biscuitdough wrote: Thu Mar 23, 2023 9:12 am It doesn’t seem like there will ever be power tubes for that again, but maybe it could be adapted to use a different power transformer and get the voltages down to what a current production 6550 can tolerate. Probably have to change the dropping resistors so the preamp gets the right voltages. Definitely looks like a challenge.

There are plenty 6550A tubes on ebay...but yeah they are $$$$.

Instead of choking it back, could a Fender 400 PS be modded to take a higher-power tube like a KT88 without a huge mod?

I read up on this amp a few times years ago and apparently it is an ODD DUCK build-wise. Most information I have ever read about this amp is at this Heaven's Gate-style site: http://www.timeelect.com/400-PS-IDX.htm

The original author (also an odd duck) lays out a case after having worked w/ Ed Jahns how "oh this is a special amp and only certain special people should work on this" and how special the 6550A tubes are...and then also has a couple photos up of the chassis with power tubes in them that are CERTAINLY not GE 6550A...
So IDK what to think here. It's a super interesting amp though for sure.

The 010309 tubes in the 400PS are just selected TungSol 6550s (it says it on the schematic). Selected for what? Voltage i'm guessing. The plates in the 400PS are run at like 700V and most 6550s are only rated up to 600V. The KT88, however, is functionally the same tube as 6550 but rated up to 800V. So yes, one could use a KT88 in this place with no mods.

Dr Tony Balls wrote: Wed Mar 22, 2023 12:26 pm Used Balls G-50 if anyone is interested. Marshall 2204 circuit that I "fixed" to remove/tame all the stuff I dont like from the 2204.

https://maindragmusic.com/collections/a ... balls-g-50

I'm actually have tempted to sell my '79 JMP 2204 and buy this.

Garth wrote: Wed Mar 22, 2023 2:44 pm

Nate Dort wrote: Wed Mar 22, 2023 12:15 pm Broken Fender 400PS for $100 in Athens

Man, you would be THE GUY who should get it because that seems like would require intense labor of love/patience/expertise.

You should hit up some of our Athens folks & see if you can get it.

SO YOU SHOULD KNOW that the guy who is selling this is exactly the guy I'd take it to if I wanted to try and fix it. If he can't fix it, it's not fixable. Abandon hope all ye who enter here. John is my favorite tech in town because he charges reasonable prices and also knows when to say "Maybe you should sit down before we have this talk" right before he tells you Ol' Yeller needs to go out behind the barn.

If he's given up on it, consider it beyond hope.

That's kinda what I figured. Looks like it already had some cap work done to it. I'm guessing it probably has 1 or more bad transformers.

Conversely, $100 for the chassis and case is probably pretty good if someone wanted to build something new under the hood?

I sent the listing to my pal in Athens and he said essentially the same thing - if that dude can't fix it, no one can.

I remember a Fender 400 sitting in the little mom and pop music store run by aging metal head. I was still in Bandit 112 land at the time, and I was just looking at this giant amp and the dude at the counter didn't even look up from his copy of Kerrang and yelled over, "Kid, that amp will kill you if you look at it wrong."

Does a PS400 need a load on all 3 outputs when running?

twelvepoint wrote: Fri Mar 24, 2023 9:05 am Does a PS400 need a load on all 3 outputs when running?

No, that was one of the brilliant aspects/innovations of this design IIRC.

dontfeartheringo wrote:

Garth wrote: Wed Mar 22, 2023 2:44 pm

Nate Dort wrote: Wed Mar 22, 2023 12:15 pm Broken Fender 400PS for $100 in Athens

Man, you would be THE GUY who should get it because that seems like would require intense labor of love/patience/expertise.

You should hit up some of our Athens folks & see if you can get it.

SO YOU SHOULD KNOW that the guy who is selling this is exactly the guy I'd take it to if I wanted to try and fix it. If he can't fix it, it's not fixable. Abandon hope all ye who enter here. John is my favorite tech in town because he charges reasonable prices and also knows when to say "Maybe you should sit down before we have this talk" right before he tells you Ol' Yeller needs to go out behind the barn.

If he's given up on it, consider it beyond hope.

I assume McNeece? If so, yes, you are buying parts, not a salvageable amp. He would have gotten it running if it was able to be fixed.

I had a friend offer to send me one of those amps from Japan. I was mighty intrigued. I read up on them, and I decided against. I already have Ampegs I gotta keep running. But if it was local and it worked, I would still be pretty interested to try it out.