[Patrick Turner]

ralf wrote:

I'm trying to build a stand alone reverb unit like the first Fender
from spare parts. I used the Fender circuit with the standard Fender
reverb transformer but the only tank I have is a Folded Line from an
old organ which says: "made in Milton, Wis. by beautiful girls in
controlled atmosphere conditions". It has low, distorted output with
some hum. Everything looks good going into the tank which seems
mechanically ok. Any ideas?

I once designed and built a suitable reverb unit that went into a
Marshall 100W head,
with the spring tank mounted away from the power tranny end of the box
to keep the hum low.

It had a paralleled 12AT7 with small ex radio 5k to 8 OPT to drive the
input end of the springs,
then a paralleled 12AX7 acting as a normal gain tube to amplifiy
the output end of the spring unit which has a similar output to a moving
magnet
phono cartridge, ie, a few mV.
The actual tranny I used was a 5W line matching tranny for 5k to 4,8&16
ohms, and ungapped,
but with only 7mA of dc a gap wasn't needed, and the tranny cost less
than $10 at
our Dick Smith Elecronics store, like Radio Shack in the US.

When mixed with the signal path before the master gain control it
made the music like it was coming from a mile along a tunnel when
turned up full and when used properly had the
splendid warming effect on the instrumental tone; a little bit of
reverb goes a long way.

A Fender schematic I saw in the Groove Tube book unit used a 6V6 as the
exciting tube to work into
OPT to cause magnetic vibration mechanically of the springs which
retain the music tones for a long time.
But EL84, or other triode tubes are OK, except 12AX7 or other high Ra
low gm tubes.

I would think that straight springs that are unfolded would be best,
and the makers don't need to be the Milton Twins, who know about organs,
and in
perfect weather.

Patrick Turner.