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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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14th Oct 2008, 9:29 pm | #1 |
Dekatron
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Hacker sovereign - no am
Hi all, reading the latest threads on hackers has prompted me to build a decent example from the 4 lying round the workshop!
The set in question is a sovereign 2 rp25b, while it works well on vhf, it is dead on mw/lw, i have a am only herald rp35(working) to use for parts. any ideas where the fault could lie? anyone had this fault? P.S. i have no signal gen at the moment Mark |
14th Oct 2008, 9:54 pm | #2 |
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Re: Hacker sovereign - no am
Hi Mark,
The most likely culprit is the big Daly-branded electrolytic that smooths the supply to the AM side of things. Maybe 300uF? There are a couple of threads here about this, started I think by Darren and Mike Phelan. Nick. EDIT... Just dug out my manual for the RP25B: Check for 6V across C24 (100uF) on the IF amp board 506. Replace the cap if it's low. |
14th Oct 2008, 10:19 pm | #3 | |
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Re: Hacker sovereign - no am
Hi Nick, thanks for the advice,
Quote:
will replace this & report back. Mark |
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14th Oct 2008, 11:06 pm | #4 |
Retired Dormant Member
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Re: Hacker sovereign - no am
Mark,
If you haven't already done so, check the wavechange (pushbutton) switches - squirt them with some Servisol contact cleaner if you can. Certainly on the Sovereign I (RP18) and probably on the Sovereign II, the supply to the AM & FM boards is switched when you change wavebands. Mike |
14th Oct 2008, 11:08 pm | #5 |
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Re: Hacker sovereign - no am
Mark, I'm being thick.
I was fooled because the manual refers to board 506 as the AM IF amp when in fact it's the FM one. What I should have said is: check for at least 6V across C21 (350V) when switched to LW or MW on the 503A panel. This is the dodgy Daly cap I referred to earlier. See Darren's thread here: https://www.vintage-radio.net/forum/...light=c21+daly And Mike's: https://www.vintage-radio.net/forum/...r+electrolytic Many apologies, Nick. Last edited by Nickthedentist; 14th Oct 2008 at 11:14 pm. |
15th Oct 2008, 1:37 am | #6 |
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Re: Hacker sovereign - no am
I don't think it would be a Daly in an RP25B: just looked at three sets here and of those an RP25 has a Daly, a 25A a red TCC and the 25B one of those metallic pale blue looking fellows - are they ITT or Philips? A worthy suspect, though, whatever it is.
Paul |
15th Oct 2008, 7:07 am | #7 |
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Re: Hacker sovereign - no am
Thanks Paul, you're a mine of useful info as usual .
Further to my above post, I meant 350uF not 350V (obviously!). Sorry. |
15th Oct 2008, 7:57 am | #8 |
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Re: Hacker sovereign - no am
No problem Nick, you did get the board no. right. Will check c21 later
Mike, yes first thing I did was to clean the wavechange switches, but as nick says, I think it is a cap problem, at least there are no nasty af*** transistors in this set. Paul, you are dead right about the caps fitted to these sets, I think the blue caps are made by Philips. Mark Last edited by Darren-UK; 18th Oct 2008 at 10:29 am. Reason: Excessive use of emoticons. |
16th Oct 2008, 9:13 pm | #9 | |
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Re: Hacker sovereign - no am
Hi all, Nick,
Quote:
any other things to look for before i replace the complete 503a panel Mark |
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17th Oct 2008, 7:33 pm | #10 |
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Re: Hacker sovereign - no am
I just fixed an all AF11* sovereign with no AM but FM was good.
In truth, it actually fixed itself...I was fiddling around trying to find a faulty transistor and after about 15 mins it slowly came to life on MW but no LW and then LW recovered. I assume the electrolytics were reforming...Peter |
17th Oct 2008, 7:50 pm | #11 | |
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Re: Hacker sovereign - no am
Hi peter, you are a lucky man
Quote:
the entire 503 board from a scrap set, will report back when finished Mark |
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17th Oct 2008, 7:57 pm | #12 |
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Re: Hacker sovereign - no am
Hi Mark,
HANG ON!!! It might not be the 503A at all. And you might have to re-align the set if you swap panels. Have you got the manual? On AM, the audio leaves the 503A board at the junction of R14 and R16. Try injecting a signal here (wet finger?) to see if you can hear a hum in the speaker. Try measuring voltages around the transistors T2/T3/T4 on the 503A board. Note that the manual quotes them with respect to HT+ which it later says is +6v with respect to chassis (i.e. they're measured WRT the +ve side of C21). Also, have you measured any voltages around the AM "front end", i.e. around TR1, BF194 (on the switch board)? Again, measured WRT the 6V HT rail. [The manual could have done with some proofreading (in addition to the AM/FM cock-up I mentioned before); sometimes these transistors are referred to as T1-T4, other times as TR1-TR4. Similarly, T1 appears to be on the switch board but the voltages page implies that it's on 503A ] Nick. |
17th Oct 2008, 9:27 pm | #13 | |
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Re: Hacker sovereign - no am
Hi Nick,
Quote:
I have re-fitted it to the doner set & it is still well dead, the c21 cap is ok & i have +6v on it, must be a dead transistor, anyway my set is now working well & just needs some cosmetic cleaning & fm aerial replaced. Watch out for it on success stories soon. Mark Last edited by Darren-UK; 18th Oct 2008 at 10:30 am. Reason: Excessive use of emoticons. |
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17th Oct 2008, 9:37 pm | #14 |
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Re: Hacker sovereign - no am
Well done Mark!
N. |
17th Oct 2008, 9:38 pm | #15 |
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Re: Hacker sovereign - no am
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17th Oct 2008, 9:51 pm | #16 |
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Re: Hacker sovereign - no am
Thanks Nick, i must admit, after that board transplant a kebab & a pint is well
deserved Mark Last edited by Darren-UK; 18th Oct 2008 at 10:31 am. Reason: Excessive use of emoticons. |