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Old 31st Oct 2019, 11:41 pm   #11
Niechcial,Steve
Hexode
 
Join Date: Jan 2007
Location: Beckenham, London, UK.
Posts: 373
Default Re: Murphy V659/759 restoration

Some progress tonight. Once I got the UHF plinth off the cabinet the UHF tuner cover was easily removable without having to remove the tuner from the plinth. You were on the right lines thanks John- somebody had fitted two PC86s instead of a PC86 and a PC88. That was causing the HT short. Unfortunately, as well as burning up the external 1.8K HT feed resistor the short also burnt up a little internal 0.25W 1.8K resistor which forms part of the oscillator anode load. I replaced this as carefully as I could, but it involved unsoldering another coil and moving it to one side. I just hope it still oscillates. Some of these valve tuners were reluctant to oscillate at the best of time and were choosy on valves. A friend of mine who used to work for RR at that time told me he always carried a rare version of the PC86 with gold plated pins for the really stubborn sets.
Switching the set on, it proved difficult to get the line output running. I traced the fault to a bad connection on the anode pin of the PY. No amount of cleaning helped and I could see sparks actually from inside the pin mounting. The only way I could get it to run was by unplugging it,dangling it from its cathode lead and connecting the valve pins with jump leads. Unfortunately the PY only has one pin connected to the anode internally so I am going to have to change the valve base.

The HT is low at about 140 volts with the rectifier surge resistor smoking.HT current is 350mA. HT resistance to chassis cold is fine. That will be the next thing to tackle.
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