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Monster Fender rig - 400 PS
Psycho Bass Guy:
--- Quote from: Tim Brosnan on January 24, 2014, 09:18:40 PM ---My understanding on the guy who designed that amp-if you called him up with a technical question about it, he would make you prove to his satisfaction that you were competent enough to work on it, otherwise he would tell you to buzz off, he wouldn't help you. Anybody know if thats true?
--- End quote ---
His name is Ed Jahns and that is true, and I don't blame him one bit. I'm not posting links because the links lead to where my amp disappeared.
--- Quote ---Now, if that amp had the kind of transformer that the SVT had-one that allowed you to put the power to one cab-could it have seriously competed with the Ampeg?
--- End quote ---
Imagine a vintage blackface Bassman tone at SVT volume: that's the 400PS. If it had been equipped with a single output, Fender would have put a serious hurting on Ampeg, Acoustic, and Sunn in the bass amp market.
slinkp:
So with the three-tap output transformer.... What happens if you only connect one cabinet? Do you safely get one-third of the power, or do you fry something?
Likewise, would two cabinets give you 2/3 of the full power?
(As you can tell, I do not know diddly about output transformers.)
amptech:
--- Quote from: slinkp on January 25, 2014, 02:06:35 AM ---So with the three-tap output transformer.... What happens if you only connect one cabinet? Do you safely get one-third of the power, or do you fry something?
Likewise, would two cabinets give you 2/3 of the full power?
(As you can tell, I do not know diddly about output transformers.)
--- End quote ---
I´ve never seen one in person, and was also under the impression that it had three OT´s.
The only info I´ve come across, is from ´the fender amp book´ by John Morrish.
The book has an early 400PS ad, one head and one cab (folded horn, but does not look like the ones in the ebay listing) and here´s the text
below: ´The 400PS was one of fender´s more bizarre efforts. A giant 440W RMS tube amplifier using 13 tubes drove a SINGLE 18in. speaker in a folded horn cabinet of frightening efficiency´
and ´…the astonishing 400PS coupled three separate 145W tube amplifiers…`
I remember reading the ´warning´from the designer, but I never found schematics for it.
Would be great to hear it though, just because.
Psycho Bass Guy:
--- Quote from: slinkp on January 25, 2014, 02:06:35 AM ---So with the three-tap output transformer.... What happens if you only connect one cabinet? Do you safely get one-third of the power, or do you fry something?
Likewise, would two cabinets give you 2/3 of the full power?
(As you can tell, I do not know diddly about output transformers.)
--- End quote ---
The three outputs are 145 watts each and if unused, like most Fenders of that era, the speaker output jacks short to ground, so you're wearing out the all tubes worse if you only use one output than if you use all three (the supply isn't strong enough to make THAT damage the tubes, but it's still not good for them). It has reverb, too. Fender really tried to throw as much stuff on it as possible, but the output scheme and those big folded horn cabinets which housed a single Cerwin Vega (IIRC) 18" were a PAIN to haul and even harder to hear than Acoustics of similar design. Against Ampeg's smart design, it didn't have a prayer. That's why there are so many old SVT's out there. They sold like hotcakes. I don't like the book overall, but Aspen Pittman's opening line in 'The Tube Amp Book' chapter describing the SVT is, "It's been on as many stages as Shure mics..." Had Fender gotten their act together, they would have had a much bigger piece of that pie.
amptech:
It´s not a good book, nor do I use GT tubes - I got the book because at the time I did not have a computer with internet.I do recall them being made at the time, but they were not very common up here in the north :) I spent much time to get schematics for amps, so the collection of schematics was very useful.
Funny thing, I remember a Musicman thread here when I mixed up Leo Fenders involvement in designing the amps; I read some pages of the Aspen book yesterday - and there it was:
´Musicman was started in the mid seventies by some of the ex-Fender employees including Leo himself in a consulting role. However,
Leo had nothing to do with the amp line… `
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