Set fixed itself within a few minutes!

[stevehertz]

Some months ago I bought a Hacker VHF Herald to add to my collection of 'premium sounding' portables. At the time I just put it to one side to wait until I had more time to fire it up. Well, I did that today. When I first switched on, the sound was very weak and very distorted. However, after fiddling about with it, basically just changing channels (it's VHF only), after a minute or so it started to work - well - as good as if it was fully restored. Ok, I've not had it in use long term since then, but after a few hours of broken period use, it is still working perfectly. I'm guessing that a dodgy electrolytic has reformed or something like that. Of course, I'll continue using it and if there is anything amiss it will surely show up eventually. But for now, like I say, it's perfect, and to me, it displayed an effect that in forty years vintage wireless, I have never experienced; a 'self fixing' set that in just 60 seconds morphs from being grossly distorted and weak to 'perfect'! (it won't last I'm sure.. )

[Hartley118]

Could have been oxidised contacts in a switch or an internal connector.

I've just had a similar revival experience with a Sony cassette machine which had been in storage for a few years and required a bit of rough treatment of its internal connectors before it would spring to life.

Martin

[paulsherwin]

I agree, it's most likely to be the switch contacts.

[mhennessy]

Apart from the power switch, this set only has switches for AFC and ISM (inter-station muting). For that reason, I'd be leaning towards capacitors. It's worth keeping an eye on the quiescent current, as leaking caps in the audio amp might upset the DC conditions. If there are any DALY caps in there - not very likely, but not impossible either - then those are "change on sight" caps. Blue Philips have a very good record in these sets, and I'd say the same about the various Japanese caps that crop up in them.

I have had exactly this happen to me before, and that was caused by blue DALY caps. It wasn't a VHF Herald though - checking my database, it was an older AM-only Mini-Herald RP17A.

[G6Tanuki]

I'd also be deeply suspicious of any Plessey plastic cased electrolytics with red-and-black half-bodies and a yellow label showing the voltage/capacitance.

Though they look 'period' they're not to be trusted.

[Phil G4SPZ]

Perhaps tarnish on the variable tuning capacitor's shaft contact that was wiped away as you re-tuned?

[Hartley118]

Originally Posted by G6Tanuki

I'd also be deeply suspicious of any Plessey plastic cased electrolytics with red-and-black half-bodies and a yellow label showing the voltage/capacitance.

Though they look 'period' they're not to be trusted.

Certainly agreed, but I don't think they magically reform.

Martin

[crackle]

Steve
I have experienced a few transistor radios which have not worked initially, then slowly come to life. In some instances these radios have included the red and black plastic electrolytics with the yellow pealing labels. Capacitors can sometimes take a while to reform themselves after a very long rest period. But they may still be iffy and the radio may benefit from fresh electrolytics being fitted.
The Plessey red and black caps, Callins caps, and the blue Daly caps are all ones to be view with suspicion, and if faulty can cause excessive current as already mentioned.


Mike

[mhennessy]

Happily, Hacker generally didn't use most of those types. Apart from the blue Daly types, they also liked the red TCC Elkomold types - pretty, but always suspect. I've found these in sets as late as the Sovereign II (always on the AM IF PCB)

In one RP17 in my collection, they used a pair of Hunts that are plain white. Never seen those before or since, and I must've seen hundreds of Hackers in the last decade...

[stevehertz]

Thanks everyone. I tend to 'agree' with the caps camp here as the miracle happened gradually over that 60+ period, not in response to any vigorous switching. The idea that it could also be due to an initially poor tuning cap slider contact is also a strong possibility. Meanwhile i will keep listening and when i get round to it, overhaul the audio board and apply servisol to relevant pots, switches and connectors. Thanks again.

[boxdoctor]

If this set contains lockfit transistors (which I think it might), I would not be celebrating just yet.... Tony.

[Paul_RK]

I've an RP25A Sovereign which would take some time to produce sound, initially muffled and distorted but of the expected standard after three or four minutes: never have investigated it beyond establishing that the amplifier board was responsible. The electrolytics are Philips throughout. If used again the same day it would perform well immediately, but then if left alone for a week or two the full delay applied again. Will be interesting to hear whether your VHF Herald - same amplifier and from a similar period - follows the same pattern.

Paul

[mhennessy]

That's jogged my memory, Paul. I've had that symptom in the A205 amplifier that was caused by tin whiskers in T4 (AC128) - there was mild leakage between the case and a couple of the electrodes. I'm guessing that as the transistor warmed up (it does run ever so slightly warm to the touch), there was enough change in the physical dimensions to alter the pattern of leakage.

As you can imagine, that caused some head-scratching! I think main clue was finding a DC voltage on the can of T4, which indicated some leakage was taking place. And I'm pretty sure I've seen it more than once.

The same transistor and the same problem has also been responsible for loud crackling noises, accompanied with the DC conditions moving about all over the place. It always looks so innocent under its little heat sink, but I'm always wary of them now

No idea if that is what could be ailing your or Steve's set, but I thought it was worth mentioning anyway...

[stevehertz]

Thankfully I'm used to audio boards on Hackers, probably fixed around half a dozen or so, replacing the usual suspect trannies, caps, resistors and connectors. BTW, it's still working perfectly.

[mhennessy]

That's a pain! We need it to play up again so we can diagnose it

Seriously, it'll be so much more satisfying and useful for future folk to learn what is going on. I'm never comfortable with blanket changes on these sets - those Philips caps have decades ahead of them.

What sort of capacitors are present in your set?

[john.north]

I had similar distortion on a Hacker 25B and the culprit was T4.
The giveaway was that you couldn't set the midpoint. It measured 15 volts and adjusting the pot made no difference other than more or less distortion.
Turning it anticlockwise far enough and sound disappeared altogether.
Anyway replacing T4 allowed the midpoint to be set at 8.95v and all was well.

[stevehertz]

When it goes wrong I'll take a look at it. But with enough to do for the next 50 years (not just restore vintage audio kit, if only..), I am not about to go looking for a fault that presently 'doesn't exist'. You know what I mean, you know how it is. I probably already have what, eight items in bits with difficult faults that need sorting out. The last thing I want is another one hanging around the place gathering dust.

[mhennessy]

At the very least, it's worth quickly checking the quiescent current (the whole set should take around 20mA with the volume down at minimum). That should be enough "peace of mind" until it plays up again

[Hybrid tellies]

I have a recently acquired Pye Poppet SX1072, a small radio of Hong Kong origin, which takes a few minutes to warm up. When You switch it on there is nothing but then the sound gradually fades in and after about 5 minutes it sounds loud and clear.
I suspect its an electrolytic capacitor slowly reforming.
It was going to go straight on to my to do pile but after reading this thread I am quite happy for it to jump the que and investigate further.