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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 9th Jan 2018, 4:51 pm   #21
awc
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Default Re: Regentone AHG3W Handygram Record Player - Hum problem

Well!! It seems I may have been led astray by my multimeter! It appears that when dealing with mV, the contraption has a mind of its own and shows a positive reading even without the prods connected up. So my tests may have been misleading.

I used another digital meter and although not a sensitive as the one I usually use, didn't show any volts on pin 6 at all. I have cleaned around pin 6 anyway and I'll put it all back together and check the readings again with another meter. Digital, PAH!

Alex
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Old 15th Jan 2018, 10:38 pm   #22
awc
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Default Re: Regentone AHG3W Handygram Record Player - Hum problem

Back up and running after a week off with the flu, despite having the jab!

Tried scratching/cleaning the UL41 valve base, but to no avail, so in the end replaced it with a second hand but better quality one. This has resulted in positive volts on the grid still, but just 20mV max by which I mean it rises quite quickly to this but after about 30 mins it's down to 18mV and still going down.

I assume this is acceptable but would appreciate your thoughts.

Thanks for all the help once more.

Alex
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Old 16th Jan 2018, 4:35 am   #23
Boater Sam
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Default Re: Regentone AHG3W Handygram Record Player - Hum problem

With a used or even new UL41 that would be about as good as it gets, they are problematical.
Try flashing your old one with a capacitor or a spark generator, connect all pins together except the g1, flash repeatedly between g1 and the rest, often works for me. Many links on here.
You could try making an adaptor B8A to B9A or re-basing and use a UL84, think you need to change the cathode resistor, from memory add 100 ohms.
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Old 16th Jan 2018, 10:48 pm   #24
awc
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Default Re: Regentone AHG3W Handygram Record Player - Hum problem

Tried out the few UL41's I still have and found one showing just 7 mV on the grid which slowly diminished, so will leave it in and consider the problem sorted. One of the others however showed a very large voltage on its grid, so will think about giving it the "flash" treatment suggested.

Never had to change a valve base before because of HT leakage, only wafers on rotary switches occasionally. First time for everything I guess.

Thanks again for all the help and advice, much appreciated.

Alex
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Old 17th Jan 2018, 7:55 am   #25
Boater Sam
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Default Re: Regentone AHG3W Handygram Record Player - Hum problem

Its terribly common on UL41s. If you find 10P13 it will sub but increase the cathode resistor a bit, 56 ohms extra will do, but in a DAC90A it will be fine with the original resistor, Bush under-ran the UL41 a bit.
If the price of working UL41s gets any higher, we will have to consider the UL84 or other B9A valve and replace the holder route.
A lot of sets using UL41s wired pins 3 and 4 erroneously as tag strips, they have bad problems when you change to another makers valve - sometimes, but it always increases the chance of grid current because the basic cause is the debris, darkening, in the valve base around the supports for the electrodes.
Sparking the valve thoroughly may get this debris to not conduct as much, hence no grid leakage.
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