This chassis has been a real nightmare. It's had fingers in it before I acquired it. The first thing it done when I plugged it in was fry a replacement transformer. (Seems appropriate for me) It had low volume at that time. I have a new transformer in it and That's working fine. I've fused it and still I fried a 6x5gt.
7B8 was all wired wrong. I have that straightened out. I'm replacing capacitors and I have 3 caps and 2 electrolytics left to go. But all the while I have little to no volume.
I'm finding terminals that were used once with nothing left but a clipped off lead and stuff like that. I realize I'm going to have to go over the schematic with a fine toothed comb, but where do I start on this low volume problem? Any ideas?
Neal
Best Regards,
Bill Grimm
Best Regards,
Bill Grimm
Hi Bill,
I'm at my set now. It is a .02uf and I've already changed it, darn it. My voltages on 6P5G are as follows: Pin 1= 0, Pin 2 = 6.7vac, Pin 3 = 297, Pin 5 = -2.5, Pin 7 = 0, Pin 8 = 13.
On 7B6 Pin 1= 0, Pin 2 = 92, Pin 3 = -3.7, Pin 4 = -2.7, Pin 5 = -3.2, Pin 6 = -3.2, Pin 7 = -2.7, Pin 8 = 6.7vac.
On 6AC5G Pin 1 = 0, Pin 2 = 0, Pin 3 = 295, Pin 5 = 13, Pin 7 = 6.7vac, Pin 8 = -2.7.
Hope you can read problems out of these numbers. Thanx, Neal
As a hunch, try checking the resistance of the speaker field.
If that is OK, we may look next at the IF and RF circuitry.
Best Regards,
Bill Grimm
Speaker field coil is 900 ohms. It keeps on eating up my 6X5's. It's burnt out 3 of them now. I'm on my last one. I blew one of them while I was tuning the I.F. Frequency.
With my Fluke hooked to chassis gnd, and the other lead not hooked to anything, I read from 3 to 5 vac. That seems strange to me. If I touch the other lead to the bench, I get about 60vac. So the chassis has a floating high ac voltage?
Neal
Bring up voltage slowly with a varic or lamp in series with the radio. 6X5's burn up because of excessive current. Be sure filter caps are replaced and have the right polarity. I would use 450 volt rated replacement filter caps.
First filter cap, one connected to pin #8 on a 6X5, should not be increased in value.
Replace C21, cap connected between plate and cathode of the 6AC5 tube.
Cathode of 6P5 connects to grid of 6AC5 without a resistor to B-. Adding a 27K resistor to B- will keep the circuit from running away with current. When this circuit was first developed the resistor was said not to be needed. Later it was decided to add this resistor since tubes develop leakage over time.
Norm
::Hi Neal,
:: The voltages look OK, but maybe a little high.
::
:: As a hunch, try checking the resistance of the speaker field.
:: If that is OK, we may look next at the IF and RF circuitry.
::
::Best Regards,
::Hi Bill,
:
:Speaker field coil is 900 ohms. It keeps on eating up my 6X5's. It's burnt out 3 of them now. I'm on my last one. I blew one of them while I was tuning the I.F. Frequency.
:
:With my Fluke hooked to chassis gnd, and the other lead not hooked to anything, I read from 3 to 5 vac. That seems strange to me. If I touch the other lead to the bench, I get about 60vac. So the chassis has a floating high ac voltage?
:
:Neal
Hi Norm,
I'm glad you mentioned not increasing the value of the electrolytic connected to pin 8 of 6X5. I had planned on using the 2 20uf that I have on hand to replace 2 15uf.
Now B- comes off the center tap of the transformer right? I have that fused at 1 amp, but it blows the 6x5 before the fuse. I'll get that 27K put in before I power up with my variac slowly again.
I have a great degree of difficulty in the filter cap replacement due to confinement of space and parts in the way. But I will get it done.
Do you feel like this 6x5 and my low volume problem are related?
Thanks for the heads up on this.
Neal
:
:
:
:::Hi Neal,
::: The voltages look OK, but maybe a little high.
