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Old 17th Dec 2019, 3:54 pm   #1
cathoderay57
Octode
 
Join Date: Oct 2017
Location: Bristol, UK.
Posts: 1,206
Default Marconiphone 538

Hi folks, I am the lucky owner of a Marconiphone 538 (courtesy of Yestertech) and its companion an HMV 469 (purchased at the last RWB). I have begun with the Marconi. Trader Sheet #703 refers, and covers both models. The receiver is 7-valve plus rectifier and magic eye; it has 4 wavebands and boasts a KT66 AF output valve. The cabinet is pretty good considering its age (see pic) and so I shall probably leave it as-is. Also pictured is the chassis as-found. Apart from one capacitor and one resistor plus a replacement mains lead the chassis was basically untouched. I checked continuity of the mains transformer, AF output transformer, choke, LS field coil and AF coupling transformer and all were OK. On the VCM163 all of the valves tested excellent except the 6G5 magic eye which was very dim. I have put a request in the "Wants" section - a long shot, but if you don't ask...…. Next I tackled the HT capacitors. The 16uF 500v reservoir cap reformed OK, as did the final 32uF 500v smoother. The middle 16uF 500v wouldn't fully reform but I robbed a better one from the HMV 469 to get the Marconi going. I will restuff the dodgy one when I get around to restoring the HMV. I won't bore you with the details of all the other caps but suffice it to say that all of the paper caps were showing a leakage resistance of 5M or less at 15v on the Avo so I changed all of the ones carrying HT plus the AVC decouplers. I left the paper cathode decouplers as-is and ditto the mica HT decouplers. I have kept all of the removed components and will bag them in case I or a future owner wants to take the trouble to restuff them all. There is a fourth tall can electrolytic on the chassis containing 8uF+1uF+2x2uF and all sections had changed themselves into high value resistors. I snipped the leads and soldered in discrete replacements beneath the chassis. The electrolytic cathode decouplers on the AF valves had also had it and were replaced. One was original and left in place, disconnected. The other had an old RS replacement of the wrong value (100uF vs 25uF) so I removed and discarded it. The 1M resistor in the magic eye anode feed had gone O/C so was replaced. R16 is a high power multi-section potential divider between final HT and chassis. The bottom section is supposed to be 9k but measured 800k so I bridged the connections with a couple of 18k modern resistors in parallel capable of dissipating the 1W required. I'll carry on in a new post.
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