AMPTEk

AMPTEk Valve guitar amp repairs and servicing

23/07/2026

Had a trace elliot hexa valve bass amp in 1992 model ,not many made. The customer wanted kt88s put in and of course biased. Oh what fun I had not the easiest of amps to work on. there's no bias pot so I had to get both power amp and pre amp out to find the bias circuit. The valves that are originally fitted are 6550s, out of interest I tested em all, 4 were worn and 2 failed the test, 4 out of the 6 could be used as a baby rattle lol, the customer said it was distorting ..think that might have had something to do with, anyway sorted, oh and the valves only just go in, not much room, the 6550s only just went in. Customer was happy.

20/05/2026

Had a fender 1000 performer in for repair, the amp kept wanting to change channel, usual fault with these amps and seems most fenders is putting power resistors and the 16v zener diodes hard on the board hence with the heat the board burns and dry solder joints, I replaced both diodes but used stand off to help air flow. Job done

12/05/2026

Had another couple of repairs in from the same customer, a fender Pro that was sounding a little rough, turned out to be both output valves had leaky control grid according to my orange tester. The one thing with these amps the mains transformer can't be set at 240v, so my little brain is thinking is because the heaters have a higher voltage on em? Anyway, new output valves check bias job done. Next was a Lazy J amp that's hand wired, similar to a 5e3 the customer said it had a strange intermitant hum noise, if he pushed on the back panel or the left valve the hum would start, I removed the back panel switched the amp on and pushed the offending valve, I could see as I moved it the wire on pin 5 was moving in the solder joint, resoldered that joint and there was a few more in the amp I wasn't happy with, gave both a good testing, another happy customer.

26/04/2026

Had a wem dominator mk111 in for repair and to mod channel 1 as a fender delux. Had to redue some solder joints that were a little duff, replaced all filter caps as one was bulging, and another had its inerds escaping. Tested all valves one of the EL84s was worn, so replaced em but the bias was going way up. It took me around 3 hours to find it the old mullard valves pins 1 and 2 are linked internally but new valves aren't so looking under the chassis the factory had connected to pin 1 hence I had no bias, put it this way my language cannot be repeated hear lol.any way finally sorted it and does the first channel have some, I also used the bright switch to connect a capacitor across the cathode resistor, all to what the customer wanted.

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