Vibro King- Fender Tech Note search

[WMK]

Hey there.

After searching through a 3 foot stack of Tech Notes,
I can't seem to find one concerning the early (6BQ5 rev. drvr.)
VK. I swear there was one issued for this amp (that involved
a resistive G1 anchor and etc.) but the only one I can find
refers to adding capacitance to G2 of the 6V6-version (TN 97-5).


If you have the revisions or the Tech Note, can you
kindly share it?
Thank You,

Bill

[Enzo]

My factory listing of bulletins lists only the one you mention, 97-5.

[WMK]

My factory listing of bulletins lists only the one you mention, 97-5.

Thanks for looking, Enzo, this will save me from digging
around for something that doesn't exist.

However, it is now more clear than ever why
the first version VKs shredded the EL84 rev. driver!
The first circuit capactive-coupled the '84 control
grid (between the dwell control and the grid), which
is fine and dandy, except there was no ground reference
to the grid. The second EL84 version had a 220K resistor
fitted. Once I bench this thing, it will be interesting to
see the plate current variance between the ckt. with and
without, and more so, how 'stable' the current is without
it. Also, the driver transformer is tied to the "Z"
tie point which is 477Vdc! Wouldn't it be prudent to redirect
the supply point down stream one click to "Y" which is,
iirc, 410Vdc?

Again, thanks for taking the time to look.

Bill

[Ray Ivers]

Bill,

Wouldn't it be prudent to redirect the supply point down stream one click to "Y" which is, iirc, 410Vdc?

If you do that, you may smoke R38.

Here's the Rev. D circuit:



I think I would either bias it a bit colder if it seems too hot to you, or add a parallel RC circuit between the plate and B+ to cool off the DC conditions a bit while keeping the tank drive level the same.

Ray