Another get*setgo / 300B

[TomMcNally]

This was a two evening project, I did the chassis over the weekend,
and last night when the Mouser order arrived, I put together three
circuit boards and finished this amp up. I have some of the old
Johnson style ceramic octal sockets too, so it will be a simple process
to switch to 6B4G's by changing the sockets, which mount in the
same footprint, and paralleling a 1.5 ohm filament dropping resistor
across each channel to bring the voltage up to 6.3 for the 6B4G's.

Definitely a sweet sound - the bass is incredible!

more pix at http://tmamps.com

[SVinzant]

Tom,
Great looking amp!
I did find a (small) mistake on your website
The main heading for the amp is listed as:

"January 2010 - get*set*go 300B Single Ended Triode"

(should probably be 2011)
Scott

[elbinster]

Someone finally got me a pair a 300B for Christmas! They do seem to work very well with the GSG circuit. What I was amazed by is how big they are compared to the 6B4G and 2A3. Actual listening test is still to come. Though now I'm starting to think I'll need to do more to take advantage of the 40W max dissipation JJ specs...

[SDS-PAGE]

Wow, Tom. You're off to a flying start in 2011 for tube amp building. I have lost count how many you've built since the year started! It's incredible how quickly you can whip those out.

Nice looking amp, BTW!

Min

P.S. Have you tried to up the B+ to squeeze out more watts out of those 300Bs?

[TomMcNally]

Whoops - yep it is 2011 already ... fixed - thanks.

The get*set*go doesn't run the 300B at full power, but they
still shine through. Definitely a quick and easy way to get
into an excellent sounding amp.

Min - I did build a solid state diode plug in and sent it out with
the fist g*s*g/300B ... I didn't really notice any change in the
sound with the extra voltage. Ed Brown says it kicks it up
about 45 volts. I'm going to make another today for this
new amp.

I've got enough parts to build some more, another 6V6 PP and
some g*s*g's and maybe some Darlings.

... tom

[SDS-PAGE]

Tom,

If you use SS rectification, you might want to install a soft start circuit or a standby switch to protect your precious 300Bs. Just to be on the safer side.

I actually preferred the sound of 6B4G over the 300B in GSG. The 300B definitely likes the higher B+.

Min

[Quad]

I tried a solid stage replacement for the 6AX5GT using
a couple of UF4007s and the 6SL7 died right away.

Did I need to anything else - drop the voltage to the 6SL7?
Anyways, I have just another 6SL7 with me, so can't
lose that, so no more experimenting. The 6AX5gt stays :-)

[TerrySmith]

If you use 6A3 tubes you won't need to change sockets, just the resistors.

[EWBrown]

In the 6AX5 rectified GSG, the 6SL7 runs each triode at 0.6 mA plate current, and about 160V on the plates, so I doubt that you're overpowering the 6SL7 with approx 100 mW plate dissipation on each section. I've pushed 6SL7s and 12SL7s a LOT harder than that...

Could be that your 6SL7 was on its way out, anyway.

OTOH, if you're using vintage twin-plate 6B4Gs, then the 6AX5 rectifier should be used, and NOT SS rectification.

The Sovtek / EH single plate 6B4G and 2A3 can take the higher plate voltage and current as these have a somewhat higher plate dissipation rating than the twin-plates.

The twin-plates are essentially paralleled 45s inside the jug.

/ed B

[Quad]

Thanks, Ed.
My Sovtek 6B4Gs withstood the SS experiment. The 6SL7
could have been on it's way out, as it was a old, used one.

[EWBrown]

IIRC, the Russian 6SL7 equivalent is 6N9P (or is that 6N8P), one is 6SL7 and the other 6SN7...

The Sovtek 6B4Gs, with the larger /6C4C single plates can handle up to about 20W plate dissipation, prehaps a bit more. Don't try that with the vintage twin-plate 6S4S or 6B4Gs, they are 15Watts max.

The Chinese tube numbers are mostly derived from the Russian tube numjbers, and would be 6N9, 6N8, etc. I don't know the availability of which kinds of tubes would most likely to be found in India...

The one flagrant exception to this, is the Chinese equivalent of a 12AX7, it is called 6N4, and that does not agree with any Russian "convention".

/ed B