Pre-II Cath. Foll. wiring query.

[buddam]

Hi all

I'm making a PreII CF this week-end, but without the usual first stage of making a PreII. I'm not sure of the wiring arrangements, and the WAD site 'sample only' diagrams aren't absolutely clear. Heater wire seems clear enough, and earth too. But wanted to check high voltage wiring before I fire up, especially since voltage is double that in the old PreII. Am I right that wiring to PCB from transformers is replaced by new wring direct from Cliffcon socket to PCB?

Thanks

Adrian

[Greg.]

Hi Adrian,

You've not said if you are using the converted Pre II board or hard wiring as I have.

If you are using the Cliffcon socket at the rear of Pre II, then two wires from Cliffcon pin 2 carry the 200vdc HT to pins 1 and 6 of the 6922. Cliffcon pins 1 and 4 are the heater supply to valve pins 4 and 5. Configuration is not important here. Cliffcon pin 3 is earth.

I hope that helps. Email me your phone number and I'll talk through with you if you like.

Best wishes,

Greg

[buddam]

Hi Greg

thanks for that. I'm actually going to hard-wire on top of the pcb, which will be used for the valve base only.

Home phone is 0207 249 9653. Best if you let me have yours - I could phone when I get round to soldering later this evening

Adrian

[buddam]

Nearly done but have a small query. The FAQs say

"Solder to the input PCB pins one end of a .047uF (47nF) quality polypropylene capacitor, the signal input is to the other end of the capacitor... This capacitor is necessary to isolate the Volume control from any DC leakage, do not omit it!"

The query is, surely the end soldered to the pcb i/p pin (or if hard-wired the end closest to the volume pot) is the end that takes the signal i/p. To my eyes, the cct diag also suggests this, although I see the arrow from the cap to volume pot.

I'd appreciate it if someone (greg, are you there?) could clear up my confusion before I fire up.

Thanks

Adrian

[Greg.]

Hi Adrian,

As you are hard wiring, referring to Neal's notes on the use of the PCB can bring confusion. Those notes were written by Neal so that with little alteration, the original PCB and it's circuit could be used to make the conversion.

In your case it is simply, input from the 'phono in' goes direct to the pot and then signal goes direct to the end of .047uF cap. Earth from the pot returns direct to the earth post.

Best wishes,

Greg

[buddam]

everything measures ok on both psu & preII, but i'm mystified as to why the instructions refer to 6.3vdc to heaters when i'm getting 44v & 51V which according to the psu test point data is correct. Can anyone say how this figure becomes 6.3V and why the 2 halves of the valve seem to be fed different voltages?

Rather reluctant to put my Mullard valve in till I get an answer.

Thanks

Adrian