JJ 6550 vs KT88

[godspeed68]

Hey TB,

I've used the JJ KT88's in my SVT-VR for a few years. Recently had some work done on it and the tech put in JJ 6550's. I have yet to try these out and am just looking for anyone's input/experience stories with these.

I'm sure the SVT will break up a bit earlier as a result (not necessarily a bad thing for my application)...



Thanks!

[JimmyM]

I'll let you know in a month or so when I get my Heritage SVT-CL!!!

[ThisBass]

Originally Posted by godspeed68

Hey TB,

I've used the JJ KT88's in my SVT-VR for a few years. Recently had some work done on it and the tech put in JJ 6550's. I have yet to try these out and am just looking for anyone's input/experience stories with these.

I'm sure the SVT will break up a bit earlier as a result (not necessarily a bad thing for my application)...

Thanks!

Probably the quality of break up differs a bit.
The achievable power at break up point must be the same.

[BogeyBass]

I dont think you will notice any power gains or losses

the voltage and current from the power transformer
remains the same and raising/lowering the voltage or current would be the only thing that would justify more or less power.

otherwise same old thing unless bias was off
supposedly kt88's are more efficient but its just mainly a larger glass envelope for more voltage handling

[chaosMK]

Report back to us! I've been curious about JJ 6550's. I *love* their KT-88s in my Bass 400. I have Tung Sol 6550's in it now... still very good. I got them intead of JJ's to save a few bucks.

[JimmyM]

I hear the Tung Sols are better.

[rickdog]

Well, I had a kind of disappointing experience with the Tung Sol reissues in my SVT-CL. I bought a set to replace some very tired Sovteks. They sounded good (not that I ever had a chance to really crank it up), but two of them went gassy after about a year of fairly gentle use.

I'm trying to decide whether to put in the JJ 6550s (if they're good enough for Hodgy, they should be good enough for me), or spend extra for the JJ KT88s. The biggest difference I see in their specs is the higher maximum plate voltage for the KT88s. The SVT pushes 6550s right to their limit, having some margin seems like a good idea.

I'll be watching this thread for some more opinions.

[JimmyM]

Hodgy burns in the JJ's and gets rid of the duff ones. Honestly, I've not had much luck with JJ's of any kind...the most I ever got out of one was maybe a year. But I haven't tried their 6550's since I never had an amp that used them. Two pairs of 6L6's from JJ went bad on me within a couple months. One set was a little microphonic right out of the box.

[godspeed68]

Originally Posted by chaosMK

Report back to us! I've been curious about JJ 6550's. I *love* their KT-88s in my Bass 400. I have Tung Sol 6550's in it now... still very good. I got them intead of JJ's to save a few bucks.

I ran KT-88's in my Bass 400 as well and had incredible results, although I slammed the power section a bit too hard with my boost/o.d. and blew the amp up a bit too much to continue using...i miss that one!

[godspeed68]

initial report:

tonally, the 6550's do vary from the kt-88's in my amp.

on the subject of headroom, i feel the low end breaks up juuust a bit quicker.

i had minimal amount of time to mess around with my rig, and as i'm using something like 18 pedals front-ended on this beast i will update as i get another crack at some studio time with this.

overall: so far, so *pretty* good.



tom

[Jim C]

As I recall, KT88's were made in the late 60's.
If Ampeg engineer's didn't use them it was probably for a good reason.
I would only trust information from either Jerold Tiers or an amp tech with solid tube amp credentials as everything else is heresay IMO/IME.

[chaosMK]

Originally Posted by godspeed68

I slammed the power section a bit too hard with my boost/o.d. and blew the amp up a bit too much to continue using...i miss that one!

That's funny, I run mine the essentially same with my Sansamp BDDI on "Line" level. It's the best way to maximize the power section of the 400. Haven't blown it up yet though. Lord knows I've tried.

[Downunderwonder]

Don't 400's use 6l6??

[Mr. Foxen]

Originally Posted by Jim C

As I recall, KT88's were made in the late 60's.
If Ampeg engineer's didn't use them it was probably for a good reason.

KT88 being British and Ampeg being American.

[B-string]

Originally Posted by Mr. Foxen

KT88 being British and Ampeg being American.

Tis true. The only US company I remember using the "KT' series was McIntosh.

[rickdog]

Originally Posted by JimmyM

Hodgy burns in the JJ's and gets rid of the duff ones. Honestly, I've not had much luck with JJ's of any kind...

I wonder how much Ampeg would charge for a set of "Hodgy certified" 6550s

I'd guess that the reason Ampeg engineers didn't use KT-88s back in the day was because the GE 6550A was at least as good, and cheaper too.

[hodgy]

For the record, it's the 'powers that be' that decided the JJ's were good enough for the Heritage SVTs. I'd go back to the Winged C's that were used for the first production year in a second if it were up to me.

[D.M.N.]

Originally Posted by B-string

Tis true. The only US company I remember using the "KT' series was McIntosh.

Sunns were originally spec'd with Genelex KT88s too, but switched to 6550s in 1969 when the KT88s became harder to source.

[JimmyM]

Originally Posted by hodgy

For the record, it's the 'powers that be' that decided the JJ's were good enough for the Heritage SVTs. I'd go back to the Winged C's that were used for the first production year in a second if it were up to me.

I think the Sovteks in the imported heads sound just fine. Most of the heads I get on rental gigs have Sovteks in them. I don't see what's so bad about them. I'll give the JJ's a shot but I have a couple RCA 12ax7's I might try in there, too.

BTW, I'm getting a Heritage rig, bro! As soon as you get the new batch of heads done, I'm on it.

[Downunderwonder]

You better put down a deposit. With an endorsement like that they will be all pre-sold.