Randall RG-80/100 series

The Randall RG-80 and RG-100 series amplifers were designed in the early 1980s. The primary engineer was Gary Sunda. At that time, the Randall guitar amplifier had no affiliation with Washburn.

When new, these amplifiers ranged from around $500 to almost $1000.

The RG-80 amplifier is a 'family' of units centered around a basic amplifier chassis identical in all units. An RG-80, RG-80-112SC, the RG-80-ES and RG-100 HTs are all the same chassis, packaged in different cases, with a variety of case coverings from carpet-like coverings to artificial skins in every imaginable cover.

The RG-80/100 is an all-solid-state machine, built to take a physical AND operational beating, while still having all the sound qualities of a high-quality classic tube amplifier.

The preamplifier segment consists of all FET design. High input impedance means the electromechanical load applied to the instrument is low, hence, yielding high sustain and clarity. The clean channel is very straightforward. The distortion channel is functionally very similar, with slightly different component values to allow higher interstage gain, hence, clipping. To really distort, a pull-out pot-switch on the TREBLE control connects a pair of back-to-back diodes into the signal path, clipping off the red-channel's output at 0.6v... this is where the 'mean' sound really comes into play.

Both channels are controlled by a unique footpedal- you have a 'channel select' button which toggles between red and green, and a 'both channels' button which engages both at same time. The pedal's wiring seems confusing to most, but it's extremely simple- one wire, from the amp head to pedal, shorts out one channel... while the other wire shorts the other channel. With a channel shorted, there is no signal to pass onto the equalizer, reverb, driver, and final stage.

Preamplifier signals are then passed to the equalizer stage, where a quartet of potentiometers and resistor/capacitor circuits shape the high (presence) Treble, Mid and Low frequency ranges to suit your taste.

Output from the preamp stage then goes to a buffer amplifier/mixer circuit which drives and recieves from an Accutronics spring reverb unit. The resulting signal then passes through an effects-loop, onto a trio of transistors (TIP42/TP43Cs) which then drive the final transistors.

The RG-80/100's amplifier segment consists of four svelte power transistors arranged in complimentary-symmetry, with constant bias current for full class-A operation. The transistors have a thermistor for cutoff and protection. The power transformer applies +/- 80vdc rails to the high and low sides of the bridge. It is, as a result, essentially short-circuit protected under any load condition. The power transformer is capable of providing all the amplifier can put out, and a little bit more, under the worst possible performance conditions.

The RG-80/100 circuitry was designed specifically as a guitar amplifier. Being intended for guitar use, the preamplifier is not purely linear, and not intended to be... but when operated even in the higher end of the gain range, the amplifier will remain true and clean. With appropriate experimentation between the two channels, and use of the pull-out clipping control, most any sound can be attainable at sound levels from school library to earsplitting.

Tone control and reverb mix are very smooth and predictable.


Note that, while packaged as a 'guitar amplifier', the RG80/100 amplifier is electronically well-suited to other pickup-equipped instruments, with only slight concern to the type of cabinet used. I use an RG-100-HT-ES with a single 15" cabinet for bass, and an RG-80-112-SC for electric violin... and all work just fine.

RG-80/100 is incredibly tough- nothing suffers from poor fastening, poor materials or insufficient strength. Quality of workmanship is very high. There are a few issues of connectors noted below.

(renaming the category to Weaknesses)

No machine is perfect, the RG80/100 is no exception. The amplifier has a few weaknesses as a result of an otherwise impeccable design.

The RG's FET preamp stage is VERY hot... as a result, it WILL recieve broadcast interferance through the following avenues under stronger-than-normal conditions;

Instrument cord- If there's RF noise hammering your instrument, or your wiring/shielding is marginal, the RG WILL hear it, and amplify it faithfully.

Footswitch- The footswitching technique, by nature, brings the preamp stage signals out of the cabinet, and into the ravages of the RF world. That's a long footswitch cable, and it's not shielded, so it becomes an antenna. Installing a circuit board with relays, to keep the audio controls WITHIN the amplifier's shielding solves this problem.

Reverb pan: The Accutronics reverb is a wonderful thing. Mounted in a bag in the bottom of the case, it works like a champ... BUT... as usual, it's connected with RCA plugs on input and output. These plugs are fine when new and clean, but as time progresses, they become corroded and marginal, eventually causing high noise ingress, high-frequency whistling, and other strange antics. Clip off the RCA's, slide the wire INTO the reverb pan, solder to the RCA jack's solder lugs, and call it good.

Power transformer: The RG's power transformer is located on same side as the power switch (right side on combos, left side on ES/HT's). The transformer is fairly well shielded on it's own, but will still generate a fair magnetic field, so don't put any stomp-boxes or direct boxes atop the amp in these locations.

Common problems:
Speaker jack: This is a full-wave amplifier, not ground-referenced. As a result, the speaker jack is NOT grounded to chassis- rather, it's an ungrounded type. IF you break the jack, make sure to replace it with an ungrounded type. Oftentimes, a malfunctioning RG80 can be found with an improper jack, which is grounding one half of the amplifier bridge.

Missing or damaged footswitch: While it will operate without, This amplifier is really intended to operate with the footswitch. Switch wiring is very simple... short the unwanted circuit, and light the appropriate LED. There's one wire for each LED, one wire for each channel, and a ground wire. Typically, the footswitch plug or socket becomes damaged if the amplifier is tipped over with plug installed... but only after about a dozen drops. The plug is a JONES, and readily available through outfits like Digi-Key and Mouser, or at a ham-radio swap meet.

Circuit breaker: After 20 years in smokey-barroom operation, the main circuit breaker will start to get a little funky. Usually, you'll find this by wiggling the RESET button while the unit is on... and it'll get scratchy. Replace the breaker if you can't work it clean... after 20 years, it doesn't owe you anything, anyway.

It is now 2009, I've been playing since 1975. I started working with these amplifiers in 1985, and have owned three (two RG-10-112SCs and one RG-100-ES-HT) since that time. I abuse them relentlessly, and they just keep coming back for more... something that my other amplifiers simply have not been able to do.

I've had many other amplifiers, some simple, some loaded with bells and whistles, effects and gimmicks. The RG-80/100 is a very simple, in-your-face machine, designed and built to WORK, and that it does- it will play circles above anything else. It, however, lives in a world of amplifiers designed-and-built to SELL, with consumers not willing to pay for this level of robustness. With the extensive takeover of IC-based preamplifier and amp modules, I find it unlikely that an all-discrete preamp and amplifier unit will find it's way to store shelves ever again, so the RG-80/100 is a absolute gem.