JJ EL34 Burn in Results

Following our blog on testing the 6L6 and the El84, we have now done a burn test on a JJ El34.  The test got delayed as our Avo Mk2 tester developed a fault with a worn out “backing off”  pot and I had to come up with a good repair not having the benefit of any replacement part. I guess this part has not been made since the days of Harold Wilson being Prime Minister in the UK !
The good news is that my repair has resulted in being to set and measure the mutual conductance of valves better than the original. A result !
Having seen the results of the EL84 and the 6L6, we expect that when a valve is running parameters could shift over the first 8 hours or so and any shift would be less and less over time until the valve was nearing the end of its useful life.
A JJ EL34 was set up with 250 volts on the anode and screen and 16 volts of bias. The valve was checked and the results noted every 2 hours.  Over a period of 8 hours the valve sat rock steady with 50mA cathode current and mutual conductance of 9.2.  It is clear that this JJ valve is extremely stable from new.
I therefore can see no need  for burn in on JJ EL34’s when matching pairs and quads