From what I've read, modern 6550 tube amps are also compatible with an exceptionally WIDE variety of tubes including the following:
6550A - 7D11 - 12E13 - 7027A# - KT88 - KT90 Type 2 or 3 - KT99 - KT100 - KT120 - KT150 - KT190
What I don't understand is what the advantages / disadvantages of these alternate tubes are. Is there anywhere that I might find an in-depth discussion of the relative sound of these tube types?
I've actually heard an amp (and in my own system) with a set of 6550s and the same amp with a set of KT120s - the latter had more bass, but the former had a smoother midrange & treble. But the differences may have been due to the fact that the 6550s had at least 200 hours of run time on them while the KT120s were brand new...
Looking for an education - Thanks - Boomzilla
6550A - 7D11 - 12E13 - 7027A# - KT88 - KT90 Type 2 or 3 - KT99 - KT100 - KT120 - KT150 - KT190
What I don't understand is what the advantages / disadvantages of these alternate tubes are. Is there anywhere that I might find an in-depth discussion of the relative sound of these tube types?
I've actually heard an amp (and in my own system) with a set of 6550s and the same amp with a set of KT120s - the latter had more bass, but the former had a smoother midrange & treble. But the differences may have been due to the fact that the 6550s had at least 200 hours of run time on them while the KT120s were brand new...
Looking for an education - Thanks - Boomzilla
To answer the education part..Basically, a tube has certain minimum requirements to do its job which is to amplify the signal put on its grid. The voltage and current requirements for the tube is supplied by the power transformer. The larger tubes require more current and voltage than the lower output tubes. If the power transformer can not supply the needed demand safely, the power transformer will overheat and eventually fail. It might not do it quickly but it will eventually fail if it operates out of its specs.
Last edited:
The KT120 and up may not be compatible with 6550s in a given amp because they require more heater current. The 6550 needs 1.5A, whereas the KT120 needs 1.9A if memory serves. Best to consult the amplifier specs to be sure, or contact the manufacturer.
I've really only compared old stock GE 6550A's with Svetlana Winged C's with KT120s in my amp. My experience is the KT120s easily held their own to these other two, with the KT120s offering a very nice integrated presentation top to bottom, and with slightly more bass and slightly more rolled off highs. This is subjective so take it as opinion.
I've really only compared old stock GE 6550A's with Svetlana Winged C's with KT120s in my amp. My experience is the KT120s easily held their own to these other two, with the KT120s offering a very nice integrated presentation top to bottom, and with slightly more bass and slightly more rolled off highs. This is subjective so take it as opinion.
The amp I'll be using is capable of supplying more than two amperes of bias current easily.
The amp can be supplied with anything from the 6550 to the KT120. My experience, hearing an identical amp this past Sunday with both 6550s and the KT120s is identical to yours, kward. More bass and slightly rolled off highs with the 120s.
My room / speaker / ear combo slightly preferred the sound of the KT120s. But I'm wondering if I'd get the same effect with the KT88 tubes (and for significantly less money)? Ultimate power output is not a concern - my speakers are highly sensitive, and I normally listen at significantly less than one watt.
That said, the speakers aren't as bass-rich as they are with subwoofers, and I'm trying to get away from having to use the subs. Therefore, the slight extra bass that the KT120 tubes offered was most welcome.
Thanks - Boom
The amp can be supplied with anything from the 6550 to the KT120. My experience, hearing an identical amp this past Sunday with both 6550s and the KT120s is identical to yours, kward. More bass and slightly rolled off highs with the 120s.
My room / speaker / ear combo slightly preferred the sound of the KT120s. But I'm wondering if I'd get the same effect with the KT88 tubes (and for significantly less money)? Ultimate power output is not a concern - my speakers are highly sensitive, and I normally listen at significantly less than one watt.
That said, the speakers aren't as bass-rich as they are with subwoofers, and I'm trying to get away from having to use the subs. Therefore, the slight extra bass that the KT120 tubes offered was most welcome.
Thanks - Boom
6550 is a large improved 6L6-type. I believe Ampex and Tung-Sol collaborated on a VCR servo amplifier (a real beast).
KT88 is a very similar type from Europe.
KT120, KT150, KT190 are I believe larger KT88/6550 types. Look inside: heater, cathode, grids, plate all semi-cylindrical. If you keep the same diameter, you can make this structure "taller" and have more of the same thing. (Slight adjustment to heater gauge.) In a sense: they can roll it out by the yard and slice off as many inches as you need, just like a butcher.
7027 is a 6L6GC with a modified base. 6550 is the "professional upgrade" in *some* amps that beat 7027 within an inch of their life (Ampeg VT40). Any amp that works 6550 "hard" will eat 7027 for lunch.
