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
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
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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.
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.
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 $$...
May be its better to stick with the devil you know and may be run them a couple of watts cooler.
Cheers,
Anthony
3000 hours at 38 watts is actually a good result! If you run them a bit cooler may be you could get 5,000 from a new set. The reissue TS 6550 do seem to be pretty good tube...I'll have to get a set.
KT88 might give you a little more toughness but my guess would be only a little - but in your your rig it might be worth having. The EH KT88 are pretty tough and cheap - could be worth a try. The Golden Lions KT88 are also worth looking at but things are getting more $$...
May be its better to stick with the devil you know and may be run them a couple of watts cooler.
Cheers,
Anthony
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
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
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.
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.
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
thanks
richy
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
Any help on suppliers ?.
richy
Attachments
I had a lot of problems with the Svetlana 6550B, although I will say it sounded good. The problems started at around 450V and > 60mA, (plate hot spots) mine were however very early ones - some were possibly pre-production prototypes. Later ones purchased from my supplier were not reliable either, and I quickly switched to the 6550C when it became available. I am not sure when they stopped making the 6550B.
My understanding is that the non-linearity issue with the Svetlana 6550C resulted from geometry problems with the beam forming electrodes, and I also seem to recall that this may have been a problem with the 6550B in some instances as well. I am not sure but the linearity issue might have as much to do with production QC as with any "improvement" in the design of the tube?
I believe PM components distributes "real" Svetlana/Winged C tubes in the West so perhaps you could check with them? (You probably already know this)
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Thanks Kevin. I've contacted McShane to see what he's got. The low thd from this tube in UL is quite remarkable. More UL midnight oil needs to be burnt..
richy
richy
Rich,
If you ever do try the EH KT90 please let me know how they do in Tetrode. I've been considering them for a while.
If you ever do try the EH KT90 please let me know how they do in Tetrode. I've been considering them for a while.
I've used the EH KT90s in an ST-70 in both triode and UL. Also tried them in the SimpleSE. I'm not good at describing audio equipment sounds, but I liked them for their midrange with my speakers and they could take all the current I could throw at them in the SimpleSE (switchable cathode bias). Details are in other threads.
Eli; Yes. I didn't want to delve into my NOS 6550A, but I had to prove/solve the problem. The tube nicely sorts out the chaff from the grain and all the other tubes in their class. It makes me wonder why this well designed tube was scrapped. (cost).
Time to put the Pickelhaube on.
As any designer will tell, messing about with UL o/p stages is fraught with heckuva-alot of conflicts, especially when two identical circuit amps are used but with different o/p trannies. I did these checks on my 150W lumps and in the process one ruins the sockets (which were due for change anyway). The Majestic (UK) is an Williamson 18 sect custom wound and has a response from 15Hz -3dB 90Khz; a fantastic response for an E&I; whereas the Sowter is a 14 Sect computer designed 20Hz-3dB 55Khz. However both amps show marked differences when differing tubes are used. The Sowter (UK) transformers give excellent performance when cathode dengenerative feedback is used; the Majestic shows very little advantage. Different designers, different winds hence different parasitics, so square wave shape at 10Khz will vary. This is a good indicator.
There are too many small inherent differences between all types of 6550 and KT88. Looking at the square wave shapes, generally most were similiar, but the devil is in the detail.
The KT90 was mentioned in another post. In every case configuration, this tube roughly near tripled the H3,H6,H7 distortion, and since I use MI and HiFi amps for both roles, I ruled this tube out for HiFi. I tried the trick of using degenerative feedback although this raises stage impedances, global NFB knocks this down. The NOS 6550A fits the bill perfectly for both conditions. Everyones happy. In general;
I get the same thd performance from a raft of vendors, New Svet 6550C,Sowtek 6550WA,WB, Billington KT88, EH KT88,Tesla KT88,Chelmer KT88, TungSol NEdit 6550; all these in my reference UL gave roughly 0.3% thd 1Khz with 20dB global NFB at a dB below stage clipping. One can only construe a guide here to working consistency, but the EH KT90 having a plum anode didn't look aspiring on tonal quality. I thought my tweeters were foul, so I changed them to Peerless types which are softer. So going back to 6550 class; I reverted back to the Morel. Much cleaner.
My previous mail, mentioned the Svel 6550B as my favourite, and I returned back to this. This near unavailable tube loves degenerative stage feedback for the lowest thd; in the same reference UL circuits I measured 0.05% thd at the usual dB below clipping.
So designers, and UL workers using fixed bias; If one has a spectrum analyser and /or THD meter consider the experiment using degenerative stage feedback; the 6550 likes roughly 22 ohms in the cathode leg and the usual 1K and 1-2nF between screen / anode taps and this is important as this nips any gm instability. I run my tubes hard, also in parallel pairs, to keep thd at 10Khz down. Experiment !
Picturing all this with graphs takes time; but I think I gottonclose to my goals.
Becareful: Doing high voltage hi power square wave tests into a dummy load is a severe slaughter test for all and above all it's dangerous. A slip with a probe can give a very nasty HF sting & burn.
thanks for all info
richy
Time to put the Pickelhaube on.
