Home Brew Fender PS 400

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tiozotube
Junior tube assistant
Posts: 2
(2/16/04 4:10 pm)
 Home Brew Fender PS 400
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 OK, I just cant take it anymore. I have to build my own amp. I would like to home brew a Fender PS 400. I have located the schematic, (thanks to this forum), some of the values are hard to read but I think I can make it work. I am also having trouble reading the Fender part number for the power trans. Does anyone know what the number is, or a source of supply for a suitable substitute. So you can see the same drawing I am looking at ....
www1.korksoft.com/~schem/.../400ps.pdf
If you know of a better quality schem that is posted online somewhere that may be helpful let me know please.
I have yet to search out the availability of the "special design" 6550's. Fender lists them as part # 010309. Are these available, anywhere?

At this point I am still researching parts and materials, but I expect to begin building soon. Any help would be greatly appreciated.
Thanks in advance!
mike
 
jc
I only work on Fender's
Posts: 677
(2/16/04 6:36 pm)
 Re: Home Brew Fender PS 400
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 That is a big and interesting amplifier. Maybe I am wrong but it looks like there are 2 output transformers. One is a single-ended 6L6 (they list this as the phase inverter!) that feeds the 6x 6550s. You are also going to need a huge PT to power all of those tubes.

My guess is that you probably won't find anyone who has home-brewed this amplifier. It's a little off of the beaten path!

Is this your first amplifer? It may be a little complex and out of the ordinary to get a lot of exact help from everyone. Just my opinion.

Are you going to do both channels?

Since this is a 70's era fender, have you checked ebay?
 
ganzonimx
Hey get your own solder
Posts: 386
(2/16/04 7:08 pm)
 Re: Home Brew Fender PS 400
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 It's indeed a interesting schematic. All other high powered bass amps I saw have a cathodyne PI followed by a mid mu triode booster to drive 6550 or KT88.

This circuit drives them with a power pentode into a transformer to get the necessary voltage. I always thought how high the voltage must bee to drive a KT88 and how to get that strong signal without having any distortion from the PI. This seam a good approach, but I could imagine it's not that easy to get this kind of transformer...

Cris
 
6G6
Junior tube assistant
Posts: 81
(2/16/04 7:14 pm)
 Re: Home Brew Fender PS 400
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 I like Fender bass amps as much as anyone, but I wouldn't encourage you to build that one.
There's a lot to go wrong there.
Check out www.timeelect.com/400-PS-IDX.htm
They like PS 400s real well. They also have pictures of MELTED 6550s! The mention that there is a 30 step factory procedure for biasing those and the melted tubes came from not following it.
Good luck finding all the iron involved there.
I don't know what Fender put in them, but I found pictures of them with RCAs, GEs and Tungsols.

That said, I do sorta lust after one, myself.
I saw one recently at Guitar Center in Arlington Texas for a grand with one cab.
I'd guess that's close to what you'd spend for the trannys if you can find them.

Of course you need three cabs to get full power.
I think I'd use one of the folded 18s, a ported 2-15 and an 8-10 to get a full range rounded sound.


 
bnwitt
Senior tube assistant
Posts: 292
(2/16/04 8:59 pm)
 Wow!
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 I'm speechless. A 30 step setup procedure? Holy moly. Don't let any Bass player customers get wind of this thing or you'll be building one for sure. Man I get a chubby just looking at that schematic.
 
6G6
Junior tube assistant
Posts: 83
(2/17/04 9:45 am)
 Re: Wow!
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 I'm starting to wonder who will be the first one here to take it as a personal challenge to prove that it can be done.
If someone finds a warehouse full of left over tansformers it might happen. Otherwise I have my doubts.
I always thought that amp seemed to be a product of More's law.
You know:
If some is good, more is better,
so, too much should be just right!
 
 
tiozotube
Junior tube assistant
Posts: 3
(2/17/04 10:53 am)
 background & answers PS400
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 Thanks to those that have responded thus far, JC, Ganzonimx, 6G6,and Bnwitt. To answer a few questions first. "Is this my first amp.."
No.
I have been kit building solid state and small tube projects since I was 9 years old, Lafayette, Heathkit and the like. Built a color TV at age 12, built my first "computer" at 17 (an old Heath Project my uncle had laying around). Six years military, in shop, test, troubleshoot and repair, weapons control, inertial measurement systems, flight controls, HUD units, displays and controls, radar - receivers, transmitters, and antenna's for some of the most advanced fighter aircraft in the world.
The last 13 years have been in satellite TV, cable TV (distribution or line work - from head end to tap) and most recently getting incredibly dirty working on boats, er, excuse me, Motor Yachts.

Granted I have not tackled any real project builds in over ten years, but that does not mean I have been inactive. I work with a group of young men that have a rock band, I do some of their amp/preamp work, cable repairs, sound tech etc.

Yes this is a big project, and yes, 6G6, you are probably correct in that it may be too much, but I have to do this. For my own sanity.
That being said....
Yes the Iron poses a problem, and the setup does concern me, but I believe it can be done. If Fender has called for a 30 step setup procedure, then it has to be in writing, somewhere. Since this is a given, that the procedures are in writing, someone, somewhere, must have access to them and be able to make them available.
Seems like a plan..... but if it all gets too hairy, I have "settled" on an alternative or back up plan that is more viable. A 180W Super Twin. Fender #013606 Rev A according to drawing. Drawing can be found here www.ampwares.com/ffg/ look in the left frame for the super twin reverb link to the schematic.

Thanks again for your interest, your concern, and your input. I look forward to talking with each of you at length about my project and yours. I see from scanning the boards that each of you have your own experiences and can relay much information.

mike
 
jaysterdude
Junior tube assistant
Posts: 19
(2/17/04 11:00 am)
 PS 400
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 Hey guys,
I've worked on a few 400's and his little brother, the PS 300, and the 30 page setup procedure is a real thing to deal with, you can't fudge it or skip steps. To me, they are a marvel of tube technology, but at better than 90 lbs for just the head(!), every owner had something to say about hauling it around. (And none of the comments were good!)
The 'special' 6550's were high voltage tolerant, if I remember correctly, the had to be able to stand 750+ volts, and I think the old GE's were the only ones to do it. There have been some new 6550's on the market that are supposed to be able to handle it, but in my experience, they didn't last very long and didn't sound very good. My last 400 customer ended up selling it because it was just too much of a hassle to keep going. I think his last re-tube cost him $480.00 for the 6 matched GE 6550's.....OUCH! (He didn't get them from me!)
Good luck on your quest.....maybe a SVT is another option? That amp is why Fender came out with the PS series....Ampeg was taking away all of there business in that market....
Jay
 
6G6
Junior tube assistant
Posts: 84
(2/17/04 12:23 pm)
 Re: PS 400
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 Check drtube.com for Marshall schematics.
The model 2001 bass amp uses eight 6550s for 375 watts.
It looks much simpler and wouldn't require NOS tubes.

Also, if they would be big enough for you, look into the Ampeg SVT and Fender PS 300.
Next level down (powerwise) would be the Marshall Major and Sunn S2000.

I'm not really trying to discourage you, just pointing out easier options. I think all those could be built with Hammond transformers.
 
jc
I only work on Fender's
Posts: 679
(2/17/04 6:40 pm)
 Re: PS 400
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 for sake of aurgument:

Hammond transformers
PT - 278CX 400-0-400 465ma 6.3@6A
PI OT - 1629SE 25 watts 5,000 primary
OT - 1650W 280 watts 1,900 primary

I am not sure what the choke would need to be.


  
 
 
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