best 6550's for model t

[AdmiralB]

The screen rating is exceeded in 6550's when used in a Sunn with today's wall voltages, whereas the KT88 has no problem with them.

The screen rating was exceeded back with '67 wall supply too.  If every amp maker had abided by design standards, we'd have no 6V6-powered amps.

Every single 100W Marshall sold in North America with 6550s - and about half of the 50Ws - exceeded the screen ratings of the 6550 also, but that doesn't seem to have hurt anything.  In fact, I can't think of ANY application that 6550s have been commonly used in, except for the SVT and the Fender PS series, that doesn't exceed the screen ratings.

If anything, Sunns are easier on the screens than most other amps, since the screen voltage fluctuates with the plates, as opposed to being regulated.  They may be 550V at idle but they're lower in actual use.

I'd make a wager - take a new set of JJ KT88s and a NOS set of GE 6550A, run them full-tilt in a 200S, and I'll bet a C-note the JJs die first.

[gray]

Hmm, the plot thickens!
On my Model T it's written where the tube plugs into the amp " 6550". If it's okay to plug the JJ KT88's in it, I will. But if I can find some mint NOS 6550's, I'll do that, too. I guess it all depends on what I can scare up. I may just opt for the JJKT88's out of tone quality regarding the bass and the simple convinience of availability. But if I find some good NOS 6550's, I'll get them, at least to just save for the right time.
I might add that I can certainly see a vintage tube outlasting a new tube. But I've been told that newer tubes are getting better and better as tube amps become more and more popular.

I'll add that these posts have all been very helpful; thanks.

[AdmiralB]

There's absolutely nothing wrong with JJ KT88s.  I use them in my 2000S and one of my 200Ss.  But they're not the ONLY thing out there, nor necessarily the BEST thing for every application.

If you want the absolute highest clean output, you need a set of EI KT90s.  Unfortunately good ones haven't been made since before NATO bombed the bejesus out of that area.  Jim McShane is the only dealer I would trust for a set, and since good ones are scarce, they're also quite expensive.

Myself, I wouldn't pay huge dollars for NOS tubes.  You'd be looking at at least $250 for a set of G.E. 6550As, half again that for Tung-Sols, maybe a little less for Sylvanias.  The only NOS KT88 is the real KT88, GEC, and IF you found a set, you'd probably be in the kilobuck range.  

The currently made stuff sounds good, makes good power, doesn't last as long, but costs what?  1/3 as much?

I would be very careful about differentiating between 6550 and KT88 as the terms are used today.  I would treat them as equivalent types, especially since some of the brands that do both (Svetlana/SED and Sovtek/EH) may well simply put the same guts in two different-shaped glass bottles.

Another option would be used old stock.  You could probably find a used but test strong set of G.E. for around $120.

[mcgill85]

I'm looking at buying a Model T off this guy, but I was reading on Harmony Central's reviews for the old model t's that the clean was amazing, but the overdrive didn't break up as much as they'd like.  I found this hard to believe as I'm trying to replicate the doom-y sound alot of people (sunn o))), khanate, isis, earth, etc) are achieving with this amp...

Not to change the topic of this post, but instead of achieving loud clean volume with the least breakup, what tubes could I use to get the most sustainful, creamy, sunn-y overdrive that I've heard on all these albums and concerts?  Do the KT88's produce this tone better?  Again, I've heard the 6550's have a chime-y clean sound, but leave something to be desired for full-on doom metal overdrive.

If you don't know what type of tone i'm talking about, go get Sunn O)))'s album "Black One"... I want that evil sound...

[AdmiralB]

The old Model T is a Marshall Super Bass preamp stuck onto the ultralinear 6550 power amp.  It is what it is, as far as gain - that is, not at all high-gain.

There isn't going to be a significant difference between brands of KT88/6550 in terms of amount of or type of distortion.  Power tube distortion isn't really apparent as 'distortion' anyway.

Anyone getting mondo distortion out of an old Sunn is using a pedal or other booster.

[Soundmasterg]

With a UL amp, you can disconnect the negative feedback loop and get a little more grit out of the amp....this is what Dr. Z does with his amps. Its as simple as disconnecting one wire. Doing this won't make it crunch as nice as a Marshall with EL34's though, but it is a step in that direction.

