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Cooling 813ís




 
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KC9LKE
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« on: October 13, 2011, 03:44:31 PM »

Looking for some suggestions to keep a pair of 813ís cool and happy. They are a pair running class C plate modulated, say 375 W carrier. I know the RCA data sheet says nothing about cooling as to imply natural air flow but I would like to move some air across them and help keep the deck cool also.

I have looked at the air requirements for other transmitting tubes, and have done some calcs based on wattage and temp rise.

Iím looking for how others are doing the job within reason 40-60 CFM?

Iím trying to keep the noise down and would rather NOT toss in the largest blower I can find and call it good.

Thanks again
Ted / KC9LKE
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W7TFO
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« Reply #1 on: October 13, 2011, 04:17:21 PM »

I recommend a 4" Rotron 'Whisper' fan, moves around 30 CFM with no noise.

Plenty of waft for that job.

73DG
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KL7OF
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« Reply #2 on: October 13, 2011, 04:47:39 PM »

I run a pair in class C at  more than 375 watts carrier with NO COOLING FANS......Been 10 yrs or so with no problems...Good Luck
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K1ZJH
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« Reply #3 on: October 13, 2011, 09:47:40 PM »

Ohhhhhhhhhhhhhhhhhhhhhhh man, you need these babies on your tubes!!!!  Grin

http://www.ebay.com/itm/PEARL-PCF-250-845-VACUUM-TUBE-COOLER-DAMPERS-/270654216141?pt=Vintage_Electronics_R2&hash=item3f043f97cd
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kb4qaa
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« Reply #4 on: October 14, 2011, 03:15:53 AM »

Thank goodness they have a simple 5 page Quick Start guide to installing and operating a heat sink!
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ka1tdq
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« Reply #5 on: October 14, 2011, 03:20:33 AM »

I pump in 110 CFM into my linear using a pair of 3-500's with a whisper quiet bathroom ventilation fan I picked up at Home Depot.  That's probably overkill in your situation but a smaller unit might be an option.

Jon
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Patrick J. / KD5OEI
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« Reply #6 on: October 14, 2011, 12:15:10 PM »

This 48VDC blower is probably quieter than most and will probably run silently on 28VDC and make enough air to cool anything in it's path..

If you have a 240V blower or fan you may find it will be almost silent on 120V.


* 100_0205.jpg (101.7 KB, 600x626 - viewed 228 times.)
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« Reply #7 on: October 14, 2011, 12:17:16 PM »

I pump in 110 CFM into my linear using a pair of 3-500's with a whisper quiet bathroom ventilation fan I picked up at Home Depot.  That's probably overkill in your situation but a smaller unit might be an option.

Jon
KA1TDQ

Is HD unit that a blower or a fan? I ask because my 3-500's blower is recently vibrating. Probably not good for the 3-500's either as their wind chest is mated to the blower and sits on rubber pads.
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« Reply #8 on: October 14, 2011, 01:19:38 PM »

I run a pair in class C at  more than 375 watts carrier with NO COOLING FANS......Been 10 yrs or so with no problems...

It's not a bad idea to cool any tube. However, 813s do not need a fan.

Years ago, I also ran two 813s with no fan, in GG. I didn't show any mercy to them, and neither did the ham who had that amp before I did. Years of punishment did not measurably decrease their output.

The only reason I stopped using that amp was that the pole pig in the HV supply burnt up at the end a contest.

The only 813 plans I ever saw that called for a fan was a very compact amplifier with sheet metal all around the two tubes.
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73 Mike 
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K5IIA
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« Reply #9 on: October 14, 2011, 02:25:28 PM »

No fan on my modulated 813's either.
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73, Brandon K5iia
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« Reply #10 on: October 14, 2011, 04:36:27 PM »

My 813's have a 4" muffin on the modulators and on the PA. The PA tubes have curved plates that direct the air across the surface. The fins also double as the neutralizing plates.  The modulator tubes are cooled directly by the 4" fan.  The transmitter is enclosed so it's quiet. No fan noise whatsoever.
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Bob
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« Reply #11 on: October 14, 2011, 11:24:37 PM »


I wonder just what a pair of 813s are actually capable of in ICAS service with forced air cooling? We should be able to run elevated plate voltage (if we can keep them neutralized on the higher bands) and increased plate current beyond the old standard specs.

