The Tusc DF-100 was one of the first programmable amps, allowing you to store EQ and
gain settings for its second channel.
Dear Amp Man,
I have a Tusc DF-100. I’ve never heard the amp, as it was dead when I got it, and it hasn’t been played in years. I’d like to get this baby up and running, and I was hoping you could walk me through the process and maybe give me some idea of what I have here. She’s all-tube, with four 6L6GCs and two 12AT7s. There’s reverb, and what I’m told are two 12" Fane speakers. I’m also told that channel 1 is a very blackface-like, while channel 2 has programmable digital effects. I’ll assume the preamp tubes are fine until proven otherwise, though I plan to replace the four output tubes and the electrolytics in the power section. Any assistance will be appreciated.
Thanks for writing in about this unusual early-’80s amp. No Tusc has ever crossed my bench, but I did some research, and it’s an interesting amp!
Tusc was originally based in Central Islip, New York, and apparently run by a gentleman named Craig Frye. While these amps used a tube phase inverter (driver) stage and a 6L6-based output stage, Tusc’s claim to fame was a “programmable” front end. There were no effects—or anything digital in the audio path, for that matter—but they could store and recall some gain and EQ settings for channel 2, a unique feature for the time. Many of the regular parts—passive components, speakers, etc.—were purchased from Qualtrol Electronics, a military subcontractor in the area. Qualtrol had built the earlier Earth Sound Research amps, and they liquidated the stock when that company folded.
While some Earth amps looked similar to early Peavey amps, most are covered in the beautiful tuck-and-roll style we associate with Kustom amps. This is interesting, because Earth amps were built using surplus parts sourced from the defunct Plush Electronics Company, another manufacturer of tuck-and-roll beauties. (In the words of my friend Andy Fuchs, “It’s all part of the New York/New Jersey incest of guitar amp companies that came and went over the years.”) Anyway, the Tusc company only lasted a few years. Near the end it relocated to Clifton, New Jersey, and produced the DF-55, a Portaflex-style bass amp, in conjunction with Jess Oliver, the original Ampeg Portaflex designer.
Now let’s see if we can troubleshoot your piece of amp history.
The only thing I know is that the amplifier is dead, so let’s start with the basics. First, let’s check the speakers. If you don’t have a multimeter to check their resistance, the quickest way to see if they’re working is with a 9V battery. Touch one battery terminal to the sleeve of the speaker plug and the other to the tip. If you hear a thud and the speakers move, they should make some sort of sound if the amp is working.
Now on to the amp itself. First, pull all the tubes. Now, does the pilot light come on when you switch the amp on? If not, check the fuse.
Next, see if the amp powers up in standby. If so, we can move on. If not, there’s a problem in the main part of the high-voltage power supply. Or, since this amp also has solid-state circuitry, there may be a problem in the low-voltage supply. In the high-voltage supply, either one or more of the diodes are shorted, or one or more of the main 100 uf 450V caps are shorted (Photo 1). In the low-voltage supply, it could be the diodes, caps, or transistors (Photo 2).