Gibson Ensemble GA-86 on the bench

[TubeGeek]

This cool one was in for repair this weekend. Don't see these everyday. 1960.


The 6V6 is used in a way I am not familiar with. 5VAC to the filaments. I had to double check what I was looking at.  I haven't figured out exactly what the 6v6 is being used for but I'm thinking some kind of voltage/current regulator? I didn't have a bunch of time to analyze, had others to repair.

[TubeGeek]

pic

[TubeGeek]

pic

[TubeGeek]

pic

[TubeGeek]

pic.


It's a rats nest.  I did not do the cap job. That was completed before it came to me.

[TubeGeek]

pic

[sluckey]

The 6V6 is used in a way I am not familiar with. 5VAC to the filaments. I had to double check what I was looking at.  I haven't figured out exactly what the 6v6 is being used for but I'm thinking some kind of voltage/current regulator?

Not quite a regulator but it is used to drop the B+ for the screens and all nodes downstream.

[PRR]

Related thread:
https://el34world.com/Forum/index.php?topic=25203.0

This is a cheap cheat. The regulating tube (they didn't have MOSFETs) needs an elevated heater b/c the insulation won't stand 300+V. An added winding seems wise, but costly for setup and inventory/spares. A readily-available(!) 6V6 can pass about 5 times the current sucked by the power stage screens and all the preamps. Even if run at 80% of rated heater voltage, it can probably do the job. So a stock distributor power transformer works.

[TubeGeek]

Thanks for the info and clarification Sluckey and PRR.

[Jonas]

TubeGeek,

I really like that circuit and use it in several of my amps. You can also find it on the Grommes Model 260A and the Sho-Bud Compactra 100 (W/ 6L6).

I use 6V6 for screen supply only and prefer the 100K/220K divider ratio