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Traynor YBA 6550/KT88's ?????

twinfallsbass

twinfallsbass

Jan 24, 2005
1,561
2,253
#1
I have a Traynor YBA-200 that has the stock GT 6550's in it and want to upgrade the power section. When going online to buy new tubes I see that many are labeled 6550/KT88, so what is it, a 6550 or a KT88? I know that the new YBA 200-2 now comes with the KT88's and I was told that I can't install the KT88's in my amp without modification. I hear this amp works/sounds better with the KT88's and I would like to upgrade to them. I have done extensive research through the " search " function and I am still a little confused. I see people that have put KT88's in their YBA 200's with and without modifying them, what's the real deal on this amp with those tubes?
 
#3
AFAIK, a bit of rebiasing is necessary. That might be considered a mod. Unless I was truly unhappy with the power section as is I'd leave it as-is until the original tubes failed. I've seen some mention of people replacing the 12AX-7's in the preamp section with 12AT-7's. That's a cost effective mod that would probably make more of a difference in the performance of the amp. Both the 6550's and KT-88's are good tubes. When my Traynor Mark II's power tubes needed replacing I had KT-88's put in there. All things being equal I decided on trying KT-88's, but it was a tough call - the SVT has a such a strong legacy and it's 6550 based.

The KT-88's have been good to me, but I wouldn't have switched if I had a perfectly good set of 6550's in there. It's a lot of money in tubes and tech work for questionable gain.

KO
 
#4
Thanks for posting, but what is the deal with tube suppliers saying that 6550 and KT88's are virtually the same, so much so that they are selling them as 6550/KT88's. I also wanted to change the power tubes for tonal reasons. I already have swapped out the preamp section with Ruby's.
 
#5
6550's and KT88's are very simular designs and in most cases a KT88 will work well in place of a 6550. To get the most out of the KT88, rebias would be nessary. KT88 will stand higher plate voltages so replacing a KT88 with a 6550 could cause a problem if the design is done around KT88 specs.
I would have to assume if the tubes you are looking at say 6550/KT88 they meet KT88 specs. (and should perform fine in place of a 6550).
 
#6
Genalex GEC TYPE 88 Kinkless Tetrodes, real ones are about £800 for a matched set of 4 new old stock if you can find them. Thats why chinese 6550's are just as good "according to sales people that sell them" the fact that 6550's often have the lie KT 88 written on them helps this myth.
Check your power transformers max safe heater current before you fit real KT 88's, Bias it with a scope the first time, then note the figures via the old bias probes for future reference. :D
 
#7
B-string said:
6550's and KT88's are very simular designs and in most cases a KT88 will work well in place of a 6550. To get the most out of the KT88, rebias would be nessary. KT88 will stand higher plate voltages so replacing a KT88 with a 6550 could cause a problem if the design is done around KT88 specs.
I would have to assume if the tubes you are looking at say 6550/KT88 they meet KT88 specs. (and should perform fine in place of a 6550).
Click to expand...

I guess that is where the upgrade/modification that Traynor is referring to, because my amp is " Auto Biasing ". I just don't want to harm my amp with a tube that is really a KT88 and sold as a 6550/KT88. I don't want to modify my amp right now that strictly takes KT88's. I have been looking at the Tung Sol 6550's, I guess I'll try those.
 
#8
twinfallsbass said:
I have a Traynor YBA-200 that has the stock GT 6550's in it and want to upgrade the power section. When going online to buy new tubes I see that many are labeled 6550/KT88, so what is it, a 6550 or a KT88? I know that the new YBA 200-2 now comes with the KT88's and I was told that I can't install the KT88's in my amp without modification. I hear this amp works/sounds better with the KT88's and I would like to upgrade to them. I have done extensive research through the " search " function and I am still a little confused. I see people that have put KT88's in their YBA 200's with and without modifying them, what's the real deal on this amp with those tubes?
Click to expand...

Hi twinfallsbass.

You may wish to have your YBA200 (auto bias) upgraded to YBA200-2 (manual bias) specs. before you go to a different type of power tube for reasons, which I believe, are touched upon in this thread: http://www.talkbass.com/forum/showthread.php?t=362851

The auto bias circuit in many YBA200s fried when different power tubes were used. This is why Traynor went to a manual bias scheme in the YBA200-2.

Traynor support: http://www.traynoramps.com/default.asp?p1=7&p2=0&p_id=28
 
#9
twinfallsbass said:
I guess that is where the upgrade/modification that Traynor is referring to, because my amp is " Auto Biasing ". I just don't want to harm my amp with a tube that is really a KT88 and sold as a 6550/KT88. I don't want to modify my amp right now that strictly takes KT88's. I have been looking at the Tung Sol 6550's, I guess I'll try those.
Click to expand...
Thats a very good plan because if you look at this pic:
This is the termination of the heater transformer winding of a properly designed real 4 X KT88 amp as you can see the winding is about as thick as a brazing rod and the partridge transformer the other side is as big as your head:
L0tEgc078636-02.jpg


There is no point kicking the **** out of your mains transformer without the proper bias circuit or enough plate voltage available to make best use of real KT 88's:
elJnox909979-02.jpg

Ain't they cute though.:bassist:
 
#12
twinfallsbass said:
But the Tung Sol 6550's should work, right? I should be able to use any type of 6550 as long as it's a matched quad, at least that is what I have been told anyway.
Click to expand...

