[Amps] Homebrew is back..

[Roger (sub1)]

On 3/28/2011 3:51 PM, Fuqua, Bill L wrote:
> Good 813s are often hard to find on the market since most used ones have been abused.

Yah, but you can beat the sh..er...snot out of them and they keep on 
ticking. I ran well over 1200 PEP out of a pair in GG (B&W 850A Pi-net) 
and they were as good when I moved on as they were when I started.  You 
could darn near read a newspaper from the anode glow. <:-))  That was in 
62-64 or there abouts.  I started with a $5.00 6C21. Those 813s were 
free.  Those were the days when we modified 1625s and put a bunch in 
parallel GG. There were a LOT of them running on 160.  IIRC we were 
limited to a rater low power on 160 back then so a half dozen 1625s 
lighting up the room was not all that uncommon.  I doubt that 
combination would have done well on 10, but maybe...

>    Other possibilities are 4 parallel 4CX250Bs with 50 ohm load resistor on the untuned input or
> a 200 ohm with a 1:2 turns ratio transformer.

Nearly any old timer had a drawer full of the things back then. Most of 
them were in foil packets, or OD tin cans. They were readily available 
between cheap and free and handy if you had a KWS-1.
http://www.rogerhalstead.com/ham_files/boat1.htm  Wish I had it back. 
That 75A4 and KWS-1 were mint and worked well.  That photo is from the 
mid to late 70's.

>    I really like the 4-1000A in GG but it is a bit bigger and uses much higher plate voltage.
>
> Instead of 813's a good possibility and rather cheap are 4-125As

I have a few of those too, but no two look the same.

>   or 6155. Same plate dissipation
> and work well in gg as well.  On  Ebay usually very cheap new because practically on radios use them
> and even better yet the same sockets will allow an easy upgrade to 4-250A, 4-400A or even 3-500Z tubes.

There's just something about the looks of the 4-400 that I find 
appealing over the 3-500s even if the 3-500s are easier to build up.  I 
used to work on a mass spectrometer that used a pair of them to power a 
Tesla Coil for the arc source.  Not exactly the kind of Tesla Coil you 
wanted to touch with your finger. <:-)) That thing generated an arc that 
would vaporize Silicon, or steel.

73

Roger (K8RI)


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