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Re: [Amps] more - oil bath GS-35b

To: Steve Wright <>, "" <>
Subject: Re: [Amps] more - oil bath GS-35b
From: "Fuqua, Bill L" <>
Date: Thu, 2 Apr 2015 00:32:45 +0000
List-post: <">>
  So, obviously you will transfer more heat if the anode temperature is 700 
degrees C. but that also would
be the flash point for the oil. 
  If it is a radiation cooled tube the heat transfer is proportional to the 
anodes temperature raised to the 4th power - the surrounding temperature raised 
the 4th power, also proportional to the emissivity of the radiating material.
  The heat capacity of most oils is about half that of water. 
 In this case, power dissipated is equal to the mass flow rate of the fluid 
times the heat capacity of the fluid times the temperature difference.
You as you increase the mass flow the  difference temperature decreases for the 
same power being transferred. Same as a mass flow calorimeter. 
  You guys have fun. I am done.
Bill wa4lav

From: Amps [] on behalf of Steve Wright 
Sent: Wednesday, April 01, 2015 7:54 PM
Subject: Re: [Amps] more - oil bath GS-35b

On 02/04/15 10:05, wrote:
> Once the system has reached equilibrium the radiator is doing all it can with 
>  a given air flow.
No, I do not want the cooling system running at maximum capacity at any
time.  Even at maximum plate dissipation key-down indefinitely, the
system will not continue to rise in temperature to system failure.
That's nay going to happen.  None of the systems will be running within
an inch of their lives, at the very least - not the cooling system.

> Clearly maximizing the temperature difference on the tube's anode is not a 
> good idea.
Please quote sources.

>   Also, I have disassembled several oil cooled aviation transmitters in the 
> past. The all had
> the whole tube in the bath. Both had 4CN15A tubes. They had little heat sinks 
> on the anodes that
> were very small and looked larger versions of the ones you press onto TO5 
> transistors. Also, one had
> all the connections to the base soldered and the other in sockets. Never 
> quite understood that one.
Interesting!  Maybe it is as simple as mounting a basic socket inside
some simple metal tube, but securely bonding the grid to the chassis
will be awkward.

GS-35b can be mounted on its side.

> - In a well optimized system, coolant flow is so fast that there is very 
> little
> temperature difference between the fluid moving from the amplifier to the
> radiator, and the fluid returning. Thanks to this, the whole system (all of 
> the
> tube, all of the radiator, etc) are almost at the same temperature. This 
> allows
> using the smallest possible radiator, among other advantages.
As above, I want plenty of reserve capacity available.  Plenty of
badness will occur if oil temps and pressures begin to rise and the
system has "a problem".  I have the space to run a substantial
oil-to-air cooler, and even stack a few of them if necessary.

Oil flow controls tube temperature.  High tube oil-bath outlet
temperature will swap the pump from half-speed (noise reduction) to full
speed (maximum tube cooling.)

Radiator outlet temperature is the temperature sensing point for the fans.

There is a very small reservoir, for the purpose of managing expansion
of oil due heating.  The reservoir is nothing to do with system
capacity.  The reservoir will be purged and slightly pressurised with an
inert gas.  There will be zero "air" or moisture in the system.

> I followed this thread only superficially, but I think I saw questions about
> immersing the tube and tank circuit and everything in oil. I fear that doing 
> so
> might cause trouble due to large stray capacitances. They are about 3 to 4 
> times
> higher than in air, depending on the kind of oil used.
Yes, this has been established.  A rise in the anode capacitance may
prevent 50MHz operation, but there are many tricks up sleeves yet.

> And it's a mess, of course!
> Manfred
Not at all, it'll be very tidy and clean.  I don't like scruffy, dirty,
and leaky things.  Except myself of course - I am plenty scruffy dirty
and leaky! ;)

Thanks for your help with the transformer too, Manfred!  I hope to be
winding it next week.

> Cooling a tube is a little different in that there are no tubing channels in
> this case. However if this was a tube with a water or oil jacket then
> pressure drop would come into play more so.
A diffuser will be used to direct oil through the (stock) heatsink fins.

The standard heatsink COULD be used - it would be complete overkill.  A
smaller heatsink could be used, which would nearly halve the width of
the whole unit, AND lower the anode capacitance. This is a good idea.


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