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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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16th Jun 2019, 3:02 pm | #1 |
Heptode
Join Date: Sep 2007
Location: Brentwood, Essex, UK.
Posts: 687
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Problem with Hacker Herald RP35
Hello All,
I am repairing a later model of the Herald with the silicon transistors, it was originally silent apart from a very faint station on MW but replacing TR3 on the RF Board brought it back to working well. As I had a bag of these transistors I thought I would change the others on the RF board, all went well until I changed the last one on the board TR1 ( BF194) then it didn't work at all! - on putting back the BF194 it works perfectly. Shouldn't an MPSH10 be OK in this position? this is the first time I have used any of the batch I bought but the others I have swapped are fine, I did try another in case it was a faulty one. Cheers, Steve. |
16th Jun 2019, 3:10 pm | #2 |
Dekatron
Join Date: Feb 2009
Location: Chesterfield, Derbyshire, UK.
Posts: 3,737
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Re: Problem with Hacker Herald RP35
I take it this is in the mixer /osc stage , according to the data sheet it should work , Mick.
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16th Jun 2019, 3:16 pm | #3 |
Rest in Peace
Join Date: Mar 2006
Location: N.W. Oxfordshire(Chipping Norton)
Posts: 7,306
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Re: Problem with Hacker Herald RP35
Surely, vinrads, the Mixer/Oscillator in this model is silicon (BF194)? If so, why replace it with a germanium type. For a start the BF194 is NPN, the AF12x series are PNP. I have no data on the MPSH10, but the phrase 'If it isn't broke, don't fix it' comes to mind, i.e. why replace a working transistor in the first place. The BF194/95 series, AFAIK, don't suffer from any kind of reliability problem. If this model did use the AF11x series of germanium transistors, I'd change them all on sight!
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16th Jun 2019, 3:21 pm | #4 |
Heptode
Join Date: Sep 2007
Location: Brentwood, Essex, UK.
Posts: 687
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Re: Problem with Hacker Herald RP35
Yes, it is - its only in that position that one wont work, all the others on the RF Board have been changed to these without any problem. I wondered if it is a poor spec batch of transistors I have bought and just not any good as oscillator, the radio is silent with one fitted in this position - I hope not, I bought rather a lot of them...
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16th Jun 2019, 3:27 pm | #5 | |
Heptode
Join Date: Sep 2007
Location: Brentwood, Essex, UK.
Posts: 687
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Re: Problem with Hacker Herald RP35
Quote:
Steve. |
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16th Jun 2019, 3:55 pm | #6 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,787
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Re: Problem with Hacker Herald RP35
An MPSH10 should be fine as a replacement. My guess is that something is marginal in the circuit.
Obviously you should check and double check the leadouts. I haven't found BF194 mixers to be at all critical either at AM or FM frequencies, and indeed have replaced them with BC548/2N3904 general purpose types in the past, though I do usually use an MPSH10 or 2SC2999. It might be worth trying whatever Si transistors you have to hand. The BF194/5s are Lockfits and do suffer from the usual Lockfit issues, so swapping them out is normally a good idea. |
16th Jun 2019, 4:17 pm | #7 | |
Dekatron
Join Date: Feb 2009
Location: Chesterfield, Derbyshire, UK.
Posts: 3,737
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Re: Problem with Hacker Herald RP35
Quote:
Last edited by vinrads; 16th Jun 2019 at 4:28 pm. |
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16th Jun 2019, 4:42 pm | #8 | |
Heptode
Join Date: Sep 2007
Location: Brentwood, Essex, UK.
Posts: 687
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Re: Problem with Hacker Herald RP35
Quote:
Steve. |
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17th Jun 2019, 12:36 am | #9 |
Rest in Peace
Join Date: Mar 2006
Location: N.W. Oxfordshire(Chipping Norton)
Posts: 7,306
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Re: Problem with Hacker Herald RP35
Apologies, Mick. I was confusing the BF194/5 with BF184/5 series. The latter are metal can Si equivalents and don't, AFAIK, suffer from problems. That having been said I've not had many lockfit failures-maybe I've just been lucky. I now know you deleted your reference to AF12x transitors, too!
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17th Jun 2019, 3:52 pm | #10 |
Dekatron
Join Date: Feb 2009
Location: Chesterfield, Derbyshire, UK.
Posts: 3,737
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Re: Problem with Hacker Herald RP35
Hi No problem there ,you must have seen my slip up in the few seconds , before I deleted it . Mick.
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