Retubing time!

[Keven]

it is time, my amp is due for a retube! so i'm looking at all the options and my amp can handle both EL34 and 6L6 types, this means i should be able to get E34L and kt77 and KT66. now, given that i use the amp clean but with several dirt boxes to get my distorted tone (which should be of a bone crushing metal quality but with less gain than you might think to keep clarity) and like to play at a sane volume (just enough to cut through with a loud drummer and another guitar player and a bassist) and that i love the grunt of low mids and bite of high mids with tight bass, which tube should fit my bill?

i currently do like my EL34EH but i've been tempted to try out some KT77 by JJ as they may have tighter bass and a bit more chime, since my amp is fairly dark.

as far as preamp tubes, i was looking at either JJ or TAD tubes. tung-sol seem good also. is it a really good idea to get a matched triode tube for my phase inverter as well? alot of sites seem to say so, but some of you amp builders here might say otherwise.

my clean tone needs to be jazzy and warm, and my distorted tone should be very van halen brown but with just a bit more sizzle so what when i use my 7 and 8 strings, i still get a good definition in the low notes.

[Twinfan]

Err, what's the amp?

I like JJ ECC83S preamp valves, and I don't bother with a matched triode phase invertor.  I do tend to buy the gold pin valves for a few pounds extra, but I don't think there's any real difference between those and the stock ones.

For power valves, I'd check if there's space between the sockets to fit any KT series valves.  They're quite a bit wider than a straight sided EL34!

[Keven]

it's a traynor YCS100H2. 100w class AB going into a 4x12 cab with 4 V30. nobody here knows that amp so i figured it wouldn't be very helpful to mention that!

it's a 3 channel amp. 3 preamp tubes.

the jj kt77 are a slim bottle tube so it's pretty much the same size as a EL34.

[Twinfan]

Sounds like it might be worth trying the 77s then!

[hunter]

I didn't like the KT77 when I tried em in my VHT2502. The only current production tube that does it for me in terms of upper mid crunch is the SED =C= EL34. If you bias them a bit hotter (between 70% and 80% plate dissipation) they add a fatness that no other EL34 gives. They are also a rugged design, so they can take it easily.

Another option might be to try 6550s if you want a wider frequency spectrum and more of a hollow tone for cleans, but not all transformers are able to support 6550/KT88s. Here TungSol or SED =C= seem to be good tubes.

[Keven]

Winged C was indeed another prime choice for EL34 and was recommended by a local amp tech, but they're a bit too pricey and i can't rely on power tube distortion so much, you surely know how loud a 100w can get before it crunches :D

[jpfamps]

For clean, as a rule, I prefer 6L6s.

Beam tetrodes (6L6, 6V6,  KT series, 6550) generally will give more bass than pentodes (EL34, EL84).

I initially got quite excited by the JJ-KT77s (I probably need to get out more....), as I hoped they would give more of 6L6-type sound but still with the EL34 crunch, but ultimately they proved to be a bit of a disappointment. Although they seem to have more bottom end than an EL34 they didn't sound so good in the upper mids. They do give higher measured power output, at least in the circuits were I have tested them. I also had a couple flash over on application of B+.

Matching triode sections in valves for use in phase splitters is pointless.

[HTH AMPS]

if you want bone-crunching bass end that stays tight, go with 6550s all the way - your amp will need a trip to a tech to slightly mod the bias supply, but you'll be glad you did it.

if cost is an option, you could always run the amp with just two 6550s and half the output (ish).  it'll still be br00tally loud for any application short of Wembley Stadium.

[Keven]

i'd like to avoid all that modding thing though, so from what i gather, those of you who tried kt77's expecting a middle ground between el34 and 6l6 were sorta disappointed. i'll keep that in mind.

I'm guessing a set of 4 winged c EL34 and 4 TAD 12ax7 could be a very good choice...

i also read (not heard.) that tungsols tend to break up a bit earlier than winged c.. that could tip my hat to the tung sol indeed.

[blue]

sorry to hijack, :)

can you simply substitute a KT66 or KT77 with EL34's?  that is, if your amp has one you can just put in the other, (with a rebias of course) with no modifications?  if so, does that mean EL34's will work in a Marshall Vintage Modern?  and likewise, an EL34 Marshall will accept KT valves?

[hunter]

sorry to hijack, :)

can you simply substitute a KT66 or KT77 with EL34's?  that is, if your amp has one you can just put in the other, (with a rebias of course) with no modifications?  if so, does that mean EL34's will work in a Marshall Vintage Modern?  and likewise, an EL34 Marshall will accept KT valves?

No, it's not that easy. If you can use 6L6 or other tubes in the VM depends on the amp. I suggest you ask in the Marshall VM forum, the developer is present there quite a lot, but I'm sure there are already threads about that.

[Keven]

actually blue, my traynor is built to handle either el34 or 6l6 types, it's just how the amp works, with a rebias of course. it's a fun thing, you can go from british (it's stock EL34) to american just by changing the power tubes :D

[blue]

i have a Genz Benz El Diablo that can switch between EL34 and 6L6.  i know i can't do that in the Marshall, it was the KT66/KT77/KT88 i was wondering about.  can any of those be used without modification?

[Keven]

for what it's worth when i called the amp tech at traynor, he told me that i could freely use the kt77. haven't checked for the 66 or 88 though..

[jpfamps]

sorry to hijack, :)

can you simply substitute a KT66 or KT77 with EL34's?  that is, if your amp has one you can just put in the other, (with a rebias of course) with no modifications?  if so, does that mean EL34's will work in a Marshall Vintage Modern?  and likewise, an EL34 Marshall will accept KT valves?

All the common 8-pin power valves have the same pinout (more or less) so they can be often substituted in amps are long as:

1) There is enough heater current capability in the power transformer: EL34s require 1.4 A per valve compared to 6L6s which draw 0.9 A, so in an amp designed to use EL34s 6L6s won't stress the filament supply, but the converse isn't always the case.

2) There is enough range in the bias supply to allow the valves to be biased correctly. 6L6s require a more negative bias voltage than EL34s for example.

3) EL34s need pin 1 and 8 tied together for correct operation. Amps designed for 6L6s may not have this connection.

4) There may be issues with screen current draw when swapping EL34s into an amp designed for 6L6s if the screen grid resistors are the typical 470 ohm used with 6L6s.

5) The voltage compliance of the valves is not exceeded. For example the screen voltage rating of 6L6s is lower than EL34s.

The KT77 should work in any amp designed for EL34s as it is effectively a beam tetrode equivalent. KT66s would probably require that the bias supply is modified.

Obviously in an amp that can accomodate 6L6s and EL34s you should be able to use KT66s, KT77s, 6L6s and EL34s.

It's quite interesting trying different valves in the same circuit, however you do need to bear in mind that often a certain circuit is optimized for a certain valve (e.g. drive voltage, feedback factor, plate impedance), so if you say try some 6L6s in a Marshall and you don't like the results, it could be that those valves don't work for you in that circuit rather than they are inherently "bad" valves.

This is the caveat I would apply to the JJ-KT77s, ie we weren't overwhelmed by their sound in the circuits we were using (although we were trying to design the amp around the KT77!!), however they may well be very good in other circuits.