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Data sheet discrepancies - airflow - 3CX3000




 
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Author Topic: Data sheet discrepancies - airflow - 3CX3000  (Read 1162 times)
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Patrick J. / KD5OEI
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« on: July 12, 2017, 09:45:26 PM »

What is to be made of this? Newer tubes have different radiators?

Eimac says 125CFM @ 1.4" water
Svetlana says 67CFM @ 1.2" water.

What might be the reason for this different spec?


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wa1knx
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« Reply #1 on: July 13, 2017, 04:30:05 AM »

    Theres a newer copy then 1975, of the 3cx3000 pdf (7/1/79), that has a spec that matches the Svetlana
spec 67cfm, 1.2" for 4kw plate dissipation. its at g8wrb.org.  I've eye'd that tube for years, nice choice!

73 Dean
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« Reply #2 on: July 13, 2017, 04:38:01 AM »

this reminds me of the old tempilac days at Eimac ... the concern is of course seal temperatures .... the technology needs to update to the cheap infra-red hand temp scanners now available ...
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« Reply #3 on: July 13, 2017, 09:40:20 AM »

Reminds me of my younger days.........
I was building a quad of 4CX250Bs, and the question of air flow came up.
Someone said , "Call Bill Orr at Eimac".
So I did. 

In a grandfatherly voice of profound knowledge, and a little tongue-in-cheek,
he answered, "Well, son, you should increase the air until one of the golfballs pops out of it's sockets, and then back  off just a bit."

Then he laughed, and told me to stack three rotron 100cfm whisper fans in series on the back of my amp.  He said, don't try that with just two 250bs.... too restrictive and the fans will freewheel.   Works well with the older 150s, but the newer 250s are too restrictive.

Don W4DNR
 


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KD6VXI
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« Reply #4 on: July 13, 2017, 07:16:13 PM »

Some data sheets show the value of blower for 3000 watts of dissipation.

Some shown it for 4000 watts of dissipation.

4cx5000 is another anomaly like that.

A friend has checked the 3cx3000 and the 6000 using temp crayons.

A different blower and non Eimac chimney can increase the 3k to almost 6kw of Pdiss and the yc243/3cx6k to 9kw Pdiss.

As verified with temp crayons.  The grid structures are heavy duty enough to handle the additional drive needed.

--Shane
KD6VXI
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« Reply #5 on: July 14, 2017, 10:49:59 PM »

this reminds me of the old tempilac days at Eimac ... the concern is of course seal temperatures .... the technology needs to update to the cheap infra-red hand temp scanners now available ...

It would be really attractive to incorporate one of those instruments into a piece of equipment.

I run into a sort of 'drift' discrepancy when taking the temp of something hot for a long time, like a minute or more. The temperature of something known to be stable and hot seems to drift.

Try this with something that's in the general temp range once it's reached equilibrium, like a small stove element on a large variac, a 6L6, or some idling tube in a linear amp, etc., and see if it drifts.  Mine did.

Is it  my  $50 IR thermometer being too cheap?
Is the IR lens focusing the unseen radiation on the sensor and warming it, creating the error?
Not sure what is used as a reference or calibration scheme in them.

I did a google advanced search and found data sheets both air ratings. Newer editions are the easier ones to comply with but only with a measurement could we be sure of the temperature.
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« Reply #6 on: July 15, 2017, 09:24:20 PM »

this reminds me of the old tempilac days at Eimac ... the concern is of course seal temperatures .... the technology needs to update to the cheap infra-red hand temp scanners now available ...

It would be really attractive to incorporate one of those instruments into a piece of equipment.

I run into a sort of 'drift' discrepancy when taking the temp of something hot for a long time, like a minute or more. The temperature of something known to be stable and hot seems to drift.

Try this with something that's in the general temp range once it's reached equilibrium, like a small stove element on a large variac, a 6L6, or some idling tube in a linear amp, etc., and see if it drifts.  Mine did.

Is it  my  $50 IR thermometer being too cheap?
Is the IR lens focusing the unseen radiation on the sensor and warming it, creating the error?
Not sure what is used as a reference or calibration scheme in them.

I did a google advanced search and found data sheets both air ratings. Newer editions are the easier ones to comply with but only with a measurement could we be sure of the temperature.

