• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Which KT88??

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#62
Yes I know.........JJ's are ok (nearest to orig). The orig MOV/GEC 88 Gold Lions are now £60 each........perhaps more for collectors items.
It's such a pity that MOV flogged all their UK manufacturing equip to China (mid 70's)......and the result we all know.
As I use 6550's for equip replacement (which orig used 88's) I often have to derate B+....in some cases by nearly 100V...and accept lower Pout despite anode + screen ratings being sim.
The only other method is to specify burn't/run in tubes and specify matched pairs.....even if it pays more and if one can trust the distributor.
The fact that a GEC spec 88 can run at 600V at 60mA quies, a 6550A wouldn't survive that grilling for long. The Radford STA100 amp had exactly this. That is testament to how good the 88's were manufactured. I've used JJ's without problems at 600V B+, but to be fair on repl tubes, I do derate.


rich
 
#64
SED

Gentlemen, I believe the KT88s manufactured at the ST. Petersburg factory, the old "Svetlana" brand name, is now called SED.
I still get them and the seem to work well, luckily. New Sensor got the rights to the name "Svetlana". The true SEDs from St. Petersburg have two dish getters above the plates.


Take care.
Steve
 
#69
well... I started this thread....

..and I've made a decision.

I'm going to try the Sovtek 6550 tubes.... reasons....

1. Sovtek are generally regarded as a pretty good tube
2. I run at 390v, so I can use the 6550.
3. The KT88's were a pretty tight fit with very little room between them, the 6550's will be better in this regard.

4. (and this is the clincher). I can buy them in matched pairs from my main speaker supplier at wholesale. This may end up being marginally more that I would pay if I imported from somewhere, but I have "peace of mind" if something goes wrong in the post, along with easy replacement, and quick delivery.
 
#70
Although I have thought about Sovtek time and time again I'm quite worred at my projected amplifier's voltages and what stress they'll place on tubes, therefore I'm crawling my way to a solution where the valve is the best as possible in terms of reliability of the KT88 spec, I can't afford to spend heaps on caps and resistors designed for 600volts when I can't even get near it and have to throttle back at 400v...

It looks like I may go to JJ but haven't they got the response of a guitar amp?

Cheers.
 
#72
Throttling back the juice to 400V B+ is ideal for 450V electyt's.
-> drawback of high volt supplies is staircasing capacitors....
-> When ordering <run in> matched tubes, this avoids wild o/p stage specs for circuits without bias potty's. For auto bias, this isn't so serious.
->My MI & Hi Fi friends like to thrash tubes rather hard, the distinctive sound has better attack. i.e run 6550's on 485V B+..... UL AB1 at 65mA quies per piece (no more)^. The fall out rate at this higher volatge is more noticeable (Svet take note.....)than running tubes well below their designated ratings.
Consider the case of running 6550's at 250V B+ UL class A ..(nearly) at 90mA quies per piece. 2 parallel pairs in UL push-pull will just slip 25W o/p with many sonic advantages with greater tube life. However requires beefy current PSU. The emphasis is then a decent low Z driver stage.

->The MOV appl note recommends (slight layout advantage) keeping the hottest section of the tube anodes at right angles away from each other in close proximity.
For tube longevity, the cooler the tube runs je better (the heater value remains the bogey value).
For the moment I'm gradually drifting away from 6550's and towards JJ's 88's and perhaps considering the KT90 for uprated 88 applications. ......back to shovelling snow....

🙂rich
 
#74
In Yugoslavia, the EiRC factory has been destroyed by the recent NATO bombing campaign. This was the only source for the KT90/KT99 tube; we suggest the KT88-T as an acceptable substitute/upgrade. By the way, this is one example of why VAC avoids single-source tube types, such as the 6C33, 6H22, and most of the KR range. It is important that you be able to keep your VAC component operating well into the next millennium.

By the way, all VAC electronics are Y2K compliant. <grin>

In the Slovak Republic, the government owned Tesla factory has been privatized, and continues to manufacture and develop vacuum tubes. Their 12AX7/ECC83 is an acceptable candidate.

Several factories in China continue to develop and manufacture vacuum tubes of excellent quality, including the new KT88-T and EL34-B, which are our preferred versions at this time.

In the former Soviet Union, Svetlana and Reflector ("Sovtek") continue to manufacture vacuum tubes, although there are rumors of frequent shut downs due to the extreme economic conditions there. In terms of sound quality, we generally consider the Russian tubes to be inferior to the Chinese products.
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Most notably in those quotes are "Svetlana and Reflector ("Sovtek")" aswell as "In Yugoslavia, the EiRC factory has been destroyed by the recent NATO bombing campaign."
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Are these both true claims!?
http://www.vac-amps.com/page0038.html

Am I buying Svetlana when I go for Sovtek?

Where does Electro Harmonix originate from?

Also what is the reputation of Ei KT88-90A's?

Cheers.
 
#79
L......s .....No....My recent problems with 6550's; I'm not having anymore Svetlana stuff.....that's it...I've been messed about too much by their tube problems.
JJ Tesla GL88's are good.....As for Chinese 88's,(let sleeping dogs lie)...... NO WAY....JUNK shop stuff......
Hang on..Who told you they were good ????????

rich
 
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