4-1000 question

[W1ATR]

I figured this would go here best as it's a question about the tube in this amplifier. In the pictures, take a look at the base of the tube. Note how the air vents are cut out to (I would assume) allow for greater air volume to pass into the chimney area. It would seem that there would be some negative effects there as far as shielding goes despite the extra cooling. If shielding isn't an issue here, then would this cutting away of material allow for a smaller (read quieter) blower to cool the tube? Any thoughts anyone?

http://cgi.ebay.com/Amateur-Ham-Radio-HF-Linear-Amplifier-Amp-4-1000-Tube_W0QQitemZ200047524644QQihZ010QQcategoryZ48700QQrdZ1QQcmdZViewItem

[K1JJ]

Yes, that would increase air flow through the base..

I'll bet the shielding issue would not be a factor until you hit 20M or even higher. In the 70's I ran 4X1's without grounding the tube base shields - cuz I didn't know any better - but had no instability up to 10M.

For air flow, I think a better way to do it is to drill twelve 1/2" diameter holes in a circle into the chassis - just inside the chimney perimeter.  I've done this on all my 4X1's here and it makes a tremendous difference in air flow. As you said, the blowers runs slower on variacs and less noise - more air w/o turbulance.

There IS a balance between the amount of air flowing through the tube holes (which cools the tube pins) and the amount that bypasses this area and flows through the chassis holes.

Bottom line is to get some air by the pins. In the end, ALL air flows by the tube plates/glass.

T

[The Slab Bacon]

The holes in the bottom of the socket and tube base seem to be the limiting factor. You really need a high pressure (noisy)  blower to push enough air through the base to adequately cool the tube. On my 4x1 rig, I pump just enough air through the base to keep the pins cool, but have a large muffin fan blowing right on the side of the tube to keep the envelope cool, the muffin fan is switched with the ptt where the blower runs constantly. Everyone seems to like the sound as the muffin fan spools up when I hit the button. I have been running ti for 5 or 6 years now without a problem.

                                                         The Slab Bacon

[K1JJ]

The holes in the bottom of the socket and tube base seem to be the limiting factor.
                                                         The Slab Bacon

That's a good point Slab.

I'll bet the bottom holes are the same total air area as the side slots by design. So by increasing the size of the side slots, it's probably a waste. In fact, after looking at the side slots on a 4X1 here, they may have even more total area.

Drilling 1/2" holes around the chassis perimeter is the way to go.

T

[W1ATR]

Okay, lets bait the hook fer yall book-learned types out there.

I have in my hand a brand new, NOS, unmolested, never been in a socket, or on the chicken band, never been jarred, or dropped,(not yet, the days not over), free of floating metal pieces in the envelope, and until now, free of fingerprints, Eimac 4-1000A/8166 date code 6823. It's probably no good considering I've handled it like nitro glycerin and kept it boxed for the last 10 years.

Using an extremely accurate instrument (FatMax 30 foot tape measure) to measure the vent holes in the base, we have:

(5) 1/2" holes around the pins.

(1) 15/16" hole in the center around the tipoff.

and (20) 5/16" X 5/8" slots around the outside.

Max base seal temps: 150deg C

Required airflow: 45cu. feet/meter at 1.2 in/wc

[K1JJ]

Looks like the bottom holes are about equal to the top slots in total area...

3.9 sq in for the bottom vs: 3.4 sq in for the top slots.

So as we guessed, there's little advantage to enlarging the top slots like the guy did on that amp.

I don't have any info for you regarding CFM, etc. Just put a Variac on the blower and run it so the noise is low for quiet background and the air is just warm (not hot) when coming outa the chimney top when keyed down for a few minutes.

T

[The Slab Bacon]

the more air that you can pump through it the happier it will be. However, If noise is not an issue ler it rip. If noise is an issue, like Tom says, adjust the blower for the best compromise of both. 4X1's are very tough tubes and not very demanding unless you are going to run them up to their design maximum ratings. If you are not gonna run it "balls to the wall" it all becomes much less demanding. If you plan to run it with the plate lit up as bright as the filament, better pump as much air as you can through that chimney.

                                          the Slab Bacon

[N0WVA]

I pressurize my 4x with a skwirl cage salvaged from the old family wood stove that finally burnt out. Man we would all crowd that stove on a cold morning.

Dont screw around with noise. Cut a hole in the damn wall, you can always patch and repaint if its drywall. Put that bastard in the other room. Use dryer vent stuff for ductwork.