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Old 12th Jul 2019, 6:09 pm   #1
Avid_Nerdlinger
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Default Whiskered Autocrat

Got a Hacker Autocrat RP33 on Wednesday, £12 off ebay. My first Hacker. It needed a good clean. First attempt at double-sided sellotaping the rexine back on to the handle is not totally successful. I'm not planning to sell it on though so I am not too concerned about a full restoration as you can tell from the photo.

It was dead to begin with but got progressively noisier with very loud crackling microphony which I tracked down to slightly loose screws fixing the IF PCB to the chassis (after checking several electrolytics). With that fixed it was just quiet so I took the AF117s out and measured resistance to screen with a multimeter and found some evidence of tin whiskers (this is all new to me, thanks to contributors here for the education) on T2, 3 & 4, some were only evident on 200M range which my meter fortunately has. I couldn't fix this with a 2200uF cap charged up to 27V (3 PP9s) so I torched them with a gas soldering iron. Now BBC Radio 4 was LOUD! But there was a bit too much hiss so I took out T1 again, on which there was no evidence of whiskers, and torched that as well. Fixed and sounding pretty good.

Slight bump when switched on and off, I can see the speaker move. Is this normal for Hacker radios?

I'm surprised how quiet it goes between channels. I've read somewhere that there is a switcheable feature such as this on some (Hacker?) radios, like squelch on a CB radio, could this be always-on on RP33s?
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Old 12th Jul 2019, 6:46 pm   #2
Mike. Watterson
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Default Re: Whiskered Autocrat

The whiskers will grow back.
I replace them with Russian NOS military parts off eBay. Very cheap. Look for 60MHz Ft so you get an RF/IF PNP, not an audio type.

There is a reduce gain & kill AFC button on the panel on some Hackers.

"Bump" is on most models with no output transformer. It's the main speaker capacitor charging to half the supply voltage.
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Old 12th Jul 2019, 7:01 pm   #3
crackle
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Default Re: Whiskered Autocrat

Tin whiskers normally show up in the hundred or so ohm range. You should be able to measure them on a 20k range. On a 200M ohm range you may have been measuring the resistance of your fingers.
Heat normally destroys germanium transistors, I think you were very lucky.
Inter station muting is normally associated with VHF FM sets, but the Autocrat is AM only.

Mike

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Old 12th Jul 2019, 7:05 pm   #4
paulsherwin
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Default Re: Whiskered Autocrat

I agree the whiskers are likely to grow back eventually, but this may not be for many years so it's not really an issue if you plan to use the radio yourself.

Changing AF11xs is easy enough in these sets and lots of substitutes will work - search the forum for options.
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Old 14th Jul 2019, 12:27 am   #5
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Default Re: Whiskered Autocrat

Thanks for explaining bump and muting. Started on quiet Herald RP35 which also has AF117s so they were my first suspect. Again 3 out of 4 had evidence of whiskers, or at least some measurable resistance, mostly 10s of Megaohms (defo not fingers...), the one pictured measured 28 ohms between collector and screen, the top popped off when I torched it and there was a visible whisker coming off the base terminal though this had measured several megaohms to screen, doesn't show up great in the photo though. The heat treatment cured the unwanted conductivity but radio is still quiet, I'll start a new thread for that if/when I've made some progress.
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Old 14th Jul 2019, 1:41 am   #6
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Default Re: Whiskered Autocrat

As other members have said, just replace all four AF117s with Germanium RF types. The Democrat uses a very similar IF panel and unwanted interstation muting effects, together with lack of sensitivity, can be caused by the transistors even though they may measure OK.
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Old 15th Jul 2019, 2:00 pm   #7
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Default Re: Whiskered Autocrat

That transistor I took a picture of measured about 6 ohms between base and emitter which wasn't fixed by heating. I've ordered some old Valvo AFZ12 and some 2N3906 (to combine postage, which backfired when the seller only reduce it from $9 to 8...) from Bulgaria which might do. Meantime I might see if the good ones from the Autocrat make the Herald work but I'm reluctant to risk breaking this one, which I am a bit more impressed by since I investigated the inter-station muting I previously noticed - it isn't muting between stations it's just that Radio 4 is so loud that when the volume is lowered to a respectable level any background noise between stations is inaudible, maybe better signal-to-noise performance than I am seeing on my other radios or I was just being a divvy.
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Old 15th Jul 2019, 2:42 pm   #8
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Default Re: Whiskered Autocrat

The AFZ12s should be fine. These AM IF strips really aren't very fussy, and you will probably find the 2N3906s will work too despite being silicon. You can buy general purpose Si transistors like these from Chinese eBay sellers for about a penny each, so it's worth keeping a bag of them handy.
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Old 23rd Jul 2019, 6:23 pm   #9
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Default Re: Whiskered Autocrat

Just got my Bulgarian transistors and replaced TR3 on the RP35 with a Si one, radio works now. I'll start a new thread for this one.
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