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Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 3rd May 2021, 9:21 pm   #1
cathoderay57
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Default Pye 834

I bought this Pye 834 at auction. There don’t seem to be many of them about. The top of the cabinet had a large area covered in a black sticky substance which, fortunately, responded to vigorous rubbing with a cloth soaked in white spirit. There are some chipping and scratches but overall the cabinet is in nice condition for its age and all I plan to do is give it a coat of wax polish. When I opened up the back it was clear that some attempt at repair had been made, probably quite a long time ago, as witnessed by the presence of 3 x 16uF electrolytics dangling precariously from the speaker field coil terminals. The original smoothers would have been inside a cardboard box screwed to the baffle board to the right of the speaker. The speaker and HT wiring was rubber and had perished and crumbled badly. Somebody had wrapped it in yellow insulating tape but I removed the whole cable harness and made a new one from silicone rubber-insulated wire. I first checked the continuity of the AF output transformer and speaker field coil – OK. I also checked the dc resistance of the mains transformer primary and HT secondary – OK, or so I thought. Having replaced the rotted rubber cabling going to the on-off mains switch, luckily being able to pull through new wires inside the existing braided shield shell, I applied power. Oh dear, a sizzling sound and bubbling wax started erupting from the mains transformer. I had made a schoolboy error by measuring the dc resistance between the ends of the centre-tapped winding and chassis, where the centre tap is usually connected isn’t it? Well not in this case. Checking the circuit diagram showed that there is a pair of bias resistors in the earth return between chassis and centre tap. The presence of these resistors had given me a false indication that the HT windings were perhaps in better condition than they actually were. The mains transformer was toast (almost literally). Fortunately Ed Dinning came to the rescue with a suitable replacement – thanks Ed . Meanwhile I looked over the remainder of the set. I discovered that the tuning flywheel was made of Mazak alloy(aka monkey metal) and the casting had blown causing the flywheel to jam against the cross-bracket through which the tuning spindle passes. I started another thread on this with images here: https://www.vintage-radio.net/forum/...d.php?t=179102 but suffice to say I managed to file off material from the face of the flywheel such that it would rotate OK. Not perfect but good enough to use.
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Old 3rd May 2021, 9:26 pm   #2
cathoderay57
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Default Re: Pye 834

Below chassis no real surprises – the wax paper capacitors all looked original bar one and all bar one were leaky and were replaced. I did go to the extent of restuffing the 20uF electrolytic cathode decoupler on the TDD4 detector – not something I usually bother with but the case of the component was is such good cosmetic condition it seemed a shame to just bin it. I tested the valves on the VCM163 and while the TDD4, VP4B IF amplifier and the PenB4 AF output valves tested very good to excellent the DW4/350 rectifier and the triode part of the TH4B showed very low emission so I replaced both. I bought a couple of DW4/350 off eBay one of which was excellent. The Wireless Retailer & Broadcaster sheet showed the frequency changer as a TH4A. I did have one but, on account of a wooden spacer bar across the back of the set behind the valves, it was impossible to fit a TH4A because it is fatter than a TH4B so I stayed with the TH4B. When Ed’s transformer arrived I did some careful measuring because space was tight. The replacement was a drop-through type but I made up some brackets and utilised a spare mounting frame removed from another transformer which was exactly the right size, to mount it vertically. The rectifier was mounted on a canted paxolin board on top of the old transformer but when I removed the old transformer from the chassis I saw that there was an unused spare valve-holder hole in the chassis that had been partially obscured. By re-routing the screened cables to the volume control I was able to fit a B4 valve holder and so the replacement DW4/350 would just fit into the space envelope in front of the replacement transformer. I thought I was going to need to replace the five 6.3v 300mA pilot lamps with LEDs to save some current but Ed’s transformer was rated at 4v 6A. Total heater/lamps budget was 5.75A and so I left them in and didn’t use the LEDs.
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Old 3rd May 2021, 9:28 pm   #3
cathoderay57
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Default Re: Pye 834

Having replaced the necessary capacitors, and using 10uF 450v electrolytics for the HT (originals being 8uF) it was soon time to power up. I was greeted with – total silence. I plugged in another speaker; same result. I then checked voltages and found that I only had 2.5v on the anode of the TDD4 detector pre-amp. Schoolboy error number 2 – I had connected the restuffed cathode decoupling capacitor with its 1.5k cathode bias piggy-backed resistor to the anode pin, not the cathode . Reconnecting restored correct function, and the set came to life. Remarkably the set was spot on scale calibration on SW and MW and only a smidgin out on LW. Sensitivity was very good, so good in fact I decided not to bother with realignment apart from a slight oscillator tweak on R4 LW. Voltage checks showed that on most of the valves, notably the PenB4 (anode 160v, screen 172v), voltages were lower than I wanted so although the set sounded OK I did 2 things. I had the mains transformer primary set to 240-250v and my mains hovers around 232-235v. I change the transformer primary link to 220-230v. Secondly I put a shorting link wire across R25, a wire-wound HT dropper between the rectifier cathode and the field coil. The resistor was dropping 53v which I couldn’t afford. The mains transformer is 280-0-280v and so the original must have been a bit higher. The changes did the trick. Here are the measured voltages with the service data expected values in brackets:
TH4B anode 203v (210v) screen 57v (60v) osc anode 121v (82)
VP4B anode 202v (215v) screen 125v (130v)
TDD4 anode 87v (55v)
PenB4 anode 190v (200v) screen 205v (215v)
DW4/350 cathode 295v (380)
Very happy with the result. As expected, large speaker in wooden cabinet makes nice sound. Cheers, Jerry
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Old 4th May 2021, 6:36 am   #4
Beardyman
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Default Re: Pye 834

Now that's a handsome looking set & a truly fearsome array of switching/inductors etc.!
One of these popped up on FB marketplace near me & I must say I was tempted.
Good write up, very informative & will be referred to if I decide to go & get that set. Thanks for posting.
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Old 4th May 2021, 8:24 am   #5
Gabe001
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Default Re: Pye 834

Nice work Jerry and great write up. Are all those buttons for pre programmed stations, and do they work?
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Old 4th May 2021, 10:04 am   #6
Heatercathodeshort
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Default Re: Pye 834

How manufacturers managed to make any profit from receivers equipped with these complicated tuning systems never fails to amaze me. J.
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Old 4th May 2021, 1:01 pm   #7
cathoderay57
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Default Re: Pye 834

Quote:
Originally Posted by Gabe001 View Post
Are all those buttons for pre programmed stations, and do they work?
Hi Gabriel. Yes, there are 2 buttons for LW, one now tuned to BBCR4 and 5 MW a couple of which I have tuned to stations. Remaining buttons are for manual tuning LW/MW/SW and mains off. The preset dial legends contain long gone station names including Luxembourg, London Reg, R. Lyons and R. Normandie. Cheers, Jerry
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