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Old 24th Oct 2019, 12:20 pm   #1
coopzone
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Default Murphy A122 UU6 rectifier substitute

Hello,

I have a Murphy A122 with a missing UU6 Rectifier. Since these are pricey little beasties and don't seem to have a good track record for reliability. I was thinking of using a couple of IN4005 (600 volt) diodes while i wait to see if a UU6 appears at a decent price.

Someone has already replaced the missing valve in the past with two very large RS REC 514 (i can't find data on these but i assume the 5 probably means 500volt). But no series resistors.

My question is what value, if any, resistor i should use in series with the in4005. I have calculated that the voltage drop across the valve per diode would have been around 30-40 volts (with 70ma draw) so i would think 470ohm 2 watt maybe ok? It seems a little high?

Derek
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Old 24th Oct 2019, 12:57 pm   #2
ms660
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Default Re: Murphy A122 UU6 rectifier substitute

https://www.kevinchant.com/uploads/7...placements.pdf

Lawrence.
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Old 24th Oct 2019, 1:28 pm   #3
Herald1360
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Default Re: Murphy A122 UU6 rectifier substitute

1N4005 is a bit marginal- just go straight to 1N4007 or better (less noise) UF4007.


The series resistor (from common cathodes of diodes to cathode (pin 1) of UU6 base is best chosen by experiment to get correct HT+ voltage when set is running. You won't do any harm to start from 470R then go up or down as required. Best to use a 5 or 6 watt wirewound type for reliability and not too high operating tempoerature.


There are spare pins on the UU6 valve base (2, 4 and 7) which can usefully be employed for mounting the diodes and resistor- diode anodes to 3 & 5, cathodes to 7 and resistor between 7 & 1 will work and needs no disturbance of existing connections. Should you get a replacement valve, just remove the resistor.....
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