Pre-Amp tube suggestions?

the(sims)

Member
Messages
203
I want to clean up the "green" channel in my VHT 50cl head. The amp is almost a dirty channel and a dirty channel, and I hope I can make the Green channel a little glassier and cleaner. Any alternates to the 12ax7 or brand of tube I could try? Thanks.
 

Slick51

Colonel Curmudgeon
Messages
522
Well, the 'two dirty channels' is by design on that amp....it's not advertised as a clean and a dirty (that's a 50ST). However, you could bump the first tube down to a lesser 12-group tube; a 12AT7, AY7, AU7, etc. and see if you can live with the changes on both channels.

Per Dan Torres' site (I wouldn't mod an amp using his techniques, but this info is OK), here's how other 12-group tubes stack up, gain wise, relative to the 12AX7 (using the AX7 as 100):

Tube Gain

12AX7 = 100

5751 = 70

12AT7 = 60

12AZ7 = 60

6072/12AY7 = 44

5965/12AV7 = 27

12AU7/6189/5814 = 20



HTH
Slick51
 
L

Leftee

FWIW I like a 5751 to tame a 12AX7. The 12AT7 has a significantly lower plate restance than a 12AX7. I've noticed that when I use a 12AT7 in place of a 12AX7, the amp seems to get significantly brighter/thinner. That depends on the position, but generally, I don't like a 12AT7 in place of a 12AX7. Not so with the 5751.

You can find NOS 5751's for $10 or so. There are a lot of them out there.
 

Dave B

Exit... Dual Stage Left
Gold Supporting Member
Messages
1,803
Are you aware of any other oddball tubes like the 12DW7, which has a gain factor of 100 in the first half and a gain factor of 17 in the second? I have one, and it's different. I'm curious what else is out there to experiment with.
 

Blue Strat

Member
Messages
30,194
In general, I agree that 12AT7s don't sound great in 12AX7 slots.

That was until the Mullard CV4024 (British military 12AT7) was discovered! I've had no fewer than 100 customers who have used these in 12AX7 sockets with great results.

5751s are good too but tend to be slightly "warmer" than the average 12AX7 or 12AT7.

Best bet is to try both. No one can predict what anyone else is going to like. Trust me, I've processed close to 9,000 tube orders, I know.;)
 

Wakarusa

Member
Messages
1,458
Originally posted by Dave B
Are you aware of any other oddball tubes like the 12DW7, which has a gain factor of 100 in the first half and a gain factor of 17 in the second? I have one, and it's different. I'm curious what else is out there to experiment with.
That isn't a weird one. See 'em all the time as Ampeg phase inverters.
 
B

BUDDADRIVE

>That was until the Mullard CV4024 (British military 12AT7) was discovered! I've had no fewer than 100 customers who have used these in 12AX7 sockets with great results.

Yes, I have been stashing these up. Nice tubes for the money. I use them in VHT UL's for the green channel (still not a clean channel IMO).
 

rjmmusic

Platinum Supporting Member
Messages
584
Originally posted by BUDDADRIVE
>That was until the Mullard CV4024 (British military 12AT7) was discovered! I've had no fewer than 100 customers who have used these in 12AX7 sockets with great results.

Yes, I have been stashing these up. Nice tubes for the money. I use them in VHT UL's for the green channel (still not a clean channel IMO).
In which position do you use that 4024? I have a CLX (same preamp as the UL), and would like more clean headroom too.

I've used the 4024 as a phase inverter in an Engl Savage 120 - it reduced the gain some, but made the gain much clearer so there was actually more usable gain.
 




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