750V electrolytics

[ppppenguin]

I've been give about 30 8uF 750V electrolytics (TCC brand) to sell for the benefit of the Vintage Wireless Museum. The person who donated them said he tested a couple and they reformed OK. I'll be taking them to Harpenden on Sunday.

I've never seen such high voltage electrolytics before. Any thoughts?

[Terry]

How about a PA amplifier with push-pull 807s?

When I first started work we had an idiot who'd built a PA amp using 807s for his local church hall which had developed a fault. Unfortunately I was at college the day he brought it in to work on it. Apparently, there was a loud crump and he disappeared in a black cloud from which he staggered adorned with liberal amounts of stuffing and tinfoil.

The HT was over 600V.

The main smoothing was rated at 450V max!

He left not long after that ...

[Mike Watterson]

Yes, valve transmitters, even legal Amateur ones can use even more than 1kV.
The FT101ZD family replacement kit uses 2 x 500V in series, though I'd thought HT is only about 600V. About 80W to 100W using 2 x 6146 in Class A in parallel. 1KW PAs can be legal and use very much higher voltages.

Edit:
The FT101ZD allegedly uses a voltage doubler to get about 900V from a 240 - 0 - 240 winding, though I thought the HT was less than that on the 6146 anodes. The PA lives in a perforated metal cage and dies horribly if the grid bias fails. A DAC90a with leaky grid cap can't compare.

[ppppenguin]

As Mike and Terry have said, there's plenty of applications for 750V electrolytics. The point of this thread is that I've nver seen any before and had no idea they were even possible.

They are definitely not paper caps in disguise. It says electrolytic on the can.

[jjl]

Jeffrey

I read somewhere that there is an electrochemical / physical effect that explains the upper limit of 450 to 500V on the maximum working voltage of electrolytic capacitors. Perhaps your capacitors contain 2 capacitors in series in each can.

John

[ppppenguin]

John, I have dim memories of seeing something similar. You could be right about 2 caps in series. Due to leakage currents the voltages across each part would be somewhat self balancing.