Hacker RP18 Sovereign.

[Joe]

Yes. As it said in the first post I did that and found that the amplifier board worked.

- Joe

[Joe]

It's singing! Dodgy contact on the Gram socket.

AM is still dead so more shaving still to do.

Cheers

Joe

[Mark Hennessy]

Yes. As it said in the first post I did that and found that the amplifier board worked.

Yes indeed, but these things have a habit of changing their spots when you start poking around inside them. Had you repeated that test after your earlier work today, then the next move would have been the gram input socket - with certainty. Even with these simple things, I still like to work logically.

Presumably the socket has responded to switch cleaner - but it's worth saying they can be bought from Partridge Electronics for loose change.

Either way, it's a result

Cheers,

Mark

[Yorkie]

The QT button doesn't latch. It reduces the gain of the FM IF amp (and disables the AFC) so that you can find the centre peak.

Have you an audio oscillator so you can inject a signal at the top of the volume control?

Pay attention at the back please

See Joe's comments in post #1 re injecting a signal into the volume control.

I suppose the natural thing is to assume (often correctly) that it's the infamous AFxxx 'whisker' problem, but it complicates things not being able to get to the screens to snip them off - always worth a try. Even NOS AFxxx when they turn up are no better - it's an age thing rather than whether they're used or not. How ironic that when transistors first hit the market they were thought to herald a new dawn in which - unlike valves, it was said - they'd be 'everlasting'.

Best of luck with it Joe - how you suffer for your art

[Mark Hennessy]

Ahem - you pay attention, young David

Yes indeed, but these things have a habit of changing their spots when you start poking around inside them. Had you repeated that test after your earlier work today, then the next move would have been the gram input socket - with certainty.

Sometimes, disturbing the 5-pin connector can change the way these things behave, and as he would have done that to get the chassis out...

I always advise against cutting the screen, because when the whiskers catch up with another electrode, you have a dead transistor (and perhaps not enough of a screen lead left to attach to the charged capacitor!). Seen that plenty of times :-)

To be fair to the transistors themselves, the junctions are pretty good - let's face it, they're 50 years old now. It's a shame that many manufacturers continued to use the AF11x range long after the problem was discovered, and it's also amusing that lead-free solder and platings have seen the whisker problem reoccur. History, it seems, can teach us nothing

All the best,

Mark

[Joe]

I've just been bottling my black-current wine so a celebratory pint of that is called for.

Servisol didn't appear to fix the socket but it may work when it's soaked in over-night. If not, I'll see about swapping it with the tape recorder one as the cutout on that isn't used.

It needs to be on full volume to be a decent listening level but the amplifier still has two Daley capacitors and one of those big red ones whose name escapes me so they want checking and probably changing.

Total current consumption is 25mA - it's limited to 50mA.

It's interesting to note that it's quite happy with that wrong transistor.

- Joe

[Ian E G7OLT]

I always advise against cutting the screen, because when the whiskers catch up with another electrode, you have a dead transistor (and perhaps not enough of a screen lead left to attach to the charged capacitor!). Seen that plenty of times :-)

Mark

You don't need the screen lead to 'blow' the whiskers as it's connected internally to the metal body. I solder BCE together then apply volts between the three of them and the case. If the screen lead is broken off flush with the base, you can always solder another to metal body and use that if you want to keep ' automatic whisker detection' intact.

[Joe]

I've made a start on the AM side.

All three electrolytics were dodgy so I've changed those.

The first transistor was OK but the second had shorts to all three active leads so, as Mark said above, cutting the screen lead wouldn't have done anything to help that one.

My problem with getting the chassis out was that I didn't know that they sides had to be splayed out a bit and I was concerned I'd taken the wrong screws out or that something was catching which I may damage by pulling.

As the last thing I did was a DAC90a I've been somewhat spoilt with easy of servicing.

- Joe

[Joe]

It's now working on all wave-bands at decent volume after changing the capacitors in the amplifier which I mentioned yesterday.

I'm not sure about the Bass control as I haven't got anything to compare it with. It attenuates OK but doesn't seem to do any boosting, in other words there's no difference if it's set to the mid point or fully clock-wise.

The next thing will be sorting out the Gram socket and giving it a good clean.

Thanks for the help.

- Joe

[Mark Hennessy]

Quite right Ian - indeed when doing TO1 AC128s et al, a big croc-clip on the case is what I use. It's really the final stage of my "treatment" - the bashing while volts are applied (after the initial blast) - that is easier with a screen lead. "Automatic whisker detection" - like that

Well done Joe - knew you'd get there

Your bass control is probably OK - they are a bit like that. Funnily enough, when at min, the amp is flat - in other words it only provides boost. The treble control is the same. It sounds like it's cutting simply because the loudspeaker needs a bit of "help" - as all radio 'speakers normally do...

If you look on your 'scope with 100Hz as an input, you should see an appreciable change between centre and max - but because our hearing is logarithmic, it's surprisingly hard to hear the change. From that experiment though, you should be able to see that if you use as little bass as possible, your batteries will last longer

As for ease of service, I think you should try a Grundig or a Dynatron or anything Japanese next...

Now it's working well, any comments on the performance would be interesting. I've never put one next to a VHF Herald before - I don't one fully restored yet - more than one that are 90% restored, but you know how it goes...