Friday 15 March 2024

The Hacker RP33 "Autocrat": refurb time

The Hacker brothers were great engineers.

But along the way, they built great equipment, and lost 2 companies.

Seems like the best route to success is to sell rubbish!

The first major quality brand was Dynatron, which eventually was lost to Eric Cole (EKCO).

The brothers carried on working for Eric for a few years, then in 1960 they left to form the Hacker Radio Company. They specialised in making quality transistor radios until the firm failed in the mid 1970s, against a background of miners strikes, 3 day working weeks, and a burglary loss of £50k!

There was a brief period of control under Pullmaflex using the Hacker Sound brand before the factory burnt down! ...Who writes this stuff?

Hacker RP33 Autocrat

I can't remember where I got this radio. I suspect it was in a house or flat that I bought in the 1980s, but I can no longer pull the details out of my tired old brain!

The Hacker range from the 1960s was about quality, and although they were rivals to Roberts Radio, many people in the vintage radio world still consider Hacker's to be the better sets.

Back in the 1960/70s I looked at lots of (mostly Japanese) AM radio circuits and they were usually designed around 3 transistors in the RF/IF stages.

The RP33 has 4 x AF117 transistors, including a dedicated local oscillator stage (T1);

Another notable difference is that 2 of the IF stages (T2 & T3) are controlled by the AGC (automatic gain control) signal, rather than the more usual single stage control configuration.

Despite the nice design, its was a dead set!

dismantling the radio

The back just pulls off (that's how you change the batteries).

At each end of the carry-handle the small screw covers are carefully levered off, then the screws are removed to release the handle. Now the RF/IF assembly can be lifted out.


There are 3 screws holding the chrome trim on each side. Remove these, then extract to fascia plate. Then remove the small screw holding the IF assembly screening can.

tin whiskers

I used to think semi-conductors should last forever. After all, they form part of a solid-state design ...there are no moving parts. Actually, when constructed properly and not over-run (like l.e.d. lighting) I still believe this could be true.

However, there is a mysterious effect known as tin whiskers. Mysterious because even NASA have spent a lot of time looking at it, and still don't fully understand what's happening.

The basic problem (as it relates to my radio) is that the AF117 transistor is assembled inside a tin container. Over time, little whiskers grow inside the tin case. These whiskers are very thin, maybe 10 to 100 times smaller that a human hair (just who's hair, they don't say).

As the AF117 tin can forms the screen and is connected to ground, eventually one of these whiskers touches the transistor (i.e. collector, base, emitter ...take your pick). And this is why my radio was dead.

The whole tin whisker thing is an interesting story. Solder for electronics used to be made from a mixture of tin & lead. When the E.U. decided that lead in solder was a bad thing, manufacturers had to go lead-free. A few year later, there was a spate of unexpected circuit failures; the tin whisker problem (which had first been identified in the 1940s) was re-discovered! How stupid are we?

In mission critical systems (e.g. space ships, air planes and now cars) tin whiskers must be avoided at all costs. In some cases its back to good-old tin/lead solder, because lead seems to inhibit tin whiskers!

While lead in petrol is certainly a bad thing (because it gets into the atmosphere and we breathe it in) there is some doubt over whether its a problem on circuit boards. ...just sayin'

replacing the AF117s

Having searched on the net, a few people were saying that you could replace AF117 transistors (which are germanium) with silicon transistors.

What? The base-emitter voltages are very different between germanium & silicon!

But I went ahead and bought 200 mixed transistors for no money, and picked out four BC557B silicon transistors and went ahead and fitted them. I checked each AF117 as it was removed and found the oscillator (T1) was the whiskery one!


I powered up the radio and away it went. It works, and its very sensitive on MW & LW. I can even hear Radio Caroline on 648kHz in amongst the background noise!

drive cord

I bought some 0.6mm cord from eBay. Didn't notice it was nylon (not recommended) but went ahead and fitted it anyway.


Its quite a fiddly job for old fingers.

But as for the nylon; so far, so good!

new power source

I could not justify buying PP9 batteries for this set. It will only be used very occasionally, so decided to convert to AA power. I bought a couple of AA x 6 battery holders.

These fit inside reasonably well, and I've added a few draft excluder strips so they don't roam too far. The current drain is about 15-20mA, so 2000mAh/20mA should give over 100 hours of use.

your knobs are too small

The control knobs on this radio are only about 22mm in diameter. Judging by the circular score marks around the volume control, I'd say they should be over 30mm (probably an inch and a quarter in old money).


The volume knob should also have a marker line to roughly indicate audio level, and the tuning knob should certainly be large enough to cover the B/33/8 which identifies the fascia plate.

But this early transistor radio (which is almost certainly over 50 years old) carries around its odd quirks and patina like a personal history. I wonder if it will still be around, 50 years from now?

Many thanks to:-

 Mark Hennessy

 Golborne Vintage Radio Forum 

 the Hacker Radio Group.




Info on Wikipedia

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