Good advices for a newbie (threading tools lathe)

[PJs]

Hi Stefano,

You definitely have some distortion and clipping going on from the pics and vid. Unfortunately I don't know your schematic, nor what you are measuring and where, so it's hard to make any kind of educated guess.

From the video it appears that anything above ~400mv (input? from FG?) and 120-134V (Output?) is were things go wonky. Is this the preamp stages and the pentode goes to the GU50 as a final stage? It also tells me your gain is way more than you may realize which always leads to distortion and clipping.

One thing that comes to mind is the cap between the triode/pentode may not be happy or proper. Specs for the PCL82 say .02 & .025pf. Also note the Peak Anode voltage and currents for the Pentode section...If your gain is too high it will lead to saturation and cause the plate to glow and deteriorate the filaments. Are you running the filaments on AC or DC?

Here is an old cut sheet I found for the PCL82. I assume you built the amps and coupled them around these specs??

A bit in the dark here to help any, but it does come to mind that your sound is pretty loud & clean even at the levels below clipping/distortion....even with the speaker hook up instead of the plasma. Glad you found an xformer. Also Not clear from above about the 9.1Ω Resistor with the speaker...series-//? Seems to just add a resistive load to the inductance of the speaker??

Thoughts... It's not always about power, but efficiency is king in my book. Look at the efficiency of the old ESS Heil AMT 1b's. 1W input gets 90db at 1m!!! Even though they will handle 375 watts, not sure you could stay in the same neighborhood at full power!! Mo-Power will give you cleaner sound at the clean operating parameters of your amp but anything after 90-100db is a waste in my book. Adding your horn to the plasma will give you even more sound pressure.

Thanks for the pics and vid...

~PJ

[rendoman]

Hi
I'm trying a different amplifier with 6sn7 single ended +el84 pentode. I built the circuit in rapid mode, on the table. Unfortunately I havn't 5k output transformer (only 2,5k), nor local shop has 20w 5k resistor (yes, here the quality of the shop is everyday worse!).

few words about circuit, tomorrow I connect the amp to the plasma and see what happen. Compared to old pcl82 amp this new sound better and louder. I think I need to check every stage but at first sight with same clean 0.2v rms imput I got 5 volts good output, it's more than 2x old amp (clean 2,5\3w). If I close an eye I can run circuit up to 9\10v output with some distortion, but still acceptable (5/6w). Leaving out the measures, connecting a speaker to outpu,t sound is really louder, and that's what I need in order to check spl connected to flame.
That maybe only an experiment, soon I'll try El34 tube, maybe in the same good octal relais socket, maybe the final tube I'll choose

Good thing, despite long cables and chaos, no hum, buzz, or strange sound!