20/20

[luigi]

Hi all,

I'm new to the board (just got my formula & 20/20) and I am hoping to get some help with my 20/20.

I am interested in adding an adjustable bias to my amp and I am having a devil of a time finding a schematic for the 20/20. Has anybody here done this mod? If so, could you please tell me where you got the information for the mod and schematic?

Thanks,
L

 

[Timbre Wolf]

Hi all,

I'm new to the board (just got my formula & 20/20) and I am hoping to get some help with my 20/20.

I am interested in adding an adjustable bias to my amp and I am having a devil of a time finding a schematic for the 20/20. Has anybody here done this mod? If so, could you please tell me where you got the information for the mod and schematic?

Thanks,
L

Hi Luigi -

I've looked into this. A friend of mine is a very knowledgeable tech. who did a bias mod on my 2:90 (I was glad he did). I don't remember the exact specifics about why, but when he did finally locate the schematic (which was not easy to get), he concluded that the bias mod was not feasible. It may have been more than a space issue, but the lack of room in the single-rack unit was a major determining factor.

Too bad, too, 'cause I've got some nice EL84 (Mullard, Amperex Bugle-Boy, RCA black-plate) to try in it if I could adjust the bias. The good news, for me, is that the Tungsram EL84 I tried do allow my 20/20 to operate in the correct range, and they work superbly. I highly recommend Tungsram EL84 (and I've tried a lot of the greats). I got them from a reliable dealer in Hungary: http://www.zeitmann-tubes.com/

I also recommended Mike at KCA ( http://www.kcanostubes.com/content/ ) as a source of NOS tubes: he can locate your sets that will work with the 20/20.

- T

 

[luigi]

Thanks for the reply Timbre Wolf.

I agree that it is much easier to buy the tubes that are matched for the amp, but being here in NF and having to order from the US really drives the price up. After border duties, shipping and the conversion of Canadian money into USD, the tubes usually end up being approx 2-3 times the cost of tubes I can buy here locally. That is huge for me.

At the very least, I guess I can add a couple of one ohm resistors and mount some external bias test points but I would really like to add the adjustable bias. If it takes a bit of going to get it in there it's still worth it to me. I really would love to get my hands on a schematic.

Cheers,
L

 

[MarkPurney]

There's plenty of extra room inside the 20/20 so I doubt it was a space issue. I may have a copy of the schematic on a CD somewhere, but not something I can get to right now.

 

[luigi]

Mark,

I would really appreciate a copy of it if you happen to have it. I have searched high and low on the net and I have come up completely empty.

Thanks,
Luigi

 

[MarkPurney]

I'll try and look for it soon and let you know if I find it.

 

[luigi]

Thank you, very much.

 

[imott]

Triaxis schematics can be found at http://www.tubefreak.com/tubefreak.html

 

[t0aj15]

Triaxis schematics can be found at http://www.tubefreak.com/tubefreak.html

He's not looking for Triaxis schematics, he's looking for a 20/20 schematic, which tubefreak doesn't have.

 

[imott]

Oops! My bad...I realized that last night just after my connection dropped.

 

[luigi]

Thanks for the thought though!

I have a formula preamp that I run with my 20/20. Love to have a Triaxis...can't afford it at this time.

 

[Nocki]

I used to have the Formula, 20/20 combi as well... those where nice times... I liked the pulled pot sound the best/// nice attack. I always wished that sound could be on all the channels of the formula!


Good luck!

 

[luigi]

I was going to get rid of my formula until I modded it. Now I love it. You can't beat the 20/20....man is that sucker ever loud.

"used to have"......What are you using now? Or better yet, what did you give it up for?

Cheers,
Luigi

 

[Nocki]

I always had trouble with the g-major. thats a little tonesucker! and i couldnt get the right high gain sound out of it which I liked! so I bought a Mark IV wich I still have!
But now she's going away for a triaxis and 2:90 combi!

althoug I liked the formula I really wished it had pul knobs on both channels! so both would have that great attack and sound!

I really like the 20/20 though! I sold it to some guy and 2 years later I bought it back from him!!! now its gone because I like 6l6 tubes more. I wanted to have the 20/20 because I figure 20 watts a side wouldt be so loud. now I'm older and i have learned that wattage has nothing to do with volume but with headroom an TONE!


Nocki

 

[luigi]

For me, that would be a hard call......I'm not sure I could part with a Mark IV if I had one. I would like to have a Triaxis though.....but for now, that is dreaming.