20thA XTC - EL34 Model, Pre Amp layout??

[Ventura]

Anyone care to share?? I know the V1 slot's probably closest to the input transformer/electrical input, but where are the loop and PI slots with respect to the rest??

Thanks for anyone who's chiming in...

Peace,
V.

 

[steve_k]

V1 - all channels (yes, its that hard to reach one in front of the OT
V2 - channel 2 and 3
V3 - channel 2 and 3
V4 - loop
V5 - PI
V6 - channel 1

 

[Ventura]

V1 - all channels (yes, its that hard to reach one in front of the OT
V2 - channel 2 and 3
V3 - channel 2 and 3
V4 - loop
V5 - PI
V6 - channel 1

Thanks Steve - V1 closest to the input jack, correct?

What are you using in your V1, V6 for cleans?? And what about Phase Inverter - what kinda glass?? Just wondering... Thanks man

Peace,
V.

 

[steve_k]

V1 - all channels (yes, its that hard to reach one in front of the OT
V2 - channel 2 and 3
V3 - channel 2 and 3
V4 - loop
V5 - PI
V6 - channel 1

Thanks Steve - V1 closest to the input jack, correct?

What are you using in your V1, V6 for cleans?? And what about Phase Inverter - what kinda glass?? Just wondering... Thanks man

Peace,
V.

V1 - EI Yugi
V2 - Sovtek LPS
V3 - Penta C8
V4 - EI Yugi
V5 - JJ Gold AX7 Matched/Balanced
V6 - Tung Sol

You will find that the 20X is very finicky when it comes to tube changes. This is because there 3 and 4 stages of gain spread across several tubes, which is similar to older Mesa Mark series amps. You can completely change character of the amp with a single preamp tube change, much more so than with power tubes. I am running SED's. But, I would imagine the stock JJ's to sound about the same.

 

[Ventura]

Thanks for the info Steve - this is excellent info... I'm just on the verge of loading KT77's and with this, would probably consider sharpening up the Green Channel's clean, and the PI is a key tube too. Considering that the head comes stock with Chinese B's, worse case scenario is reverting back to Chinese/Shuguang if things sound too weird. But I'm putting my glass order together for a couple amps and I want to have some spare tubes to work with and experiment with.

Awesome post - thank you.

V.

 

[steve_k]

Thanks for the info Steve - this is excellent info... I'm just on the verge of loading KT77's and with this, would probably consider sharpening up the Green Channel's clean, and the PI is a key tube too. Considering that the head comes stock with Chinese B's, worse case scenario is reverting back to Chinese/Shuguang if things sound too weird. But I'm putting my glass order together for a couple amps and I want to have some spare tubes to work with and experiment with.

Awesome post - thank you.

V.

Sometimes those Chinese B's are tough to beat. I find that one in the gain stage is great. Often though, I look to change the input driver to either a Sovtek LPS or an EI Yugi. Typically, I like the Ruby HG or HG+ Chinese in 2 and 3. A balanced JJ works well in a PI slot as do LPS or Ei's. I have a small stash of Penta Chinese 8th's that will go in V2 of some amps. For the most part though, my drawer has a pile of Ruby pre's, Sovtek LPS, several gold pin JJ's balanced, a shit pile of China 9's and a few Tung Sols.

Depends on how the amp is set up though. The XTC and Reinhold's design has 2nd and 3rd stage tube gains across 3 tubes. But, if you can get it right on the front end with a good V1 selection and one other gain stage tube change, you can really change the flavor of these amps.

Steve

 

[Ventura]

Yep. Looking at a 7025S (TAD Select) in V1, and a Sovtek LPS in the PI slot - all else remains the same...because ya, the Chinese B's are hard to beat.

We'll see... But again, thanks for the 411.

V.

 

[steve_k]

Yep. Looking at a 7025S (TAD Select) in V1, and a Sovtek LPS in the PI slot - all else remains the same...because ya, the Chinese B's are hard to beat.

We'll see... But again, thanks for the 411.

V.

Best way to do it, is take the chassis out of the shell, get your tube arsenal lined and start playing and changing, starting with V1, V2, V3, V6, V5, V4.