:::
::: As a hunch, try checking the resistance of the speaker field.
::: If that is OK, we may look next at the IF and RF circuitry.
:::
:::Best Regards,
:::Hi Bill,
::
::Speaker field coil is 900 ohms. It keeps on eating up my 6X5's. It's burnt out 3 of them now. I'm on my last one. I blew one of them while I was tuning the I.F. Frequency.
::
::With my Fluke hooked to chassis gnd, and the other lead not hooked to anything, I read from 3 to 5 vac. That seems strange to me. If I touch the other lead to the bench, I get about 60vac. So the chassis has a floating high ac voltage?
::
::Neal
Work on the blowing rectifier problem first. Once that's fixed volume may come up?
A 1 am fuse is too large in center tap of a high voltage winding. A 6X5 is rated to .07 amps. There are other things that can happen to a 6X5 that fusing the CT won't protect. If the radio draws too much current and a 6X5 arcs over it can still short plate to plate.
You could measure current from the 6X5 by lifting the wire on pin #8. Measure current between pin #8 and the wire.
Believe you mentioned the power transformer was changed. Any chance CT and one high voltage end wire was reversed? This will cause voltages to be high and a 6X5 to arc over.
Using an ohm meter measure center tap to each outside lead of the high voltage winding, plates of the rectifier. Should be close in resistance but not excact.
Norm
::Hi Neal
::
:: Bring up voltage slowly with a varic or lamp in series with the radio. 6X5's burn up because of excessive current. Be sure filter caps are replaced and have the right polarity. I would use 450 volt rated replacement filter caps.
::
:: First filter cap, one connected to pin #8 on a 6X5, should not be increased in value.
::
:: Replace C21, cap connected between plate and cathode of the 6AC5 tube.
::
:: Cathode of 6P5 connects to grid of 6AC5 without a resistor to B-. Adding a 27K resistor to B- will keep the circuit from running away with current. When this circuit was first developed the resistor was said not to be needed. Later it was decided to add this resistor since tubes develop leakage over time.
::
::Norm
:
:Hi Norm,
:
:I'm glad you mentioned not increasing the value of the electrolytic connected to pin 8 of 6X5. I had planned on using the 2 20uf that I have on hand to replace 2 15uf.
:
:Now B- comes off the center tap of the transformer right? I have that fused at 1 amp, but it blows the 6x5 before the fuse. I'll get that 27K put in before I power up with my variac slowly again.
:
:I have a great degree of difficulty in the filter cap replacement due to confinement of space and parts in the way. But I will get it done.
:
:Do you feel like this 6x5 and my low volume problem are related?
:
:Thanks for the heads up on this.
:
:Neal
::
::
::
::::Hi Neal,
:::: The voltages look OK, but maybe a little high.
::::
:::: As a hunch, try checking the resistance of the speaker field.
:::: If that is OK, we may look next at the IF and RF circuitry.
::::
::::Best Regards,
::::Hi Bill,
:::
:::Speaker field coil is 900 ohms. It keeps on eating up my 6X5's. It's burnt out 3 of them now. I'm on my last one. I blew one of them while I was tuning the I.F. Frequency.
:::
:::With my Fluke hooked to chassis gnd, and the other lead not hooked to anything, I read from 3 to 5 vac. That seems strange to me. If I touch the other lead to the bench, I get about 60vac. So the chassis has a floating high ac voltage?
:::
:::Neal
I have the transformer (275-0-275) leads hooked up correctly. I've had alot of experience in the last 6 months with transformer replacements. I have measured my 275vac and 300vdc and they are really close to spec. The intention of the fuse was to protect the transformer. I have a line fuse also that blows along with the 6X5.
I measured the two outside leads from center tap and they're both around 52 ohms.
I have removed the electrolytic can. It has problems. The 3 electrolytics inside should be 5uf, 15uf, 15uf. Removed from circuit they measure 7uf, 20uf, and 22uf. I don't have any replacements yet, but they are on order. I'll get them installed, then we can continue troubleshooting from there. Thanks for your time spent on my behalf.
