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Old 4th Jul 2017, 1:09 pm   #224
Diabolical Artificer
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Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,639
Default Re: 807 (maybe) amplifier build. Now EL34

Thanks David, that clears Thevinin up somewhat. I was actually thinking of Kirchoff when I wrote Thevinin which is another bag of mind bending terms and concepts. I take your point that with application one can get one's head round these Theorem's, I dare I'll do so in the end. I managed to slay the dB dragon this weekend that has been eluding me for some time. I do find this stuff easier to assimilate if I apply it a few times in a practical situation.

Thanks Howard, I'll check that out. I've learned a great deal from The Valve Wizard site, whose content I struggled with at first. After I'd applied it a few times on the bench, most of it sank in.

Back to the amp I swapped over the grids at the weekend which was pointless thinking about it. With a normal LTP with a resistor as the tail you can change which anode has the inverted signal out. With my LTP as set up, with a CCS as the tail and one grid grounded, you can't. The grounded grid triode will always have the non inverted OP, it is this that dictates that PFB will be seen at V1 IP- with the primaries as is.

So, I've done as Howard suggested and swapped the primary over. The amp is now oscillating, which I find quite funny on two counts. Every time I fix one problem another pops up, which results in a wry smile on my part. Secondly I'm trying to fix an oscillator (RF sig gen) that won't oscillate but have an amp that should'nt oscillate, oscillating. Obviously there's some cosmic joker looking over my shoulder laughing at my puny attempt's to bend electrons to my will.

Not to worry, it's good craic and I have an idea why it is mucking me about this time, thanks in part to you all imparting your knowledge.

Andy.
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