Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on February 09, 2013, 06:15:48 pm

Title: What is doing V9 in the Gibson Ga 46 ?
Post by: kagliostro on February 09, 2013, 06:15:48 pm

Is the V9 tube (a 6V6) there as to reduce or stabilize the voltage for G2 of the final tubes ?

http://www.el34world.com/charts/Schematics/files/gibson/GA-46.pdf (http://www.el34world.com/charts/Schematics/files/gibson/GA-46.pdf)

Thanks

K

Title: Re: What is doing V9 in the Gibson Ga 46 ?
Post by: DummyLoad on February 09, 2013, 07:04:24 pm

yes, voltage regulator for the 6550 screens.

thanks for posting that link K. :-) interesting amp - they wiggle the screens of the 5879s for tremelo.

--pete

Title: Re: What is doing V9 in the Gibson Ga 46 ?
Post by: kagliostro on February 09, 2013, 08:29:05 pm

Thanks Pete

Something like the 6be6 here ?

(http://www.ozvalveamps.org/playmaster/pm103cctamp_2joe.jpg)

Franco

Title: Re: What is doing V9 in the Gibson Ga 46 ?
Post by: HotBluePlates on February 09, 2013, 09:06:42 pm

Yes and no.

The 6BE6 is a penta-grid tube, also called a heptode or converter. There is a 2nd, and lower gain, control grid (G3) between the normal control grid (G1) and the screen (G2 and G4).

Think of it as a triode with 2 inputs, and different gain for each input.

Title: Re: What is doing V9 in the Gibson Ga 46 ?
Post by: kagliostro on February 10, 2013, 04:52:31 am

Thanks HotBluePlates, PRR sometime ago explained me about the 6BE6

I was wondering if the 5879 is used in the same manner or I would like to have a bit of further info about the GA-46 circuit function around this tube

K

Title: Re: What is doing V9 in the Gibson Ga 46 ?
Post by: HotBluePlates on February 10, 2013, 08:40:55 pm

Quote from: kagliostro on February 10, 2013, 04:52:31 am

I was wondering if the 5879 is used in the same manner or I would like to have a bit of further info about the GA-46 circuit function around this tube

No, because the 5879 is a pentode. 5 elements in the tube.

The 6BE6 (http://www.mif.pg.gda.pl/homepages/frank/sheets/093/6/6BE6.pdf) has 7 elements in the tube.

I think you'll have to do your trem the old-fashioned way.

Title: Re: What is doing V9 in the Gibson Ga 46 ?
Post by: kagliostro on February 11, 2013, 03:30:56 am

Quote

I think you'll have to do your trem the old-fashioned way.

Sure about that  :smiley:

The way they draw the GA-46 schematic is confusing me a lot

What I was saying is that I didn't understand well how in the GA-46 the V3 5879 mixer amp acts

I'll redraw it as to try to understand better

Thanks

K

Title: Re: What is doing V9 in the Gibson Ga 46 ?
Post by: sluckey on February 11, 2013, 06:09:17 am

Quote

...V3 5879 mixer amp acts...

V3 acts exactly like V4, but it has one additional input. Once you redraw the circuit rotated 90º CCW, you'll see that it's just a standard pentode amplifier stage exactly like the EF86.

The only difference is that the tremolo oscillator signal is applied thru a .1µF cap to the screen grid. This causes the screen grid voltage to vary at the same speed as the tremolo oscillator. Varying the screen voltage causes the current thru the tube to change (similar to the way the control grid operates), thus modulating the guitar signal that passes thru the tube.

I've recently seen a schematic that showed the tremolo actually modulating the screen grids of the output tubes, but I can't recall which amp. If it had been a popular or very effective method of implementing tremolo, I'm sure we would have seen a lot more amps using that method.

Title: Re: What is doing V9 in the Gibson Ga 46 ?
Post by: kagliostro on February 11, 2013, 08:03:22 am

Thanks Steve

About

Quote

If it had been a popular or very effective method of implementing tremolo, I'm sure we would have seen a lot more amps using that method.

you are referring to the final tube grid modulation or to both circuits, final tubes and GA-46 circuit ?

Franco

Title: Re: What is doing V9 in the Gibson Ga 46 ?
Post by: sluckey on February 11, 2013, 10:21:09 am

both