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:[email protected] > > 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/ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
