Amp cooling questions

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

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KM1H Ham Member QRZ Page

KK4YDR said: ↑

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.
Click to expand...

Now you went and did it! Reality is not permitted here.
All those who believe otherwise will now waste pages on counter theories, whining about what others post, cant read the tube manufacturers spec sheets before passing gas, ad nauseam.

KM1H, Jan 31, 2016

#51

K8PG and KK4YDR like this.
N4EYZ Ham Member QRZ Page

G1TPA said: ↑

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

View attachment 276810 View attachment 276811 View attachment 276812
Click to expand...

David--
I appreciate your reply and all the good information. You are dead on concerning the safety issues with my amp and I am aware of the hazards and plan to make up a sheet metal covering for both sides of the amp. I think it was initially rack mounted which would have addressed those issues. I have a rack but it's not a total enclosure so some side covers are needed and planned. Thanks again!

Wayne
n4eyz

N4EYZ, Feb 1, 2016

#52
WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

If you have a compatible rack cabinet, just install the amp in that. You won't be able to touch anything once it's installed.

You could add a microswitch to kill to HV if the amp is ever slid out of the rack cabinet. Those are available commercially for about twenty bucks, although it wouldn't be difficult to homebrew the same thing.

WB2WIK, Feb 1, 2016

#53

KM1H and N4EYZ like this.
KM1H Ham Member QRZ Page

WB2WIK said: ↑

If you have a compatible rack cabinet, just install the amp in that. You won't be able to touch anything once it's installed.

You could add a microswitch to kill to HV if the amp is ever slid out of the rack cabinet. Those are available commercially for about twenty bucks, although it wouldn't be difficult to homebrew the same thing.
Click to expand...

Desktop rack cabinets can be as low as $5-10 at some hamfests as very few use them any more, look for the ones with side and rear louvers.

KM1H, Feb 2, 2016

#54

N4EYZ likes this.
N4EYZ Ham Member QRZ Page

KM1H said: ↑

Desktop rack cabinets can be as low as $5-10 at some hamfests as very few use them any more, look for the ones with side and rear louvers.
Click to expand...

A very good idea and one I hadn't thought of. We have a local hamfest this Saturday (Richmond, Va Frostfest). I'll add this to my shopping list. Thanks!

N4EYZ, Feb 2, 2016

#55
WA4SIX Ham Member QRZ Page

GE MASTR repeater racks are out there by the hundreds. About 3' high & perfect for your amp.

Ed

WA4SIX, Feb 2, 2016

#56
KK4YDR Ham Member QRZ Page

Dip in plate currents... I always see a dip in plate current but I tune for power regardless of plate current as long as I am putting enough load to lower my plate current and maintain acceptable power out. I consistently get 500 watts out PEP on my 811 amplifier. When I tune just plate dip I find that my power is lower, much lower in most cases.

Since I use a tuning pulser I don't really see dips anyways. I find acceptable power and then make sure my grid isn't peaking past safe limits with a quick carrier check.

KK4YDR, Feb 3, 2016

#57
KJ4YEV Premium Subscriber QRZ Page

KA9JLM said: ↑

You could use one of these to set the fan speed that you want.

Click to expand...

Or use a rheostat, dial it in for the speed you want, then measure it and replace it with a fixed resistor close to what you want.

KJ4YEV, Feb 3, 2016

#58

N4EYZ likes this.
KH2G Ham Member QRZ Page

N4EYZ said: ↑

I have a home brew amp that uses a pair of 572-B's. It came from a SK, I've owned the amp about 2 yrs and have used it very little but plan to use it more very shortly. The builder had a good reputation for quality work and that rep seems to be demonstrated in this amp. My question(s): This amp has a 5" muffin fan that is a bit of a howler........lots of air movement and the resulting fan noise. How much cooling does a 572 require? I think this amp is electrically similar to an SB-200, weren't they pretty quiet operating? Thinking of making some fan changes but don't want to damage the tubes. All I do is light to average rag chewing. No high duty cycle modes.

thanks
Wayne
n4eyz
Click to expand...

http://www.bmlenterprises.com/hacke...14 Handbook/ARRL 2014 Handbook Content/17.pdf This is a web page with a great write up on tubes and really gets into cooling. FWIW Dick KH2G

KH2G, Feb 4, 2016

#59
AC8AC Ham Member QRZ Page

nice little amp . what do the home brew guys do for coating the tank coils ? I just always left mine bare copper

AC8AC, Feb 8, 2016

#60

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