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| High Voltage Warning! |
CAUTION: This web site contains information about high
voltage electronic circuits intended for qualified service
technicians. High voltage electricity can be dangerous or
even lethal if appropriate safety precautions are not
observed. Circuits may still contain dangerous high
voltage electricity even when unplugged and switched off.
If you don't know what you're doing, don't attempt to
build, repair, modify, or otherwise work on such circuits
yourself. Any use of the information on this web site is
AT YOUR OWN RISK. The author(s) of this web site disclaim
any and all liability for consequences of your use of this
Here are the schematics for some gadgets I built just for
Tube Mic/Line Preamp ( Schematic )
- This is a simple tube preamp based on the Altec
1566A, an industrial / commercial preamp from the 1960s. Has
low and high impedance inputs and outputs for compatibility
with a wide variety of musical and studio equipment.
Treble Booster Pedal ( Schematic + Layout )
- This is a simple effect box for electric guitar,
using one germanium transistor. Based on a 1960s vintage
effect called the ''Rangemaster'' which was sold by
Dallas-Arbiter. It shifts the frequency response curve
toward the high end and significantly boosts the signal
level from the guitar, which makes it ideal for overdriving
Simple Attenuator and Dummy Load ( Schematic )
- Useful for testing amps at full power without
damaging your hearing and pissing off your neighbors. This
version will handle amps up to 40 Watts.
High Voltage Flash Trigger ( Schematic + Layout )
- This has nothing to do with amps, but I found it
useful for photography. It's a simple circuit that safely
interfaces vintage high-voltage flash units to modern
cameras that can't handle the high voltage. Most modern
digital SLR cameras can only handle a few volts on the sync
circuit. For example, most of Canon's EOS digital cameras
are only rated for 6 volts on the sync circuit.
Unfortunately, many of the large flash units available on
the used market put much higher voltages on the
sync circuit, reportedly even as much as 400 volts on a few
Here are a few schematics of other manufacturer's amps that
I needed to repair but couldn't find schematics elsewhere
for, so I ended up having to trace the wires and draw the
schematics myself. I'm putting these up here in case any
other amp techs need to work on similar amps. The amps I
worked on could have been previously modded or hacked
before I received them, so these schems might not match the
original amps exactly. Use at your own risk.
In case it's not obvious, I'm not affiliated with the
companies that made these amps, so I can't really answer
questions about them.
Electromuse Model 8A ( Schematic )
- A typical house-branded Valco/National amp from
the lap steel era. A small vinyl-covered box with the amp
chassis facing rearward on a shelf above the 8-inch
Gregory Mark 1 ( Schematic )
- An el-cheapo practice amp from the 1960s.
Kay Model 750 ( Schematic )
- The K-750 was only made in 1967 (right before Kay
went bust), so nobody ever seems to know anything about
this particular model. It's electrically identical to the
'C' version of the Kay 703 amplifier, but looks completely
different on the outside.
Kent Models 1475, 2188, 2198 ( Schematic )
- This schematic applies to some of the USA-made
Kent amplifier models from the early 1960s. The Kent name
was also used on Japanese import amps in the late 1960s and
1970s, but the construction of the Japanese units was
similar to the prior US units (i.e. very cheap). Kent
amps seem to always fail from bad tube sockets. Try
replacing the sockets before fixing anything else.
London Electric Model 8 ( Schematic )
- A practice amp from the 1960s with a built-in
tremolo effect. ...and groovy paisley pattern grill cloth.
Supro Valkyrie ( Schematic )
- This Supro is unusual because it has 7355 output tubes.
It's otherwise very similar to several other Supro/Valco models.
This model was probably not manufactured in very large quantities
before the 1967 merger of Valco and Kay.
If you were looking for schematics of Rick-Tone amps,
If the schematic you need isn't here, there are loads of
other guitar amp schematics over at Larry's
SchematicHeaven.com. Check it out.
Danelectro 59 DC Re-Issues
( Schematic )
( Upgrade Photos )
- When I was working on some Danelectro guitars, I had
trouble finding schematics for any of the two-pickup
versions so I ended up drawing them myself. The drawing
shown here includes two schematics. The first is for the
2007 Danelectro 59 (made in China re-issue) with two knobs
(one volume, one tone). The second is for the 1999
Danelectro 59 DC and DC PRO (made in Korea re-issue) with
two pairs of stacked concentric knobs (two volumes, two
tones). Also see the photos of a 2007 re-issue I upgraded
to the vintage style concentric controls.
Table of primary impedance values for common 70v/25v audio line transformers.