Golborne Vintage Radio

Hi folks, ive managed to buy three avo mk2 valve testers they are all working but 2 off them have worn set zero pots , there are 2 pots both work with one spindle one behind the other , one is 1400 ohm and the other is 500 ohm , now there only appears to be three wires connected on the circuit diagram , both pots are one turn , I have read on another forum that someone has replaced both pots for a 470 ohm 10 turn pot
which works fine you just have to remember to back it right off before starting the test , I have the parts list and wiring diagram but cant get my head around it , I think the current goes throuth both pots at the same time they are r1 and r2 , on the mk4 you have course and fine , if
I show a picture of the wiring diagram would someone who may be a little bit more intelligent than me have a look and say what you think , thanks phil.

some pictures

more pics

struggling with attachments but ive got the idea now

The last ones 

You probably need to take out extra House Insurance with that lot

What's the Lathe and Drill?

Alan

Hi alan , The lathe is a woodhouse and michell  junior £50 about 15 years ago , the drill is an  atlass   ive had that about 15 years aswell , the
lathe is a great tool so useful , I found a couple off military pots that might do the job on ebay  

  http://www.ebay.co.uk/itm/360539774987?_trksid=p2060353.m1438.l2648&ssPageName=STRK%3AMEBIDX%3AIT


http://www.ebay.co.uk/itm/like/WIRE-WOUND-POTENTIOMETER-1-5K-50-WATT/230543488333?hlpht=true&ops=true&viphx=1&_trksid=p2050601.c100103.m2451&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20150422114059%26meid%3Deb8da90ec38e497683eb7a89e4b7b582%26pid%3D100103%26rk%3D3%26rkt%3D4%26sd%3D360539774987%26clkid%3D644716952512699260&_qi=RTM2065550

I would have to extend the shaft on the first one somehow to work the other one , still looking but these are high amperage and well made , me phil.

Splendid. I couldn't do without my Lathe and Drill etc 

A bit of gentle drilling and gluing should extend the front Pot OK.
The Colvern Pots would be OK for the 'Back' one.
I expect there's plenty of Chinese ones but getting at the back of the Spindle might not be very easy.

Alan

Hi alan , what do you think about these , 25w jobbies


http://www.ebay.ca/itm/CERAMIC-WIRE-WOUN...XlPhwQqvpQ


http://www.ebay.ca/itm/CERAMIC-WIRE-WOUN...XlPhwQqvpQ


well made I would say and close to the desired value of 1400 ohm and 500 ohm

I would think they'd be a vast overkill.
The 500R Pot is dissipating all of 80mW end-to-end and the other one around 25. If the Voltage was only across 10% of the Track, which it never will be a 1 Watt Pot should be adequate.
They would have used WW Pots back in the day because they were more accurate and wear-resistant.
2 Watt Cermets would be fine, and I wouldn't worry about using 47R and 1500R.

Alan