[Boatanchors] Diode replacements for 866 tubes, ratings needed ?

[Gary Schafer]

Hi Rick,

Diodes are so cheap that a couple of extras is a non issue. Diodes are not
as forgiving as tubes.

You have to be careful if you put 572,s in there and jack up the voltage.
The plate tune and other caps as well as the band switch may not be able to
handle it.
Also the transformer may not like the much higher peak current that will be
present with a capacitor input filter. Then again it may be just fine but
you never really know with old transformers designed for choke input
supplies. 

A 3-500 would have some of the same issues with component voltage ratings
too. And at only around 2100-2200 volts, that is a little low for a 3-500.
if you used a bridge on the transformer you would end up with twice that and
for sure the RF components in the amp would not be happy. You would probably
end up replacing most parts in the amp to make it work.

That's some of the problems with these old rigs.

73
Gary  K4FMX

> -----Original Message-----
> From: Boatanchors [mailto:boatanchors-bounces at mailman.qth.net] On Behalf
> Of Rick Poole WA1RKT
> Sent: Wednesday, November 12, 2014 8:55 PM
> To: boatanchors at mailman.qth.net
> Subject: Re: [Boatanchors] Diode replacements for 866 tubes, ratings
> needed ?
> 
> 
> From: "Gary Schafer" <garyschafer at largeriver.net>
> Sent: Tuesday, November 11, 2014 3:07:56 PM
> >>
> >> I would probably use around 12 diodes in each string.
> 
> Good evening, Gary.
> 
> The 866A is rated at 10 KV PIV, and so is the 866A solid state
> replacement (can't think of the 1N number right now).  Seems like any
> more than ten 1KV PIV diodes in each leg is a waste.
> 
> >> If you eliminate the choke that would solve those
> >> high spike problems but then the transformer would
> >> be putting out too much voltage for the 811A's.
> 
> I was considering doing that, and converting the amp to use only 572Bs
> at more nearly their rated power than is normally done in 811A amps in
> which people use 572Bs.  If I could get some decent 572Bs I might have
> done that, but those don't seem to be on the horizon.  At least I can
> still get some NOS Cetron 811A tubes, for now at least.
> 
> There's plenty of room in there to just convert the thing to use a
> single 3-500, and I haven't yet completely rejected that notion.  I need
> another 811A/572B amp like I need a hole in the head.
> 
> I'd like to find a decent-condition Chippewa...
> 
> Rick WA1RKT
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