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Does anyone know how to --or have any experience with-- water or oil-cooling the anode? Since forced-air cooling is required, the sound from the blower and the exhaust air would be too noisy for my ears.

They look similar to an 8877, but have removable finned copper anode coolers. GS35B

I have two of those tubes, and I would love to build a legal-limit amplifier using at least one of them.

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    $\begingroup$ A water cooling system does not eliminate the need to dissipate heat via fans or refrigeration unless you are accepting a reduced duty cycle; you have a dispensable source of cool water; or you have a large cool water reservoir (e.g. a pond). Can you be more specific as to what you are trying to achieve and how you envision it working? $\endgroup$ – Glenn W9IQ Dec 16 '18 at 11:26
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    $\begingroup$ having never worked with higher power tubes: gs35b.com/gs35b : Dissipation 1.5 kW. Yowza, that's a lot of power. In fact, that's a small-to-medium stove that you have to keep below 200 °C. Sounds like radiator oil, a steady pumping, a heat exchanger from oil to a larger water cycle, possibly cooling with your neighbor's brook. Or something like that. You could also look into a heat exchanger into one or multiple of gaming/modding PC water cooler systems; I believe they can be designed to carry kWs of power using multiple radiators and even more silent, large diameter fans. $\endgroup$ – Marcus Müller Dec 16 '18 at 13:55
  • $\begingroup$ @GlennW9IQ Question edited. I have no experience with water cooling in this application. $\endgroup$ – Mike Waters Dec 16 '18 at 17:19
  • $\begingroup$ @MarcusMüller Thank you. 1500W output is the legal limit in the USA. Possibly, I might parallel two GS-35Bs to extend their life. However, doing that might come with its own issues (very low plate impedance). Right now, I just need to wrap my head around liquid cooling them. For now I'm using this amplifier. $\endgroup$ – Mike Waters Dec 18 '18 at 5:10
  • $\begingroup$ I got the 1.5 kW from the "dissipation" entry of the "operational limits" of that page, not as the legal output power constraint. $\endgroup$ – Marcus Müller Dec 18 '18 at 11:34
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The GS-35A tube is the liquid cooled version of the same tube. Some hams have fabricated their own version of a liquid cooling jacket to replace the fins on the GS-35B:

enter image description here

The designer of this jacket correctly highlights the challenges of selecting and maintaining the liquid medium since it is exposed to the full anode high voltage. Deionized water will require regular maintenance to maintain its insulating properties. Generally a liquid with lower maintenance requirements is selected with the tradeoff being lower specific heat.

While liquid cooling does reduce the in cabinet blower noise, the liquid medium will require cooling in the form of forced air, mechanical refrigeration, or other means. The result is that the noise can be relocated to an area away from the operator, but not entirely eliminated.

You will still require some forced air cooling in the cabinet in order to keep the seals of the tube intact.

With all of that being said, if noise reduction in the shack is the goal, I would design the amplifier to be blower cooled and remotely controlled. A few servo motors, some bandswitch relays and some remote metering seems much more practical and hassle free.

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    $\begingroup$ That link was also helpful! You should quote the relevant portions of that page into your answer. That way if it disappears, it won't become a dead link. See ham.stackexchange.com/help/how-to-answer, 5th heading item. :-) $\endgroup$ – Mike Waters Dec 16 '18 at 16:47
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    $\begingroup$ A useful link about cooling systems from that page. Also, high-power broadcast stations extend the life of their cooling water by making the non-conductive water pipes or tubing quite long. $\endgroup$ – Mike Waters Dec 16 '18 at 17:54
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One might consider using "Latent heat of vaporization" to transfer many BTU's away. Liquid water turning to vapor (steam) will rise and can carry a large amount of heat to a condenser and flow back to the boiler (tube) via gravity. Keep it a closed loop system. https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1966/05/page18/index.html

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