Hi Mike.
Tubes with external anodes need plenty of air flow as well as back pressure.
I converted an AL1200 to GS35B and found the original blower insufficient to
cool that tube.
Don´t forget that those tubes anode core temperature must be limited to 200°
and the ceramics/seals to 120°, where Eimac specifies on their tubes 250°
and 200-250° respectively°.
A better way to reduce noise and that?s the way I prefer and do it, is to
use a large overrated blower and reduce its speed by driving it with lower
voltage on it, when I have installed a 240V blower I feed it with 120-150V
via a variac or thyristor.
I do not believe that a smaller blower then that for the 4CX1600 will be
big enough.
We operate 2xGS35b push-pull in 2m contests and are really happy that the
blower is that large
73
Peter
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Mike
Sent: Donnerstag, 12. Januar 2006 21:32
To: amps@contesting.com
Subject: Re: [Amps] GS-35B Vertical Mounting & Input Impedance
Hello Tony,
Thanks for the info., especially about the amount of air needed at sea
level.
The only reference regarding the amount of air needed was for the 88
CFM and never saw any air density reference. Right now I have a
screaming blower on the amp. On a previous amp, a blower was mounted
in the garage. The separation of the wall between the shack and
garage reduced the blower's operating noise. Their was less air than
if the blower was mounted on the back of the amp in the shack but the
air flow was sufficient for the 4CX1600B running 1200 Watts RTTY.
Your information just put the screaming banshee blower back in the
garage and maybe won't have to use the noise reduction headphones.
At 09:41 AM 1/12/2006, Tony King - W4ZT wrote:
>GM3SEK wrote:
><snip>
> > It also allows the tube to be operated in any orientation and even under
> > quite high G forces in airborne equipment. (How they ever lift that lump
> > of copper off the runway is a totally different question.)
>
>There's more to the huge piece of copper than meets the eye. Although
>the small data sheet says the anode dissipation of the GS-35B is 1500
>Watts, the amount of heat that can be removed from the tube depends on
>the air flow AND the air density. If you apply the same physics to the
>GS-35B that you will to the 8877 and say the YC-156 and look at the
>altitude to air flow charts, you'll realize that the 1500 Watt limit for
>the '35B was at an altitude much higher than sea level. Work the curve
>backwards and you get 1500 Watts off the GS-35B anode with something
>like 22 CFM at sea level... or a LOT more with the "rated" air flow of
>about 88 CFM.
>
> >
> > If you're looking at the photographs, note the reinforcing bars to
> > prevent the grid from flexing as it gets hot and expands. Also note the
> > extremely effective grounding of the grid, which makes for high
> > stability - no long, inductive grid leads here!
>
>and that's why we shouldn't CREATE inductance in the way we mount that
tube.
>
><snip>
> > Steve was making a serious point: if there is any loose cathode material
> > sitting on the grid, it can emit electrons if the grid becomes hot.
> > However, a good tube should have no problems with being operated
> > upside-down. The main reason why they don't normally design an amplifier
> > that way is not the tube, but the problem of blowing hot air out into
> > the small gap between the base of the cabinet and the desk.
>
>Amen
> >
> > 73 from
> > Ian GM3SEK
> >
>73, Tony W4ZT
>_______________________________________________
>Amps mailing list
>Amps@contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
73,
Mike, K4GMH
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