How to repair noise Fender Dual Showman 100 watt 6L6 tube guitar amp 

This is the 1st Showman to come into my shop. I would have replaced the eyelet board, but my investment is quickly equaling the amps value. Yes, it was loaded with bad connections. A new eyelet board would do this thing wonders.

Bob Barcus not this one. It was poorly built at the factory as you just saw.

Terry is not Uncle Doug.

Hello, I'd say the OT primary was mis-matched after adding the two extra 6L6's. However if it didn't melt down and sounded OK, mission accomplished. Theres nothing wrong with experimenting + enjoying the hobby. Of course, these days collector value would make this mod a second thought. Do you still have the amp?

No, it was sold or traded in on a guitar back in '67. As they say, I was young and stupid, oblivious to the fact that 50 years afterwards these would be highly sought after as collectors amps. Had I managed to hang on to it all these years, I would have done a more scientific measurement re-mod, doing a plate current/primary winding impedance match and set the bias accordingly. Replacing the o/p transformer with beefier version from Hammond or other manufacturer. Same with some Kalamazoo made Epiphones that I traded for something else that I would have held onto today...who knew back then. As it turned out, the o/p tubes and transformer held up remarkably well to normal guitar volumes, a testament to how good these 60s Fender amps were put together, but I never did an audio generator frequency sweep on it with a proper 50watt load resistor to find out what kind of power I actually gained by doing this seat of the pants mod.

The suspect tube was microphonic. Then of course there wer other sources of noise. I just take it one step at a time.

+D-lab Electronics Thanks.

The signal generator is used to produce a nice clean sine wave at a constant frequency. A guitar chord progression would hard to use to diagnose.

Orange drops are the widely used choice of today for most amp shops. Ceramic disc caps are very robust though and rarely go bad.

Hello, it is a moving target. Cost is hard to specify until I see the patient.

I believe I found the schematic on Wattstubeaudio.com

I've found a few schematics but I guess my real question is which one is the right one for my particular Dual Showman. Some of the options were the AA270 schematic another was the AA769. I've heard one way to tell is to look at the tube layout diagram inside; however, my diagram must be missing the part with the schematic number on it. Is there any other way of telling which schematic to go by? Also, at cursory glance the circuit layouts look the same so any variations would be minor. Are there any particular nuances I could look for in the amp that might indicate which Dual Showman schematic to go by?

For that same amp as a twin it is circuit sf100. Mine is a 73 twin

Yes, in that ball park, unless they are still matched, not noisy and the customer is good with the sound/performance

Hello, no worries on the board shorting. If the owner requested it replaced, I'd hop to it. I agree, the board is in sad shape. TD

My AB763 board had an internal short (many old fenders do) and made noise. So I sandwiched a piece of plastic between the 2 layers of board. I cut the plastic from a Large Folgers coffee can.

Often, noise is from a tube that's old and worn out. The tube farthest from the big power tubes is usually the culprit. But not always, because the outputs from that tube go through more stages of gain than the rest of the tubes, and any noise there gets the most gain. You can try putting in different tubes, and see if that works. Use a 7025 for that first tube, it's a military-spec 12AX7 that's been selected for low noise output. If you try new tubes and still have noise, here's an inexpensive thing to do: If the noise is a fairly steady hiss, the chances are that it's caused by certain old resistors in the preamp. Those are almost always 100kOhm resistors in Fender amps, on the tube plates and grids. Replace every 100kOhm resistor in the preamp section, and see if the hiss goes away. If the noise is a steady hum, it's probably the large capacitors in the power supply, the ones under the pan. Follow our Uncle Doug's safety precautions and discharge those caps using a resistor. Use an insulated alligator clip to hold the resistor to the leads of each cap, with the other end of the resistor connected to ground, and give each cap several seconds to discharge, The longer, the better. Even then, caps have a "memory", and won't be totally discharged, so be extremely careful. Do not touch the leads while you replace those caps. While you're in there, look over everything carefully, and check for any loose solder connections, damaged wires, burnt areas, etc.. Always leave the standby switch in the "off" position when you turn on your amp, and try to leave it for at least 5-10 minutes before turning the standby "on". Stripping is for dancers, not cathodes. If you aren't sure what you're doing, take the amp to a qualified repair person. Just my two cents' worth, hope it helps.

Hi im so tks for this help... and im very sorry.. becouse i didnt tell u that my amp is solid state amp type... is it the same ? What i can check before go tu the assistance?

I agree, not a barn, but maybe a humid Michigan basement

I know what's that like... Being from the Cleveland area... lake humidity.

What were they called?

molex sockets

www.fishpond.co.nz/9319236845264

www.karltone.co.uk/valve-tube-sockets-79-c.asp

www.aliexpress.com/item/9pin-Belton-Style-Tube-Socket-Bottom-Mount-12AX7-EL84/2031085874.html?spm=2114.40010708.4.19.3WsoCw