How should I punch 3" by 3" holes in the original ST-70 cage for additional ventilation?

I recently purchased two American-made "whisper fans" which I have placed on the top of my ST-120 cage (the vintage brown ST-70 one) but I suspect that the efficiency of heat removal could be greatly increased by cutting some holes in the top. I lay the cage on the chassis rather than screwing it down, so there is a proper chimney effect going on - plenty of open space at the bottom but the top could use, I suspect, some additional openness.
So how should I cut some holes in the very solid top with common household tools?
Aesthetics are not an issue. I'm a single male slob who just don't care what it looks like.

Is a 4" hole saw a common household tool? Harbor Freight item #68111.

What makes you think your amplifier needs active cooling?

Good question.
I have recently acquired a quad of ancient British-made KT-88s, which do their magic best at a high bias of 62mA. The additional heat under the hood - from power tranny and tubes themselves is considerable.
Cage is necessary due to pet-friendly environment - otherwise I'd un-cage the beast and place it on top shelf.
Louder fans, which might be acceptable for some, are out of the question because of my ungodly taste for delicate chamber music. The intrusion of even a computer fan on the table before me is repugnant. Thus the recent acquisition of a computer with an SS drive. I know I'm weird. But peace of mind is a nifty goal (though piece of mind is too often my neurotic reward).
Actual temp readings under current conditions should probably be the next phase.

Maybe go with a bigger fan ... I used a laptop cooler on my HTPC for years before upgrading the box to a 60w APU that doesn't generate much more heat than your average burrito fart ...

This just sits on top of the case.



Add a 5v power source (those cute lil USB adapters that plug into a standard outlet work great) and yer good to go. Probably best you find one with a metal case.

PS ... look for fans with a dimpled surface similar to what you get with a golf ball. The dimpling lets them move a LOT more air at slower (and quieter) speeds.

Kentley wrote:I recently purchased two American-made "whisper fans" which I have placed on the top of my ST-120 cage (the vintage brown ST-70 one) but I suspect that the efficiency of heat removal could be greatly increased by cutting some holes in the top. I lay the cage on the chassis rather than screwing it down, so there is a proper chimney effect going on - plenty of open space at the bottom but the top could use, I suspect, some additional openness.
So how should I cut some holes in the very solid top with common household tools?
Aesthetics are not an issue. I'm a single male slob who just don't care what it looks like.

Mounting the fan(s) at the back side , pressing air into the cage is probably the best
way.
Sucking hot air is less efficient as the air is less dens, it also will shorten the
fan life with extended temperatures. Topmounted fans is a danger if the fans
by some reason wont turn as they will further block air and raise temperature even more.

Backside mount is optimal on st70/120 as they cool the trannys most, and leaves the hottest parts closest to the exit side. Cutting holes in the cage for the fan(s) will increase airflow and let the air flow with less noice

All solid advice.
Keeping with the gear I have, but utilizing the fans BLOWING into the rear rather than sucking from the top of the cage is probably my easiest upgrade for now. {sorry for the explicit language}
Will report back.

HACKSAW

Or you could just let it be. Tube amps get hot by design.

Kentley wrote:All solid advice.
Keeping with the gear I have, but utilizing the fans BLOWING into the rear rather than sucking from the top of the cage is probably my easiest upgrade for now. {sorry for the explicit language}
Will report back.

Fans BLOW. Vacuum SUCKS?

draw out your circle with a compass,or whatever,even better yet. make yourself a jig taking into account the cutter center to outside distance of dremel/router.(dremel having the router attachment),using a metal cutting bit like this. https://www.dremel.com/en_US/products/-/show-product/accessories/9901-tungsten-carbide-cutter

Aye captain, she's gone from suck to blow!!

After I install my AB board, w/ LED mod, and Weber SS in my ST120, I will complete my cage fan setup.

