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Old 13th November 2005, 07:30 PM   #1
kjunom is offline kjunom  United States
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Join Date: Jan 2004
Location: NJ
Default FS Moog amplifier

This Moog amp was purchased in the 80's, but never used. I was going to drive a subwoofer, but never got to it. A friend used one in his church PA system for years. I did resolder some bad solder joints and that got rid of the spurious noises. Markings on the pc board identify it as USC-8-1.

It is 12" long. The heat sink is 4" tall with four 2 9/16" fins. There is a 1" integral mount running the length of the heat sink on which are mounted a thermal cutoff switch and a thermistor wired into the biasing circuitry.

The output is quasi-complementary with 8 RCA 8102 output transistors. Each bank of four is driven by an RCA 410. All 10 of these TO3 transistors are mounted on the heatsink. There are 3 metal can transistors - a 2N5415 and two 2N3440. Each has their own heatsink. There are other smaller transistors.

The board has markings for +/-65V power supplies. I tested with regulated +/-50V supplies. The heatsink did not get hot while testing, but the resistor loads did..

Measurments with +/- 50V supplies
No Load
freq (Hz) 100 1K 10K 20K 50 40 30 25 20 16
Vin (Vpp) 2 2 2 2 2 2 2 2 2 2
Vout (Vpp) 44.4 48.4 47.2 44.4 38 34.8 30 26.4 23.2 19.6

8 ohm load
freq (Hz) 100 100
Vin (Vpp) .508 1.00
Vout (Vpp) 12.8 23.6

4 ohm load
freq (Hz) 100 100
Vin (Vpp) .50 1.00
Vout (Vpp) 12.8 24.4

So the output can drive low impedance loads, and in fact seems like it has negative reistance characteristics. The output had a .264V offset, but there are 2 pots on the board and one of them quite liketly will null out this offset. I didn't get any schematics with the amp. There may be a DC servo that needs adjusting and perhaps the low end could also be adjusted by a pot or a parts substitution.

I couldn't track down what is causing the low frequency loss - it wasn't the front end. I didn't spend a lot of time looking.

That's the only data I have.

The PCB is very nice, as is the heatsink, which also has a very nice shield around the output devices.

I would recommend this for guitar or PA applications because of the rolloff in the lower frequencies. This is not a "finished" product. There is no chassis, input jacks, output jacks or power supplies. But it is a pretty nice compact amp worthy of use or experimentation.

Email me for a higher resolution pic,

If you have a use for it, I'll send it to you for $27.50 shipped (US 48 states).
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Old 13th November 2005, 07:59 PM   #2
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Join Date: Jul 2004
Location: BC, Canada
I'll take it.
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