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US Audio Amplifier

artsybob

artsybob

Active Member
Hello all. I was at a flea market and spotted a stereo tube amp that was manufactured by a "US Audio Corporation" in Bronx, NY. I had never seen this amp before and thought it might have been a kit, but according to radiomuseum.org this was a factory-built unit: http://www.radiomuseum.org/r/usaudio_stereophonic_high_fidelity_amplifier_310.html
I tried to look up more info on this company but the radiomuseum link and this other link to a long-ago auction of another unit where the *only* information I could find on it. Does anyone here on Audiokarma know about US Audio amps? Are they any good?
 
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No experienced wirh this amplifier, but based on its physical construction and the kind of transformers and tubes it has, it looks like an entry level amplifier which can put out about 4.5W per channel. Those transformers won't do deep bass, but it could give you a taste of tube amplifier sound. I wouldn't pay more than about $100 for it assuming good physical condition.
 
That choke is in the photo from the radio museum site, not the OP's. Looks like a reasonable build.
 
I got to take a couple shots of the actual amp in question. It's labelled as "Northport" but its made by US Audio. I'm starting to lean on maybe holding out for something more powerful, plus it still has its original capacitors so it definitely needs recapping. Does anyone else out there have any opinions? Here are some pohots of the actual amp in question.
 

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appears to be single ended, I only see two output tubes. Figure 3-4 watts a channel. Transformers aren't massive so probably not a bass machine either. Performance wise its probably on par with a number of console amplifiers from the period. It might be able to be upgraded some, but in it's day this would have been a fairly entry level piece and age won't have made it a top shelf piece of gear. If the price was right and you had efficient enough speakers it might be a decent amp but I wouldn't pay anywhere near the price on that tag.
 
Can't quite tell for sure but it looks like it could be push/pull or two output tubes per channel. If so depending how good the output transformers are, it could produce 12 - 14 watts per channel. A little less if the tubes are 6BM8 or 6GW8.

Might be a good entry level amplifier.

We just need a good top view shot with the top removed.
 
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Speaking of console amps, the amp inside my Westinghouse console looks beefier than the US Audio one by comparison. I'll just stick with the Westinghouse until I find something better
 

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7591's, though those replacement Electro-Harmonix tubes are pretty big. They're about the same size as the 5U4GB rectifier. It's a shame the original 7591 tubes it came with were whitecapped when I acquired the console.
 
artsybob said:
Hello all. I was at a flea market and spotted a stereo tube amp that was manufactured by a "US Audio Corporation" in Bronx, NY. I had never seen this amp before and thought it might have been a kit, but according to radiomuseum.org this was a factory-built unit: http://www.radiomuseum.org/r/usaudio_stereophonic_high_fidelity_amplifier_310.html
I tried to look up more info on this company but the radiomuseum link and this other link to a long-ago auction of another unit where the *only* information I could find on it. Does anyone here on Audiokarma know about US Audio amps? Are they any good?
Click to expand...

Ha!

That's my amplifier on radiomuseum.org! Somebody copied the images I posted when I was trying to sell it on eBay. It's about as stock as a 427 Cobra is a stock production Ford.
The original circuitry is only vaguely similar to its current configuration. It is single ended and does 4 watts/ch into 8 Ohms. It sound really good, especially when hooked up to my A-7s.
The hardware is not bad but the stock built circuit is pretty sad. I converted the supply to choke input and DC heaters. The phono pre was horrible. I managed to get it pretty close to RIAA. The tone controls were reminiscent of a 1950 guitar amp. I rewired them to Baxandall. The volume control is permanently wired as a loudness control. I had to add a tube to get the power amp up to reasonable snuff. There was already a hole for a socket in the chassis, so it didn't require any metal work. It was fun project but definitely not cost effective, time wise. I've never seen another one, so you have definitely found a rarity.

Did you buy the amp? If you did, my schematic is probably on radiomuseum.com along with the photos. Just be prepared to see only superficial similarity between my schematic and what's inside that amp. I did use the original transformers, so it would be possible to duplicate my build. I tried to attach the schematic to this post but the file was too big.

Tom Garson
 
tgarson said:
Ha!

That's my amplifier on radiomuseum.org! Somebody copied the images I posted when I was trying to sell it on eBay. It's about as stock as a 427 Cobra is a stock production Ford.
The original circuitry is only vaguely similar to its current configuration. It is single ended and does 4 watts/ch into 8 Ohms. It sound really good, especially when hooked up to my A-7s.
The hardware is not bad but the stock built circuit is pretty sad. I converted the supply to choke input and DC heaters. The phono pre was horrible. I managed to get it pretty close to RIAA. The tone controls were reminiscent of a 1950 guitar amp. I rewired them to Baxandall. The volume control is permanently wired as a loudness control. I had to add a tube to get the power amp up to reasonable snuff. There was already a hole for a socket in the chassis, so it didn't require any metal work. It was fun project but definitely not cost effective, time wise. I've never seen another one, so you have definitely found a rarity.

Did you buy the amp? If you did, my schematic is probably on radiomuseum.com along with the photos. Just be prepared to see only superficial similarity between my schematic and what's inside that amp. I did use the original transformers, so it would be possible to duplicate my build. I tried to attach the schematic to this post but the file was too big.

Tom Garson
Click to expand...

Hi Tom,

No I didn't buy the amp. I waited out on eBay until I found something I liked and eventually scored a nice Realistic SAF-40D tube integrated amp for the same price as this one. I had to recap it, replace the selenium rectifier and buy a new power cord for it, but still it's relatively cheap fixes. Hopefully this amp found a nice home, if not it might still be for sale at the Oldsmar Flea Market in Oldsmar, FL
 
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