I'll be sure to install that 27k resistor...Neal
Hi Neal
:
: Work on the blowing rectifier problem first. Once that's fixed volume may come up?
:
: A 1 am fuse is too large in center tap of a high voltage winding. A 6X5 is rated to .07 amps. There are other things that can happen to a 6X5 that fusing the CT won't protect. If the radio draws too much current and a 6X5 arcs over it can still short plate to plate.
:
: You could measure current from the 6X5 by lifting the wire on pin #8. Measure current between pin #8 and the wire.
:
: Believe you mentioned the power transformer was changed. Any chance CT and one high voltage end wire was reversed? This will cause voltages to be high and a 6X5 to arc over.
:
: Using an ohm meter measure center tap to each outside lead of the high voltage winding, plates of the rectifier. Should be close in resistance but not excact.
:
:Norm
:
:
:
:::Hi Neal
:::
::: Bring up voltage slowly with a varic or lamp in series with the radio. 6X5's burn up because of excessive current. Be sure filter caps are replaced and have the right polarity. I would use 450 volt rated replacement filter caps.
:::
::: First filter cap, one connected to pin #8 on a 6X5, should not be increased in value.
:::
::: Replace C21, cap connected between plate and cathode of the 6AC5 tube.
:::
::: Cathode of 6P5 connects to grid of 6AC5 without a resistor to B-. Adding a 27K resistor to B- will keep the circuit from running away with current. When this circuit was first developed the resistor was said not to be needed. Later it was decided to add this resistor since tubes develop leakage over time.
:::
:::Norm
::
::Hi Norm,
::
::I'm glad you mentioned not increasing the value of the electrolytic connected to pin 8 of 6X5. I had planned on using the 2 20uf that I have on hand to replace 2 15uf.
::
::Now B- comes off the center tap of the transformer right? I have that fused at 1 amp, but it blows the 6x5 before the fuse. I'll get that 27K put in before I power up with my variac slowly again.
::
::I have a great degree of difficulty in the filter cap replacement due to confinement of space and parts in the way. But I will get it done.
::
::Do you feel like this 6x5 and my low volume problem are related?
::
::Thanks for the heads up on this.
::
::Neal
:::
:::
:::
:::::Hi Neal,
::::: The voltages look OK, but maybe a little high.
:::::
::::: As a hunch, try checking the resistance of the speaker field.
::::: If that is OK, we may look next at the IF and RF circuitry.
:::::
:::::Best Regards,
:::::Hi Bill,
::::
::::Speaker field coil is 900 ohms. It keeps on eating up my 6X5's. It's burnt out 3 of them now. I'm on my last one. I blew one of them while I was tuning the I.F. Frequency.
::::
::::With my Fluke hooked to chassis gnd, and the other lead not hooked to anything, I read from 3 to 5 vac. That seems strange to me. If I touch the other lead to the bench, I get about 60vac. So the chassis has a floating high ac voltage?
::::
::::Neal
Those filter cap values are ok. Electrolytic caps have a wide tolerance. Some are rated +80% to - 20%.
Read the lower right part of this article:
http://www.gvtc.com/~edengel/ZenithWW-II.jpg
They use .15 amp lamps as fuses. Just fusing the CT won't protect a transformer in all cases. A 6X5 can have both plates short to cathode. This will short both ends of the winding together. It's better to fuse each plate lead like mentioned in the Zenith article. They knew there were problems 60 years ago.
This won't fix your radio but it will protect the transformer.
Norm
::Hi Norm,
:
:I have the transformer (275-0-275) leads hooked up correctly. I've had alot of experience in the last 6 months with transformer replacements. I have measured my 275vac and 300vdc and they are really close to spec. The intention of the fuse was to protect the transformer. I have a line fuse also that blows along with the 6X5.
:
:I measured the two outside leads from center tap and they're both around 52 ohms.
