Amp tinkerers and people who aren't afraid of 700 volts or so in here....

Moderators: Slowy, Capt. Black

BY Jay
#862917
Hopefully the knowledgeable toob people can help out with the following;

I have a spare triode (ECC83 or similar) in my amp and wonder if it can be used for a slight boost with a bit of 'grit' purpose. If it is possible, I am thinking of making it foot switchable and install a pot on the front panel for 'grit' depth.

Rereading the valve wizard triode chapter and appears it might be possible but no idea how such circuit would look.

Any help appreciated.
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BY sizzlingbadger
#862921
Certainly possible, would need the current amps schematic to advise any further.
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BY Reg18
#862923
I’m not an amp tech at all
But I do own an old Fender amp
With a push/pull master volume that adds a boost to the amp.
It’s done by using the other half of the reverb driver 12ax7
From what I’ve read, so yes I’m sure can be done.
Does it sound good? Not really! I’d rather just use a boost pedal going into the amp. But I’m sure Mike C, Anvil Amps, PaulWD or many other amp builders on here will have the schematics to show you how it’s done.
BY Jay
#862939
sizzlingbadger wrote:Certainly possible, would need the current amps schematic to advise any further.


It is V1 in the Jansen 4/12 copy I built last year. I' ll find the link to the circuit diagram. (I think I posted it on the forum)
BY Jay
#862957
Found the post;
So I am thinking of a the boost/overdrive section to be switchable between the anode output of V1 (first triode) to the grid of the second triode in that valve and the tone stack. Hope that makes sense. I realise that the second triode may need its own biasing.

Image
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BY sizzlingbadger
#862993
You could add a gain knob... and vary your boost as required.

gain-stage.jpg
gain-stage.jpg (155.22 KiB) Viewed 68 times
BY Jay
#862997
Thanks SB, that looks simple enough to implement.

I presume the bias cap is an electrolytic 10uF?

To make it switchable, can I just switch the top of R6 between the 'bottoms' of R4 and the newly introduced 100K resistor?
That probably would have to be a relay as I don't want to extend high voltage to a foot switch.
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BY sizzlingbadger
#862999
Yes & Yes - with a relay