Steve

 

[Ventura]

Yep. Looking at a 7025S (TAD Select) in V1, and a Sovtek LPS in the PI slot - all else remains the same...because ya, the Chinese B's are hard to beat.

We'll see... But again, thanks for the 411.

V.

Best way to do it, is take the chassis out of the shell, get your tube arsenal lined and start playing and changing, starting with V1, V2, V3, V6, V5, V4.

Steve

I think I'll be tweaking the pre's along with installing the new KT77's this weekend, just for science.

Will post my thoughts, maybe some clips - first is the Mak4 though

V.

 

[Ventura]

So the KT77's are sitting in their respective BiasRite sockets, just waiting to drift, oscillating between 31.2mA and 33.6A, my guess is they're fine right where they are. Plate voltage is steady at 550... Just going to let these sit for a bit and then call it a day.

And oh ya, crank this bitch and see what the new glass does for 'er!! I'll be letting you know Gary, don't you worry, I'll be letting you know

Peace!!
Mo

PS - knocked it back to 29mA-31mA, there's a bit of spread between the tubes and one of 'em was always 2mA higher. I didn't want to push that particular tube, so I backed everything off a hair and we're well within safety now with that 1 tube at 31.9mA Going to give 'er a rip right now

 

[glip22]

So the KT77's are sitting in their respective BiasRite sockets, just waiting to drift, oscillating between 31.2mA and 33.6A, my guess is they're fine right where they are. Plate voltage is steady at 550... Just going to let these sit for a bit and then call it a day.

And oh ya, crank this bitch and see what the new glass does for 'er!! I'll be letting you know Gary, don't you worry, I'll be letting you know

Peace!!
Mo

PS - knocked it back to 29mA-31mA, there's a bit of spread between the tubes and one of 'em was always 2mA higher. I didn't want to push that particular tube, so I backed everything off a hair and we're well within safety now with that 1 tube at 31.9mA Going to give 'er a rip right now

 

[Ventura]

So the KT77's are sitting in their respective BiasRite sockets, just waiting to drift, oscillating between 31.2mA and 33.6A, my guess is they're fine right where they are. Plate voltage is steady at 550... Just going to let these sit for a bit and then call it a day.

And oh ya, crank this bitch and see what the new glass does for 'er!! I'll be letting you know Gary, don't you worry, I'll be letting you know

Peace!!
Mo

PS - knocked it back to 29mA-31mA, there's a bit of spread between the tubes and one of 'em was always 2mA higher. I didn't want to push that particular tube, so I backed everything off a hair and we're well within safety now with that 1 tube at 31.9mA Going to give 'er a rip right now

You were sooooooooooooooooooooooooooooooooooooooooooooo right...!!!

Mo

 

[glip22]

Wait until they break in some. These tubes need a little break in. Moreso than EL34's.

 

[Ventura]

Wait until they break in some. These tubes need a little break in. Moreso than EL34's.

Quick re-bias after about 20 hours perhaps??

Mo

 

[glip22]

Wait until they break in some. These tubes need a little break in. Moreso than EL34's.

Quick re-bias after about 20 hours perhaps??

Mo

Yep. I would run them at around 60-63% instead of 70 but they can take it. Mine have been going strong for a bit now. Just pulled them to retest and they are still reading good for micromhos.

 

[Ventura]

Wait until they break in some. These tubes need a little break in. Moreso than EL34's.

Quick re-bias after about 20 hours perhaps??

Mo

Yep. I would run them at around 60-63% instead of 70 but they can take it. Mine have been going strong for a bit now. Just pulled them to retest and they are still reading good for micromhos.

Well, interestingly enough, the tubes from left to right were somewhat incrementally different. The 1st tube was 29.0mA, 2nd was 29.9mA, 3rd was 31.4mA and 4th was 32.0mA or something like that... I figured WTF, just let 'em break in and I'm sure they'll even out. I'll yank it in a month and see where she reads.

But dude, what a great upgrade!! I've been sitting on my sofa, 1/2 stack in front of me about 12 or 15 feet away, just wankin' like there's no tomorrow!! LOVING it!!

Peace,
Mo