:
:I have removed the electrolytic can. It has problems. The 3 electrolytics inside should be 5uf, 15uf, 15uf. Removed from circuit they measure 7uf, 20uf, and 22uf. I don't have any replacements yet, but they are on order. I'll get them installed, then we can continue troubleshooting from there. Thanks for your time spent on my behalf.
:
:I'll be sure to install that 27k resistor...Neal
:
:
:
:
:Hi Neal
::
:: Work on the blowing rectifier problem first. Once that's fixed volume may come up?
::
:: A 1 am fuse is too large in center tap of a high voltage winding. A 6X5 is rated to .07 amps. There are other things that can happen to a 6X5 that fusing the CT won't protect. If the radio draws too much current and a 6X5 arcs over it can still short plate to plate.
::
:: You could measure current from the 6X5 by lifting the wire on pin #8. Measure current between pin #8 and the wire.
::
:: Believe you mentioned the power transformer was changed. Any chance CT and one high voltage end wire was reversed? This will cause voltages to be high and a 6X5 to arc over.
::
:: Using an ohm meter measure center tap to each outside lead of the high voltage winding, plates of the rectifier. Should be close in resistance but not excact.
::
::Norm
::
::
::
::::Hi Neal
::::
:::: Bring up voltage slowly with a varic or lamp in series with the radio. 6X5's burn up because of excessive current. Be sure filter caps are replaced and have the right polarity. I would use 450 volt rated replacement filter caps.
::::
:::: First filter cap, one connected to pin #8 on a 6X5, should not be increased in value.
::::
:::: Replace C21, cap connected between plate and cathode of the 6AC5 tube.
::::
:::: Cathode of 6P5 connects to grid of 6AC5 without a resistor to B-. Adding a 27K resistor to B- will keep the circuit from running away with current. When this circuit was first developed the resistor was said not to be needed. Later it was decided to add this resistor since tubes develop leakage over time.
::::
::::Norm
:::
:::Hi Norm,
:::
:::I'm glad you mentioned not increasing the value of the electrolytic connected to pin 8 of 6X5. I had planned on using the 2 20uf that I have on hand to replace 2 15uf.
:::
:::Now B- comes off the center tap of the transformer right? I have that fused at 1 amp, but it blows the 6x5 before the fuse. I'll get that 27K put in before I power up with my variac slowly again.
:::
:::I have a great degree of difficulty in the filter cap replacement due to confinement of space and parts in the way. But I will get it done.
:::
:::Do you feel like this 6x5 and my low volume problem are related?
:::
:::Thanks for the heads up on this.
:::
:::Neal
::::
::::
::::
::::::Hi Neal,
:::::: The voltages look OK, but maybe a little high.
::::::
:::::: As a hunch, try checking the resistance of the speaker field.
:::::: If that is OK, we may look next at the IF and RF circuitry.
::::::
::::::Best Regards,
::::::Hi Bill,
:::::
:::::Speaker field coil is 900 ohms. It keeps on eating up my 6X5's. It's burnt out 3 of them now. I'm on my last one. I blew one of them while I was tuning the I.F. Frequency.
:::::
:::::With my Fluke hooked to chassis gnd, and the other lead not hooked to anything, I read from 3 to 5 vac. That seems strange to me. If I touch the other lead to the bench, I get about 60vac. So the chassis has a floating high ac voltage?
:::::
:::::Neal
Another thing about those filter caps. I had 90 ohms from negative to chassis ground on 2 of the three negative pins. They should have been O ohms.
Anyway they will be replaced.
I read the document you suggested. That is a great idea. It will give me something to work on while I'm waiting on caps. I live in a small town and I hope I can get bulbs like that and mount they're sockets in the chassis wall.
Thanks for your continued help...Neal
:Hi Neal
:
: Those filter cap values are ok. Electrolytic caps have a wide tolerance. Some are rated +80% to - 20%.
:
: Read the lower right part of this article:
:
:http://www.gvtc.com/~edengel/ZenithWW-II.jpg
:
: They use .15 amp lamps as fuses. Just fusing the CT won't protect a transformer in all cases. A 6X5 can have both plates short to cathode. This will short both ends of the winding together. It's better to fuse each plate lead like mentioned in the Zenith article. They knew there were problems 60 years ago.
