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Old 7th Oct 2013, 7:22 pm   #1
AD360 Rob
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Default Pye P115U "Piper" re- restoration

Afternoon all,

After a successful period restoring transistor sets, I decided it was time to look at some of the valve sets I have on display in my front room. these were previously restored (or partially restored) by me and a colleague some 10 - 15 years ago at work. One set that we never really bothered to test after replacing most of it's components and cleaning it up was this little Pye piper, I think the reason being, it has odd knobs, a nasty printed circuit and was generally very cheap looking inside. Anyway I decided this was the current candidate.
I opened it up and removed the chassis and speaker, first thing of note was the O/P transformer was an RS type and was fitted neatly where the original would have been so not a problem as far as I could tell but I did wonder what caused the original to fail.
Oh well, I thought, lets apply a bit of power and see what happens (I'd already checked the smoothing and reservoir caps and the mains filter had already been replaced with a WIMA branded one, also I had changed all the waxed paper coupling and decoupling capacitors all those years ago so I felt pretty confident that it wouldn't go bang or cause any other damage. I plugged in and turned on, waited for the valves to warm up, expecting some sort of noise to be produced but got nothing, totally silent so, out came the multimeter to do some checks. Probing around the output pentode (UL41) revealed there were no voltages other than heaters present so suspicion fell on the rectifier and smoothers. Measuring the UY41 Anode gave me the expected 225vAC, cathode measurement gave me nothing, that's right, zero volts (well, if I'm completely honest, 0.7volts dc). Next I checked the smoothers again for leaks or short circuits but they were both fine as before so, in went a good second hand UY41, switched on again and watched the meter connected to the cathode start to rise nicely as it warmed up, it settled at a nice steady 218 volts, a few volts low according to the service info but not worth chasing. Best of all was I was now getting some sounds .

After reconnecting the throw out wire aerial I had a tune and pulled in the local Gold station at good volume and not too much interference so I left it to play whilst I had a cup of tea. . . there was still something niggling me about the set even though it was working just fine. . . . . . . just after I finished my tea it came to me. . . I had yet to measure the UL41 grid voltage.
a quick probe with the meter revealed about 5 volts on the control grid, That can't be right I thought as it's working so well, no distortion, nothing appeared to be getting hot but I knew this voltage should be at zero so, first thing was to replace C21 (mnfrs) even though it had been replaced during the last resto, whilst it was out, I measured it on my capacitance meter and whilst there was no discernible leakage, the value was almost 30nF (it should be 10nF or 0.01uF) so I fitted a nice shiny new one rated at 400v. rechecking the grid volts revealed that it was now sitting at about 2v, still not good enough so I fitted a replacement UL41, now I was getting the expected zero volts on the grid so no danger of output transformer damage. . . I wonder if the UL41 had been the cause of the replacement output transformer ! an interesting (for me) point about the capacitor C21 is that when I replaced it during the first resto, I used a military grade component yet it had, to all intent, failed.
I'm now using this as my bedroom set (giving the Decca Debonaire a rest) as it has the advantage of a non directional aerial which is hidden under the bed and contrary to a review I read, sounds quite pleasant too !

Rob
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Last edited by AD360 Rob; 7th Oct 2013 at 7:28 pm.
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Old 7th Oct 2013, 7:31 pm   #2
G6Tanuki
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Default Re: Pye P115U "Piper" re- restoration

UL41s and their friend the EL41 are prone to odd internal leakages: a year or two back I refurbed a Pye P75 whose EL41 was leaking between the grid and either the anodem or the screen-grid and so was passing excess current.

The "military grade" capacitor you used first time round - was it current-production, or was it old-stock? Just because something was made to comply with a MoD spec back in 1980 doesn't necessarily mean it is going to be good today.
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Old 8th Oct 2013, 8:59 am   #3
AD360 Rob
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Default Re: Pye P115U "Piper" re- restoration

If I recall, the capacitor used was one we were using quite regularly at work so I assume it would have been a recent manufacture rather than one that had been sitting around since the 1960s (which a lot of components we were using at the time had been).
Had the set on for a bit last night and apart from the rather poor LW performance which isn't an issue for me, I am still very pleased with the sound and MW reception on this cheap little set, it's amplifier stages are quieter than the Decca it replaced meaning that low volume listening isn't awash with hiss.
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Old 8th Oct 2013, 11:19 am   #4
SeanStevens
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Default Re: Pye P115U "Piper" re- restoration

I might just have a knob to complete that radio

Remind me by PM tomorrow


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Old 8th Oct 2013, 10:22 pm   #5
JoshWard
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Default Re: Pye P115U "Piper" re- restoration

Nice work! I have one sitting here in the 'to do' pile, sadly it is missing it's original tuning dial knob
Glad to hear the sound isn't too bad, maybe I will have to have a go at mine sometime soon!

Josh.
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Old 9th Oct 2013, 8:40 am   #6
AD360 Rob
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Default Re: Pye P115U "Piper" re- restoration

Morning Josh,
Thanks for that, yes, it's really not that bad a set to listen to, I would describe the sound as Inoffensive, just the thing for bedtime listening. I would suggest that the only things you need to watch out for on this chassis is PCB print lifting and UL41 leakage. Change C21 as a matter of course (UL41 Grid coupling cap).
Hopefully, a request for a tuning knob on here might produce results. Mine isn't perfect having the odd crack near the centre but I can live with that.

Good luck with yours

Rob
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