6v6 push-pull cathode wiring

[Anthony]

Looking at a Gibson GA-30 Invader manufactured in 1959, I found that there are a resistor and polarized capacitor paralleled between pin 8 on the 6V6 tubes.  This is not consistent with any Gibson schematics I have seen. 

Pouring through a lot of other 6V6 push-pull schematics, pin 8 for both power tubes always share a connection to a resistor and capacitor that are paralleled to ground.

Was this an error or is this a effective method that I am not familiar with?

[sluckey]

I don't think the amp can possibly work if wired as you say. The cathodes must be connected to ground somehow. Is the cap/resistor the only thing connected to pin 8?  Can you post a hi rez pic that clearly shows how that resistor/cap is connected?

[shooter]

Was this an error

Gibson schematics have had errors, kinda like where's Waldo, only funner

here's a link to how it probably should be;

http://el34world.com/charts/Schematics/files/gibson/Gibson_GA-30RV.pdf

[sluckey]

I think he is saying the actual amp is wired that way, not a schematic error. All the GA30 schematics I've seen show pin 8 wired correctly.

[Anthony]

  The error was mine.

I was looking at the wrong pin.  Pin 1 on both sockets is being used as a tie to chassis ground (out of convenience I imagine), since pin 1 on a 6V6 is not used.  There is actually a yellow wire connecting pin 8 from the left socket to pin 8 of the right socket.  Pin 8 from the right socket has a paralleled resistor and cap tied back to pin 1 on the left socket. From there, pin 1 on the left jumpers back to pin 1 on the right.

I have noticed a few places in this amp where the wiring gets all zig-zaggy (<--technical term).

[shooter]

where the wiring gets all zig-zaggy

  Gibson did like that style lead dress
I've worked on a handful of GA-5s n 8's, built my version of an 8
I picked up this one, they probably fired the guy cuz he was so neet

[PRR]

> Pin 1 on both sockets is being used as a tie to chassis ground (out of convenience I imagine), since pin 1 on a 6V6 is not used.

Technically: there was a 6V6-no-G, metal shell, on pin 1, and for safety you should tie pin 1 to ground.

I have seen a picture of a metal 6V6 but they are incredibly rare.

FWIW: the metal base on 6550 and a few others, and the shell on a metal 6L6 (now rare because once common and widely abused to death in amateur radio rigs), should be grounded just in case something comes loose inside.

[Anthony]

To make sure I am understanding you (PRR): are you saying the metal version had a pin 1 and that pin was connected to the metal can so that the tube could be grounded?  And are you saying the 6V6 tubes that were originally in the GA-30 were metal?

[PRR]

> are you saying the metal version had a pin 1 and that pin was connected to the metal can so that the tube could be grounded?

Yes.

> And are you saying the 6V6 tubes that were originally in the GA-30 were metal?

Very unlikely.

They may have grounded pin 1 just-in-case metal 6V6 became common. More likely it was just handy for grounding other things. Like that cathode resistor.

[DummyLoad]

> Pin 1 on both sockets is being used as a tie to chassis ground (out of convenience I imagine), since pin 1 on a 6V6 is not used.

Technically: there was a 6V6-no-G, metal shell, on pin 1, and for safety you should tie pin 1 to ground.

I have seen a picture of a metal 6V6 but they are incredibly rare.

FWIW: the metal base on 6550 and a few others, and the shell on a metal 6L6 (now rare because once common and widely abused to death in amateur radio rigs), should be grounded just in case something comes loose inside.

i didn't think that they were that rare...

https://www.dropbox.com/s/vc82rz97owdhdoq/6v6-metal-20170901_022851.jpg?dl=0

i acquired that pair in the pic from an estate sale about 10 years ago. damn time flies by...

--pete

[PRR]

OK, now I can say I know a guy who can post a picture of a metal 6V6.

I still think in vintage 6V6, glass outruns metal 99:1, and new-made is all glass.

Wikipedia says the coke-glass came first, a metal right after, but by 1943 the metal cost more so became less common. Especially after the straight-side bottle came out (cheaper).

KCA sells assorted metal 6V6 cheaper than branded glass 6V6.