[crackle]

I have a bit of a confession to make. I was going round with a capacitor testing to see if I could reduce the 50Hz pulses you can see on my traces and I found the HT smoothing could be improved by almost halving the ripple by the addition of a 47uf cap.
When I checked I had only fitted a 47uf in there originally, I cant remember exactly what happened now as I built that module over a year ago, but I probably intended it to be a temporary fit until I had ordered a 100uf.
As this makes a significant difference to the "look" of the trace on the anode under high loads, what is the maximum size capacitor I could safely fit in this place with out damage to the HT winding and diodes.

I was testing some EL84 valves last night and found that 4 out of the 5 I had all seemed to go into what looked like oscillation at or near the recommended grid bias. (It is very useful to have a scope on the anode whilst testing valves).
Whilst the valve was in this condition the anode current and GM values were jumping up and down by a few mA. By giving the bias a bit more negative volts they tended to stabilise.
I then found that when resting my arm on the patch panel wires that the oscillation stopped.
Would this tend to indicate that the valves doing this are better or worse than the one which did not tend to oscillate. The anode current and GM values were not much different to the one that did not oscillate.

I also tested some EF80's 86's and ECC83's and 81's and some of these came up with very good results. I also identified a couple where anode A was no where near the results for Anode B. (down to .3mA)

With regard to EL34 valves and matching a set of 4 for use in say a 100 watt guitar amp, is it best to match the anode current or the GM value when pairing them up.

Thanks
Mike