Preamp tubes for Blackface Champ

Ryan Donahue

Member
Messages
258
I have a '66 blackface Champ that has two good old RCA tubes in the power tube slots. The preamp tube is an Electro Harmonix 12AX7eh. I have on hand a JJ ECC83 and a NOS Phillips Jan 12AT7WC. Are all three of these interchangeable? I'm thinking either of the other two would be better quality than what's in there now but I'd like to swap them all out and figure out which one I like best. I just want to make sure I don't screw anything up.
 

WaltC

Member
Messages
2,126
if the amp is a real Champ then it has one rectifier tube (5Y3) and one power tube (6V6) and the one preamp tube. The design for the preamp tube is for a 12AX7. It won't hurt the 12AT7 to be tried in the amp, and you might like it (lower output power, cleaner...) but the only way to really know is to try. I suspect that it's a toss up between the EH and the JJ, I lean toward the JJ but opinions vary <G>. Try 'em and see which ones you like.

As for varieties of 12AX7/7025/5751/etc., new and old, there are almost as many opinions as there are people with tube amps. Again, try 'em and see which ones you like best.
 

wyatt

Member
Messages
4,167
Yes, those three are interchangeable. But I don't see why you assume either will be better than the EH? They could be, but you haven't shown your math.

The JJ is often considered to be a dark sounding tube. And because of the 12AT7's internal resistance, it won't bias the same in a spot for a 12AX7 and you might find it anemic and bright.But it doesn't hurt to try.

And there is only ONE power tube. The other is the rectifier. Are they original to the amp?
 

RussB

low rent hobbyist
Messages
11,157
First of all, you have 1 rectifier tube (5Y3) 1 power tube (6V6) and 1 pre-amp tube (12AX7, aka ECC83 aka 7025)


Swap the 12AX7 with your JJ for a direct replacement. You can try the 12AT7, but I reckon it wont sound all that good, but as they say, tone is subjective
 

Ryan Donahue

Member
Messages
258
I should have specified between power amp tube and rectifier tube. Sometimes my head just differentiates between preamp and power amp. Thanks for the info, at least I know that I won't break anything if I swap them in and out.

I don't think this is going to fix the issue I am having with tons of headroom out of this thing (I know, a Champ with too much headroom, crazy). I'm thinking my best bet is to swap out the ceramic Jensen that is in there now for an alnico Weber but mine as well test with what I have on hand.
 

Rob s

Member
Messages
1,033
Those champs are pretty clean.
I did a few easily reversible and little things to mine.
You can get a 50k pot with a switch that youcan put in on the intensity pot.
And make it so it will break the ground thus bypassing the trem.
That will give you some gain as the trem loads it down some.
You can also put the neg feedback on a switch and that will give you stock tight(blackface)
Or bypassed raw tweedy feel.
If that isnt enough you can do the same with tone section by making that bypassable with breaking ground
from the me resistor pre set on the bass pot.
Now its sort of like a tweed champ with no nfb and no tonestack.
It will be angry
 
Messages
1,657
Too much headroom? Changing the 12AX7?

Well, I know this is a bit of a random tube, but I found Ei Yugo 12AX7's (the early ones, with the telefunken-style smooth plates) to have a much earlier breakup than any other 12AX7 I've tried (and I've tried a lot).

However, Ei Yugo 12AX7's are notoriously microphonic. Personally, I bought a quad and had 1 microphonic right out of the box. The other three have held up well, and so I just moved the micro one to a V2 position.

Being potentially microphonic might be particularly bad for a Champ, a 1) combo amp and 2) an amp which often gets tossed around a lot because of its light weight and portability.

Still, if I were looking for early breakup from a 12AX7, the early era Ei Yugos have been such tubes.
 




Trending Topics

Top