Within the same type number, every brand, lot , and tube is different. Between vintage Tung-Sol, last-batch GE/Kentucky 6550, and new Sovtek 6550, I did not observe much difference in audio (I am not golden-ear) but the old tubes *creaked* on warm-up and cool-down while the Sovs were dead silent. Obviously there are differences with construction and age.
> discussion of the relative sound
"Sound" is the tube AND the amplifier AND the speaker AND the listener. There should not be gross differences. There may be many subtle differences and these may pull in different directions.
Tube Depot has a 6550/KT88 page that has blurbs on the several brands they sell. Of course they all sound wonderful (in TD's opinion), but they say different praises.
KT88 is a very similar type from Europe.
KT120, KT150, KT190 are I believe larger KT88/6550 types. Look inside: heater, cathode, grids, plate all semi-cylindrical. If you keep the same diameter, you can make this structure "taller" and have more of the same thing. (Slight adjustment to heater gauge.) In a sense: they can roll it out by the yard and slice off as many inches as you need, just like a butcher.
7027 is a 6L6GC with a modified base. 6550 is the "professional upgrade" in *some* amps that beat 7027 within an inch of their life (Ampeg VT40). Any amp that works 6550 "hard" will eat 7027 for lunch.
Within the same type number, every brand, lot , and tube is different. Between vintage Tung-Sol, last-batch GE/Kentucky 6550, and new Sovtek 6550, I did not observe much difference in audio (I am not golden-ear) but the old tubes *creaked* on warm-up and cool-down while the Sovs were dead silent. Obviously there are differences with construction and age.
> discussion of the relative sound
"Sound" is the tube AND the amplifier AND the speaker AND the listener. There should not be gross differences. There may be many subtle differences and these may pull in different directions.
Tube Depot has a 6550/KT88 page that has blurbs on the several brands they sell. Of course they all sound wonderful (in TD's opinion), but they say different praises.
S11E12
An externally hosted image should be here but it was not working when we last tested it.
The OP could try tone controls. They will provide a much wider (and cheaper) method of adjusting the frequency response to suit his tastes, speakers and room. Valve choice only has a very minor effect on frequency response, although in some cases the amount of distortion can be misperceived as a frequency response change.Boomzilla said:
7581 and 7581A are - rather good - commercial versions of the 6L6GC, thus not being viable substitutes for 6550s. TT21 and TT22 are KT88s with their plates brought out on a top cap. They both can withstand higher plate voltages than 6550s and KT88s. Besides this, only the T21 is a substitute, as the TT22 being a version with 12.6 Volts heater.Best regards!
I know this information, but the anode surface of all these tubes is the same!
Thanks, DF96 and PRR -
Excellent info and good points. Ultimately, a preamplifier with tone controls may well be in the works.
And since the major "advantage" of the KT tube models is increased power output (that I don't need or use), I've decided to stick with the original 6550 tubes.
A different question, if I may? - The amp I'm getting also allows operation in either triode or pentode mode. Obviously, there's less output wattage with the triode mode, but for me, that's not an issue. I can listen for myself to select what I think is the "best sounding" mode, but will running in triode mode (should I prefer that option) affect the longevity of the tubes? It would seem that since less power is being produced in triode mode, that the tubes would run cooler that way (thus increasing longevity). Is that correct?
And finally - the driver board on this amp uses a trio of 12AU7s, but the manufacturer states that 12BH7s can also be used. Is there any advantage / disadvantage of one over the other?
Many thanks - Boomzilla
Excellent info and good points. Ultimately, a preamplifier with tone controls may well be in the works.
And since the major "advantage" of the KT tube models is increased power output (that I don't need or use), I've decided to stick with the original 6550 tubes.
A different question, if I may? - The amp I'm getting also allows operation in either triode or pentode mode. Obviously, there's less output wattage with the triode mode, but for me, that's not an issue. I can listen for myself to select what I think is the "best sounding" mode, but will running in triode mode (should I prefer that option) affect the longevity of the tubes? It would seem that since less power is being produced in triode mode, that the tubes would run cooler that way (thus increasing longevity). Is that correct?
And finally - the driver board on this amp uses a trio of 12AU7s, but the manufacturer states that 12BH7s can also be used. Is there any advantage / disadvantage of one over the other?
Many thanks - Boomzilla
The pros and cons:
12AU7: Pro - less heater power, smaller envelope; con - lack of linearity
12BH7: Pro - almost linear as a 6SN7; con - twice the heater power of a 12AU7, taller envelope (if that matters at all...).
Best regards!
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.