Discussion in 'Amateur Radio Amplifiers' started by KN4CTD, Jan 20, 2019.
So.....the cooling holes aren’t as close together as I thought. There is a space between the cooler and chimney also obviously
This is how the tube and chimney are mounted......everything else is Ameritron. Well, besides the filament transformer and bias zeners.
The IR thermometer is a handy tool. If you determine the tube is running too hot, you want to reduce airflow restriction and/or increase the blower output. The 200C (392F) limit is A LOT hotter than a 1500W space heater would/should get. Measure the temperature.
What's not immediately obvious about the W4ZT "socket" I used is, the total area of the 1/4" holes greatly exceeds the area in the GS-35b's cooler, AND is greater than any number/size of holes you can place under the anode cooler & inside the chimney. It's clear that you have significant restriction thru the chassis. As N8CBX stated, for the least loss in cooling air, the chimney needs to fit CLOSE to the anode cooler. It appears you have leakage between the chimney and anode cooler. A strip of silicone sheet would seal it.
I’ll pick up one of those cheap IR thermometers and check it. A new silicone chimney that hugs the cooler tightly won’t be a problem. Originally, I wanted to use a socket but I never could locate one at an affordable cost. I guess they’re kind of rare from what I’ve seen. I know that Ron, K4POZ, was still selling the W4ZT sockets for the gi-7b tubes at the time but unsure if he makes the 35b sockets. If the anode temperature ends up being too high, I’ll look into using a proper socket. The idea of mounting these to a plate with clips appealed to my wallet, but it does make changing tubes more complicated and time consuming.
Did you build that socket yourself or did you purchase it?
The GS-35B doesn't need a socket because it can be dogged down with metal tabs or a metal ring to the chassis. This looks like what was done here. I suggest to opening up some of the larger holes with a step-drill.....Jan N8CBX
I should’ve made a two part mounting plate with the grid ring/plate mounted underneath in the cathode compartment. Then the hole in the upper plate could’ve been almost the same diameter as the cooler or the inside diameter of a tight fitting chimney. I would think it would be hard to get any more airflow than that.
The gap between the anode and the chimney will definitely lose a lot of air that isn't going through the tube cooling fins.
I've made my own "chimneys" lots of times just using high-temperature silicone rubber purchased in sheets from Alpha (the amplifier company) years ago. I don't know if they still sell that, but they used to use it in their own amps and that gave me the idea. You can cut it with scissors but it's pretty thick; I wrap it completely around the anode cooler and tighten it with a SS hose clamp that pinches the material tightly to the anode.
In the case of the amp shown in the picture, it looks like "one wrap" of that stuff around the anode would probably close the gap to the glass chimney shown and provide a lot more air through the tube.
In the end, you can sound like this guy popular for his fan....