I'm not sure about the radiation but I would take a look at an emissivity table to get an idea of how accurate the IR temp gun will be on the surface you're shooting. Some higher end guns have an adjustable setting for this. Maybe there's something in the manual about it for your gun. It's not always possible in cases like this but painting the object flat black helps accuracy when making comparisons.
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« Reply #7 on: July 18, 2017, 05:08:49 PM »

Shane

 Uses the same grid structure as the 3cx6000A7. John C. at Econco informed me of that.

John N8QPC



As verified with temp crayons.  The grid structures are heavy duty enough to handle the additional drive needed.

--Shane
KD6VXI
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John K5PRO
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« Reply #8 on: July 24, 2017, 07:49:20 PM »

When I design thermionic amplifiers (usually at work), I start with worst case airflow requirements, derate for elevation (7000 feet above sea here) and also derate for blower filter, ducts, and EMI screens. Then, get the closest blower to these requirements, get it running, and measure the pressure across the tube radiators, across each obstruction, before running filament power. Having a blower or fan curve for 50 or 60 Hz performance is very helpful. Knowing the total back pressure that the blower is operating into, in inches of water, can then see the volume of air in CFM. Once the baseline is established, then I apply Tempilaq (now available from Omega as well) to at least 4 locations around the tube, on the filament stem, on the ceramic (tiny spots) near the screen grid contact, near the anode contact, and on the anode radiator itself. These days I only use water cooled tubes so the last stuff is omitted. Run for 12 hours under RF power, observe, and then if the paint is same, go to full power. This is all documented and ensures that the tubes should have a long life, and also protects us for any warranty claims. Any IR spot temperature device should be checked/calibrated against some contact method such as paint or a non-metallic probe like a Luxtron (now Accutemp) fiber optic thermometer.

I have recently gotten one of the MicroEpsilon IR spot thermometers and it is really nice. It has built in microcontroller so that you can set a limit where a contact opens and the display changes color. Once emissivity is known, the results can be absolute temperatures. I don't know about glass tubes, but for metal radiators and ceramic insulators, it should be possible. The IR unit needs to be shielded, so I have it in a waveguide beyond cutoff, a small tube that is about 5 times longer than the diameter. This is a piece of copper pipe. Right now it is looking into a large coaxial line at an insulator.

* dax--thermoMETER-CTfast--en-us.pdf (1063.28 KB - downloaded 18 times.)
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DMOD
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« Reply #9 on: July 25, 2017, 11:27:16 PM »

You know you have enough airflow when the tube elevates 0.1" above the chassis. Grin

Phil - AC0OB
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John K5PRO
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« Reply #10 on: July 26, 2017, 03:08:08 PM »

25 years ago I was testing with a brand new 4CX3500A at Broadcast Electronics, inc. in a new cavity amplifier at 100 MHz. Eimac had sent us, Continental and Harris each this new tube, to convince us to quit overdesigning with the 4CX5000A (a very old design) for 3 KW rig. During a cleaning, a tech left a rag under the tube socket in the blower outlet. When we turned on and ran (didn't have air switches yet), I watched the plate tuning drift off of normal, then smelled hot metal. That tube, while it survived, baked the silver plating to oxidation, and warped internally so it would never tune the same.
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« Reply #11 on: July 26, 2017, 05:33:22 PM »

In 2004, in an amplifier that I designed, water got shut off to the tubes and the flowmeter interlock didn't kill filament power. Don't ask how, its complicated.These are TH555 shortwave tetrodes, pair running about 100 kW output at ~2800 KHz, pulsed class A, for a proton accumulator ring at particle factory. Both tubes were destroyed. Argh...


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« Reply #12 on: July 27, 2017, 03:20:03 PM »

You commercial guys are scaring me  Grin. Wonder where the curves cross for loss of or payback of lost ad revenue vs. tube and repair / cavity replacement? 

No wait;  no curve "crossing."  You have to add all losses together along with the program director's and manager's ire, loss of job and bad references.  A life event fer sure.

Or maybe I should have stated where does the curve cross for all your losses vs. almost getting fired?  Grin. Probably pretty low for second offense.

"Say I got this great engineer looking for an nice mid-market job. You'll love him! "
Um hmm.
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