As any designer will tell, messing about with UL o/p stages is fraught with heckuva-alot of conflicts, especially when two identical circuit amps are used but with different o/p trannies. I did these checks on my 150W lumps and in the process one ruins the sockets (which were due for change anyway). The Majestic (UK) is an Williamson 18 sect custom wound and has a response from 15Hz -3dB 90Khz; a fantastic response for an E&I; whereas the Sowter is a 14 Sect computer designed 20Hz-3dB 55Khz. However both amps show marked differences when differing tubes are used. The Sowter (UK) transformers give excellent performance when cathode dengenerative feedback is used; the Majestic shows very little advantage. Different designers, different winds hence different parasitics, so square wave shape at 10Khz will vary. This is a good indicator.
There are too many small inherent differences between all types of 6550 and KT88. Looking at the square wave shapes, generally most were similiar, but the devil is in the detail.
The KT90 was mentioned in another post. In every case configuration, this tube roughly near tripled the H3,H6,H7 distortion, and since I use MI and HiFi amps for both roles, I ruled this tube out for HiFi. I tried the trick of using degenerative feedback although this raises stage impedances, global NFB knocks this down. The NOS 6550A fits the bill perfectly for both conditions. Everyones happy. In general;
I get the same thd performance from a raft of vendors, New Svet 6550C,Sowtek 6550WA,WB, Billington KT88, EH KT88,Tesla KT88,Chelmer KT88, TungSol NEdit 6550; all these in my reference UL gave roughly 0.3% thd 1Khz with 20dB global NFB at a dB below stage clipping. One can only construe a guide here to working consistency, but the EH KT90 having a plum anode didn't look aspiring on tonal quality. I thought my tweeters were foul, so I changed them to Peerless types which are softer. So going back to 6550 class; I reverted back to the Morel. Much cleaner.
My previous mail, mentioned the Svel 6550B as my favourite, and I returned back to this. This near unavailable tube loves degenerative stage feedback for the lowest thd; in the same reference UL circuits I measured 0.05% thd at the usual dB below clipping.
So designers, and UL workers using fixed bias; If one has a spectrum analyser and /or THD meter consider the experiment using degenerative stage feedback; the 6550 likes roughly 22 ohms in the cathode leg and the usual 1K and 1-2nF between screen / anode taps and this is important as this nips any gm instability. I run my tubes hard, also in parallel pairs, to keep thd at 10Khz down. Experiment !
Picturing all this with graphs takes time; but I think I gottonclose to my goals.
Becareful: Doing high voltage hi power square wave tests into a dummy load is a severe slaughter test for all and above all it's dangerous. A slip with a probe can give a very nasty HF sting & burn.thanks for all info
richy
Personal Experience:
Power handling:
1) GE 6550A
2) JJ KT88
3) Gold Lion KT88 (Russian Repro)
Sound quality
1) Gold Lion KT88 (Russian Repro)
2) JJ KT88
3) GE 6550A
The GE 6550A was developed to survive the Fender 400ps bass amp. This amp will actually melt the glass of lesser 6550s. The JJ KT88 has a bad rep because the first units were crappy. But what other tube can you put 850V on and not have it arc over? I've had Svetlanas arc over at half that voltage. And in my opinion, the EH KT90 just doesn't sound good.
For me the best all around 6550 family current mfg tube? Gold Lion KT88 (Russian Repro)
The JJ KT88 I find a highly durable tube whatever volts thrown at it; with some bias differences but maybe I ought to re try it. My earlier UL performance notes, it behaves more as a line o/p tube, with highish thd. I only wish it had another style envelope. The KT88 Gold Lion Russian new ed. Is this just another Svet version in disguise ?
The internals nearly all look the same.
richy
The internals nearly all look the same.
richy
The New Gold Lion tubes are another New Sensor tube. I have tried Electro-Harmonix and new Gold Lion tubes. They look the same internally except for the extra getters on the Gold Lions. Electrically, they are not the same. In Triode mode, the Gold Lions required about -10V more at the grid to bias at the same current, putting it more in line with the GEC data sheet. Also, the Electro-Harmonix tubes have a bit of blue fluorescence on the glass. The new Gold Lion's do not.
One difference I have noticed between the New Sensor KT88s and 6550s is that the KT88s seem to have extra fins welded to the plate structure. You may get better life out of New Sensor Gold Lions than you got out of your New Sensor Tung Sol 6550s for that reason. Plus, you would hope that they would cook it a bit longer than the others since they are charging so much.
Edit: the top mica wafers are different between EH and GL tubes as well, minor difference.
One difference I have noticed between the New Sensor KT88s and 6550s is that the KT88s seem to have extra fins welded to the plate structure. You may get better life out of New Sensor Gold Lions than you got out of your New Sensor Tung Sol 6550s for that reason. Plus, you would hope that they would cook it a bit longer than the others since they are charging so much.
Edit: the top mica wafers are different between EH and GL tubes as well, minor difference.
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