[Tubesforme]

I am wondering if anyone has checked the ohms on a Philco Model 20 power transformer using a DMM? I am interested in the reading between the CT, pin 6 of the power transformer to pins 1 and 2 (2.5VAC). Reading without any tubes or the pilot lamp installed. I understand that you should read .1 to .2 ohms, on either side, however my DMM reads 0.F on the auto range and on the manual range 0F. meaning 0 ohms. From pin 1 to pin 2, I measure .3 ohm. It is as if the CT is missing. I have checked and re soldered the terminals of the transformer and nothing changed.

I am checking this because of a 60 HZ hum that can only be eliminated by grounding the grid of the 27 audio tube. ALL COMPONENTS HAVE EITHER BEEN REPLACED OR SUBSTITUTED EXCEPT THE POWER TRANSFORMER. I am questioning the transformer because after turning it on and off a number of time, while testing, with or without tubes, I get a quick ARC sound out of the power transformer. I found out grounding the chassis to the house ground, blows the circuit breaker.

[Radioroslyn]

I am wondering if anyone has checked the ohms on a Philco Model 20 power transformer using a DMM? I am interested in the reading between the CT, pin 6 of the power transformer to pins 1 and 2 (2.5VAC). Reading without any tubes or the pilot lamp installed. I understand that you should read .1 to .2 ohms, on either side, however my DMM reads 0.F on the auto range and on the manual range 0F. meaning 0 ohms. From pin 1 to pin 2, I measure .3 ohm. It is as if the CT is missing. I have checked and re soldered the terminals of the transformer and nothing changed.

I am checking this because of a 60 HZ hum that can only be eliminated by grounding the grid of the 27 audio tube. ALL COMPONENTS HAVE EITHER BEEN REPLACED OR SUBSTITUTED EXCEPT THE POWER TRANSFORMER. I am questioning the transformer because after turning it on and off a number of time, while testing, with or without tubes, I get a quick ARC sound out of the power transformer. I found out grounding the chassis to the house ground, blows the circuit breaker.

Hi,
> It is as if the CT is missing.
I'm not sure what the ct of the heater winding is doing. It's tied back to the bias buss (ct of HV winding) but the tubes that are connected on that 2.5v line are indirectly heated (will have no effect on the tube because the filament is isolated from cathode). My thinking is that it will work without that connection.

< I found out grounding the chassis to the house ground, blows the circuit breaker.
Really! Well if true and it's not tripping a GFI outlet I'd be looking for a power transformer(internal short)
If you need one I think I have a spare you can have for the shipping from Pa.

GL & Merry Christmas!
Terry

[morzh]

Well this means you have something, likely the transformer, breakdown. You do not need to know anything exact about measurements, all you need is to buzz primary to chassis, if there is anything detectable, it is the breakdown.

[Radioroslyn]

<buzz primary to chassis
Methinks that's slang for measuring the resistance from the transformer primary to the chassis.

Terry

[Tubesforme]

<buzz primary to chassis
Methinks that's slang for measuring the resistance from the transformer primary to the chassis.

Terry

Terry, I found the source of my problem,. The CT for the 2.5V is open. I have another transformer I just compared it too and it shows the CT is there. Yes, the radio will work without the CT, but there is a hum and it is coming directly from the 27 audio tube. I have the transformer out of the radio and did a direct comparison to a known good transformer.

[Tubesforme]

I am wondering if anyone has checked the ohms on a Philco Model 20 power transformer using a DMM? I am interested in the reading between the CT, pin 6 of the power transformer to pins 1 and 2 (2.5VAC). Reading without any tubes or the pilot lamp installed. I understand that you should read .1 to .2 ohms, on either side, however my DMM reads 0.F on the auto range and on the manual range 0F. meaning 0 ohms. From pin 1 to pin 2, I measure .3 ohm. It is as if the CT is missing. I have checked and re soldered the terminals of the transformer and nothing changed.

I am checking this because of a 60 HZ hum that can only be eliminated by grounding the grid of the 27 audio tube. ALL COMPONENTS HAVE EITHER BEEN REPLACED OR SUBSTITUTED EXCEPT THE POWER TRANSFORMER. I am questioning the transformer because after turning it on and off a number of time, while testing, with or without tubes, I get a quick ARC sound out of the power transformer. I found out grounding the chassis to the house ground, blows the circuit breaker.

Hi,
> It is as if the CT is missing.
I'm not sure what the ct of the heater winding is doing. It's tied back to the bias buss (ct of HV winding) but the tubes that are connected on that 2.5v line are indirectly heated (will have no effect on the tube because the filament is isolated from cathode). My thinking is that it will work without that connection.

< I found out grounding the chassis to the house ground, blows the circuit breaker.
Really! Well if true and it's not tripping a GFI outlet I'd be looking for a power transformer(internal short)
If you need one I think I have a spare you can have for the shipping from Pa.

GL & Merry Christmas!
Terry

I misspoke. All of my outlets are on GFI's. That is the way all new buildings are built here in LA. It is the GFI that controls that outlet, that pops, not the circuit breaker itself.

[morzh]

Aha! Yep, that's different. Still means you have some leakage between Chassis and primary but not a short necessarily.
Open winding does not cause this, but the reason for the open winding and the leakage could possibly be the same.
Like corrosion. As it takes quite a wallop to open 2.5V winding due to over current.

[Tubesforme]

Aha! Yep, that's different. Still means you have some leakage between Chassis and primary but not a short necessarily.
Open winding does not cause this, but the reason for the open winding and the leakage could possibly be the same.
Like corrosion. As it takes quite a wallop to open 2.5V winding due to over current.

Thanks, I had written circuit breaker when I met GFI and only caught the error once I had posted it so left it alone. I totally agree with you. I only asked the question to see if anyone had the same ideas I had. I believe any transformer of this age might easily have some leakage and corrosion. However the replacement transformer has solved my problem.