Premier 120 - Inoperative Tremolo

[mike356]

Well, I haven't seen that version of the schematic before. Apart from almost going blind trying to read parts values from it, I redrew the tremolo circuits, and they are nearly identical to what's in my drawing.

The input jacks appear to be grounded, as I found in my amp. Usually when you find isolated jacks, you will find them grounded somewhere in the circuitry, usually to create a single chassis ground point to eliminate ground loops. Considering how many ground points I found in the Premier amp, that's clearly not something the designers cared about.

From that circuit, it appears that the foot switch jack is configured exactly as it is in my drawing, meaning it's isolated from the chassis.

I ran across a schematic of the 120R amp (presumably R means reverb). It doesn't actually show the jack, but it might be of interest to you if you haven't seen it. It's clearly a later version.

I notice the resistor in question is 6.2K in that diagram, as it is in the Hardy diagram. It's certainly possible that I made a mistake in my diagram, and there really is a 6.2K in there.

I'm not in any position to comment on the sound of the tremolo. I have to confess-I'm not a guitar person, and can't play a note! But I find early guitar amps are interesting on several levels, and tremolo is pretty rare on early amps.

[Iron Works]

I have a Premier 120R that I'm servicing. I have the same schematic as the previous poster, which appears to be the only one available for this particular model with reverb. I also have 4 different versions of schematics for the 120 non-reverb model. I've attached them here along with a schematic of the tremolo circuit with my voltage readings. This circuit is causing me some confusion: there is up to 150 volts DC on the trem control pots and 5 to 7 volts on the grids of a 12AX7 in the tremolo circuit. Is this normal? Or at least "correct" for this somewhat unusual circuit design? Any thoughts on this would be appreciated! My voltage readings are in the file called "DC on POTS...". The three caps in the trem circuit are new (.047, .02, .01).

Some previous posters in this thread have wondered about the pot in the chassis across the cathodes of the 12AT7 trem tube. This is a "beat control" to adjust the thump out of the tremolo. It works well on my amp. The tremolo works and sounds good, just some scratchiness while adjusting it (as per the DC on the pots) and those strange voltage readings on pots and grids.

DC on POTS - Premier 120R tremolo circuit.pdf

[martin manning]

I don't think the voltages you are seeing are out of line, and the pulsations are just the oscillator working.