The schematic says 120V for one of the cathodes of each 6N8P , the pin 6 of one tube and the pin 3 of the other.
On that position I have 100V electrolytics.
100V may be short, I think about replacing them.
I already ordered 100uf 200V Nipon Chemicon 105°, and I will bypass them with 4.7uf 250V CBB Metalized film that I already have.
I read that the more H the choke is , the more the bass response is effective.
My theory on electrolytics and films, is that film and ceramic caps with low ESR corrects the flaws of the electrolytics when added to, there is no point to remove any lytics.
And adding too low value bypass cap contribute to increase inductance.
Yeah, I listen a lot,
I started decoupling electrolytics using 2.2uf film capacitors, and I realized later how much of an improvement the 4.7uf does.
The 0.1uf 1000V Ceramic disc capacitor does another type of improvement.
Both combined can give one of the finest sound in my oppinion.
Cathode poisoning takes quite a long time to happen. Days to weeks. Don't worry if it was off for a hour or two.I don't want to forget the B+ offline and cause cathode poisoning to the tubes.
Your schematic looks odd. Shouldn't the 470 go to the plate? Plus, why not earth ground it. It only makes it safer to run.I am about to add a 4.7uf 630V CBB bypass caps to the big 330uf 450V electrolytic, and something caught my attention.
Please, look at this pic, clic on the link at the right of "Document Joint" to see full size image.
https://www.cjoint.com/c/HGkriBpp0qs
The small capacitor at the right of the big one seems to be tied directly to a black wire of the PT.
This is not on the schematic, this is the only capacitor that is not on the schematic.
View attachment 1231584
Maybe to isolate the center tap of the PT from the ground ?
The chassis is not grounded with the 3rd prong of the power cord, and I hesitate to take it grounded.
From the GEC KT88 data page. "the outside of the bulb should not exceed 250 deg.C." That's 482 deg. F. Why are you so surprised ? These suckers get damn hot !Sorry to be skeptical, but I do not think the glass reach 340°F, that would lead in instant burn to the skin to touch for a 1/10 or even 1/20 fraction of a second
I made a quick search on the internet to see what people say about that and it seems that the simple answer is "that depends".
But, maybe the glass can be a part of the infrared thermometer temperature calculation.
Cathode poisoning takes quite a long time to happen. Days to weeks. Don't worry if it was off for a hour or two.
Your schematic looks odd. Shouldn't the 470 go to the plate? Plus, why not earth ground it. It only makes it safer to run.
From the GEC KT88 data page. "the outside of the bulb should not exceed 250 deg.C." That's 482 deg. F. Why are you so surprised ? These suckers get damn hot !
Well, then grab it when its running and let us know how hot it gets.Yes, but runned at maximum plate dissipation.