Repairs

PedalDoctor FX Featured Repair

Click on the images to download
the schematic and layout
diagram.
(just right click on the image and
select "save picture as")
These are the original
schematics for the 6G15 Reverb.
I highlighted the caps that are
most likely in need of attention
and the photos above have
arrows pointing to them for
reference.

Designed by the late Caesar Diaz who was famous for his incredible
ability to squeeze absolutely the best tone out of vintage amps, the
Tremodillo reflects this rule for cool. With the addition of a "Depth"
control and a "Speed" switch that allows the user to toggle detween
normal and double the pulse time, Diaz had taken a cheap, simple
circuit and made it an interesting, useable Trem. If you an get your
hands on one of them, make sure to spend some time noodling with it.
It's nothing like the "ebb-and-tide" tube tremolos found on the early
tube amps but it is a pretty cool alternative to the standard trem.
This project may not be for the fainthearted. The Tremodillo has more
than a hard outer shell. It's PC board is ferociously protected by a
generous glopping of hardened goop. Hang out with me as I work to
get a pulse on this tough little critter again. -"Doc"

Schematic and Layout...

I've often found that musicians will discard a pedal
that no longer works because of the
cost of repairs. Please call me if that favorite old
stompbox finally (or suddenly) quits working. You
may be surprised at how little it costs to revive it!

Last Issues Featured Repair...

1961 Fender Reverb
6G15

Not every featured repair will be a pedal. This issue
I had the pleasure of working on a real piece of
music history; a '61 Fender Reverb Unit! These
sonic beauties are getting harder to find and are
definately worth having if you can find one for the
right price.

When this unit came to my shop, there wasn't a
great deal wrong with it. It needed the standard
tune-up: electrolytic caps, filter caps and it had
some minor tube issues. The real problem was
that it did have a bit of hum when the "Mix" control
was turned up. It didn't hum nearly as much if the
footswitch was disconnected. Strange?!? Hmm...

The first thing on the todo list:
Replace the electrolytics! After
more than fourty years, it's a
pretty fair assesment that they
would need to be replaced and
they did. They were quite dry
and crispy.(photo shows new
caps installed)

The next obvious step was replacing
the filter caps:
Even though the filter caps had been
replaced before and weren't
extremely old, they had been
replaced at different times and were
even mismatched values so it's a
good practice to upgrade them and
make sure that they are in good
order. (inset shows new caps)

Step-By-Step Repairs
With Some Sensible
Modifications

Reviving A Diaz
Tremodillo

...not only does this prevent the
12AX7 from "running amok" if the
reverb tank return cable
accidentally becomes disconnected,
but it also alters the grid return
impedance and will produce a
much sweeter tone. Quick, Easy,
and Cheap; Try It!

Here's a minor "safety" mod that I
learned from Gerald Weber's book:
A Desktop Reference of Hip
Vintage Guitar Amps.
Just hang a 220k 1/4-watt resistor
across the leads on the footswitch
jack...

Click on the image
to read the article

1961 Fender Reverb Unit