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Firestone 4A22 - Printable Version

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Firestone 4A22 - Eric - 08-12-2015

Firestone 4A22
I had this around for a while and thought I would give it a try so I recapped and checked the tubes all went well and I hooked it up to the variac and brought it up. It played good for about 2 days (not continuous) when I heard some crackling form the speaker and lost the station so I shut it down. Went back over my work and all was OK started voltage checks which ran about 20% higher than posted values and ran into a problem on the Plate of the 6K6 output tube would start to build then drop to about 2v  . From there I started checking the output transformer and the primary is open. I dug into the leads to check the soldering and connection and it looked good. 
 
  I have an output transformer a PT-291 8 watt, should I use the full primary 491 ohms?

http://www.nostalgiaair.org/pagesbymodel/233/M0006233.pdf

Unfortunately the print here is not complete I have vol 15 so it was not a problem for me.

Thanks Eric  

RE: Firestone 4A22 - Radioroslyn - 08-12-2015

Hey Eric,
What you are looking for is a transformer with a primary impedance of 8000 ohms. This is NOT dc resistance. So what is the impedance of your transformer?? Replace the cap that going from the plate of the 6K6 to the chassis. If it is bad it will take out the transformer.

Terry

RE: Firestone 4A22 - Eric - 08-13-2015

(08-12-2015, 08:39 PM)Radioroslyn Wrote:  Hey Eric,
What you are looking for is a transformer with a primary impedance of 8000 ohms. This is NOT dc resistance. So what is the impedance of your transformer?? Replace the cap that going from the plate of the 6K6 to the chassis. If it is bad it will take out the transformer.

Terry
Terry
 The info sheet I have for the output doesn't give me the Z of the primary here is the data sheet  https://www.tubesandmore.com/products/P-T291#files_and_docs

The cap is new #60 (.004) That I can check or just replace

RE: Firestone 4A22 - Radioroslyn - 08-13-2015

One other thing I forgot to mention is that that transformer is a bit of an overkill as it is for a push pull output and is good for 8w. I would not use it as your set doesn't require one that big. You'd be lucky to 2w on a good day. If you have any junkers around with SE output stage that are not battery/portables I would snatch it up and use rather that the hammond.

Terry

RE: Firestone 4A22 - Eric - 08-13-2015

(08-13-2015, 06:30 PM)Radioroslyn Wrote:  One other thing I forgot to mention is that that transformer is a bit of an overkill as it is for a push pull output and is good for 8w. I would not use it as your set doesn't require one that big. You'd be lucky to 2w on a good day. If you have any junkers around with SE output stage that are not battery/portables I would snatch it up and use rather that the hammond.

Terry

I hooked it up,  I wanted to see if it would work or did I have other issues. it seems to play fine. Now I'm going to dig into the old one to see if I can fix it. and I do have some junkers in my shed so I'll look it see if I have one that is smaller. lots of veneer work to do so this will be awhile. 
Thanks for the help.
Eric

RE: Firestone 4A22 - Radioroslyn - 08-13-2015

Everybody should have a shed full of junkers... I do.
GL
Terry