You may wish to play it safe. Traynor support: http://www.traynoramps.com/default.asp?p1=7&p2=0&p_id=28

Many YBA200 amps have failed after a power tube change due to a flawed auto bias scheme which Traynor ditched in favor of the manual bias used in the YBA200-2.

You can have your YBA200 upgraded to a YBA200-2, an upgrade which also includes KT88 power tubes, by contacting Traynor for details.

(Please note: I am not an expert, but I have read a lot of the YBA200 & 200-2 threads on TalkBass because I was thinking of getting one of these amps.)

Please contact Traynor before you do anything to your amp, and PLEASE read the safety tips in this thread: http://www.talkbass.com/forum/showthread.php?t=362851 if you are even thinking (if you are) about opening you amp's chassis for any reason.

There are voltages in there which WILL KILL you if you don't completely understand what you are doing. Safety first bro'. :)
 
#13
MIJ-VI said:
Many YBA200 amps have failed after a power tube change due to a flawed auto bias scheme which Traynor ditched in favor of the manual bias used in the YBA200-2.
Click to expand...

Hi, thanks for the info. Is there anyone out there in TB land that has had this experience with their YBA-200's. Has anyone had good results by changing out their stock 6550's for another brand 6550?
 
#14
Mine had the stock Sovtek 6550WE tubes, the resistor fried and I had it repaired. I replaced the tubes with a matched quad set of the same tubes. I used the same tubes that were in it originally, I liked the sound, I was hoping the matched set would avoid more problems.

The second time the resistor fried, sent to Yorkville, they did the -2 conversion and put in the KT88 tubes. I believe it takes it to 225 watts with the KT88's. It still sounds good to me, but I have not had a chance to play it much, so I can't vouch for long-term reliability. I think the KT88's would be alright to use, but you might want to contact their tech support first.

On an unrelated note, I would like to see an original YBA200 and YBA200-2 pictures in the "Amp guts" thread. Due to work commitments, I can't provide pictures of mine right now.
 
#15
Read it and weep:
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I bought a matched sextet of EH KT88s from a reputable dealer and have to rate them about twice as good (Punch and clarity) than the JJ 6550s they replaced.

The data sheet for the KT88 has about twice as much plate-to-plate resistance as a 6550. Just something to ponder.

EH KT88s in a pretty decent power amp:
Invalid Link Removed
Invalid Link Removed
 
#17
I must have missed something. Who's misleading photo. Which link? JJ tubes are made in Europe as far as I know, and are being sold by reputable dealers here, probably getting them thru New Sensor. I would avoid anything coming out of China right now, political issues aside.
 
#18
Buster,
Using your link and then going down to ****THE KT88 CURRENT PRODUCTION LIST**** , it shows "JJ" on the left, with a short description on the right, but for some unknown reason it has a photo of two tubes that say "Shuguang China" underneath JJ. This Chinese company may also be producing them, but there is no description to the right. When I first looked at it, it appeared the photo went with the "JJ" description, therefore my comment that it looked misleading.
 
#19
Anytime you change output tubes the bias levels should be checked and reset as required.

6550s and KT88s are indeed similar but they are not equivalents. Their heater requirements are similar, as are IIRC plate dissipations. Plate loadings are different as are bias requirements. The fact that some manufacturers are classing them as basically the same tube is, IMO, troubling. Perhaps that is an indication of how far from the original specs these manufacturers have strayed. This is possibly why folks are having trouble with modern versions dying a premature death!

Paul
 
#20
BassmanPaul said:
Anytime you change output tubes the bias levels should be checked and reset as required.

6550s and KT88s are indeed similar but they are not equivalents. Their heater requirements are similar, as are IIRC plate dissipations. Plate loadings are different as are bias requirements. The fact that some manufacturers are classing them as basically the same tube is, IMO, troubling. Perhaps that is an indication of how far from the original specs these manufacturers have strayed. This is possibly why folks are having trouble with modern versions dying a premature death!

Paul
Click to expand...

That's one of the reasons I was willing to try the the EH over other brands. Despite New Sensor's variable reputation over the years they seem to have cleaned up their act recently, and they make a clear distinction between the tubes; 6550A vs. KT88.

And I think it somewhat sophmoric to buy tubes based on how loud they make the amp sound. I buy tubes based on timbre (I think that's what the marketing and boutique guys call "Tone.")

As Paul astutely points out plate loading matters because, among other things, of the change in damping factor: how much control the amp has on the speaker cone. Mis matched and the tail wags the dog: flabby low end.

BTW, It is not a bad idea to have a separate 6.3V heater supply just for the output tubes. I think mine sink something like 1.3A each.
 

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