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38-12 Code 121 Tube Dilemma - Printable Version

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38-12 Code 121 Tube Dilemma - Buzz - 07-24-2013

Hello Gang:
Here's my story. I bought a Philco model 38-12 Code 121. It didnt work, replaced some caps and got it working. While cleaning the tubes, I noticed that the schematic said the DET-OSC tube was a 6A7.
Mine had a 6A8. The tube had a sticker that said it was replaced in 1947! Those 2 tubes are not interchanagable, are they? Could this have been modified so a 6A8 would work? The under chassis looked untouched. I had a similar problem on my Zenith that I posted a few days ago. What can I look for under the chassis? Need some Philco Gurus help on this Icon_e_ugeek.
Thanks, Buzz

RE: 38-12 Code 121 Tube Dilemma - Ron Ramirez - 07-24-2013

If it has a 6A8, then somebody replaced the original 7-pin socket with an octal socket.

The 6A7 and 6A8 are electrically identical, but as mentioned above, the 6A7 requires a 7-pin standard socket, while the 6A8 requires an octal socket.

RE: 38-12 Code 121 Tube Dilemma - BrendaAnnD - 07-24-2013

Indeed, a 6A7 is a 6 pin tube, while the 6A8 is an octal. Either the set has been modified or there was a production run change. This set was in the era where octal tubes were in pretty wide use.

RE: 38-12 Code 121 Tube Dilemma - Ron Ramirez - 07-24-2013

BrendaAnnD Wrote:Indeed, a 6A7 is a 6 pin tube

Seven, Brenda:

http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6A7

Icon_smile

RE: 38-12 Code 121 Tube Dilemma - Buzz - 07-24-2013

Hi guys.
You are right, this socket is an octal. Didnt notice it was diff from the others. Looks like a good job, not a hack job. So, i guess ill leave it as is, since it works ok..
thanks, Buzz

RE: 38-12 Code 121 Tube Dilemma - codefox1 - 07-24-2013

And the reverse might just happen today depending on what we have in the shop. Guilty as charged for some swaps. Try to leave a note somewhere in the set so the next person doesn't have to take a wild guess.