Here's what I did so far-

I put a Noctua 120 x 15mm 12v fan inside the top of the cage. I painted the exhaust side. The fan came with speed reducer cables. It's mounted for now with zipties (those silicone fasteners don't fit the cage's smaller holes) I may hot glue this and will hot glue the wire. It will connect thru a hole in the back of the cage to a 12v fan adapter- it's possible to get grid power but I'm not 100% exactly sure how to do this. I also put 4x 1 1/4" holes in the sides of the cage near the power tube bases. I backed these with black painted perforated s/s and epoxied them in. I did an informal test and the temp near the left rear 6550 and 5AR4 was lowered by about 70˚ at probably half speed. My hope is for it to look factory. I still have to paint the edges of the holes I made, change the zipties out for tiny black ones, and grind down the epoxy but hopefully, this helps.

Noctua was helpful as was Kevin from Dynakit (cage), Bob, Roy, Vintage tube audio- fan power questions, and Doug de Young via Bob's FB (he rear mounted a fan). BTW, that cage is very solid.

And please, no comments about my copper cables :p

That is pretty slick, and a more finished version of my current setup. Putting fan inside the cage rather than laying it on top would, I suspect, increase the airflow dramatically.

Thank you sir.

I tried it on top but couldn't get past the look. It also seemed like a bandaid to me. IIRC, this fan (Noctua) made noise (turbulence) sitting on top too. It's only 15mm thick. I did my first test with a cheaper (cooler master) usb fan but that one was almost twice as thick and I didn't want it that close to the internal components figuring it wouldn't capture much heat in the process.

I forget the name but there's a company that makes those low profile fans but I wanted to mount that on the bottom of the shelf above the amp but the seller said they were meant to sit on top of the audio component. I love the classic look of the Dyna and didn't want to screw with it too much.

Worst case, I could still put another fan on the rear by the transformers if need be.
Come to think of it, there's possibly room to do 2 side by side in the top. I didn't want to get that crazy- like Bob and others say, they're designed to run hot. I just think there's a better place for a panini grill...

I think opening up the sides helps a lot with the airflow too.

I'm also waiting on a pearl tube cooler for my Weber. I was looking to tone down the copper. Also the WS1 runs cooler w/o the sag resistors)

I use two of these side-by-side. The second one plugs into the first via USB, so only one AC outlet is needed. (AC converted to DC - 5VDC? - by wall-wart type transformer.)
Note handy speed control. Even at top speed, these are almost entirely unnoticeable from listening position. And they have eight nicely designed soft foam feet, so they can be used laying down as either blowers or suckers. And - GASP! - they are entirely Made in USA.
https://www.ebay.com/itm/MULTIFAN-S3-P-Quiet-120mm-AC-Powered-Cooling-Fan-for-Receiver-DVR-XBOX-Cabinets/332094286044?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

I think that's the company that makes the enclosed ones I was looking at. It would've gone 10" above my amp under the shelf above it. I didn't get the feeling it would move that much air at that distance. The seller was pretty responsive. I looked for a long time. I'm glad yours are silent.

The Noctua is of Austrian "design" and has a long warranty (if you don't paint it) and excellent support. It's quiet too. I wanted the 12v wall wart so at some point, I could run it internally from the amp. It would run at reduced speed and be quieter. I got this:

https://noctua.at/en/products/fan/nf-a12x15-flx

They only make fans and CPU coolers. 85% of them come only in ugly beige as they're mostly for computer cooling. Their tech support guy is a tube head and good guy as well!

Looks like a great unit. And only 15 mm deep!
Yes, I think you are correct about the Multifan. It does seem to need to be really close to heat source. Which is what sparked my original concern about increasing airflow by means of additional openings to enhance the chimney effect.

Anyway, I just performed the temp tests I should have done before I started this. My laser thermo tells me I have nothing to worry about. Nowhere can I find a temp under the hood higher than 140F. I think I'm fine [Famous Last Statements].

That seems very cool!
Mine was double that with the fan on top for the cage w/o the holes. 351F down to 282F at the rectifier tube. I'm using a giveaway thermometer that came w/ my variac and the thermocouple is touching the tube. The room was probably 70F.

Your readings are probably technically more accurate, with a thermocouple. But what concerns me is the general heat conditions under the cage. Those things that get hot are gonna get hot. What I consider most important - and someone who knows more correct my logic - is the 'stagnant heat" which might degrade components not designed to withstand such torture, like the caps, resistors, signal tubes, etc.

