Amp cooling questions

Discussion in 'Amateur Radio Amplifiers' started by N4EYZ, Jan 18, 2016.

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  1. N4EYZ

    N4EYZ Ham Member QRZ Page

    The 200 watts was measured out of the amp, (Bird 43) I then checked just the rig itself and measured 25-30 out. I said that just after the 200 watt measurement. Probably should have phrased it better. But I hadn't thought about the driver. I'll check that as well. I have an old tube tester, time to use it. I realize I can't do much in that regard with the finals but I also have an old HW-101 that uses the same three tubes. A parts source in a pinch!
    On the 520se, I'm seeing 25 or so on 10, 50 or so on 15 and about 100 on 20 thru 80. My first rig in 1978 was the HW-101, spent much time on learning how rigs operate and alignment procedures. Time to refresh my memory and abilities and play with this 520.
  2. WA4SIX

    WA4SIX Ham Member QRZ Page

    Have you tried tuning the radio up on a dummy load with a meter inline?

  3. CE4SFT

    CE4SFT Ham Member QRZ Page

  4. N4EYZ

    N4EYZ Ham Member QRZ Page

    Yes, straight into a Bird 43 and load. It's low on 15 and 10. I'll look into testing the driver and alignment tomorrow. I had also noted that maximum power out did not correspond with the lowest dip in the plate current so that was another indication that it may be time for attention. I am worn out from shoveling snow today. We had about 24" fall between Friday and yesterday. Too tired to play with it this evening.
    WA4SIX likes this.
  5. N4EYZ

    N4EYZ Ham Member QRZ Page


    What are you thanking me for?
  6. VE3TMT

    VE3TMT XML Subscriber QRZ Page

    I mounted a 120mm x 120mm (~5" x 5" for you guys south of the 42nd parallel) 12V fan above the 572B's on my 2100B. I slowed it down a little with a 33 ohm 2W resistor. The noise in not objectionable and it goes a long way to keep the tubes cool, even after many long winded QSO's.
    N4EYZ likes this.
  7. N4EYZ

    N4EYZ Ham Member QRZ Page

    I will end up using a resistor(s) to slow mine down a bit. I spend far more time listening then I ever do on the air so from all I read here I feel I'm safe. Heading to a local Va hamfest next weekend so some appropriate resistors are on the shopping list.

    FWIW--I replaced my driver tube (thank you WB2WIK) and all is good again. Thanks again for all the advice and direction!

  8. G1TPA

    G1TPA Ham Member QRZ Page

    The only thing people should post is either clarifying questions about the kit or a concise answer, yet as usual it has descended into a slagging match because one person disagrees with another.

    Why waste everyone's time with this backbiting? I'm here because I was interested in that answer as my own 4 tube based 572b amp is also a bit on the loud side, others will be here as they have some experience they wish to impart that may help Wayne, you two children though are doing neither but making yourselves look silly and nasty to boot, I wonder if you would both act this way in public, backbiting is not a good look, it's actually a bad advert for the hobby.

    Wayne, nice looking amp, it does not look at all 'homebrew' it will be a nice piece of kit to help you when the bands drop off. Someone else mentioned about safety and I think it's worth reiterating, I'm sure you are already aware, but for those reading this that are not, valve kit generally uses highly dangerous voltages, if you are careless it's not like mains which will just give you a jolt, it's lethal, so even if you are the only one with access to it perhaps consider adding some outer casing (if it has none) accidents always seem to find a way of happening, about 35 years ago I got cocky with a string of large paper capacitors and gave myself a jolt, I still have the 10mm or so hole that it burned into my leg, the spasm threw me backwards out of the room which amused my friends, I know most would not have lived to tell the tale and I've not played with KV voltages since!

    As for the airflow requirements, that will vary not just from valve to valve but also manufacturer to manufacturer, a handy reckoner is that nothing is 100% efficient, if we say yours runs at 50% efficiency the amp will then put out as much in heat as it does in RF and that ignores the 4Amps each 572b filament takes to run (on my amp the 16amps the filaments use raise the case temp by 5C over ambient before I even key up) I think some else mentioned the analogy of a hair dryer which I think was a great way to describe the issue.

    To reduce the noise down on my amp I have fitted a cardboard vent to pipe the airflow down and away from the wall which I found simply amplified (excuse the pun) the fan noise, it's much quieter now just from doing that and I don't think it has decreased the airflow. when I tested the amp on RTTY (into my load with a random text file to keep it going for 10 mins) it only showed a temperature rise of 14.5C above ambient (the Termaline load went up by more 16.3C during the same test) which probably means I could reduce the cooling fan RPM a bit, I will do some tests during the summer when the ambient temperature is higher and see how much or little it takes to keep it around the same rise for the same type of input.

    I have seen the posts that say fans are not required for the 572b valves, that they can handle x amount of heat and that convection is all that is required, are they right? who knows, I do know that none of these people has provided any test data to show how their personal amps performed with and without cooling so I personally would question such claims (though of course those that advocate it can remove their fans and enjoy a much quieter life) I also doubt that every amp manufacturer can be wrong on this too. I don't view more noise and a higher ticket price (from fitting redundant components) as a selling point when I purchase shack equipment (normally the opposite) my manufacturer has even fitted a rather expensive Papst 4850N (10W 230V) fan, clearly an idiotic waste of money when nothing or the cheapest would do! but all joking aside I do know that for me 4x 572b valves (even the Chinese ones) is far too much money to risk on not trying to dissipate some of that 50% or so of wasted energy that was turned into heat so I will stick to just tying to reduce the noise rather than removing the airflow.

    As I can handle the 500 or so watts of heat coming out the back of my amp into the shack I'm sure I can handle the flaming that will no doubt come from those on here who value opinion over fact, is now the right time to drop my ace card and quote my qualifications?

    David G1TPA

    Pictures show the card vent cover (silver foil coated) how it attaches to the back of the amp and the view of the valve heaters through the fan

    1.jpg 2.jpg 3.jpg
    N4EYZ likes this.
  9. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The Heathkit 'Compact Kilowatt' amp, from the engineers at Heath, used a pair of 572Bs with no fan cooling at all. I posted a photo of its interior earlier.

    That was fine and the tubes didn't overheat; the difference is that was an 'RF deck' amp only, with an outboard power supply. Amps that have the power supply and tubes in the same enclosure should have some fan cooling, mostly for the power supply. Note the cooling system in the Ameritron amps using such tubes draw cool air in to the power supply, pull it past the power supply components, and then exhaust it across the tubes. This is really the right way to do it, as it provides the coolest air to the power supply filter capacitors; the air is warmed a bit by the PSU components and then the warmed air is exhausted past the tubes.

    The Heath Warrior and Gonset GSB-201 used four tubes each and used a small phono motor fan with small blades at low speed for cooling. They were very quiet because the fan hardly did anything; it was mostly there to keep the power supply components cool.

    Remember with glass tubes the thermal resistance from anode to surrounding air is darned close to infinity; you could use a jet engine to blow so much air past the tubes they'd blow out of their sockets and that wouldn't reduce the anode temperatures. The moving air is to cool the glass seals, not the tube elements.
  10. KK4YDR

    KK4YDR Ham Member QRZ Page

    Adding a cooling fan to cool a vacuum tube is a moot point. The stock cooling fan in most systems should be sufficient. Even the strongest wind hitting the tube is not going to cool the components inside since they are in a vacuum.
    Last edited: Jan 31, 2016

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