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Station X · 21st Dec 2009, 9:18 pm

The readings in post 173 for the 42 don't look too bad to me.

Unlike in post 171 the readings of both cathodes (pin 5) are the same. They should be, as they're joined together!

I'm a bit concerned that you can't measure the resistance from pin 4 to chassis. What do you get if you measure the 510K resistor which was removed from the circuit?

Are the valveholder contacts clean and making good contact with the valve pins? If they're not it could account for the flucuating voltage readings.

I'm trying to reverse engineer the circuit from the pictures you emailed me, but it isn't easy. As PJL says if you could sketch the wiring around the 75 it would be useful.

21st Dec 2009, 9:18 pm	#176
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: Newb Stumped on a Derwent The readings in post 173 for the 42 don't look too bad to me. Unlike in post 171 the readings of both cathodes (pin 5) are the same. They should be, as they're joined together! I'm a bit concerned that you can't measure the resistance from pin 4 to chassis. What do you get if you measure the 510K resistor which was removed from the circuit? Are the valveholder contacts clean and making good contact with the valve pins? If they're not it could account for the flucuating voltage readings. I'm trying to reverse engineer the circuit from the pictures you emailed me, but it isn't easy. As PJL says if you could sketch the wiring around the 75 it would be useful. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.