easier), if your meter has a miliamperage setting that will take the current that the tubes draw. Be sure that your meter is hooked up appropriately (positive to cathode and negative to the resistor), and be absolutely sure that your meter is set to the right settings before turning on the set. If not, you will either blow the fuse in your meter, if it has one, or blow the meter, or both, though usually the fuse protects the meter.
::::
::::If the voltage to the amplifier plates is accurate now, with the addition of that B+ resistor, then all of your current readings within the amplifier should be correct, assuming that the amplifier is functioning properly.
::::
::::Thomas
::::
::::Thomas