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Techman · 20th Jan 2023, 10:12 pm

I think...you've got no HT.

Without a working MU14 rectifier, nothing in the set will work!

Check its heater for continuity/resistance with the valve removed from the set.

If the heater shows continuity, then it could be that it's not getting any voltage, so check for 4 volts AC, but be careful - there's high AC voltage direct from the transformer around the base of that valve and it can kill, so be very careful to measure the correct pins or you'll blow your meter if you have it on a low voltage range and you get it wrong.

The MU14 takes 2.5 amps for its heater and at this sort of current it's quite common to get oxidised connections both in the valve base socket or the actual valve pins themselves.

Edit: I see it has two rectifiers - I'm not familiar with the set. Check for heater voltage all the same. Just seen the post by Leon.

20th Jan 2023, 10:12 pm	#28
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 5,000	Re: What did I get myself into? Murphy A40C. I think...you've got no HT. Without a working MU14 rectifier, nothing in the set will work! Check its heater for continuity/resistance with the valve removed from the set. If the heater shows continuity, then it could be that it's not getting any voltage, so check for 4 volts AC, but be careful - there's high AC voltage direct from the transformer around the base of that valve and it can kill, so be very careful to measure the correct pins or you'll blow your meter if you have it on a low voltage range and you get it wrong. The MU14 takes 2.5 amps for its heater and at this sort of current it's quite common to get oxidised connections both in the valve base socket or the actual valve pins themselves. Edit: I see it has two rectifiers - I'm not familiar with the set. Check for heater voltage all the same. Just seen the post by Leon.