The basic amp design is from the 1950's and Bob's temps seemed a little bit hotter w/o the cage than mine with. In the pic on FB, he had KT120's. He's said that it's all normal and part of the design. What sucks for me is the un-airconditioned room it's in and the NE summers.

I'm running TS 6550's at .50ma. @118 VAC. When the AB board goes in, I'll up the bias .55-60ma. It may run a little cooler w/ the Weber- it uses about 17 volts less. Someone chime in if this is incorrect. Most of the caps, resistors, etc are not in that hottest area.

The Weber WS1 is the coolest rectifier. But you must be aware that, first, it offers no B+ delay whatsoever - you MUST have the TDR board (cheep enuf).
I'm always concerned with too much heat. Heat is the wasted energy that is not sound. Tube amps, while providing, for me and many others, the truest sound, are incredibly wasteful. And heat ages equipment {and humans}.
This is a most important subject. Would the Big Brains weigh in, please?

And the Weber WS1 will increase your B+ voltage significantly. Depending on your incoming AC line voltage, this could be an issue.

nice your doing a fantastic job. allow me to share some insight.
i am a mechanic/technician for a mailing company.
ive experienced some situations on our machines we've had for many years where heat accumulates on a lesser level than tube amp enclosures, such as vaccume/air pumps - motors in unvented enclosures - computers and plc units in cabinets, and ive seen hot glue,clear epoxy and silicone put in places by manufacturers that have released due to heat degradation,clear epoxy not as bad as hot glue,silicone lasting longer. but yet places where there is some kind of hard dark epoxy has stood the test of time. jb weld perhaps, or some other dense epoxy.
im thinking that a hard epoxy may be a better choice for bonding the vent hole screens and such, it is also workable(drillable-grindable-sandable) and of course paintable. you could bond small square or round channel to the chassi to run wire through,that would also shield the wires.
also. i had a 1976 100 watt marshall plexi, it had a fan installed in the inside of the head to flow left to right,it made a frequency from the vibration of the fan/motor running that you could hear in the output,from vibrating the tubes no doubt. thing is fans can have a frequency vibration, especially when they age.i would mount the fan using some sort of soft rubber plugs that space the fan from the cover, so as not to vibrate the cassi/tubes.

Great info.
The devil is in the details, no? It's a rare skill to see the big picture, and simultaneously attend to the little details which can easily throw our entire perspective into Never-Never- Land.
I like your style. {Not to mention your substance}

post #21-  I got the WS1 to use with the AB (auto-bias) board I will soon install. It has about a 1 minute delay. Don't need the TDR. I've had a lot of back and forth with Pavel, Roy, and Kramer. I've tried to do my homework. I read each and every related post. It sounds great now and I don't want to mess it up. I've read all the posts about old ST70s and gooey chokes, etc. My 121-ish VAC line voltage comes thru a variac at 118VAC. I've run a lot of this through Bob as well. I tend to take care of my stuff.

post #22-  That IS JB-Weld white marine epoxy holding on the perf'd stainless steel. I also dremeled off the paint before gluing and ground down the edges so I don't scratch my tubes. In high school I had a marine mechanics class and we fixed a damaged outboard engine. A spark plug thread and part of the cylinder head was repaired with Marine-Tex and a heli-coil. The engine got a new lease on life. Our teacher had worked with Caroll Shelby and Ford. The fan Im using has silicone pads in the corners (the brown parts in my photo (post #12). This fan has a 6 yr warranty it's in post #16. It didn't sound microphonic/ distorted with either fan I tried. I would love to find silicone fasteners that fit the cage holes but haven't so far. The preamp tubes I got are platinum or platinum +. I was just going to put the fan cable to the corner and use dots of hot glue. I like things neat, and if possible, reversible (not like the 4 holes I drilled). RTV gets messy.

It's the details you don't see that are most important to me! Thanks, I do appreciate your concerns.

ahhhh/ nice. very well thought out.
these supposedly work very good
https://www.quietpcusa.com/Noctua-Anti-Vibration-Fan-Mounts-NA-SAV2-P1028.aspx