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-   -   Hacker Autocrat RP33 (https://www.vintage-radio.net/forum/showthread.php?t=156806)

martin.m 26th May 2019 12:56 am

Hacker Autocrat RP33
 
3 Attachment(s)
This AM only radio dates from the late 1960s and uses AF117s in the RF and IF stages. I bought it as non working and was surprised to find that these transistors had been replaced with shiny new-looking AF124s. There was no sound but the audio amp was working as there was a faint hiss when the volume was turned up. The Autocrat runs from an 18 volt supply provided by a pair of PP9 batteries. However the supply for the RF/IF circuits is dropped down to around 9 volts by a 1.5k resistor and decoupled with a 350uF electrolytic capacitor. Measuring this supply rail produced a reading of only 4 volts. I changed the capacitor, which is next to the volume control, for a new 470uF 25v. This restored the 9 volt supply and the radio burst into life. The Hacker Democrat uses a very similar IF panel and the usual cause of low supply voltage is inter electrode shorts in the AF117 transistors.

Kentode 27th May 2019 10:49 am

Re: Hacker Autocrat RP33
 
Crikey Martin, 90 views and not one comment!>((

Well done, it looks really nice with the wood cheeks and must have gathered many envious looks when it was first purchased.:clap:

Andrewausfa 27th May 2019 11:14 am

Re: Hacker Autocrat RP33
 
Nice sets these, that capacitor causes issues in quite a number of Hacker sets, particularly of that manufacture. You can use a permanent marker pen and fill those missing paint flecks on the grill.

Andrew

martin.m 27th May 2019 10:36 pm

Re: Hacker Autocrat RP33
 
Ken and Andrew, thank you for your comments. I had never heard of Hacker radios before joining this forum. They must have been expensive when new. The big speakers and 18 volt supply rail certainly make a difference to the sound. Thanks for the tip about touching up the speaker grille with a black marker pen. I tried this with one of my Democrats and it has worked well. I've noticed that with these radios the volume control only need to be turned about 20 degrees for the sound to be really loud. I was thinking of adding a resistor in the top end of the control to make setting the volume level easier. (This would not have bothered me when I was a teenager)

Hybrid tellies 28th May 2019 10:17 am

Re: Hacker Autocrat RP33
 
A nice tidy radio. Well done on finding that fault. This same cap can cause all sorts of strange problems on other Hacker radios.

Phil G4SPZ 1st Jun 2019 4:19 pm

Re: Hacker Autocrat RP33
 
Yes, well done indeed!

Quote:

Originally Posted by Hybrid tellies (Post 1148692)
This same cap can cause all sorts of strange problems on other Hacker radios.

And not just on Hacker radios. I’ve encountered exactly the same fault on Philips, Grundig, Yaesu, Aiwa, Sanyo and many other makes of equipment where an electrolytic capacitor is used to decouple a resistively dropped supply rail. Electrolytic caps of this vintage are presumably coming to the end of their working life, albeit after several decades. They can of course fail open-circuit as well, and I’ve come across several of those, but going short-circuit is the most common failure mode in my experience.

Such a failure will put stress on the dropper resistor, which is often a low-wattage component, so it’s worth checking that as well before you box it up.


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