Discussion in 'Amateur Radio Amplifiers' started by W8JX, May 15, 2015.
That would be way cool
Until it is a tube you paid $85.00 for......
So you think the grid wire goes open circuit inside the valve?
(the 572Bs do tend to get very hot in these small Linears, somtimes the anodes glow really bright red, even with the extra fans I use)
Is this sudden lack of conduction something other people have experienced with 572Bs too?
That is true. You should only use your old tubes.
The cost is nothing compared to the cost of the Destructive test we did at NASA. That you paid for.
Thank You for letting me play.
Yes if there is a defective weld.
Seen it happen in a 5894, except it was one of the anodes. (a 5894 has two anodes)
I don't know if anybody has experienced it with 572s it happens in other tubes and is dependent on the construction technique used.
Keep in mind what the person I quoted said.
it was a general statement about tubes, no tube type was specified, even though the thread was about 572s...
Anybody who knows vacuum tube theory knows what I am saying is factual.
If a grid floats in ANY vacuum tube that has more than two elements the cathode to anode current flow will be cut off within a very short time after anode voltage is applied.
How much power are you running from your linears when the 572B anodes glow bright red?
In my Heath SB-200, when run at the 600-watt output level, which is the normal output for a pair of 572B tubes, the anodes of the Cetron 572B tubes don't show any "red" that I can detect. I don't know if that is true of the various Chinese 572B tubes that have been previously available. My Cetron tubes are original, made in U.S.A., as are my NOS spare pair of 572B tubes. I am pretty sure that, with the spare tubes, my SB-200 is going to outlive me! Of course, the 8874 tubes in my Henry/Tempo 2001 don't show any color. If those external anode tubes start showing a red color, I most certainly need to "head for the hills"!
Id call that air leaks in order to differentiate between the anode outgassing which is a normal process when not regularly regettered.
Neither was Eimac in 1988 or so when they moved the glass tube manufacturing to Salt Lake City, many went to air in a year until the new facility learned how to seal them consistently.
Where did you ever get that idea?
Its been done and with low profile electrolytics a 10V 10A open frame transformer fits well. With good tubes 600-700ma is possible and 470-680 uF caps keep the HV reasonable on SSB peaks. Ive been tempted to try 814's and see how much over their spec they can be pushed
AFIK they always have or at least soon after introduction as the T-160L. For most brands it was a two step process, the traditional flash getter and then the red graphite anode during burn in. Svetlana used the anode as the only getter. The two Chinese companies who stopped building 572B's were excellent for processing and Shuguang was hit and miss. Once I stopped buying from RFP and went direct to China quality was excellent. I suspect RFP kept driving prices down and quality suffered. If a customer demanded RFP or Taylor branded in a repair the odds were that 1-2 out of 4 arced at turn on or soon after, even at 1700V.
About 600W peak output (or 600W CW) - that's all you can get from the Yaesu Linears, I guess due to the power supply.
But they ALWAYS glow red after a long over - that's with the original Cetron valves. (perhaps an exaggeration to say bright red - that's probably only when you're REALLY overdoing it!)
And I don't just mean MY Linear, they all did it - back in those days I was Service Manager for the main UK Yaesu importer.
I can't see why the anodes wouldn't get that hot in an SB200 too, if you're running the same power . . . the reason is the small dissipation of the valves themselves.
The SB-200 will show a bit of red on the left tube even in TX with no drive if left on awhile; clip out the 5pf ALC cap and it goes away.
Graphite anodes take awhile to come to color and certainly not on just SSB. A steady carrier or some AM use and they will blush at you. This holds with all 572B's irregardless of country of origin.
It boils down to simple basics. At 1000W input, 600W out, and 125-160W PD per tube, some moderate color is to be expected and normal.
But that's not the only consideration.....
There are lots of old pair-of-572B amps out there for relatively-low prices. For a single-3-500Z amp I think the SB-1000 is the oldest.
If you're a homebrewer, there are lots of relatively-easy-to-buiild 572B designs. Where those designs shine is in the overall-cost-to-duplicate - lower B+, 6.3 volt filament voltage, common socket and plate cap, horizontal mounting OK, etc.
Back in the bad old days the SB-200 and similar were popular with CW ops because they would run the old 1000 watt legal limit on CW. Why have more amp than you need?