ECC83 spec.

[Phil Y]

Hello all,

After the recent failure of a PIO cap in my (WD) Phono, I thought I might as well test the valves. The one in the CF is a 60's Mullard which measures pretty well bang on spec. ie 1.2mA 1.6mA/V both halves.
In the first stage I am using Sovtec LPSs which sound fine to me but they measure off spec. I have 3 of them (1 as a spare) and they measure:

1.7mA 2.7mA/V
1.75mA 2.9mA/V

1.2mA 2.25mA/V
1.0mA 1.9mA/V

0.9mA 2.1mA/V
1.0mA 2.3mA/V

Obviously the first one is the most 'out' but do signal valves normally vary this much and does it matter if they do ?

Thanks in advance, Phil.

(AVO Mk3 Tester)

[Richard]

Hi Phil,

The top one is "very lively" as I say to myself when getting a result like that and I would be a bit wary to match it with similar if it might make a difference. With those 3 for example you could put the top one in the CF of Phono and the other 2 in the amp stages no probs.

You've probably noticed only the better old factories produced stuff which came in close to the book every time. Maybe they scrapped more or just tighter production control.

That said these are all good slopes. When a valve gets tired slope and current goes low and with new ones it's rare to find slope less than spec.

[Phil Y]

Thanks for that Richard.
I Knew the current falls as a valve gets tired and it being higher than spec. is not a problem, (within reason) but I assumed the slope was more to do with the design of the valve and would not very that much with sample/make.
I should do more reading on valve theory !

Regards, Phil.

[Richard]

Hi Phil,

I'm sure your reading is good!

In practice I found both happens, lower current and lower slope. Just checked all my and Gerry B's 300b's. We both use these amps and so have gathered a load of unknown ones which had been changed over the years.

Here's 2 of mine, damn, I was unlucky with the broken one, hit the shelf above the amp in the rack when pulling it from the amp. The glass there is 0.3mm = 11 thou thick Fortunately its brother shows they were well worn anyway,



Unfortunately again though I can't give either to Gerry to make up his set of 4 which are all good except for this one below. He thought it sounded off so swapped them out and this one has 2 filaments gone. If anyone has one/any of these EH Gold Grids in used but running order it would be good to buy them from you, please drop me a pm. Likewise if you need yours testing/matching let me know and we can maybe make up useful sets or known value spares.