avo mk2 valve tester help required

[oceanobsession]

Hi folks , I have purchased three avo mk2 valve testers they all work but the
set zero pots on two off them are worn , its a wirewound rheostat pot , im
having problems understanding the values , there is only three wires r1 and r2
on the wiring diagram , I think its 500 ohm to 1400 ohm , could someone have
a look and advise me please

[oceanobsession]

pictures , im trying to find a replacement but they may clean up or could they be rebuilt , I have just found out that there is two pots one in front of the other , cheers phil

[John Caswell]

Hi Phil,
If that is as you say that the two pots are connected to a single shaft, then the only solution is to try and clean/repair them as you will not find a replacement for them as they are an AVO special;.

John

[oceanobsession]

After looking all day on the internet I fear you may be right , I'm looking for 2
single turn wirewound pots one 500 ohm and the other 1400 ohm but so far no good . someone has replaced both pots with a 470 ohm 10 turn resister and they seem to think that it works fine but you have to turn it fully back before testing , I'm going to have a look at how there wired . cheers phil.

[oceanobsession]

Managed to find some pots that should do the job with a bit off drilling on the lathe

http://www.ebay.co.uk/itm/2520601859...%3AMEBIDX%3AIT


http://www.ebay.co.uk/itm/2617729142...%3AMEBIDX%3AIT

ordered so we shall see if this works , me phil .

[bob orbell]

Why can't you clean and lubricate the original? IPA to clean them and a spray of electolube, as John says, they are made to AVO's requirement,or made by AVO. BOB

[oceanobsession]

Oh sorry forgot to say that the track / wire has completely worn through on 2
of the testers which causes the vu meter needle to go all over the place , you
can get away with only the 500 ohm pot but its a bit course , both 500 ohm and 1400 ohm sweeper are joined , it may be possible to rewire the track 0.23
thickness wire , I may try this first , it would be nice to keep it original , but you wont a one time repair , I don't wont to keep stripping it down and them
Russian military pots look great to me we shall see . me phil.