Does anyone down saaarf have a valve tester as I have got 4x 300b’s and I’d like to see if I can match two pairs as close as possible?
Just bought an old AVO 2-panel tester, but haven’t ‘tested’ it yet myself (did you see what I did there??)
You are welcome to use it once I’ve confirmed it works - I’ll let you know. I am just north of Bristol btw, in case you are anywhere near here…
@coco has one of course. I assume it’s OK for 300Bs
Graeme @valvebloke is in Didcot, a quick jaunt up the A34 from Southampton. I’d be astounded if he didn’t have a perfectly calibrated one.
Cheers Nick, Bristol may be a bit far from southampton.
Yes, I have one, I’m nr St Albans.
Oh bollocks, that’s where I picked the valves up from yesterday, unfortunately it’s a 2 hour drive from here.
Pete i cannot remember if I have asked before but - Does your tester work for 2A3 valves?
Yes, does most apart from stuff like 211/845.
Thats good I would like to get a 4 old RCA valves checked - One I know is dodgy hopefully the others are all OK?
Out of interest, are they for a push/pull amp or PSE?
I recently bought a tester which allows measurement of Mutual Conductance (a.k.a Transconductance) & various other parameters but it might be argued that static current draw is a more significant consideration certainly in a PP amp. Most valve testers don’t test power valves at the working point they’re likely to be used at and most don’t give a measure of standing current drawn under static conditions either.
When testing 6550’s to go in a push pull stage or indeed EL84’s, I have a jig which allows me to measure the current drawn with a particular HT and bias resistor in circuit. (ie the conditions where they are going to be used)
Ideally you’d run through a large batch of valves & match for both current draw and mutual conductance & then choose your pairs from those. Trickier when the batch size is 4. Hopefully being nice WE ones they’ll be fairly consistent anyhow.
For single ended so only two are needed.
The guy I bought them off didn’t want to split so I bought all four, I suspect they should be fairly closely matched as they were supplied by border patrol in a P20 EXD amp.
Plan is to put the closest match in the amp and either keep or sell the other two.