How To For Dummies: GSG 6V6 ?

[fooster]

Hey all,

I found a couple posts talking about swapping the 6B4G with 6V6's. I'm not new to amp building, just 6B4G's. Can someone post a diagram of how to hookup the 6V6?

Thanks,
Fooster

[Geek]

Hi,

Those are very different animals. 6B4G is a 6V filament 2A3. All rules for a 2A3 apply.

6V6 is an octal 6AQ5 and is a pentode. You need a screen voltage, about 1/3 the bias, the plate resistance is wayyyyy higher (add a goodly amount of NFB or fuggetabboudit), the gain is higher, the transconductance and plate dissipation is lower and the required plate load of the 6V6 is three times higher.

Cheers!

[fooster]

Thanks for the info Gregg. I figured they were way different.

This is the post I saw http://www.diytube.com/phpBB2/viewtopic ... 8&start=10

Given that the 6B4G (or 6A5G) is essentially pin-compatible with the standard 6L6 / EL34 pinout, and that the James OPTs already have a UL screen grid tap, the following little bit of evil hallowe'en thought occured to me:

Wire the SG connection from pin 4 of the tube socket to the OPT's UL/SG tap, and add a 1.2K WW resistor, for each channel, which could be switched in parallel across the existing 1100 / 900 ohm cathode resistors, in order to accomodate the 6CA7s. Use the plug-in SS rectifier to replace the 6AX5, and presto! you have a 5 to 6 watt UL SEP amp! This way, it is simply a matter of swapping the rectifiers and flipping a switch, to use either triode or pentode modes!

If this seems a tad complex, just use a 6V6GT instead of EL34, stay with the 6AX5 rectifier, and adjust the switched-in extra parallel cathode resistance as required to bring it down to around 330 to 360 ohms (12-13V @ 35-40 mA)..

The EL34 is happier with a 3.5K plate load, and the 6V6 with 5K, YMMV, etc...

[EWBrown]

You would have better results using 6AV5GAs for a 6B4G replacement, I've done that, and it is documented earlier under this topic.

http://diytube.com/phpBB2/viewtopic.php?t=4551

The 6AV5GA pinout is different, and since it has a cathode, that should be connected directly to the "top" of the (900 ohm) cathode resistor, the two "test points" on the GSG board are a very convenient place to do this.

This modified G*S*G served as a test bed for the "next generation" of 6AV5GA SE amp, which was also loosely based on SorenJ's design from a few years earlier.

http://diytube.com/phpBB2/viewtopic.php ... sc&start=0

/ed B

[fooster]

Thanks Ed. I was just reading about the 6AV5GA yesterday. Looks great!

[ramkumar]

EDBrown is a regular to reply most of the post, his answers are very logical and inspiring. Thanks Brown.