I just finished a thorough continuity test, per the servce notes (page 29), on the tuning section of my RCA Radiola 66. I found a poor replacement of the AF Audio Transformer mounted below the tuner deck (old work). I found the original (in square can)transformer primary and secondary windings are open. The replacement transformer windings are also open and the RF by-pass condensor has been removed (between P and c of socket 6). How was this radio working? Answer: Surprisingly well but with a pronounced hum. Some other condensors may be bad too.

I need to find a replacement and was wondering how to find or calculate the values needed to insure I get the right one. The service notes state on page 23, that the resistance through the primary should be about 1,000 ohms and the secondary should be around 5,200 ohms. I don't know much about transformers.

CT primary?
CT secondary?
Load Capacity?
Other needed?
Good source for transformers?

Thanks
Jeff

Hi Jeff

Although resistance is mentioned, impedance is important. Modern transformers will have lower resistance but be close in impedance. You can buy replacements from AES, tubesandmore.com or Play Things of Past, oldradioparts.com . Audio interstage transformers A-53C or A-63C (better frequency response) will work.

The secomdary may be open and a radio still operate but there wouldn't be a grid return. This would cause hum. The radio will work better with a good transformer.

You should add the missing cap. It helps remove RF from your audio signal.

Norm

: I just finished a thorough continuity test, per the servce notes (page 29), on the tuning section of my RCA Radiola 66. I found a poor replacement of the AF Audio Transformer mounted below the tuner deck (old work). I found the original (in square can)transformer primary and secondary windings are open. The replacement transformer windings are also open and the RF by-pass condensor has been removed (between P and c of socket 6). How was this radio working? Answer: Surprisingly well but with a pronounced hum. Some other condensors may be bad too.

: I need to find a replacement and was wondering how to find or calculate the values needed to insure I get the right one. The service notes state on page 23, that the resistance through the primary should be about 1,000 ohms and the secondary should be around 5,200 ohms. I don't know much about transformers.

: CT primary?
: CT secondary?
: Load Capacity?
: Other needed?
: Good source for transformers?

: Thanks
: Jeff

Hello once again Norm. I have to say I very much appreciate your kind assistance. How long did it take you to learn all this stuff? You are a great help! Thank you!

Hi Jeff

: Although resistance is mentioned, impedance is important. Modern transformers will have lower resistance but be close in impedance. You can buy replacements from AES, tubesandmore.com or Play Things of Past, oldradioparts.com . Audio interstage transformers A-53C or A-63C (better frequency response) will work.

: The secomdary may be open and a radio still operate but there wouldn't be a grid return. This would cause hum. The radio will work better with a good transformer.

: You should add the missing cap. It helps remove RF from your audio signal.

: Norm

: : I just finished a thorough continuity test, per the servce notes (page 29), on the tuning section of my RCA Radiola 66. I found a poor replacement of the AF Audio Transformer mounted below the tuner deck (old work). I found the original (in square can)transformer primary and secondary windings are open. The replacement transformer windings are also open and the RF by-pass condensor has been removed (between P and c of socket 6). How was this radio working? Answer: Surprisingly well but with a pronounced hum. Some other condensors may be bad too.

: : I need to find a replacement and was wondering how to find or calculate the values needed to insure I get the right one. The service notes state on page 23, that the resistance through the primary should be about 1,000 ohms and the secondary should be around 5,200 ohms. I don't know much about transformers.

: : CT primary?
: : CT secondary?
: : Load Capacity?
: : Other needed?
: : Good source for transformers?

: : Thanks
: : Jeff