:
: This won't fix your radio but it will protect the transformer.
:
:Norm
:
:::Hi Norm,
::
::I have the transformer (275-0-275) leads hooked up correctly. I've had alot of experience in the last 6 months with transformer replacements. I have measured my 275vac and 300vdc and they are really close to spec. The intention of the fuse was to protect the transformer. I have a line fuse also that blows along with the 6X5.
::
::I measured the two outside leads from center tap and they're both around 52 ohms.
::
::I have removed the electrolytic can. It has problems. The 3 electrolytics inside should be 5uf, 15uf, 15uf. Removed from circuit they measure 7uf, 20uf, and 22uf. I don't have any replacements yet, but they are on order. I'll get them installed, then we can continue troubleshooting from there. Thanks for your time spent on my behalf.
::
::I'll be sure to install that 27k resistor...Neal
::
::
::
::
::Hi Neal
:::
::: Work on the blowing rectifier problem first. Once that's fixed volume may come up?
:::
::: A 1 am fuse is too large in center tap of a high voltage winding. A 6X5 is rated to .07 amps. There are other things that can happen to a 6X5 that fusing the CT won't protect. If the radio draws too much current and a 6X5 arcs over it can still short plate to plate.
:::
::: You could measure current from the 6X5 by lifting the wire on pin #8. Measure current between pin #8 and the wire.
:::
::: Believe you mentioned the power transformer was changed. Any chance CT and one high voltage end wire was reversed? This will cause voltages to be high and a 6X5 to arc over.
:::
::: Using an ohm meter measure center tap to each outside lead of the high voltage winding, plates of the rectifier. Should be close in resistance but not excact.
:::
:::Norm
:::
:::
:::
:::::Hi Neal
:::::
::::: Bring up voltage slowly with a varic or lamp in series with the radio. 6X5's burn up because of excessive current. Be sure filter caps are replaced and have the right polarity. I would use 450 volt rated replacement filter caps.
:::::
::::: First filter cap, one connected to pin #8 on a 6X5, should not be increased in value.
:::::
::::: Replace C21, cap connected between plate and cathode of the 6AC5 tube.
:::::
::::: Cathode of 6P5 connects to grid of 6AC5 without a resistor to B-. Adding a 27K resistor to B- will keep the circuit from running away with current. When this circuit was first developed the resistor was said not to be needed. Later it was decided to add this resistor since tubes develop leakage over time.
:::::
:::::Norm
::::
::::Hi Norm,
::::
::::I'm glad you mentioned not increasing the value of the electrolytic connected to pin 8 of 6X5. I had planned on using the 2 20uf that I have on hand to replace 2 15uf.
::::
::::Now B- comes off the center tap of the transformer right? I have that fused at 1 amp, but it blows the 6x5 before the fuse. I'll get that 27K put in before I power up with my variac slowly again.
::::
::::I have a great degree of difficulty in the filter cap replacement due to confinement of space and parts in the way. But I will get it done.
::::
::::Do you feel like this 6x5 and my low volume problem are related?
::::
::::Thanks for the heads up on this.
::::
::::Neal
:::::
:::::
:::::
:::::::Hi Neal,
::::::: The voltages look OK, but maybe a little high.
:::::::
::::::: As a hunch, try checking the resistance of the speaker field.
::::::: If that is OK, we may look next at the IF and RF circuitry.
:::::::
:::::::Best Regards,
:::::::Hi Bill,
::::::
::::::Speaker field coil is 900 ohms. It keeps on eating up my 6X5's. It's burnt out 3 of them now. I'm on my last one. I blew one of them while I was tuning the I.F. Frequency.
::::::
::::::With my Fluke hooked to chassis gnd, and the other lead not hooked to anything, I read from 3 to 5 vac. That seems strange to me. If I touch the other lead to the bench, I get about 60vac. So the chassis has a floating high ac voltage?
::::::
::::::Neal
Hi Norm,
I've got my electrolytics installed and am looking for the right lamp.
