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Old 23rd September 2017, 06:14 PM
moley moley is offline
Join Date: Nov 2014
Location: Sheffield
Posts: 30
Default Re: WD Phono 3 - DC on Output?

Hello folks,

I finally got chance to get my PSUIII and PhonoIII on the test bench.

I swapped all the ECC83 (TJ Full Music) valves around and tested the output of the Phono 3 measuring voltage with a 50K dummy resistor load connected across the output.

The large spike at switch on still occurs and shortly after switch on I still have
an ever changing reading dancing from -40mV to +90mV.

I do have the 100UF cap and correct resistor installed in the Phono III and I do have close to 270V (267v) coming in to the Phono III.

I then ran through all of the checks detailed in the manual. It passed everything apart from the following two tests :

- Check the heater voltage at the heater pin points on the top of
the PCB (HTR+). It should read close to 45 volts DC.
= I get 56 volts

-Remove the negative lead of the multimeter from the earth
terminal and check the heater voltage across the positive and
negative pin points on the PCB (HTR+ and HTR-). It should be
between 5.9 volts and 6.7 volts DC.

= I get 6 volts here so does that mean the 56 volts measured above is inconsequential since I have the correct HTR- & HTR+?

Check the Cathode voltage on pin 8 and pin 3 of the output valve
(junction with R23/R24). It should read about 110v DC.

= I get 118 volts and 124 volts here! Is this potentially linked to my issue of DC offset at the outputs?

I haven't yet ventured to changing the 2.2UF output caps and trying a smaller value to increase the corner frequency of the RC filter.

As always, any help or suggestions gratefully received.
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