[Amps] GS-35B Vertical Mounting & Input Impedance

[Tony King - W4ZT]

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