I saw this one pop up recently and decided to take a punt on it (thanks Damian). For the money, I figured it was worth a look even if it only ended up being a decent chassis and set of transformers.
Turns out that this amp is a testament to the quality work that Goldetone produced - despite what has clearly been a very hard life, she works just fine (apart from the heavily corroded reverb tank).
image from the eBay listing
Cosmetically, it has had a bit of a rough life (perhaps an understatement). Where to begin? The original combo was cut down to a head, tolex removed, it was painted yellow, then black, and at some point it was covered in 1970s or 80s woodgrain vinyl. 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 too - maybe the dodgy paint work protected it?
The reverb tank, on the other hand, was absolutely covered in heavy corrosion- no chance of salvage.
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 - 1755 SLIMLINE
I believe this is a Goldentone Model 1755 Slimline, based on the schematics I've seen. Circa 1965, serial number 3967.
The 1755 is regarded as one of the classic Goldentones - after a bit of time playing it, I can understand why.
FEATURES
Two channels, both have bass and treble controls. One channel has reverb and trem.
40watts
The original open back cab would have had 2 x 12" alnico speakers.
PREAMPS
Miniwatt 12AX7s.
Tone controls
James style, bass and treble
Reverb / trem channel
First gain stage
Ra 220k
Rk 3k3, 25u bypass
Second gain stage
Ra 220k
Rk 1k8, 25u bypass
Normal Channel
First gain stage
Ra 100k
Rk 3k3, 25u bypass
Second gain stage
Ra 100k
Rk 3k3, 25u bypass
All pots 1MC (Volume, bass and treble)
REVERB
Valve driven, Miniwatt
6GW8Pioneer EAV-201 reverb tank fitted (very small, 2 spring)
Rola LRH3 transformer
Transformer bench measurements
10.4v, 440Hz sine wave applied to primary: result, 3.3v on secondary
That gives a turns ratio of: 10.4 / 3.3 = 3.15:1
Because impedance ratio is the square of turns ratio: 3.15² ≈ 9.9:1
So the transformer reflects about 10 times the tank/input impedance back to the 6GW8 pentode.
As a replacement, I'm using an old reverb tank from a Peavy. Part number 710-1111. DC resistance measures: input ~50 ohms, output ~250 ohms. It's probably an Accutronics 4EB2C1B, 600ohm input impedance, which will reflect 6k to the 6GW8. That’s a very reasonable load, and it sounds great.
Reverb level is completely independent from the preamp volume control. i.e. the channel volume can be all the way down, but you can still hear the reverb. The reverb send is post tone controls - before the volume control (attached to pin 3 of the volume pot).
Reverb can be turned off via a foot switch.
TREM
12AX7 oscillator, modulating the cathode of a preamp triode.
No depth control, just speed.
The trem pot is also the power on / off switch for the amp. The trem is turned on / off by a foot switch.
PHASE INVERTER
12AX7, longtail pair
100n coupling caps
22k negative feedback from OT secondaries
POWER AMP
2 x Hitachi
6DQ6-B fitted - although schematics show 6DQ6-A (6GW6)
47 ohm resistor to screen
10k grid stopper resistors
470k grid leak resistors
Fixed bias -30 Bias not adjustable - no pot
OUTPUT TRANSFORMER SPECS (OT)
A&R 2700
Primary 3k3
Secondaries 16, 8 & 4 ohms
Output transformer bench measurements
84 ohms DCR primary
Test conditions:
10.5v, 440Hz sine wave applied to primary: result, 0.58v on secondary
Turns ratio 18.1:1
Primary
2.6kΩ at 8 ohms
5.2kΩ at 16 ohms
This is different to the specs above - possibly the result of construction variations and a low-voltage test.
POWER SUPPLY
A&R 5892 (which is different to schematics)
Silicon bridge rectifier
Rola choke 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.
A&R 5892 power transformer & a big Ducon filter cap for the power supply.
Choke & reverb transformer& 6GW8 valve for the reverb
Prior to dust removal - all the mustard caps look fine, no cracks. Can't see any resistors that have been heat-stressed.
They used an interesting method to mount components on the preamp and phase inverter. There's a thread through the valve base, with another valve base on the other end of it. It kind of makes a little tree for components to be vertically mounted.
It is kind of difficult to get to the valve socket end, so maybe not the most practical method when compared to the tag stip mounted components.
This was a reverb tank at some stage in life.
This is after most of the horrific vinyl has been removed, showing the remnants of various paint jobs underneath.
SCHEMATIC, GOLDENTONE MODEL 1755
Compared to some schematics floating around, mine has a few differences. Worth noting that there are some major changes between the 1755 and some later Reverbmasters.
- Some preamp plate and cathode resistor values differ
- Reverb send and return paths are different
- 47Ω screen resistors, not 47kΩ as shown on the schematic
- 10k instead of 180ohm resistor used for screen power filtering
- 4n7 capacitor across the reverb level control
- different power transformer is used
The measured voltages in my amp are very close to the schematic values overall, although the screen voltages are slightly lower, possibly due to the larger resistor in the filter section.
I liked the look of this schematic, so I made a few rough and ready modifications to match the values in my amp.
GOLDENTONE CATALOG IMAGES
FURTHER READING
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.webp "Vintage Goldetone amp advertising")
