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 Post subject: Belmont 665A Output transformer
PostPosted: Sep Sun 05, 2021 7:23 pm 
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Joined: Aug Wed 06, 2008 9:37 pm
Posts: 28
Location: West Monroe Louisiana
Greetings,
Got around to evaluating an old Belmont 665A radio and doing resistance checks of the coils and transformers I found the output transformer primary was open.
I carefully opened it up to see if i could repair it but the open was deep inside so time to replace if feasible.
My manual doesn't tell me what the primary and secondary resistance is but I can say that the RCA tube manual for the 6AC% output states that for a Class A Dynamic coupled output section at 210 Plate Volts calls for a 7K ohm primary with a 8 Ohm secondary.
They appaerently used the 6AC5 tube data to design there output circuit because everything matches the specifications in the manual.
The output on this thing maxes out at around 3.5 watts with a gallon of distortion.
Anyway, looking for a suitable replacement, I don't have a big enough radio boneyard to borrow from. This radio may be a candidate for the boneyard because it has several issues which comes close to not repairing it but I just hate to DOA them you know.
Thanks

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Sam


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 Post subject: Re: Belmont 665A Output transformer
PostPosted: Sep Tue 07, 2021 5:43 am 
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Joined: Oct Wed 14, 2009 6:36 am
Posts: 6561
Location: New York USA
Here is a cheap 5K ohm to 8 ohm single-end, close enough https://www.tubesandmore.com/products/t ... ngle-ended


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 Post subject: Re: Belmont 665A Output transformer
PostPosted: Sep Tue 07, 2021 12:23 pm 
Member

Joined: Aug Wed 06, 2008 9:37 pm
Posts: 28
Location: West Monroe Louisiana
That’s pretty cheap compared to a new Hammond.
Found one on eBay that may work.
Thanks

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Sam


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 Post subject: Re: Belmont 665A Output transformer
PostPosted: Sep Tue 07, 2021 10:26 pm 
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Joined: Jan Tue 16, 2007 7:02 am
Posts: 4724
Location: Lexington, KY USA
This is not a HiFi monoblock amp. The output transformer is not very critical at all.

You can sub-in a different output transformer until you come across the right one.

An AA5 output transformer will work pretty well. The 2k or 2.5k primary impedance won't let the radio play quite as loud, but you may not notice the difference.

Ted


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