Greg

[AdmiralB]

True.  I've never tried that on a Model T; doing it in one of the older amps will likely cause instability, although you can increase the value of the feedback resistor.

One of my 200Ss was a little nastier than the rest; turned out the 1K feedback resistor had drifted up to about 2K.

[Soundmasterg]

Yes, you might get instabilities if you disconnect the NFB loop, and then you would either have to reduce gain, or connect the NFB up again or change the layout. You could also brown it up a bit by going with a large series resistance on the screens of the poer tubes, but when running UL, this can be a problem if the mismatch between the screen and plate is very big. Lots of ways to get more grit though. Lowering preamp and phase inverter voltages is really easy too and sounds and performs well.

I've never played a Model T, but from what I can find out about them, they sound similar to a 2000S with a master volume and some preamp changes. Is that close to the mark?

Greg

[Tom Loizeaux]

You asked for the "best 6550s" for vintage Sunn amps...
well Tung-Sol made 6550s ARE the best! Nothing else sounds quite as nice or holds up nearly as well.
If you really want the sound these heads were made to deliver, get the original Tung-Sol 6550s. They were branded as Tung-Sol, RCA, and GE. They are the "coke bottle", or ST shaped tubes, but not to be confused with the several versions that have come from China and Russia in recent years.
Go for the real thing!

Tom

[AdmiralB]

Tung-Sol made 6550s ARE the best! Nothing else sounds quite as nice or holds up nearly as well.

Well, the first part of that is in the ear of the beholder, is it not?  Personally, I would agree with that statement, *for guitar*.  However to say that nothing else holds up is debatable; certainly G.E. 6550A outstrip the T-S in terms of performance.

If you really want the sound these heads were made to deliver, get the original Tung-Sol 6550s.

That would be true if Model Ts ever came with Tung-Sols, which they did not.  They came with G.E. 6550A.

[Soundmasterg]

Yeah, people seem to forget often that the Model T didn't come out until the early 70's, by which time Tung-Sol was gone I believe. Tung-Sol 6550's are very nice sounding, well made, and long lasting tubes for sure. They were the original tube in my '67 200S that I sold years back, and sounded great. I think for bass however, KT88's sound better, and the 6550A from GE will hold up better in that circuit too due to the higher ratings. The new Russian made Tung-Sol 6550 has been getting good reviews.

Greg

[Isaac]

I have a Concert PA that still has the original KT88 tubes in it. Maybe I should try those in my 200S, or Sentura II.

[Tom Loizeaux]

You may be right that model T heads were originally fitted with GE 6550As, but every model T I've seen (and owned) had Tung-Sols installed.
I've tried some GE 6550As and found them to be a little noisey and prone to microphonics compared to the Tung-Sol 6550s.
The only "new release" 6550s I've tried were the first and second edition of Svetlanta 6550s a few years back. They were prone to over heating, couldn't disapate the voltage and often went into runaway!
I went back to my stock of Tung-Sols and have never had any problems with them! I fit all my Sunn tube bass heads with these Tung-Sols and love the rich, punchy sound I get.

Tom

[Soundmasterg]

The first two generations of the Svetlana (now known in the US and Canada as Winged C or SED) 6550's were very poor, which is why they were discontinued. The Winged C 6550C is an excellant tube that sounds and performs well. I use six of these in my vintage Ampeg SVT and they have been holind up to that brutal circuit for 4 years now with moderate use with no problems at all. Most of the new manufacture tube companies have been forced to improve their quality because NOS is fast disappearing on a large scale, and OEM manufacturers have been putting pressure on them to improve quality. As a result, you have the Winged C's, the new Tung-Sols, Chinese made stuff, the EH 6550, and then many KT88's too like JJ's for instance. They all sound pretty good, and hold up quite well over time to use and abuse. The 6550/KT88 family is a long lived tube anyway because of how it is made, but the modern stuff is very good. If you get some nice NOS stuff, its better in most cases, sometimes not in sound though, but in longevity for sure, because NOS stuff is better made all around. But its going away and will be gone within 10 years most likely. You may as well support the new manufacturers so that they can stay in business and build us good sounding and good quality tubes. Just do some research before you buy would be my suggestion.

Greg