Re: Tube coils

["Steve Rimsa" <srimsa-at-xxxxxxxxxxx> (by way of Terry Fritz <twftesla-at-xxxxxxxxxx>)]

Steve:

Your best source of TC tubes may well be a ham radio flea market.  Find a
person
who is a ham and ask them.  Transmitting type tubes are preferred.  Most
coilers
use old WWII vintage surplus "800" series triodes and tetrodes (with grids tied
together).  These older tubes are becoming more difficult to obtain and
expensive.
 You must also consider filament power requirements as many ran on 10 or 7.5
volts.  The best commercial sources for TC suitable power tubes are probably
RF parts www.rfparts-dot-com, antique radio supply www.tubesandmore-dot-com. and
surplus
sales of Nebraska.  You can also try EBAY but they don't come cheap!  Svetlana
is also a source of modern construction power triodes which are suitable for
TC service (833, 572B 811A etc).  Just make sure the tube you select has
adequate
voltage rating and power handling capability for the power supply you use. 
The grid coil is used to provide feedback to the oscillator.  Check a copy of
the ARRL handbook for more info.  I hope this helps.

Steve

>Original poster: "Stephen Carpenter" <sjc-at-carpanet-dot-net> 
>
>Ive been thinking about my next coil....
>
>Thought of getting NSTs and this and that...then thought, why not try
>a tube coil. However...I am a bit perplexed. I have found some scematics
>and things, but very little good information (for an added bonus I can't
>check the list archives here - the website is down it seems)
>
>I noticed a couple of things...
>
>It looks like a fairly simple tube based occilator. I havn't had time to 
>really to a close hard look at them (its been a few years since i really
>read any scematics) but they are efinitly more complicated than the
>simple tesla coild tank curcuit.
>
>So I have a couple of questions....
>
>1) What is a "grid coil"? 
>2) Are both the "grid coil" and "primary" coupled with the secondary?
>3) Does anyone know of a good source for vacuume tubes (the MIT flea 
>marker doesn't open again ttill april or I would look there) either
>online or local to boston? (Going to check the store down the street
>that buys old sound equipment...they have tube amps in there often)
>
>Any advice or comments would be appreciated. 
>
>-Steve
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