[Elecraft] 100 Watts or 500 Watts

[Vic K2VCO]

I have worked as a BC engineer and I'm very, very careful. In addition to following work 
procedures like the use of a 'shorting stick', there are various design principles 
important for safety. There should never be a way for someone to come into contact with 
HV, no matter what component or combination thereof fails (within reason, of course).

Just for example: you often see a 'safety' RF choke across the output of a pi-network. 
Supposedly this will cause a fuse to blow if the plate blocking capacitor breaks down and 
puts HV on the antenna. But most such chokes are too puny -- they will blow before the 
fuse! Interconnections between remote power supplies and RF decks are another risky area. 
I prefer to put it all in one box, or at least an enclosed rack.

I only work on such projects when I am feeling 1) alert and 2) patient. 'Patient' is 
really important. If you are operating in the 'every time I try to fix something I break 
something else' mode, then STOP. I like to spend a lot of time thinking about what I'm 
about to do before doing it.

This is getting off-topic for the reflector, so this will be my last post on the subject!

On 12/22/2010 11:36 AM, Ron D'Eau Claire wrote:
> Good point George. The question was specifically about the 813 and it's a
> "nostalgia bottle" for many of us. It was popular after WWII because you
> could get them for as little as 50 cents each in the USA. Even in the 60's
> they were still available 'surplus' for a few dollars. Typically the socket
> cost far more than the tube.
>
> The biggest cost in a tube amp is in the power supply (including high
> voltage hardware) and in the input/output network components that can handle
> the voltages involved.
>
> You can avoid those costs by buying a used amp, even if it's not functional
> (but hopefully has a good power transformer).
>
> Other than learning to work around thousands of volts (only one mistake
> allowed per lifetime) tube amps are extremely simple things compared to most
> high power solid state amps. And tubes tend to be much more tolerant of
> abuse than solid state.
>
> But that comment about only one mistake allowed per lifetime around the
> typical tube amp power supply was serious. I'm always very cautious about
> encouraging today's typical ham to mess around with even moderate or low
> power tube gear if he/she has "grown up" around solid state running from a
> few tens of volts at the most. One needs a wholly different set of
> procedures, concerns and attitudes to work around even a few hundred volts
> safely.
>
> Over the years we've lost a number of wonderful, bright, prolific designers
> and builders in the Ham community to one momentary mis-step around a high
> voltage power supply.
>
> Ron AC7AC
>
>
> -----Original Message-----
>
> Just  some simple questions.  Why use an 813 for an amp.   125 watt plate
> dissipation,  50 watts of heater power, and a large physical size.  The
> "modern"
> 572b uses 25 watts for heater power has 225 watts dissipation and is cheap.
> I
> have two SB200s they put out 800 watts PEP and they can be bought real
> inexpensive. Every couple of years I stick new tubes in them for kicks and
> use
> the pulls as spares or "presents".
>
> I love building, but I am practical too.  But have fun guys and please be
> careful.
>
> George, W6GF
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

-- 
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/