Anybody want to make an educated guess as to how much power we might reasonably expect from a pair running CW class AB1 under those conditions?
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73 Mike 
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ka1tdq
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« Reply #12 on: October 15, 2011, 06:44:16 AM »

The Home Depot blower is a squirrel cage blower with a standard outlet for a dryer vent size hose.  I use PVC pipe to directly force the air into the tube sockets.  I'm not sure what your setup is for air inlet into your amp but you might need to do some plumbing to make everything match up.

Jon
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« Reply #13 on: October 15, 2011, 09:47:59 AM »

A 3" flange and hose would work there. Would need a 90 deg turn but it is doable.
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« Reply #14 on: October 15, 2011, 10:15:48 AM »


I wonder just what a pair of 813s are actually capable of in ICAS service with forced air cooling? We should be able to run elevated plate voltage (if we can keep them neutralized on the higher bands) and increased plate current beyond the old standard specs.

Anybody want to make an educated guess as to how much power we might reasonably expect from a pair running CW class AB1 under those conditions?

In summary, I guess 1254W @ 4KV in AB1, and 1200W in class C, both with a 25% duty cycle.

----
If you consider the plate modulated class C information, then:

pair -
icas table
300W @ 2000V/200mA - carrier

1200W @ 4000V/400mA - 100% modulation
Pd=200W per tube
===============================
ccs table
180W @ 1600V/150mA - carrier

720W @ 3200V/300mA - 100% modulation
Pd=120W per tube

``````````````````

The above is just from the TT-4 book, but the voltage and current are not exagerated, they are the conditions that would exist at the peak of the modulation cycle.

A CBer I knew in the 1980's claimed to make a 1KW carrier with four of them and 4500V as a linear amp, but consider the source and I never saw the amplifier. I imagine he did not engage in rag chews with that.

================

Taking the AB1 data and extrapolating to 4000V, which is allowed in class C as a peak voltage:
--pair @ peak conditions - or if CW, then key down:
490W @ 2500V/290mA - AB1 peak output by the book
Pd=117.5W per tube
G2 input=20.25W per tube

at 4KV -
1254W @ 4000V/464mA - same load impedance 4750 Ohms per tube (Rl=2375 Ohms), and other voltages but extrapolated to 4KV plate
Pd=301W per tube ?
G2 input per tube - I don't know how to estimate it but I think it decreases as Eb increases. rating is 22W. Will it be a factor?

```````````````````

Why run AB1 for CW? 200W dissipation per tube in class C vs 300W in AB1.

Can CW be described as about a 50% duty for 30 seconds, then off for 30 seconds?
That would be an integrated duty cycle of 25%.

If so, then with this 25% duty, 4X the dissipation might be ok, depending on whether the plates melt before the end of each 30 second transmission.


* 813 class c.jpg (1115.76 KB, 1344x1999 - viewed 245 times.)

* 813 class AB1.jpg (1104.21 KB, 1344x1999 - viewed 181 times.)
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KL7OF
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« Reply #15 on: October 15, 2011, 04:25:16 PM »



I wonder just what a pair of 813s are actually capable of in ICAS service with forced air
Class C blown @   2600 volts......  around 900 watts carrier
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« Reply #16 on: October 15, 2011, 05:30:04 PM »

they blew up at 2600V and 900W output?
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« Reply #17 on: October 15, 2011, 05:46:45 PM »

I think blown means forced-air cooled.

Otherwise, they WOULD blow up!

73DG
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KM1H
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« Reply #18 on: October 15, 2011, 06:34:29 PM »

Its always a good idea to provide a bit of air with graphite plate tubes that are being pushed to a bit of color. Not much is needed, even a SB-200 type fan is sufficient and very quiet. One of those 3-500 style finned caps is a good idea, typically $3-5 on Fleabay. The 572B, 811, 813, and 4-1000 are a few that use the same size hole but the Eimac HR-8 would be a bit overkill.

Carl

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KL7OF
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« Reply #19 on: October 16, 2011, 11:50:50 AM »

No .I had a blower on them...I also put about 4 volts of bias as they were getting a little red in the face....

they blew up at 2600V and 900W output?
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KC9LKE
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« Reply #20 on: October 18, 2011, 07:23:08 AM »

Great! lots of good input.
OK so not really needed, Iíll use a small quiet fan to remove some heat.
Many ideas here.

Thanks again
Ted / KC9LKE
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K5IIA
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« Reply #21 on: October 18, 2011, 08:46:36 AM »

No .I had a blower on them...I also put about 4 volts of bias as they were getting a little red in the face....

they blew up at 2600V and 900W output?

i bet someone 5kc from you would have been even more red in the face. thank god for dummy loads. Grin
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Be kind, for everyone you meet is fighting a hard battle.

73, Brandon K5iia
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