Re: Suggestions on tube rolling for Jet City 20 Watt Combo
The first issue you should get rid off is microphonics.
Being a combo, you need at least your first tube to be microphonics-proof.
Then, tone wise, there are some other considerations:
It's your clean headroom enough? would you like more or less headroom (or an early preamp break-up)?.
Lastly, high gain amps are a bit tricky and tube swaps not always work in the expected way.
For V1:
You need a tube with a good output, capable to push the rest of the chain with ease.
Any NOS 12AX7, in principle, should do the trick but, man, you have an EI tube there and, this is damn good or damn bad.
If your tube is one of the good ones, your tone will be incredible and the tube will remain quiet and without microphonics issues.
If your tube is one of the bad ones, your tone will be incredible while it lasts, and it can last really few.
Respect of tone, EI are awesome, respect of noises or microphonics, you are rolling dices there. Try it, maybe you are lucky this time.
A good alternative for this position could be also a Sovtek 12AX7-LPS or the JJ ECC803S but, those have long plates and, long plater are more prone to microphonics in Combos. But, try also that ECC803 in V1, if EI doesn't work.
JJ ECC83S has the max output level and, this is really good to push the rest of the chain. It has a good clean headroom (breaks up in distortion late than most of the rest). Its short plate is less prone to microphonics than the ECC803 or the LPS.
Tung Sol has also a very good output level but, IMHO, it's a bit unbalanced respect of EQ. Lows are powerful and they kick hard. Highs are also very dominant and, mids seems to be plane or a bit recessed. Maybe, in a Soldano-like amp, that is a bit dark by nature, you should go for a plain EQ or some slight bump in mid-highs.
If all these fail, throw that EH without thinking it more. EH is what you need when everything else went wrong. Nice crunch, good definition, quiet, and pushes high gain stages really good.
Forget 12AX7WB and Ruby's for V1. Even that the WB can be quiet enough, tone-wise lacks some magic, as their cousins the WA and WC. Ruby's are just tested rebranded Sovteks, chinesse or EH.
But, if you want a higher clean headroom, considere to use there a 12AY7 or a 5751 (NOS!, there is no good current production 5751).
For V2:
There, you can use that ECC803S (or Sovtek 12AX7-LPS) or throw one more EH or ECC83S.
If you find that a 5751 or 12AY7 in V1 weaks a lot the amp but, you still wanted more clean headroom, throw that 5751 or 12AY7 on V2, instead.
For V3 / PI:
This gives you the overall feel of the amp, how it reacts to your playing.
Two things to consider here: maximal transconductance (for inmediatness and clearity note to note) and power amp clean headroom.
A 12AX7 tube there will give you an earlier break up so, you will be able to krank the amp at lower loudness levels.
A less gainy tube will give you more clean headroom.
The tubes I liked more in this position are: NOS 5751, Sovtek 12AX7-LPS, Mullard 12AX7 re-issue and last generation Chinesse tubes. 12AT7 has even more transconductance than 12AX7 or 5751.
Clean headroom? NOS 5751 or NOS 12AT7 or EH 12AT7.
Earlier break-up? Chinesse, Mullard reissue
Even that the LPS works very well here, in some amps doesn't stand the stress and wear really fast (rolling dices, once more).
EH and JJ do a good job but, they haven't the same inmediatness than the other mentioned above.
Power amp:
JJ EL84s are really good tubes and, a bit bumped on mid-highs. They are powerfull and really loud. With a good 3D representation. But, I personaly like them while they remain clean. I don't like the way they break up, the distortion grain is not what I expect from an EL84. Mids are a bit confussing when pushed hard.
Tone wise, my prefered current production one is the Genelec Gold Lion EL84 but, those doesn't last more than few hours in combos and, very specially, in cathode-biased amps.
My prefered current production one, therefore, is the Mullard EL84 reissue because, it has everything. Tone wise, same as the Gold Lion. 3D representation is just a hair less than the Genelec and one or two steps over the JJ or the TAD. They last long time and work good from clean to high saturation, without loosing the focus, very linerarly, and delivering an outstanding crunch that goes better the more you krank it.
Just my 2 cts (or 2 dollars).
k:
