GOLDENTONE: Model 1958 Reverbmaster

Nice little Goldentone 1958 Reverbmaster - it's a great little amp, 12w with a single 12" speaker, reverb and trem.   It's quite a clean amp, as it's missing a gain stage that is normally part of the phase inverter.

GOLDENTONE, MODEL 1958 REVERBMASTER

circa ~1968

As you can see by the size comparison to my cat - it's quite a compact amp.

Goldentone have made use of their unusual valve socket construction technique - they connected another socket to the base, creating little trees to suspend components from.  It's compact, but not always easy to work on.

A&R reverb transformer, with 6GW8 driver.

Rola output transformer, dated 26 August 1968.

Reverb

The reverb is valve-driven using a 6GW8 & a transformer.  It's a very small, low-impedance tank mounted on the side of the combo.  The reverb send and return bypass the amp's volume control, meaning that it is completely independent of it.

Speaker

Single 12" speaker, which looks to be a MSP Hi-Flux based on the shape of the frame.  Not much of a magnet (assuming ceramic), so low wattage.  It's also quite low-profile.

Valves

3 x 6GW8 (ECL86 combinded pentode / triode), 1 x 12AX7

Inputs

2 x inputs, both identical. 

47k  grid stoppers, 470k grid leak (shared)

Preamp / tone controls

Input  >  triode  >  bass, treble, volume  > triode > phase inverter

A 12AX7 is doing the work - nothing out of the ordinary.

First gain stage:  Ra: 100k,   Rk: 1k8 / 22u bypass

Second gain stage: Ra: 100k,  Rk:  2k2 / 100n bypass

Coupling cap:  22n.  Volume pot:  1meg 

Not unlike the classic Fender bass treble set-up.  250k pots

Tremolo

The tremolo uses one of the triodes from a 6GW8 - it's a very standard oscillator, feeding the bias of the output pentodes.  The speed control is also the power on / off switch for the amp.

Phase inverter

Cathodyne phase inverter using one of the triodes from the 6GW8 valves in the power section.  It does not have a gain stage, just the inverter.  

Ra 47k, 1m on grid, Rk 1k8 / 47k.  10n coupling caps. 

Power amp

Push-pull, fixed bias.  

Power

Power transformer, silicon bridge rectifier / 50uf   >  1k dropper / 50uf  > 10k / 8uf 

B+ ~240v

Negative bias for the output pentodes.  Diode, and a 40uf cap, 100k resistor to ground (yes, I need to update details)

Repairs

The previous owner thought that it just needed new input jacks - not quite.   100k plate resistor in the preamp had split, the resistor on the tail of the tone stack had a broken connection and the caps in the trem oscillator all needed replacing (as it was not oscillating).   I also changed the coupling caps from the phase inverter, as they were the same type as those used in the phase inverter.  

Valve sockets all needed a good clean & there were the remains of a very large huntsman spider to remove from the speaker.

I also replaced the 8uf cap in the power supply, as it had a decent sized protrusion on one end.