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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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16th Aug 2018, 9:41 am | #1 |
Hexode
Join Date: Mar 2015
Location: York, North Yorkshire, UK.
Posts: 254
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PYE Achoic Distorted / Low Output
Hi Folks,
I'm messing about with a PYE Achoic and I wondered if anyone could shed some light on my problems. Faults are distorted / low output on both channels, here's what I've done so far: - Found a faulty output transistor on the left channel, I've replaced the pair in that channel, they're substitutes not the original Newmarket's as these are pricey, but they will do for test until I can get the amp in a working state then I will fit the correct ones. They're not matched but close enough for test purposes. (I've also set the DC balance control as per the service sheet) - Checked any caps in the signal path, I found most of these to have crazy high ESR values, and most wouldn't even open the eye on my Heathkit IT-28 near their working voltage. It made sense that these would be the culprit but no such look. - Replaced a few resistors but probably clutching at straws, out of spec but not that out of spec. I have noticed that the interconnects from both the speakers and the amps are troublesome, I have cleaned the pins and sockets on both. However I have noticed when I tap the one from the amp it will intermittently cut power to the amp, I have continuity on all pins but is it possible that this could be related to my issue? I find it interesting that the distortion / low output problem effects both channels, it makes sense to me that it has to be common to both, although I know things don't always work like that! Input wise it's being fed from a genny which rules out the cartridge. After reading a few other posts on these beasts it's clear that they can be a pig to work on. I should probably add the output is both distorted and very low, the loudness control makes little difference to the overall level. I've also replaced C21 & C23 on each channel as they seemed the obvious culprits. I don't have any hair so none to tear out, so if anyone could shed some light on the above it would be greatly appreciated. Many thanks in advance, Darren.
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16th Aug 2018, 10:17 am | #2 |
Dekatron
Join Date: Sep 2015
Location: Southwold, Suffolk, UK.
Posts: 8,327
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Re: PYE Achoic Distorted / Low Output
These are a real minefield to service and I would not wish that one anyone!
Using Newmarket transistors would have been the ideal. Also the components you fit must be as close as possible in value and tolerance to the originals. Don't mess with the speaker wiring as these have unique phasing arrangents. Make a diaagram of anything you have to move/dissconnect first. Good luck!
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Edward. |
16th Aug 2018, 9:58 pm | #3 |
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Location: Wembley, Middlesex
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Re: PYE Achoic Distorted / Low Output
I have found by experience that you MUST fit the original Newmarket transistors, nothing else will work.
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17th Aug 2018, 7:43 am | #4 |
Hexode
Join Date: Mar 2015
Location: York, North Yorkshire, UK.
Posts: 254
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Re: PYE Achoic Distorted / Low Output
Thank you Michael, I still have the originals in one channel, but do they all need to be Newmarket's for it to work correctly?
Many thanks, Darren.
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17th Aug 2018, 10:11 am | #5 | |
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Location: Middlewich, Cheshire, UK. & Winter in the Philippines.
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Re: PYE Achoic Distorted / Low Output
Quote:
As its both channels, would that not suggest that it is the power supply as that is common? Sorry, no circuit to hand just a thought Sam.. |
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17th Aug 2018, 11:36 am | #6 |
Dekatron
Join Date: Sep 2015
Location: Southwold, Suffolk, UK.
Posts: 8,327
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Re: PYE Achoic Distorted / Low Output
Michael is quite correct. The whole circuitry in the 1005 is very intolerant of anything other than that which was originally specified. Some Dealers had to return them to St. Andrews Road, Cambridge, to be fixed in the Labs!
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Edward. |
18th Aug 2018, 11:26 am | #7 |
Hexode
Join Date: Mar 2015
Location: York, North Yorkshire, UK.
Posts: 254
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Re: PYE Achoic Distorted / Low Output
Thank you all for your comments - Sam that also occurred to me re the power supply but everything checks out voltage wise.
Unfortunately it would seem I will have to track down some NKT 453u's, I have no idea where though I have already tried a wanted post and the usual auction sites. Unless a donor machine comes up with functioning transistors I might be out of luck Would a Newmarket equivalent be suitable or does it need to be the exact ones? Many thanks, Darren.
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18th Aug 2018, 3:52 pm | #8 |
Dekatron
Join Date: Sep 2015
Location: Southwold, Suffolk, UK.
Posts: 8,327
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Re: PYE Achoic Distorted / Low Output
In many case a "Newmarket Equivalent" is, er, not quite.... A donor machine which has other faults is an option.
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Edward. |
19th Aug 2018, 12:29 am | #9 |
Dekatron
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
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Re: PYE Achoic Distorted / Low Output
Carefully disconnecting the original amplifier so it could be reinstated in future and fitting a modern replacement would be yet another option, but this is complicated by the centre channel. This is wired to produce a difference signal; but the phase is reversed on one channel, at both the speaker and cartridge ends, so the centre channel actually produces L - (-R) = L + R, and the right hand speakers play -(-R) = R. You would need to choose output devices that could work into the awkward combined impedance of the speaker systems. One benefit of this would be that you could easily add an op-amp wired so as to invert the phase of one channel of an auxiliary input.
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19th Aug 2018, 9:19 am | #10 |
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Re: PYE Achoic Distorted / Low Output
A word of caution:
These amplifiers are designed for positive earth, I tried to do just that and it was fraught with problems, I gave up in the end. |
21st Aug 2018, 8:46 am | #11 |
Hexode
Join Date: Mar 2015
Location: York, North Yorkshire, UK.
Posts: 254
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Re: PYE Achoic Distorted / Low Output
Thank you folks for all your input on this, it seems there are very little success stories about regarding this amp.
It's a shame as it's a nice looking player, but unless I can find some output trannys for it looks like being a back burner project for now Thanks again, Darren.
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