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Lloyd 1985 · 7th Mar 2020, 12:16 am

Time for a bit of an update, I’ve got myself a replacement TH233 valve, the original valve had an O/C heater, a long wait paid off, there were replacements on eBay, but they were £30! Far too much, eventually someone listed a box of 5 valves for 99p, and I was the only bidder!

So with the heater chain complete, I decided to give it some beans and see what happened. Not much was the answer to that! It all lit up, heaters glowed, and a slight hum from the speaker, but nowt else. A check with the meter revealed positive volts on the grid of the PEN383, C30 was high on the suspect list, with that snipped out the +10V was still present, I thought oh no, not another duff valve? Out it came and a quick test with the Megger showed leakage between the screen and grid, and also between the cathode and grid, then there was a click and the Megger went nuts showing ‘E09’ on the display and making weird noises, which it normally does when you draw an arc between the probes! I must have blasted whatever it was away, because on refitting the valve the positive volts were gone! And the quiet hum had been replaced with a healthy amplifier buzz and interference!

I replaced C30 with a new cap, just tacked in for trial purposes, and had a tune about with the workshop aerial connected, discovered the set was switched to LW, and there isn’t much on there, switching to MW gave nothing, wiggling the wave change switch produced lots of crackling and occasionally some noise, so I gave that a squirt of switch cleaner and exercised it and eventually it started working, I tuned in Absolute radio very loud and clearly! Listened to It for a while then turned off, despite all the wax caps still present it sounded alright, they will be replaced with new ones soon, and I’m sure the radio will sound even better for it.

One other thing I discovered and need to put right is the dial string, the pointer moves the wrong way when the knob is turned! Just need to reverse it where the string wraps round the tuning knob shaft. Oh, and the dial bulb is the wrong type, should be a 3.5v 0.1a, and I’ve got a 6V 0.3a one, and it’s like a candle that’s just been blown out...

Regards
Lloyd

7th Mar 2020, 12:16 am	#18
Lloyd 1985 Nonode Join Date: Jun 2008 Location: Coningsby, Lincolnshire, UK. Posts: 2,820	Re: Making a Murphy SAD94L happy again! Time for a bit of an update, I’ve got myself a replacement TH233 valve, the original valve had an O/C heater, a long wait paid off, there were replacements on eBay, but they were £30! Far too much, eventually someone listed a box of 5 valves for 99p, and I was the only bidder! So with the heater chain complete, I decided to give it some beans and see what happened. Not much was the answer to that! It all lit up, heaters glowed, and a slight hum from the speaker, but nowt else. A check with the meter revealed positive volts on the grid of the PEN383, C30 was high on the suspect list, with that snipped out the +10V was still present, I thought oh no, not another duff valve? Out it came and a quick test with the Megger showed leakage between the screen and grid, and also between the cathode and grid, then there was a click and the Megger went nuts showing ‘E09’ on the display and making weird noises, which it normally does when you draw an arc between the probes! I must have blasted whatever it was away, because on refitting the valve the positive volts were gone! And the quiet hum had been replaced with a healthy amplifier buzz and interference! I replaced C30 with a new cap, just tacked in for trial purposes, and had a tune about with the workshop aerial connected, discovered the set was switched to LW, and there isn’t much on there, switching to MW gave nothing, wiggling the wave change switch produced lots of crackling and occasionally some noise, so I gave that a squirt of switch cleaner and exercised it and eventually it started working, I tuned in Absolute radio very loud and clearly! Listened to It for a while then turned off, despite all the wax caps still present it sounded alright, they will be replaced with new ones soon, and I’m sure the radio will sound even better for it. One other thing I discovered and need to put right is the dial string, the pointer moves the wrong way when the knob is turned! Just need to reverse it where the string wraps round the tuning knob shaft. Oh, and the dial bulb is the wrong type, should be a 3.5v 0.1a, and I’ve got a 6V 0.3a one, and it’s like a candle that’s just been blown out... Regards Lloyd Attached Thumbnails