Neal
:Hi Norm,
:
:Another thing about those filter caps. I had 90 ohms from negative to chassis ground on 2 of the three negative pins. They should have been O ohms.
:
:Anyway they will be replaced.
:
:I read the document you suggested. That is a great idea. It will give me something to work on while I'm waiting on caps. I live in a small town and I hope I can get bulbs like that and mount they're sockets in the chassis wall.
:
:Thanks for your continued help...Neal
:
::Hi Neal
::
:: Those filter cap values are ok. Electrolytic caps have a wide tolerance. Some are rated +80% to - 20%.
::
:: Read the lower right part of this article:
::
::http://www.gvtc.com/~edengel/ZenithWW-II.jpg
::
:: They use .15 amp lamps as fuses. Just fusing the CT won't protect a transformer in all cases. A 6X5 can have both plates short to cathode. This will short both ends of the winding together. It's better to fuse each plate lead like mentioned in the Zenith article. They knew there were problems 60 years ago.
::
:: This won't fix your radio but it will protect the transformer.
::
::Norm
::
::::Hi Norm,
:::
:::I have the transformer (275-0-275) leads hooked up correctly. I've had alot of experience in the last 6 months with transformer replacements. I have measured my 275vac and 300vdc and they are really close to spec. The intention of the fuse was to protect the transformer. I have a line fuse also that blows along with the 6X5.
:::
:::I measured the two outside leads from center tap and they're both around 52 ohms.
:::
:::I have removed the electrolytic can. It has problems. The 3 electrolytics inside should be 5uf, 15uf, 15uf. Removed from circuit they measure 7uf, 20uf, and 22uf. I don't have any replacements yet, but they are on order. I'll get them installed, then we can continue troubleshooting from there. Thanks for your time spent on my behalf.
:::
:::I'll be sure to install that 27k resistor...Neal
:::
:::
:::
:::
:::Hi Neal
::::
:::: Work on the blowing rectifier problem first. Once that's fixed volume may come up?
::::
:::: A 1 am fuse is too large in center tap of a high voltage winding. A 6X5 is rated to .07 amps. There are other things that can happen to a 6X5 that fusing the CT won't protect. If the radio draws too much current and a 6X5 arcs over it can still short plate to plate.
::::
:::: You could measure current from the 6X5 by lifting the wire on pin #8. Measure current between pin #8 and the wire.
::::
:::: Believe you mentioned the power transformer was changed. Any chance CT and one high voltage end wire was reversed? This will cause voltages to be high and a 6X5 to arc over.
::::
:::: Using an ohm meter measure center tap to each outside lead of the high voltage winding, plates of the rectifier. Should be close in resistance but not excact.
::::
::::Norm
::::
::::
::::
::::::Hi Neal
::::::
:::::: Bring up voltage slowly with a varic or lamp in series with the radio. 6X5's burn up because of excessive current. Be sure filter caps are replaced and have the right polarity. I would use 450 volt rated replacement filter caps.
::::::
:::::: First filter cap, one connected to pin #8 on a 6X5, should not be increased in value.
::::::
:::::: Replace C21, cap connected between plate and cathode of the 6AC5 tube.
::::::
:::::: Cathode of 6P5 connects to grid of 6AC5 without a resistor to B-. Adding a 27K resistor to B- will keep the circuit from running away with current. When this circuit was first developed the resistor was said not to be needed. Later it was decided to add this resistor since tubes develop leakage over time.
::::::
::::::Norm
:::::
:::::Hi Norm,
:::::
:::::I'm glad you mentioned not increasing the value of the electrolytic connected to pin 8 of 6X5. I had planned on using the 2 20uf that I have on hand to replace 2 15uf.
:::::
:::::Now B- comes off the center tap of the transformer right? I have that fused at 1 amp, but it blows the 6x5 before the fuse. I'll get that 27K put in before I power up with my variac slowly again.
:::::
:::::I have a great degree of difficulty in the filter cap replacement due to confinement of space and parts in the way. But I will get it done.
