Tube Rolling

[Coolhandjjl]

I have my Orange TB1000. Came stock with two JJ 12AX7 tubes. I'd like to drop he gain on V1 a bit, this thing is great, but I'd like a bit more rotation on the gain before it gets crunchy. Suggestions I found here (from 80% down to 19%) were 5771, 5751, 12AT7, 12AY7, 12AV7, & 12AU7. The only extra one I had was the AU7, but it's output is too low, hardly gets a chance to get crunchy at all. I don't know what 5771 or 5751 tubes are, so I'm looking at suggestions for 12AT7 tubes.

I was planing on leaving the stock JJ 12AX7 in V2.

 

[Bassmec]

You will need a tube with a gain of 85 MU the 12ax7 is 100 MU and the 12au7 is 20 MU.
So the tube you are looking for is the Military Spec CV4004 normally made by Mullard or Brimar.
Good Luck! we used to use them to take the fizzy out of Mesa Dual rectifiers for metal recording.

 

[Passinwind]

5771 is not a correct sub. 5751 OTOH is an excellent one for your situation, usually much better than 12AT7 IMO and IME unless you plan on doing circuit mods at board level as well. NOS 5751s are kind of spendy, most people seem to dig the GE ones the most.

Another possibility is having a tech change the effective taper of the gain control, which can be either simple or a huge PITA depending. Personally, I would just mod the first stage's gain at board level, but again, could be a can o' worms.

 

[Coolhandjjl]

Here's a gain chart I found:

100% 12AX7 | ECC803 | E83CC | 7025 | 6681
85% . CV4004
70% . 5751
60% . 12AT7 | 6679 | 6201
45% . 12AY7 | 6072
41% . 12AV7 | 5965

So I'm looking for either NOS GE 5751, or NOS Mullard or Brimar Mil Spec CV4004.
Never bought NOS before.

A quick look at ebay, the CV4004's are around $100~150. A bit out of reach for me unfortunately.

The 5751's are $20~60. More affordable to me. The GE's have things like black plate, 3 mica square getter, O getter, halo getter, square plate, ribbed plate, not sure what to look for.

 

[beans-on-toast]

Fender used to use the 6072 in the v1 position in some tweed amps. Also found in some mic preamps. Depends on how much gain you want to loose. It gives a nice smooth front end.

 

[Passinwind]

I highly suspect that 5771 as a preamp tube is the product of some dyslexic's imagination: http://www.radiomuseum.org/tubes/tube_5771.html

You could just try a new stock 5751 to see if you like it, I have no experience with these though. I wouldn't spend more than $30-35 for NOS, personally. Brent Jesse has GEs for 30 bucks at the moment, and he is a solid vendor who takes returns even if you just dislike the way a tube looks.

 

[Coolhandjjl]

I highly suspect that 5771 as a preamp tube is the product of some dyslexic's imagination: http://www.radiomuseum.org/tubes/tube_5771.html

It seems you are right.

You could just try a new stock 5751 to see if you like it, I have no experience with these though. I wouldn't spend more than $30-35 for NOS, personally. Brent Jesse has GEs for 30 bucks at the moment, and he is a solid vendor who takes returns even if you just dislike the way a tube looks.

Thanks for the lead.

 

[JGR]

The at7's have about the right MU but they don't sound very nice - good for a PI, but not in the preamp circuit IMO.

 

[beans-on-toast]

I highly suspect that 5771 as a preamp tube is the product of some dyslexic's imagination

Dyslexics can be very creative in finding connections that others don't see.

 

[Coolhandjjl]

Dyslexics can be very creative in finding connections that others don't see.

Naah. Lets blame this guy:
http://www.talkbass.com/threads/official-orange-club-ii.942246/#post-13611877

 

[BassmanPaul]

I highly suspect that 5771 as a preamp tube is the product of some dyslexic's imagination: http://www.radiomuseum.org/tubes/tube_5771.html.

Mind you a pair would make one hell of a loud bass amp!!

 

[B-string]

Mind you a pair would make one hell of a loud bass amp!!

Yes but the transformers would need their own bedroom!