Supro 600R Reverberation Unit

Supro 600R Reverberation Unit in grey tweed covering with the Supro script logo and diagonal grille
Supro 600R Reverberation Unit, serial T49754.

This write-up tracks the restoration and repair of a Supro 600R Reverberation Unit. Valco in Chicago made the 600R as an add-on reverb unit that works off of an amp’s extension speaker output; it was meant as a pair with the 1961 Supro 1600R Supreme. The work focused on making it safe to plug in — replacing the original two-prong line cord and “death cap” arrangement with a grounded three-prong cord — plus a replacement handle and a check of what amps it can safely be driven from.

Status (September 2023): 3-prong AC cable done, upgrade design confirmed, replacement handle found, speaker-input wattage/impedance confirmed, parts bagged and labeled. Supro logo and power cable strain relief skipped (see below); grommet install still open.

Unit

Field Value
Model Supro 600R Reverberation Unit (Valco, Chicago)
Serial T49754
Manual schematic Amplifiers Model No. 510-120, revised 6/2/61 (replaced 12AX7-A with 6EU7); Reverberation Unit Type 4F
Tubes (1961 spec) Preamp: one 6EU7 · Output: one 6V6GT · Rectifier: 5Y3
Controls Intensity; Speaker Connection and Foot Switch inputs
Speaker Jensen Special Design C8R (8″)
Output Approximately 5 watts RMS

Companion amp: 1961 Supro 1600R Supreme

The 1600R is 17 watts, so whatever amp drives the 600R’s speaker input should be under 17 watts. The pair can be heard on Over the Hills and Far Away at 4:05–4:50.

Hookup

The unit sits between the guitar amp and its speaker: a cable from the unit’s Speaker Connection jack clips onto the two speaker terminals of your regular amplifier, the foot switch plugs into the Foot Switch jack, and the unit runs off its own 110–120 V AC line cord.

Page of the original Reverb Power Unit set up instructions with a hookup diagram
Original “Reverb” Power Unit set-up instructions.
Supro reverb unit next to a Vox combo amplifier on a rug
Set up next to a Vox combo.
Yellow cable plugged into the Supro unit's control panel
Cable into the unit’s control panel.

Schematics

Original Supro manual schematic, Amplifiers Model No. 510-120, with 6EU7, 6V6GT and 5Y3GT tubes and Reverberation Unit Type 4F
Schematic from the original manual: Model No. 510-120, 6EU7 / 6V6GT / 5Y3GT, power transformer E-3036, output transformer E-2640.
Close-up of the manual schematic power section with an arrow at the .01 capacitor to chassis
Power section of the manual schematic: the .01 capacitor from the line to the chassis.
Supro Reverb schematic drawn by H.A. Dumble
Supro Reverb schematic drawn by H.A. Dumble (reference).

Debug notes

Death cap

L = Line, N = Neutral, GND = Ground. The death cap in the Fender 5F1 Champ connects a power cord wire to the chassis — an identical setup to the 600R.

Hand drawing comparing stock two-prong wiring with a 0.01 uF cap to chassis against three-prong wiring with Cx across the line
Stock [OG] 2-prong vs. 3-prong: the 0.01 µF cap moves from line-to-chassis to across the line (Cx), and ground goes to the chassis.
Hand notes of new wiring with hot, neutral, fuse and transformer, and part values for R1 and C1
New wiring notes and the parts read off the original power section.

Original power-section parts (from my notes)

Part Value
C1 RMC .01, 20%, Z5U — P/N CD103Z1KVZ5U-20x10: 0.01 µF, 1 kV DC
R1 Orange-orange-brown: 330 Ω ±10%
Fuse 2 A (stock)
Power transformer E-3036

Safety caps

A Y2 capacitor can safely be used in place of an X2 capacitor, but an X2 should not be used in place of a Y2. An X2 would filter noise fine, but it would not meet the line-to-ground safety standards. Y2 safety capacitors are more robust, withstand higher peak impulse voltages, and are designed to fail open instead of failing short. Advice I collected also pointed away from a .1 cap here, toward .01–.015 µF.

Slide showing Class X line-to-line and Class Y line-to-ground safety capacitor placement
Class X (line-to-line) vs. Class Y (line-to-ground) safety capacitors.

Inside the chassis

Supro cabinet with the back open showing the chassis wiring and speaker
Back open: chassis and speaker.
Chassis pulled with point-to-point wiring visible next to the speaker
Chassis wiring next to the speaker.
Close-up of original cloth wiring and an orange disc capacitor
Original wiring close-up.
Line cord leads at a terminal strip under the chassis
Line cord leads at the terminal strip (9/3/23).

Debug priorities

Item Result
Handle Replacement handle found
Confirm functionality Wattage/impedance of speaker input confirmed: 1600R is 17 watts, so < 17 watts
Supro logo Skipped — $40 for plastic is too expensive
Power cable strain relief Skipped — deemed safe by angle and robustness of cable
3-prong AC cable Complete; upgrade design confirmed
Contact Jeff Complete
Bag / label parts Complete
Grommet install Open — measure power cable girth and cable hole, then pick a rubber grommet or strain relief bushing
Old handle hardware: a metal loop and bracket
Original handle hardware.
Measuring a replacement handle with a tape measure
Measuring for a replacement handle.
Serial number plate reading T49754 on the tweed covering
Serial plate: T49754.

References

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