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Hello Forum Peoples!
My brother and I own four Fender 400 PS anchors, beastly bass amps dating back from 71-76 rated for roughly 480W of AB2 RMS power (160W RMS conservative on 3 seperate 4 ohm taps). The PI is a transformer driven by a 6L6GC. Apparently on a fresh set of glass and some tweaking, it can reach an outrageous 600 clean RMS watts (out of 6 power tubes... ridiculous).
http://www.timeelect.com/400-PS-IDX.htm
So, as the story goes, this amp and the GE 6550A were a match made in heaven. This amp will literally melt anything substandard to
THAT particular 6550 tube (see link). Apparently, the magic is in the screens and their ability to "take the abuse", as Richard Koerner once told me. So, my question is the following:
Does anyone know of a new, current production 6550/KT88 tube, that comes close to the 6550A by GE? I've tried the JJ KT88 with success but I find it's sonic character all-too-different compared to a GE 6550A. Never attempted the JJ 6550. Scared of trying anything except a Gold Lion from New Sensor. As for Chinese tubes, I'm curious to try the Penta KT88 as I have a quad of those in a 100W and they're pretty awesome, but any others make me very wary. Any thoughts?
And if anyone is adventurous enough to explain to me how this amplifier achieves what it does, please share, cause I'm still confused. I mean, it'll pull some 1-2A at 600V from the power section. But, how it doesn't outright melt ANY kind tube when outputting up to 200W from each tap is a mystery to me. Is it in the tubes themselves, the transformers, or is it the AB2-ness of the amp.
Thanks a bunch guys. Your input produces fantastic output every time.
Donovan
Follow Ups:
Yes, the GE 6550A has VERY tough screen grids. Nothing else comes close. Those bruiser bass guitar amps are specifically designed to use the GE tube.
For all practical purposes, the SED (=C=) 6550C is history too. Replacing the power O/P tubes at relatively modest expense is an enormous problem. The practical solution to retubing may be current production Sovtek 6550s and the installation of g2 current limiting resistors. G_D alone knows how that setup will sound.
BTW, the EH KT88 is an excellent value, but it can use a bit more bass extension.
Eli D.
It is worth mentioning that this amp (and lots more from this time period) run the screens atapproximately 1/2 of the plate voltage. This increases reliability tremendously.
Lots of modern amps (both Hi-Fi and musical instrument) now run the screens near plate voltage. Perhaps modern designers should relook at older designs in the interest of reliability.
Well...you could always use NOS GE 6550A in them. I just happen to know someone who has a very large supply of NOS/NIB JAN GE's.
Drop me a line if interested in that.
V/r
jstrm
No Sir, this topic has been gone over on the Fender Vintage Amp forum. To get the OEM output you'd need GE made 6550A. Or perhaps selected TS 6550.I must also remind you, that this amp takes several other unique step to yield a reliable amp, even with GE tubes. Do you have these & adept at using them? Maybe send a message to the author of that great site... for current techs in the know.
Edits: 08/31/12
Schemo. Fender usually shipped the amp with 12AU7A in V4 position.
Oh man, I'm well in the know when it comes to this beast. Like I said, I've spoken to the owner of TimeElect personally, and he's taught my local amp tech the ins-and-outs when it comes to properly servicing them. I don't have said tools and certainly not enough expertise to be comfortable sticking my hands where they don't belong. 600V at 1-2A? No thanks. I'll live another day.
I guess you're right, if I wanted to run it like it ran before, then GE is the way to go. However, the point of looking for a new tube would be to avoid the outrageous cost of the GE. Frankly, I don't have $1000 to blow on a sextet for matched GE 6550A's, let alone for 4 amps. That's ridiculous. This is why I posted in the tube forum; it's in the hopes someone would have more extreme use with a tube, not so much the amp.
And I don't if they cleaned their closets, but I don't see any relevant info on the Fender forums :( In fact, this thread comes up as the 4th result when googling "vintage fender forum + "Fender 400 PS""
Sorry, OT was something not related to the 400PS, then digressed (I know you find that hard to believe --- digression on a Board).... 8^)
Into 20 pages on the amp, speaker arrays, Ed Jahns, and inadverted welding, in the shop.... 8^)
Doesn't help you... Final thoughts were = Owensboro GE 6550A, period AND you better know what you are doing or there goes $4K worth of Hold tubes.
