Jon Ogden wrote:
>Hi all,
>
>I am in the process of putting my 4-1000 amp back together. YES!
>
>Anyhow, the original builder used silicone between the part of the
>chassis underneath the blower and the bottom panel. I'll call the area
>underneath the blower the RF chamber since that is where the tube and
>most of the RF circuitry is. Anyhow, he used the silicone to attempt to
>make an air tight a chamber as possible. The problem is it made a mess
>if you had to take the bottom cover off.
>
>So is sealing off the RF chamber really necessary? I have replaced the
>original blower with a 3300 RPM blower with a 3.5" squirrel cage. It
>really moves a LOT of air.
>
>Should I seal it up, or just rely on the mechanical pressure I get from
>the screws that hold on the bottom cover?
Screws are fine, unless the blower performance is marginal. Using
silicone is liable to spoil the RF shielding because it means that the
screws themselves are the only contact between the box and the cover.
If you connect a water-gauge manometer to measure the pressure in the
grid/cathode box (assuming that's where you're blowing into) and then
slacken off the screws, you'll find very little decrease in pressure
until almost the last moment.
BTW, if you want to make measurements of heater voltage right at the
pins, you can stretch Saran wrap over the grid/cathode box instead of
the cover, and poke meter probes through it. It balloons up something
alarming, but it keeps the air inside, and the little holes make no
difference.
A related follow-up question:
Who are the makers of good, low-cost, amateur-size blowers in the USA,
please? The only firm I've heard of are Dayton, but do the amplifier
manufacturers have other sources?
Any contact addresses, or better still, web sites? (Routine web searches
only produce info on blowers for HVAC or K5PRO-size tubes, or more info
than anybody ever wanted to know about Dayton, Ohio :-)
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.demon.co.uk/g3sek
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