3cx1500a7 max exhaust air temp?

[FlatlandBusa]

What is the maximum safe exhaust air temperature I should see off of a 3cx1500a7 in a AL-1500? This amp has tube stack mod to keep the band switch and tank circuit area cooler, plus the fan is on the high speed setting. Also running @ 4000 volts on the plate with the upgraded 10 capacitor filter board. Currently seeing up to 110°C after very long key downs on SSB. The tube specs say a max of 250°C at the seals.

 

[nomadradio]

Gotta wonder how much the temperature of the tube's exhaust air will drop between the tube and the temp sensor.

I'd figure 110 C air sounds like a safe zone. But the surfaces of the tube are bound to be hotter than the air passing over them. Just don't know how much.

Any idea what volume of air the tube is getting?

73

 

[FlatlandBusa]

The temp sensor is directly in the air stream off the tube so the temperature likely isn't dropping much at all.

I don't know the volume of air, I'll measure the velocity tonight and calculate the CFM. It's the stock AL-1500 blower on high speed.

 

[nomadradio]

The max temp for that tube is about twice what you're seeing. Sounds to me as if you're in a reasonable safe zone.

73

 

[FlatlandBusa]

The tube duct diameter is slightly larger than 3.25, so I'll use that dimension to be conservative. The velocity measured with my wind wizard 1/2 inch away from the tube duct outlet is 3.6 MPH, 6 inches away from the duct outlet velocity is 2.8MPH so again I'll use the conservative number. Using 3.25" & 2.8MPH in an online calculator, I came up with 56.78CFM, which should be plenty per the tube spec sheet. I'm running this amp around 1.5KW PEP and it has been tested into a dummy load @ 2.9KW,.

Some one smarter than me will need to check these numbers...

 

[nomadradio]

That's pretty much the way I'm used to doing it.

73

 

[FlatlandBusa]

Thank you nomad for answering my questions!