6550 which breed can take the flog ?

[richwalters]

Some of my 6550 New Edit TungSols after 3000hrs hard flog are showing power distress; that is can't hold up sustained power. The getters on some are pretty greyish but the idle currents remain rock steady; on-load currents do begin to droop when I thrash'em hard, 85mA quies at 450V i.e 38W point but when playing Trumpet and particulary my Fender bass I'm beginning to detect sonic breakup.
They still sound good on HiFi, but has anyone bettered these New Edition types or do the others, EH,Sovteks or other 6550's hold up better being thrashed ? I could go to KT88's but I can't see the point. At 450V, nearly the same tube.
A while ago I remembered a similiar remark on another site but not sure where.

richy

[Eli Duttman]

Rich,

Easy it's not, but try to scrounge up some GE 6550As. Can you say tough screen grids? Remember, GE developed the variant specifically for use in high power Fender bass amps.

[Anthony Dockril]

Hi,

3000 hours at 38 watts is actually a good result! If you run them a bit cooler may be you could get 5,000 from a new set. The reissue TS 6550 do seem to be pretty good tube...I'll have to get a set.

KT88 might give you a little more toughness but my guess would be only a little - but in your your rig it might be worth having. The EH KT88 are pretty tough and cheap - could be worth a try. The Golden Lions KT88 are also worth looking at but things are getting more $$...

May be its better to stick with the devil you know and may be run them a couple of watts cooler.

Cheers,

Anthony

[Geek]

6550 which breed can take the flog ?

This sounds like a question for George

Cheers!

[winslow]

SED Winged C 6550s?

[richwalters]

Thanks for replies. Not clear cut. The problem with trumpet is mighty harsh harmonics, esp when EQ is used, straining the screen dissipations or rather the whole tube...High quiescent currents are required to force a softer transition zone in class AB. So near full o/p = ca 140mA per tube current. On stage; ear splitting, but running them this hard keeps the upper end definition up. In pentode mode with higher B+ the sonic breakup is worse, and I notice the screen supply demands go up and stay up a while; indicating slight runaway emission effects. I will do some grid leakage checks to check for gassiness and blue zone.
Yes Eli, I do have some original 6550; I know these are worth the poke but I don't really wanna to press these wonderful oldies in service (true NOS price & collectors quality )
I might try EH KT90's or JJ88's; but as I see it, for lower B+ the standard KT88 are 6550 are pretty close retrofits. Perhaps even with the same innard geometry.
richy

[kevinkr]

Originally Posted by Eli Duttman

Rich,

Easy it's not, but try to scrounge up some GE 6550As. Can you say tough screen grids? Remember, GE developed the variant specifically for use in high power Fender bass amps.

I still have a set, and they are pretty rugged. Personally I thought the Sylvania version (rather rare at this point) performed better at voltages of >500V - seemed less gassy certainly than late production MPD versions of the GE 6550A.

I would nix the JJ KT88 due to quality control concerns. I designed a PP amplifier nearly 20 yrs ago based on Citation II iron, and these tubes have blown up in nearly every one of those amplifiers still in use.

IMO Either the Tungsol reissue 6550 or New Sensor's best KT88 variant would be my recommendation.

I would contact Jim McShane for his recommendations and would recommend him as a good source for a replacement set.

3K hours IMO is not bad. My recommendations for replacement were in the 2 -3K hour range for the Svetlana 6550C I used to sell.

[HollowState]

I can attest to the GE 6550A's durability. I've been running JAN GE 6550A's (green labels) for years at 600 volts in ultra linear. And that's through a real output transformer. (Acrosound TO-600) No problem-o. They just won't die.

[richwalters]

Thanks Kevin. Jim McShane....that's it. shall contact him. Otherwise back to TungSols NE. My collegue in the east mentions EH KT90 have a proven track record. Correct ? Might try these in as well.

thanks

richy

[richwalters]

Nirvana. Settled: I'm after the 6550B Svetlana. This version is fast disappearing and in my view, this tube produces by far the lowest thd of any recently made power tube and the best optimised for UL. The C version with overrated gold flannel produces roughly double thd in the same power circuit.
Any help on suppliers ?.
richy