The Amp Garage

I mght do that for a valuable and all original vintage Marshall, but for this amp, if the pots are bad, I just replace them. It's so far from being original that there's no point polishing those turds!

Yes, I have Tektronix scopes on both my benches, and load resistors. I'm fairly well equipped. I'm ironing out problems in this 400 PS and it's getting close to finished. I've had to replace a few pots, and expect to replace one or two more. If Deoxit D5 won't bring a pot back, it's done. replace it.

I've heard reports that recently made EH KT88s are junk that fails quickly.

KT120s are an option. I have six Sovtek 6550WEs to try in it, if there are no horror stories about that tube in this amp type.

Getting worthy tubes for these things can be an issue, as they were built around the Tung-Sol 6550A and were the incentive for the development of the GE 6550A. Neither tube is impossible to get today in NOS condition, but they're not exactly cheap. No, they can be stunningly expensive. However I've ...

I spent most of the day on this beast today, to good results. It's now running more or less as it's supposed to. Yes it gets VERY loud. I've got three cabinets hooked up to it and it's not lacking for power, that's for sure! That's not to say it's complete yet but I was able to identify the parts of...

Thank you! That will certainly help!

I'm bringing the 400PS back to life. It had already been rebuilt by a friend of mine but he didn't complete the job and he's dead now so I don't expect him to finish it. It's only got a little bit of work left to do to complete it. Reinstall the reverb transformer that went missing, troubleshoot a v...

Rather than add parts to an already good sounding circuit, I recommend starting by adjusting component values to achieve what you want to achieve. I would, in this case, start by increasing the values of R4 and R7, the plate resistors for V1A and V1B, from their default values of 100K to some higher...

Master volume circuit restored. I now have a running amp. It's not totally right yet, the volume level is really low, but I know that there's more to be done, and now that I have a complete signal path, I can find and correct that and other issues.

Closer investigation reveals that the circuit is less complete than I originally thought. Note that the cables at the master volume control are cut short. There IS no master volume circuit, at the moment, and yes, some of the missing connections do involve that 6L6. I'm going to have to rebuild from...

I've acquired the monster, the beast, the highest output production bass/guitar tube amp of all time, the mighty 435 watt Fender 400PS. Who here has any experience with these? I may have some questions and it's efficient to ask experienced people who can shorten my path to learning. First off, I'm a...

Yeah, I'll probably just try to rebuild it to stock condition, and when it's working right, sell it and let somebody else do what they want with it. I've got a Fender 400PS to occupy my time when I'm not busy working on my '63 Tremolux, '67 Vibrolux, and '65 Super Reverb, all of which are other proj...

I CAN build purely from the schematic. I've only got about 35 years of experience as an electronic technician, and I've worked on every kind of equipment you can imagine. Audio, video, radio, avionics, medical, test and measurement, pretty much every category there is. But in this case I want to reb...

I'm starting to rebuild a partially disassembled Bassman 135 that was partially taken apart by a friend of mine, who was going to modify it, but he died before the job was done and I "inherited" the amp. I want to rebuild it to stock specs FIRST before I make any decision as to what to do with it. I...