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Old 24th Dec 2015, 2:20 am   #130
bikerhifinut
Octode
 
Join Date: Nov 2013
Location: Penrith, Cumbria, UK
Posts: 1,993
Default Re: EL34 power amp project

well it urns out that the EL34 itself was a duffer. annoying as its only had a hundred hours or so use. Sovtek EL34G one of a matched pair.
So its a new pair of valves for that amp and probably a quad to do both.
Those old Sovteks usually are ok so maybe i was just unlucky.
I'll probably give the Brimar lads a call after the hols.
And here's another thing, i measured my mains again tonight as the voltages on the heaters and off the transformer were crazy, 7+ V on the heaters and 463V for the 410V secondary. Turns out our mains rockets to 253V after about 11pm. No wonder we keep blowing light bulbs regularly. I think the grid wallahs want a rocket up em.
in view of that I shall revert to the 470 ohm anode resistors rather than the 330 Ohm and live with a reduced HT during the day. I was putting 460V on the anodes.
I think this goes a long way to explain the noisy transformers and why i have had trouble in the past with overvoltage on projects.
the transformers are still a bit noisy but I will have to learn to live with it.

A.
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