• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Use for 5K:8 PP OPT?

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Look at the "toroidal amps" thread and you'll see two different implementations of the bias I described. Unfortunately it most definately places some woping big caps in the signal path. However I think your fear is a little overstated - but thats just my opinion. I suppose its a good thing to aim for though.

Shoog
 

GK

Disabled Account
Joined 2006
How much are NOS 6B4G's?
I've got about 20 or so originally boxed, un opened US Army NOS 6B4G's in my collection, so I'm ordering a pair of Hammond 1615's (5kCT primary) with my 1650W's (for another project) to make a ~7W push pull class A.
 
I've got about 20 or so originally boxed, un opened US Army NOS 6B4G's in my collection

You might want to open one box and look carefully at the tube itself. There were some "6B4G's" made by Sylvania or Phillips that were actually re pinned 6AV5GA's. A true 6B4 is DHT. You should see a filament and one grid. Most are of the twin plate variety similar to a 2A3. Sylvania made some "6B4's for the US Army that contained 6AV5GA guts. They have straight sided glass, and contain a beam pentode that is triode wired. I have "tested" one of these and they don't sound half bad, and seem to function like a 6B4 should. I ran mine in SE mode and had no problem getting 7 watts out of one tube, but I might have ignored the ratings a bit.
 

GK

Disabled Account
Joined 2006
tubelab.com said:


You might want to open one box and look carefully at the tube itself. There were some "6B4G's" made by Sylvania or Phillips that were actually re pinned 6AV5GA's. A true 6B4 is DHT. You should see a filament and one grid. Most are of the twin plate variety similar to a 2A3. Sylvania made some "6B4's for the US Army that contained 6AV5GA guts. They have straight sided glass, and contain a beam pentode that is triode wired. I have "tested" one of these and they don't sound half bad, and seem to function like a 6B4 should. I ran mine in SE mode and had no problem getting 7 watts out of one tube, but I might have ignored the ratings a bit.


I’m reasonably sure they’re of the curved bulb variety. Not sure about the brand. I’ll have a look tonight if I get the time.


tubelab.com said:
I ran mine in SE mode and had no problem getting 7 watts out of one tube, but I might have ignored the ratings a bit.


LOL. Just a little.


Geek said:
I sold a used pair for $80. So, not cheap ;) Depends on brand though.

Cheers!


:bigeyes: Not an economical alternative to new 2A3's then.

Cheers,
Glen
 
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