:::::
:::::Do you feel like this 6x5 and my low volume problem are related?
:::::
:::::Thanks for the heads up on this.
:::::
:::::Neal
::::::
::::::
::::::
::::::::Hi Neal,
:::::::: The voltages look OK, but maybe a little high.
::::::::
:::::::: As a hunch, try checking the resistance of the speaker field.
:::::::: If that is OK, we may look next at the IF and RF circuitry.
::::::::
::::::::Best Regards,
::::::::Hi Bill,
:::::::
:::::::Speaker field coil is 900 ohms. It keeps on eating up my 6X5's. It's burnt out 3 of them now. I'm on my last one. I blew one of them while I was tuning the I.F. Frequency.
:::::::
:::::::With my Fluke hooked to chassis gnd, and the other lead not hooked to anything, I read from 3 to 5 vac. That seems strange to me. If I touch the other lead to the bench, I get about 60vac. So the chassis has a floating high ac voltage?
:::::::
:::::::Neal
:I got my lamp inline and have since blown another 6x5. Now my r7 is overheating. 10K power resistor. Still no audio output. I can hear and injected frequency tone (and that is weak) but that's all...Neal
:
:Hi Norm,
:
:I've got my electrolytics installed and am looking for the right lamp.
:
:Neal
:
::Hi Norm,
::
::Another thing about those filter caps. I had 90 ohms from negative to chassis ground on 2 of the three negative pins. They should have been O ohms.
::
::Anyway they will be replaced.
::
::I read the document you suggested. That is a great idea. It will give me something to work on while I'm waiting on caps. I live in a small town and I hope I can get bulbs like that and mount they're sockets in the chassis wall.
::
::Thanks for your continued help...Neal
::
:::Hi Neal
:::
::: Those filter cap values are ok. Electrolytic caps have a wide tolerance. Some are rated +80% to - 20%.
:::
::: Read the lower right part of this article:
:::
:::http://www.gvtc.com/~edengel/ZenithWW-II.jpg
:::
::: They use .15 amp lamps as fuses. Just fusing the CT won't protect a transformer in all cases. A 6X5 can have both plates short to cathode. This will short both ends of the winding together. It's better to fuse each plate lead like mentioned in the Zenith article. They knew there were problems 60 years ago.
:::
::: This won't fix your radio but it will protect the transformer.
:::
:::Norm
:::
:::::Hi Norm,
::::
::::I have the transformer (275-0-275) leads hooked up correctly. I've had alot of experience in the last 6 months with transformer replacements. I have measured my 275vac and 300vdc and they are really close to spec. The intention of the fuse was to protect the transformer. I have a line fuse also that blows along with the 6X5.
::::
::::I measured the two outside leads from center tap and they're both around 52 ohms.
::::
::::I have removed the electrolytic can. It has problems. The 3 electrolytics inside should be 5uf, 15uf, 15uf. Removed from circuit they measure 7uf, 20uf, and 22uf. I don't have any replacements yet, but they are on order. I'll get them installed, then we can continue troubleshooting from there. Thanks for your time spent on my behalf.
::::
::::I'll be sure to install that 27k resistor...Neal
::::
::::
::::
::::
::::Hi Neal
:::::
::::: Work on the blowing rectifier problem first. Once that's fixed volume may come up?
:::::
::::: A 1 am fuse is too large in center tap of a high voltage winding. A 6X5 is rated to .07 amps. There are other things that can happen to a 6X5 that fusing the CT won't protect. If the radio draws too much current and a 6X5 arcs over it can still short plate to plate.
:::::
::::: You could measure current from the 6X5 by lifting the wire on pin #8. Measure current between pin #8 and the wire.
:::::
::::: Believe you mentioned the power transformer was changed. Any chance CT and one high voltage end wire was reversed? This will cause voltages to be high and a 6X5 to arc over.
:::::
::::: Using an ohm meter measure center tap to each outside lead of the high voltage winding, plates of the rectifier. Should be close in resistance but not excact.
