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Need help with VibroVerb clone

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7/20/2000 4:20 PM

Need help with VibroVerb clone

Hi,

I just finished my VibroVerb-clone
(well almost), at first I had about
415 volts at the plates, it hummed
big time and squealed some. I shut
it down and rewired a fault at the
oscillator tube and shifted the plate
opt connections.

When firing up again I still had the
hum, the squealing was gone, the
vibrato and reverb sounds as if they
are working but the vibrato mostly
affects the hum. This time the b+
went up to 470 down to 430 and the
bias acted strange too.

I have changed the bias diode and cap
but now when I put in the 6L6-pair
they don't seem to draw any current
'cause the b+ is still wailing
between 470 and 430

The hum only goes away when pulling
the pi-tube.

Any suggestions please, oh it's the 6G16
circuit

7/21/2000 9:21 AM
Nils	Update Now I've fixed the b+, the hum still remains and it seems to be around the pi. The top side draw way too much current. The voltage at the top reads 160,it should be 250 on the low side it is 260 as it should. Please help me. Nils

7/21/2000 9:35 PM
Tom	Nils- Pull the PI tube...what are your voltages now? Are you getting any DC on the input grid? Tom

8/2/2000 6:25 AM

It's working, but have some questions

Tom,

Sorry for my late reply, but yesterday I found
the cure. It was a combination of wrong opt phase
connection and floating speaker jack.

So, now it works, but I still have some questions.

On the layout drawing of the 6G16 there's a 100pF
cap between the anodes of the pi, what's the purpose
with this, prevent oscillations only or?

I would like to be able to dial in a deeper intensity on the tremelo, is this possible.

I read in another post about not using 12AX7 as
a driver for the rev. pan, this amp uses 12AX7's
in all six positions. Any comments?

Nils

8/2/2000 12:27 PM
A.S	I don´t know about the reverb or the tremolo but that 100pF cap is there to prevent oscilations as you said. Marshall uses a 47pF cap in that position for the same purpose. A.S

8/6/2000 4:46 PM
Benjamin	Tom, You might try lowering the 4700 cathode resistor a litte in value to goose a some more depth out of it. I don't know if this will work on the 6G16 but it's a good trick that works on the 100k Rk in the blackface tremelo circuit. Good luck, Benjamin

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