Looking for suggestions on repairing an old Fuzz Tone. Issues No output Broken leg on final 2N270. Replaced with a general purpose PNP for now. On/Off is integrated in VOL pot and is open. Jumping for now. Output cable is incomplete. I am using jumpers for now to connect to guitar amp. Signal seems to flow from right to left on the attached schematic (which I hope to be the correct schematic). I have audio signal at the collector of the first 2N270, no audio after that. I have -2.7 to -2.5 VDC at all collectors. Pedal passes a clean signal. When I click to footswitch there is nothing ..read more

Mysteriously this Randall RG50TC (3x12AX7 pre-amp, 12AT7 PI, 2xEL34 power amp) will sometimes buzz when switching from clean to overdrive when input jack in socket. Buzz stops when jack removed (so input is then shorted to ground) and is gone when jack re-inserted, till next unpredictable time it happens. I thought it must be a ground/power supply thing, but when I put scope on speaker the frequency is 45Hz, not the expected 60Hz of our local mains power. Does this mean the buzz is some oscillation? The history is I was asked to look originally at low volume from amp, and found half of the O ..read more

Hey all.... I got a doozie. Dude brought me a 2006 Marshall JCM 2000 Triple Super Lead that comes on, but no sound. Ok. I crack it open and someone had already replaced R6 and R9 (1 ohm in power section) as I assume they burned up. Well, they were open again. And C46 looked like a piece of charcoal. R76 (1k 5watt screen resistor) was burned open. Only, it looked fine... I was only able to tell it was open by meter reading. Bias is at pin 5 on the EL-34s like it should be, and it is solid..what has me buggered is, on pins 3 and 4, im only reading approximately 225-250 Volts DC. I was pretty sur ..read more

I wonder what it is ... ​ Fully transistorised, (very modern) germanium transistors throughout ... More to follow ..read more

I acquired a Fender G-DEC a few years ago, without a power cable. I used the power source from my Behringer VT-15 to try to get it powered up, it didn't function properly. I then ordered a fender G-DEC power cable from sweetwater then tried that, didn't function properly. I did a bit of research online and watched a video, a bulletin was out by fender about updating the amp with a midi cable, I ordered a midi cable then tried to update the amp but still its not functioning properly. It powers up fine but it's not functioning properly. I decided to take on the G-DEC issue and try to fix it. I ..read more

Most of the time when I plug an amp into mine, if it's good, the light is pretty dim. But sometimes it is a little brighter but not totally bright. What does that signify ..read more

I've got an older one of these that came in with the 1A fuse blown, and it appeared that all heaters lit except v1 and v2. No sound of course 3A mains fuse was fine. Caps are leaking. Pulled all power tubes, insert fresh 1A fuse, and the mains 3A blows! 1A still good. I pulled the cube of death board, replaced 3A, with all secondaries disconnected from board, and amp powers on fine. Performed cap job, still no power tubes, and amp is still blowing 3A mains, but 1A is still fine. Where should I look next? 10A fuse has been fine the whole time edit: amp holds steady when I pull the red HV seco ..read more

What would cause this sine wave to clip on the positive cycle? This is that 70's Silverfaced Princeton tube amp that I am still fooling with ..read more

I have a VTM 120 on the bench in which the customer requested a full recap and a bias pot. Done. He brings me NOS Phillips ECG tubes and the plate current is high ~ 55ma plate current at 482v plate volts (measured with my euro tubes bias probe). Even if I give it all of the -56v bias the amp can provide, it is still above 70% dissipation. Well, I just so happen to have a second one he dropped off with old caps and when I put the same tubes in this amp, I'm at 28mA plate current and 428v plate volts. These new F&T caps seem to have raised my plate voltage to the point where I can't bias the ..read more

I fixed a bad ground on a BA115HP that was causing a bad buzz on the output. Before putting the amp back together I wanted to run through the test voltages on the schematic. I've set the correct test conditions (pre-amp and master vol at max, 170mV input). All is fine up to the power amp. TP12 should be 800mV and I measure 1.0V which is fine I think. At the speaker output (there's no speaker connected) TP11 should be 26.3V and I get 32.2V, also fine. What's baffling me is that I see nothing at TP10 with a scope, and nothing at the pin 5 input to that U5 op amp! So there's 1V at the end of R2 ..read more