BR 6 Gibson amplifier

[BlackBart]

Any one with experience with the Gibson BR6? thx

[Stevem]

Well I have got 2 up and running like 25 years ago so I might be of some help.

[sluckey]

I've seen the schematic. Looks pretty simple.

[Stevem]

Let me guess your question is about replacing the shot original speaker, or why NOS Octal preamp tubes are so over the top expensive?

[Colossal]

I'm going to revive this thread. I was reading about classic amps for classic jazz tone and the BR6 got mentioned. Seems like a wonderfully simple amp. Paralleled 6SL7, 6SN7 paraphase inverter and a pair of 6V6s running about 10W for the pair.

Stevem, how do you find the input and Volume control arrangement at the front end of the amp? The input network is 100k/100k-> 500kA, which might seem lossy on inspection, but that might be good to keep the amp cleaner overall.

Do you have the original field coil speakers in your amps or did you need to replace? Have you measured the operating voltages? I might guess they are fairly low; B+1 in the low 300s

Thanks.

EDIT:
Given that the amp has an unbypassed 200R cathode resistor for the power tubes, it is running in Class A push-pull. The 6V6 datasheet gives us settings for 285V and 250V plates and screens and -19V and -15V respectively for the cathode. The whole power supply is "choked" by the 1000R field coil choke so ripple should be pretty low.

[didit]

Hello --

Yes. Spare a bit attention to the wiring of the rectifier secondary, specifically where/how the first bulk filter is connected. Your guess about the electrical parameters of the field coil is perhaps better than mine but a 1000 Ohm with at least 20 Henries is fair starting point. A full inline choke serves well. And yes, deep A that could range to AB under real duress. Top plate voltage of 280 with 15-20V trimmed by the cathode resistor should play nice. The output primary should be 8-10K. With a sensitive alnico speaker you oughta be pleased. Paraphase provides a unique voice.

As you say, it's an elegantly simple design. Breadboard it, for nostalgia even literally, as in building it up with sockets and terminal strips on a small chunk of wood and experiment before migrating into a permanent safe enclosure.

..

[Colossal]

Hello --

Yes. Spare a bit attention to the wiring of the rectifier secondary, specifically where/how the first bulk filter is connected.

Yes, it's a C-L-C arrangemwnt before B+1, so despite the lowish filtering (20uF-1000R/?H -10uF - 47k - 10uF), I would think it ahould be pretty quiet at idle.

Your guess about the electrical parameters of the field coil is perhaps better than mine but a 1000 Ohm with at least 20 Henries is fair starting point. A full inline choke serves well. And yes, deep A that could range to AB under real duress. Top plate voltage of 280 with 15-20V trimmed by the cathode resistor should play nice. The output primary should be 8-10K. With a sensitive alnico speaker you oughta be pleased. Paraphase provides a unique voice.

I think those assumptions are probably very close to spot on and they fit with the classic Class A/AB push pull examples for the 6V6. 15V/200R = 75mA for two tubes which is very close to the stated 70mA idle current in both applications.

I am guessing the transformers coule have been Triad? Maybe Stancor?

[dcribbs1412]

https://ampgarage.com/forum/viewtopic.php?t=18722
From a few years ago, some info.
It is a cool little vintage amp

[Colossal]

https://ampgarage.com/forum/viewtopic.php?t=18722
From a few years ago, some info.
It is a cool little vintage amp

Thanks for posting that link and nice work on the rescue. I saw a video with a guy playing Jingle Bell Rock on a Gretsch through a BR6 and gotta say it sounded excellent.