:::::
:::::Norm
:::::
:::::
:::::
:::::::Hi Neal
:::::::
::::::: Bring up voltage slowly with a varic or lamp in series with the radio. 6X5's burn up because of excessive current. Be sure filter caps are replaced and have the right polarity. I would use 450 volt rated replacement filter caps.
:::::::
::::::: First filter cap, one connected to pin #8 on a 6X5, should not be increased in value.
:::::::
::::::: Replace C21, cap connected between plate and cathode of the 6AC5 tube.
:::::::
::::::: Cathode of 6P5 connects to grid of 6AC5 without a resistor to B-. Adding a 27K resistor to B- will keep the circuit from running away with current. When this circuit was first developed the resistor was said not to be needed. Later it was decided to add this resistor since tubes develop leakage over time.
:::::::
:::::::Norm
::::::
::::::Hi Norm,
::::::
::::::I'm glad you mentioned not increasing the value of the electrolytic connected to pin 8 of 6X5. I had planned on using the 2 20uf that I have on hand to replace 2 15uf.
::::::
::::::Now B- comes off the center tap of the transformer right? I have that fused at 1 amp, but it blows the 6x5 before the fuse. I'll get that 27K put in before I power up with my variac slowly again.
::::::
::::::I have a great degree of difficulty in the filter cap replacement due to confinement of space and parts in the way. But I will get it done.
::::::
::::::Do you feel like this 6x5 and my low volume problem are related?
::::::
::::::Thanks for the heads up on this.
::::::
::::::Neal
:::::::
:::::::
:::::::
:::::::::Hi Neal,
::::::::: The voltages look OK, but maybe a little high.
:::::::::
::::::::: As a hunch, try checking the resistance of the speaker field.
::::::::: If that is OK, we may look next at the IF and RF circuitry.
:::::::::
:::::::::Best Regards,
:::::::::Hi Bill,
::::::::
::::::::Speaker field coil is 900 ohms. It keeps on eating up my 6X5's. It's burnt out 3 of them now. I'm on my last one. I blew one of them while I was tuning the I.F. Frequency.
::::::::
::::::::With my Fluke hooked to chassis gnd, and the other lead not hooked to anything, I read from 3 to 5 vac. That seems strange to me. If I touch the other lead to the bench, I get about 60vac. So the chassis has a floating high ac voltage?
::::::::
::::::::Neal
In replacing C21 I have discovered there isn't a capacitor there. Pin 5 to Pin 8 right? Anyway, there wasn't and now there is. Another one is missing and I can't read the cap# on my schematic. It's the one below (or between if you will) C21 and gnd. This set has been thoroughly tampered with by someone.
Can you read that cap value on your schematic. If we can decipher it I'll put it in.
Hi Neal
:
: Bring up voltage slowly with a varic or lamp in series with the radio. 6X5's burn up because of excessive current. Be sure filter caps are replaced and have the right polarity. I would use 450 volt rated replacement filter caps.
:
: First filter cap, one connected to pin #8 on a 6X5, should not be increased in value.
:
: Replace C21, cap connected between plate and cathode of the 6AC5 tube.
:
: Cathode of 6P5 connects to grid of 6AC5 without a resistor to B-. Adding a 27K resistor to B- will keep the circuit from running away with current. When this circuit was first developed the resistor was said not to be needed. Later it was decided to add this resistor since tubes develop leakage over time.
:
:Norm
:
:
:
:::Hi Neal,
::: The voltages look OK, but maybe a little high.
:::
::: As a hunch, try checking the resistance of the speaker field.
::: If that is OK, we may look next at the IF and RF circuitry.
:::
:::Best Regards,
:::Hi Bill,
::
::Speaker field coil is 900 ohms. It keeps on eating up my 6X5's. It's burnt out 3 of them now. I'm on my last one. I blew one of them while I was tuning the I.F. Frequency.
::
::With my Fluke hooked to chassis gnd, and the other lead not hooked to anything, I read from 3 to 5 vac. That seems strange to me. If I touch the other lead to the bench, I get about 60vac. So the chassis has a floating high ac voltage?
::
::Neal