Convert the normal channel of a Blackface to Brownface spec?

[VintageCharlie]

Hi folks,

i'm wondering if it is easy to mod a blackface spec amp into a brownface?

I have a super reverb clone in the works and would like to hear brown-face tones without building another amp.

Afaik the voltages on the brownfaces were higher, which would require a new PT - i would leave that aside in this case.
I am also not after the brownface type tremolo.

But otherwise, are the circuits easy to moddable and reverse modabble? Let's say a BF super reverb -> brownface vibrolux. I'm not good with schematics, but comparing gutshots, they do look very similar to my uneducated eye.

I just suspect that the brown amps might be THE tone - they seem to have a great balance of everything, even the drive seems almost Marshallish, but smoother and "polite". So i would like to try it, and go back to stock, if i do not like it.

Ideal would be something like a brown normal channel and a black reverb/trem/bright channel.
The phase inverter seems to be similar too? If that's correct, then it might be doable, right?

Thanks and regards!

VintageCharlie

[Mark]

One issue you will have is the treble pot used on the Brownface amps. There are tapped pots available but the tolerance is all over the place and the taper is 15% instead of 30% so it doesn't feel right.

I'd be inclined to use a 250K pot with a 30% taper and a resistor and cap.

The PI is quite different on Brown and Blackface amps. The Brown uses a 12AX7 while the Black uses a 12AT7. The AX7 has a gain of 100 while the AT7 has a gain of 60.

http://en.m.wikipedia.org/wiki/12AT7

http://www.turretboards.com/layouts_sch ... _6g11a.gif

http://www.turretboards.com/layouts_sch ... _ab568.gif

[VintageCharlie]

Thanks, Mark!

Ok, then it's probably best not to tinker in that direction. That might be a different project then.

Regards,

VintageCharlie

[Mark]

The tweed/brownface PI has a certain sound about it, so I suspect you wouldn't be satisfied with the results or you'd try a brown (6G series) amp and realise how different it sounds to your amp.

Speaker choice has a lot to do with the sound of the brown amps too, my Bandmaster sounds very different with a 10" speaker in an open back. I was almost tempted to go the the three 10" path with it.

[Mant]

You could still fiddle with just the preamp of the channel just for different flavor. I convert the bassman bass channel to tweed/ jtm 45 vibe.
Change the tonestack as well.
Now there are two differrent sounds out of one amp.
Works great.

[Mark]

The Super Reverb doesn't have a mid control, maybe an AC-30 tone stack would work, it is bound to sound different. James and Bandaxall tone stacks might be interesting?

Try Duncan's tone stack simulator that could be a good place to start.

[VintageCharlie]

thanks for the tips, guys! i see it is not possible to have all you want in one box, which is probably the usual case, when you imagine, how nice it would be to have, for example, a blackface, a jtm and an ac30 in one box
so that's a seperate project then. though it would be interesting to play around with the tone-stack, just for the fun of it.

[Mant]

easy to add the mid range control.
use the ext speaker jack as a place for the pot.
you can use a 25k 50k pot.
swap it out for the 6.8k or 10k midrange preset resistor in the tonestack.
boom mid range control.
if you used a switched pot it can be a tonestack bypass by breaking the ground connection of the tonestack.
then you would have about a 13db boost from the next make up stage that is no longer making up the gain loss of the passive tonestack.