Wednesday, 4 April 2012

Easco Electrical Holdings Ltd. Type FA64 serial 669

Badged by Easco Electrical Holdings Ltd. Type FA64 serial 669

All the valves are Mullard & probably original parts.

The valve line up is:

  • Rectifier- EZ81
  • Preamp- ECC83 (12AX7)
  • Amp & Phase splitter ECC83
  • Push-Pull output pair EL84 (x2)

The all metal chassis & box are of passivated steel with some pretence at a rack mounting style with draw handles but not to standard dimensions.  The knobs are of the instrument type (chicken-beak).
There is no date - but internal parts suggest mid-1960's because of the volume/tone pots the use of wax covered silver mica high spec capacitors, the two smoothing electrolytics (one reservoir) are at odds with each other for vintage.  One is very 50's whilst the other is late 60's.

There is no indication of the speaker impedance required but probably 16 ohms for valves.  At around 20watts is the best guess.  The speaker output transformer is the smaller of the two transformers and does not indicate great power capability.

There is a large transformer for the mains conversion for HT & valve heaters.  The 300-0-300v secondary is rectified by the EZ80 to produce around 350v of DC High Tension for the valves.  The heaters are 6.3v AC all wired in parallel. However, there does appear to be two groups.

There are two inputs, one microphone (higher gain and input impedance), and the other for a "gram".  This is probably for the speaker output of a radio-gram since it appears to be wired directly to a balun transformer or other modular matching device.

CAUTION! It is vitally important that the amplifier is never operated without a speaker load.  The voltage produced in the windings can swell to the point where they can cause the insulation to break down and subsequent arc-over.  This will always damage the output transformer irrevocably.  However, an exact match isn't absolutely necessary.  Mismatches will cause loss of transferred power, and slight distortion.

There are one or two paxolin plugs & sockets that smack much more of the 1950's even though such parts continued to be used much later than then.  The pilot light deserves special mention, being enormous by the standards of today, and fit to illuminate the whole room!
Note that in addition to the speaker, mains adjustment and jack sockets, there is also an auxiliary output socket that carries both HT & LT voltages. It is there to power a tuner etc.


WARNING! This all metal chassis must be earthed!  The raw mains goes via the switch & fuse to the mains transformer after which it is at least isolated.  However, the mains earth must be maintained for the sake of safety.

The electrolyte capacitors have lost a lot of their capacity and after several tries the electrolyte reformed.  The volume pots are very noisy and although much better, refused to respond to anti-oxidant lubricant to a full degree.  
There is evidence of track wear and, whilst not impossible, it would be difficult to replace the gain pots.

The jack sockets are both 1/4 inch as opposed to the 6mm standard in use now.  These could be replaced, but seem to have responded well to the cleaning agent.

Both inputs work OK and have differing levels of gain.  The GRAM is approx. +30dB (Line level gain of 100) but the microphone is around +50dB. (A gain of around 500).

The circuitry is all hard wired point to point and is in good condition.  The unit tends to run very hot by the standards of today, but seems none the worse off for having done so for it's 40-50 years on the planet.  That amount of heat in quiescent mode suggests this is a class A or AB amplifier offering pure sine wave amplification with minimal distortion.