Thread: Pye 834
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Old 3rd May 2021, 9:28 pm   #3
cathoderay57
Octode
 
Join Date: Oct 2017
Location: Bristol, UK.
Posts: 1,388
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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