Edits: 09/03/12 09/03/12 09/03/12
Yes, prices for NOS GE are very high...all a function of supply and demand, and the supply is extremely scarce...especially for matched pairs, sextets, octets..etc. Got any idea how many tubes have to be gone through correctly to get a truly matched octet? A lot!
The ARC guys sure like them! But I understand your desire to make your gear work at minimal cost...most of us are in that boat.
My post was just to give you an option.
jstrm
Much appreciated guys. JSTRM, I appreciate your offer, and if all else fails in my quests, I may contact you for those tubes.
And Eli, ya, I thought of that, but frankly, I'm not a fan of trying to mod this amp without some advice/guidance/assurance from Richard of TimeElect. I'd agree the EH KT88 has great value. I like it in my Ampeg V5's because it lacks that bass extension. It makes for a great rock and metal tube. I found the JJ KT88 extends the bass more than the GE, but you also lose the 6550's midrange punch.
Sigh... I need few thousand dollars of tubes, a hundred hours or so, and some patience trying each out, and try to make them melt...
Interesting point:
" A year or so back I had a 400-PS owner stop in with a set of NEW Russian 6550WE tubes to be installed. I really had to play games with that 400 to get those tubes to run. This was their best day right out of the box for these tubes, and the best they could do was 124 watts per load at 100 Hz for a 372 watt total output from a conservatively 435 watt rated amp.
After 72 hours of hard dynamic signal running time and a re-adjustment, that 372 watt total figure dropped by almost 50 watts.
It's one thing to print the specs for a tube, and quite another to make the tubes that live up to those specs with LONG continued service life.
Here are the GE-6550A data sheets for you to see if the other so called 6550's measure up to the high performance GE-6550A standard.
High performance with long service life is the hallmark of the GE-6550A. "
BTW... you need very good speakers for this amp. As you prolly already know. I love the K-series JBL's. These these make a Twin Reverb SING! But, any high powered quality instrument speakers will do.
IMO 372W from an amp rated 435W is not bad.
Do bear in mind that that amp needs 120VAC line voltage for full power output. It pulls a lot of line current. It is fused at 10A. If your AC line sags a bit under load, 372W may be normal.
It is permissable to insert dummy plugs into unused outputs in order to get full power fron one or two outputs. Each output jack turns on a pair of 6550's by completing the cathode to ground connection, but you probably already knew that.
mt
Just got this puppy! Pretty cherry 1971 silverface Vibrolux Reverb.
Edits: 09/01/12
Oh Yea!
Very nice indeed!!!
V/r
jstrm
Ya, see that's one of my fears. I noticed that with some of our 400 PS amps: so-so tubes lose output and life VERY quickly. It's downright scary how quick it is. But, the one loaded with GE 6550's in it still sounds pretty amazing (even with its tired set). Ya, I'm thinking more and more I may have to bite that bullet...
Hmm, and yes! Very sexy amp, sir, very sexy indeed! That thing is VERY clean. Closet piece?
And ya, I have the speakers and cabs for the 400PS. And it's funny, except one 8x10 loaded with Jensens, my bass cabs are all JBL-loaded, a mix of K and E series. Stunning sound. I'm hard-pressed to find comparable equipment. I am a HUGE fan of the E-120. And a recent and interesting catch is the G-125. For bass speakers, I have a lot of option as well, but not the space and hours to properly test them.
Here's a portion of the collection shared between my brother and myself.
If there is any way to scrape together what it takes to get the GEs - DO IT!There is nothing wrong with a Sovtek 6550WE - except it's not a GE 6550A. That amp was designed around that tube. The GE is VERY underrated BTW, specs-wise. The 400 chews up and spits out other similar tubes, the GE survives.
It has crossed my mind that the KT-120 MAY be a tube the amp can use. I talk to Rich Koerner all the time - we've been friends for a long time - and I will mention that to him.
I believe the Ei KT-90 type III (properly made) might have been another tube that could have worked, but it's a moot point since they are nearly extinct as well. But the KT-120 might just be worth investigating if I can talk Rich into it. DO NOT put KT-120s in your 400 until much more is known about their use in that amp!!
Edits: 09/04/12
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