GOLDENTONE: Reverbmaster 40watt guitar amp, Model 1755

I saw this one pop up recently and decided to take a punt on it (thanks Damian).  I haven’t fired it up yet, so we’ll find out later whether that was a wise decision.  For the money, I figured it was worth a look even if it only ended up being a decent chassis and set of transformers.

Cosmetically, it has had a bit of a rough life (perhaps an understatement).  Where to begin? The original tolex has been removed, the cabinet was painted yellow, and then at some point it was covered in some kind of 1970s or 1980s woodgrain vinyl, to cover up the yellow paint.  The head still feels solid, so there’s something to work with.

I didn’t think the original faceplate was on the amp, so I was pleasantly surprised when the silver paint started wiping away with isopropyl alcohol, revealing the original panel underneath. It's still in good shape by what I can see so far.

The reverb tank, on the other hand, is absolutely cooked.  It is in terrible condition, so that will be going straight in the bin.

Inside the chassis was a much nicer.  It looks to be all original, with no obvious signs of previous work or failed parts.  It was dusty as hell, but I’ll take dust over a butchered circuit any day.

GOLDENTONE - REVERBMASTER 40 (Maybe 1755)

There are a couple of possibilities as to exactly what model this is - but I'm just calling it a Reverbmaster for now.

Preamps

12AX7.  Bass and treble controls using a James style tone controls

Reverb

Valve driven (6GW8), using a Rola LRH3 transformer & a short tank

Trem

12AX7 oscillator, modulating the cathode of a preamp triode.  No depth control, just speed.

Phase inverter

12AX7, longtail pair

Power stage

2 x 6DQ6B fitted, fixed bias (although schematics often show 6DQ6A).  The 6DQ6 is not traditionally associated with audio - it's meant for TVs, so the data sheets are light on specs in this regard.

Output transformer

A&R 2700

Primary 3k3

Secondaries 16, 8 & 4 ohms

Power supply

A&R transformer

Silicon bridge rectifier

Rola choke marked TV301, May 1965

B+ about 360v

My little moment of joy, finding the original faceplate under the silver paint.  They may be original knobs, but I'm not sure. 

The 6DQ6 valves have their anode on a top cap - hence the warnings. 

Choke & reverb transformer& 6GW8 valve for the reverb

Prior to dust removal

This was a reverb tank at some stage in life.

SCHEMATIC

There's also this version by Peter Hutch, on Aussie Guitar Gear Heads - which has a few variations by the look of it.