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Shaman · 13-04-2011, 02:04 PM

Hi, this little set has the U series valves, LW/MW/VHF, suddenly developed a loss of two heaters UCC85 no heater, UABC80 no heater, the rest fine ht fine, have traced around cannot find any break in the heater circuit, dial lamp glows, has anyone got any idea,s, valves replaced with NOS, to no avail, dropper is ok...regards...Alan.

**Steve_P** · (This post was last modified: 13-04-2011, 02:59 PM by Steve_P.)

Are you sure it is a U472? If so, try removing the 10C14 (UCH81) and see if the rest light up. If not, try a replacement here. It might be shorting the heater to deck. There are also a few capacitors on the heater line which cause trouble as well as L23.

Are the other valves 'U' or 'E' series. If they are 'E' series, then 'U' ones will not do in these positions.

Generally speaking, 'U' series valves are in series, so pull one and the rest should go out. 'E' series are in parallel, so lifting any one should leave the others alight.

Have you got the circuit?

Cheers,

Steve P.

Shaman · 13-04-2011, 06:21 PM

Hi Steve, the Set is Murphy Model U472. All valves are the U series, i will post circuit, and indeed there are caps in the heater chain, unless one or more have gone down, the radio was fine, turned it off, then back on later and the UCC85 on the VHF Tuner head also the UABC80 failed to light. I will check circuit and caps now, i did fit a NOS UCH81 to no avail the heater comes off this, to the tuner head, then to the UABC80 then chassis...regards Alan.

**Steve_P** · (This post was last modified: 13-04-2011, 06:39 PM by Steve_P.)

The UCH81 isn't the problem. Drat. Check that the wiring is OK and check C67.

Cheers,

Steve P.

Shaman · 13-04-2011, 06:56 PM

Hi Steve, just cut the heater feed to the tuner head, hey presto sound, going well minus of course VHF, so will check tuner head heater cap for short, or oc heater feed.....regards.....Alan.

**Steve_P** · 13-04-2011, 07:35 PM

There shouldn't be. All the valves in this are in Series, so by cutting the loop all the valves should go out. Unless the Irish version of this set is different!

Strange....

Cheers,

Steve P.

**tiv48** · 13-04-2011, 10:19 PM

c67 0.01mf is the only thing i can see on the circuit that would cause that fault
rob t

Shaman · (This post was last modified: 19-04-2011, 01:45 PM by Shaman.)

Hi Steve, i meant cutting the heater supply to the tuner head, soldering the feed to-gether so as remaining valves are in series again. it works less VHF of course, there was a condencer 0.01uf, to earth from heater supply, this had shorted. Rob, the only duff component was this condencer, cut one end, reconnected tuner feed it now works fine, will have to try to fit another, but there is no room to solder components, screening etc in the way.... thanks everyone for your replies, Rob has a gold star, regards....Alan.

**tiv48** · 14-04-2011, 10:36 AM

glad its fixed just shows one of the best service aids is the circuit diagram
cheers rob t

Shaman · 14-04-2011, 02:09 PM

Sure is Rob, thanks and to everyone who helped regards....Alan.

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