Monster Fender rig - 400 PS

[gearHed289]

Wow, I never knew these things had three output transformers. Not a fan of the folded horn, but this is just plain cool!

http://www.ebay.com/itm/370988628220?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

[Highlander]

[jaw-dropping] Gosh... [jaw-still-dropping]

[Granny Gremlin]

I saw one of those cabs IRL once in a store. The grill was gone though.  Just so massive and impressive looking - I woulda grabbed it if not for the HUGE!  God damn having to hump 3 of them around.

Also r right next to it they had a similarly shaped (but not horn loaded?  can't recall) 4x12 (Bassman cab I think).  I was very surprised at how quickly those got sold (they weren't there more than a week or 2 - I lived around the corner from the store at the time so I popped by on the regular), which was the even more amazing thing.

[Psycho Bass Guy]

Wow, I never knew these things had three output transformers. Not a fan of the folded horn, but this is just plain cool!

They DO NOT have three output transformers. They have three taps on the transformer secondary split from a single primary winding. I HAD one until I sent it away for cosmetic restoration and it, the nice set of NOS GE 6550A's, and the custom roadcase it was in disappeared into New Jersey.

[pilgrim9]

I saw a head with one cabinet in a pawn shop 35 years ago. The guy turned it on and it started on fire so I never got the chance to try one.

[Rob]

They DO NOT have three output transformers. They have three taps on the transformer secondary split from a single primary winding. I HAD one until I sent it away for cosmetic restoration and it, the nice set of NOS GE 6550A's, and the custom roadcase it was in disappeared into New Jersey.

Thanks PBG!  I was trying to figure out what the third trans would be for 

Ummm Jersey Devil?

[Psycho Bass Guy]

I saw a head with one cabinet in a pawn shop 35 years ago. The guy turned it on and it started on fire so I never got the chance to try one.

Yeah. They'd do that. The amp runs its six 6550A output tubes so hard that it uses a 6L6GC for a DRIVER tube and has a large interstage transformer, a pretty rare thing for a bass amp. CBS Fender was trying to compete with Ampeg's SVT and Acoustic's 360, and it was probably some marketing "genius" who came up with the idea of requiring three cabinets to get full power out of it- to increase cabinet sales of course. I'm sure the design engineers were cussing them up and down, because making it with a single output like of all the OTHER amps on the market would have done nothing to increase the cost and would have made the amp far more reliable, but once the custom OT was in place, there was no going back. I suppose if you knew how to wind transformers, nowawdays a person could make a single replacement OT for it. If it were a toriod, it wouldn't even be much bigger than the original, but that output stage is VERY unforgiving: Class AB2 AIN'T for the average Marshall or Fender tinkerer.

Fender ALMOST learned its lesson and gave the 300PS, the 400PS's lesser powered successor, a single output, but to save money on the output transformer, that single 300 watt output was at 8 ohms ONLY. Folks who put a four ohm load on it were treated to watching their output tubes literally melt because unlike most other tube amps, the 3/400PS had a supply (HUGE power transformers) capable of delivering the extra current the tubes were trying to dissipate and where they were being asked to get hotter with current instead of being the voltage amplifiers they were designed to be, they overheated and melted their envelopes. The 300PS used a quartet of 6550A's with a  6V6 for a driver.

[Psycho Bass Guy]

Thanks PBG!  I was trying to figure out what the third trans would be for 

Ummm Jersey Devil?

No. It MAY be recoverable, but with my health and employment situation, I've not had the money or energy to chase it.

[fealach]

That's pretty impressive looking.   Tough to find someone local who likes that sort of thing and has the money and space for it.  I have no idea what the cabs sound like, but I like my 400PS head. I could live without its bizarre output configuration, but it sounds good to me so I'm happy.  At least until the day it needs work.

They DO NOT have three output transformers. They have three taps on the transformer secondary split from a single primary winding. I HAD one until I sent it away for cosmetic restoration and it, the nice set of NOS GE 6550A's, and the custom roadcase it was in disappeared into New Jersey.

That's terrible.  Especially with those tubes!   

[Tim Brosnan]

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?


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?

[Psycho Bass Guy]

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?

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.

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?

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]

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.)

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]

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.)

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... `