Gibson BR-6F Rebuild

[dcribbs1412]

Local guy gave me a old Gibson amp he was given in '74 by an old timer
I've identified it as far as I can tell as a 1950's BR-6F.
It's in rough shape, cab has been painted over and tons of stickers on it, but as far as I can tell mostly original..caps, resistors, tubes, 10" field speaker etc. I have not powered it up but was told it works...sortof
Thinking about stripping the cab and recovering with something...not sure what.
Wondering if anyone has any suggestions or tips for recapping and such.
Attached is a schem with some voltages/mods I found.
Any comments/suggestions are greatly appreciated.

Thanks
Darin

[Phil_S]

Here are some pictures of what it looked like long ago... http://www.superiormusic.com/page041.html

It looks like you've got 3 filter caps. The 20uf needs to be 450s or 500V rated. I think I'd want the two 10uf caps to be rated 400V or higher.

I'd hold off on the 20uf cathode bypass cap on the 6SJ7 until I was sure they need replacement, but if you are ordering, you might as well get it because otherwise the postage will get the better of you and a $1 cap will be $11. I might be tempted to try a 20uf bypass cap on the power tube cathodes. So, that makes two of them, 25V rated should be good.

I might also fiddle with the dressing of the 6SJ7 to get the plate voltage up to around 135-140, where I think that tube will really bloom. Try dropping the plate load resistor from 220K to 150K.

Good luck.

[statorvane]

... and a three-prong power plug.

[surfsup]

I would be interested in hearing your comments on how this amp sounds, or a clip. I am planning a 6SJ7/6SN7 build with 6V6 next that I refuse to start until I fix an oscillation problem on my last amp. I would love to know what this amp sounds like. TIA

[dcribbs1412]

Here are some pictures of what it looked like long ago... http://www.superiormusic.com/page041.html

It looks like you've got 3 filter caps. The 20uf needs to be 450s or 500V rated. I think I'd want the two 10uf caps to be rated 400V or higher.

I'd hold off on the 20uf cathode bypass cap on the 6SJ7 until I was sure they need replacement, but if you are ordering, you might as well get it because otherwise the postage will get the better of you and a $1 cap will be $11. I might be tempted to try a 20uf bypass cap on the power tube cathodes. So, that makes two of them, 25V rated should be good.

I might also fiddle with the dressing of the 6SJ7 to get the plate voltage up to around 135-140, where I think that tube will really bloom. Try dropping the plate load resistor from 220K to 150K.

Good luck.

Thanks guys
Phil
I have most of the parts for replacing...
I've got some 8uf 450v Sprauges and F&T 500v 22uf. Also thinking about replacing the .05 and .01 grey tiger caps with some Russian PIO caps.
I'll shoot for the voltages you suggest on the 6sj7.
Will also be switching over to a 3 prong plug asap...
surfsup...will let you know how she sounds when I get her up and running.
It will be nice to bring something this old and tired back from the brink.
Especially if it can rock n roll...

Darin

[Phil_S]

I'm not a cork sniffer when it comes to caps. If the existing caps aren't leaky, I would do nothing about them.

FWIW, I am thinking those PIO caps are an audiophile thing and I'm not sure if they are considered a good choice for a guitar amp. I expect this particular amp (though I've never heard one) has not much clean headroom. For this reason, any inexpensive coupling cap (polyester, mylar, polyprop) will do a perfectly good job.

[dcribbs1412]

I'm not a cork sniffer when it comes to caps. If the existing caps aren't leaky, I would do nothing about them.

FWIW, I am thinking those PIO caps are an audiophile thing and I'm not sure if they are considered a good choice for a guitar amp. I expect this particular amp (though I've never heard one) has not much clean headroom. For this reason, any inexpensive coupling cap (polyester, mylar, polyprop) will do a perfectly good job.

Thanks Phil
Not much of a aficionado myself when it comes to caps(although I drink the NOS kool-aide every so often)...I did a quick check the day I got it and all the caps tested out of spec.(did not remove them from the circuit for tests). FWIW I have the PIO's on hand and have used them in other circuits with decent results. I have some mylar and polys I can try also. I'm hoping to do as little as possible to the circuit and after testing/replacing some tubes(6SJ7, 6SN7, and 5y3 tested low), possibly get some decent grind/tone out of her.

Darin

[dcribbs1412]

Got her up and running...replaced caps a few way out of spec resistors and
she has a some tone. Actually sounds decent with a boost pedal. Volume wise its not usable for any kind of band situation. Voltages are way lower than expected. I replaced most tubes and have 300V out of the 5y3(was looking for around 400V), 6V6;s are at 250V or so 6sj7 is around 97V. There is a 20k wirewound on a 6V6 from pin 4 to 8 I'm not sure about...it's not on the schem. I may try it without it to see voltages...I dont want to mess the speaker up. Any comments/suggestions are greatly appreciated

Darin

[dcribbs1412]

Went back over schem and realized I had missed a 20uf cap off the rectifier.
Added (33uf on hand) and voltages came up closer to expected...375V...amp got a little tighter/quieter sounding.(still needs a boost pedal to get where I like it). Also changed out the scratchy 500k pot.
Gonna check grounds one more time and start looking at redoing the cab.

Darin

[dcribbs1412]

Stripped and refinished cab...my feeble attempt at a relic job
Color is sorta sea-foam green "Catalina Mist". Just could not bring myself to make it the brown stock color. Sorry if this upsets anyone.(could not find any tolex that looked close and oh ya I don't know how to tolex).
Made the back cover from old wine box. New grill cloth tried to relic it also.
Not sure about the G logo...made it in paint...does it look too cheesy?

Darin

[Reeltarded]

Not at all! Nice treatment! Looks like what a fashionable person of the period might have tried, actually..

[Phil_S]

Hey, it looks good to me! When you get a relic in such poor condition, there's nothing that says you have to restore it so it looks original. I think, if I got one that was 8/10, I'd do what I could to restore it. Your situation wasn't even close to that. The painted G looks great in the photos.

[dcribbs1412]

Thanks guys
I cleaned it up a little more and put back together.
Really liking the tones this little thing puts out.
Feel good about saving it from the dumpster.
Thanks again Phil_S for your links and tips...

Darin