Heathkit RA-1, not used for 5+ years - precautions before switching on?

[marqueemoon]

I used to use this set a lot; it pulled in stations well using a very rudimentary antenna (bit of wire thrown out of an upstairs window!), although it did drift off frequency a bit, even when warm. Time passed, and other radios came along, as they do, and it got shoved in a cupboard and forgotten... until now.

It must be at least five years since I last used it; it is totally unrestored and to the best of my knowledge it's never had any work done on it. I'm just conscious of it's age now, and wondering if there's anything that should be checked/done before I plug it in again? Cheers.

[Chrispy57]

Hi - after 5 years of inactivity in a 50+ year old valve receiver I would suggest that you employ "the usual" precautions when initially powering it up. The circuit diagram shows that there are 4 smoothing/reservoir capacitors on the HT lines that would benefit from a slower reforming than just applying mains voltage would achieve. Do you have a capacitor reformer, or a Variac for that purpose? A lamp-limiter in series with the mains lead would be sensible, and is easily improvised if you don't already have one.

There is a capacitor (C65 0.005uF) feeding the grid of output valve (V6A - ECL86) that should be tested or replaced as a precaution. Blow out the dust and give it a quick visual once over while you have the cover off.

Basic electrical safety tests including inspecting mains plug wiring and fuse, and earth continuity and insulation resistance checks would be sensible measures.

Operate all the switches and potentiometers over their full ranges a few times to clean contacts prior to powering up.

Good luck, and enjoy your long-lost old friend!

Cheers
Chris

[marqueemoon]

This is great, thanks Chris!

Had a quick read about what a lamp limiter is/does (new to me), and I'm confident I can knock one of those up OK. I don't have a capacitor reformer or a variable transformer... IIRC the idea is that you gradually bring up the voltage to the set to allow the settled electrolyte in the capacitor to reflow? Would something like this do the job? Thanks again.

[Chrispy57]

You're right about gradually bringing up the voltage, but that device is NOT the way to achieve this objective - I'd stay well clear of it! What you linked to is a thyristor driven device that chops the AC voltage waveform along the time axis rather than reducing it on the voltage axis. So you still get similar peak voltage pulses, but for shorter periods each cycle, giving a lower average value, suitable for heaters, lights or motors etc.

Capacitor reformers use a variable DC voltage, at suitably limited current, to provide the gradually increasing DC voltage required to reform the electrolyte over a suitable timeframe. You would use it on each disconnected capacitor in turn as a maintenance procedure.

A variac/variable transformer would gradually bring up the "mains" input voltage to the set, relying on the action of its internal transformer and rectifier to provide a slowly increasing smoothed DC voltage to the capacitors. This is like a prolonged, slow start up procedure.

With a knowledge of your available facilities I would suggest that a practical approach for this one-off task would be to make a simple lamp-limiter for use with the un-cased receiver, after doing the basic safety checks. Then, with a finger on the power switch, watch the capacitors for any smoke of flashes, perhaps whilst monitoring the DC voltage and AC ripple voltage on each in turn with your DVM. A touch-test to check their temperature occasionally (after switching the power off) during this confidence building exercise would be good too.

Cheers
Chris

[G6Tanuki]

I've never used a variac or a lamp-limiter; my way of 'waking up' stuff that's not been used for a while is to apply full mains-voltage for maybe 30 seconds, then switch off and leave it for a few hours to rest.

Repeat a few times, with the time between power-cycles shortening rapidly - let's say an hour, 20 minutes, 5 minutes, 1 minute - then give it uninterrupted power.

Simples!