Tube amps get pretty warm - especially in the summer (photo)

Bob, All,

Do you think the use of an Amp/tube cage helps or hurts with the heat? I have a tube cage on my ST120... The cage gets hot... I've debated if the cage overall helps or hurts with the heat.

One thought I had is that the cage helps absorb the heat of the tubes and transformers and then the perforations in the cage help spread out the heat like a radiator on a car... The other thought is that the cage just holds the heat in.

I dun know…

Andy

I think a cage will increse temps. You would have to place the cage, then remove it just prior to taking temps.

Also, just to point out, these thermometers like Bob used do not have infinite range. I've seen people walking around manufacturing facilities chasing pipes and checking temperatures 20ft or more away. This is not a proper use! There is something called spot size that it averages the temperature over, which does not correspond to the size of the laser dot necessarily. Read the instrucitons that come with your unit. Most units work to max of a few feet, but the further away, the bigger the spot of the average temp. Nevertheless, these are excellent tools to have around for all kinds of things, checking your A/C, your car/boat cooling system, etc. Use them properly and it will all be good!

Don't think you can sit on the couch and check the temp of your amps from across the room.......unless your room is really small!

HI why such a difference in output tube temps? Is it just the position? Or a driver issue?

Joe

HI Bob,

I have some other questions about the ST 120. I would really like to get one of these in the future but I don't like the tube rectifier at all. They should have used 2 of them, but again I dislike tube rectifiers because of the wasted energy. That said I am a little leery of using a solid state rect. since the voltage drop of the RT tube will end up on the B+ Line though out the amplifier circuits. It may be good for the output power but what about the filters? bias on driver stages Ect ? Then throw in a high line AC condition (we get 120+ here all the time) You could end up stressing the circuits too much. My guess is about 35 to 50 volts extra from the rectifier and this could easily erase any design margin left for surges ect.
I was thinking if you could buy the kit without the power transformer you could get one from Hammond with A slightly less Plate winding voltage. It may cost 150 or so. Then you could just wire the existing tube socket with diodes for a couple of bucks and be done with the situation once and for all. I'm not too worried about the quick turn on for plate voltage as I have never seen an issue with it either on tube TVs (70s) or modern audio tube amps like the one I have now.
I don't want to do like the engineer did for the CS3 version of just burning power in a regulator circuit but that would be a solution too just an ugly one.

What has been your experience using solid state rectifiers in these amplifiers? is there enough margin not to worry about high line conditions? Sorry about all the questions but I am new here and have not had time to read everything.

Thanks in advance

Joe

OK Great that Is what I wanted to hear.

Thanks
Joe

I believe Bob is correct about being closer to the rectifier. But the difference I notice more is the front and back power tubes which show 100 degree+ difference. I attribute that to airflow, where the rear tubes are near the transformers, and probably 120 arc or more does not have airflow, nevermind the effect that it blocks any across airflow with a wall behind it. It would be interesting to repeat with a small desktop fan blowing across from left to right or vice versa, and then see what the temperatures were in a well mixed environment. It probably wouldn't remove all the intereffects of the heating and airflow, but it would level it out a bit I bet.

I remember a test question from college, insulate the pipe for maximum heat loss.......... Yes, you can insulate a pipe, with certain insulating material, so to speak, and have heat loss increase, given the right criteria......Obviously, most of us think of it as a heat sink, but the point was you can actually insulate something thinking you are doing good, and have the reverse effect, always check that actual effect!!!!

Interesting topic to think about.

Jason

Hi Jason,

I think you are correct in you assumption about the tube heat. I can't comment on the rectifier other than the fact SS rectifiers should not get too hot because the power dissipated is fairly low. Who knows what is inside of that device though. I can say this, it's good thing the tube rectifier was not in there.

So My conclusion is the bottles are a little too hot on the back tubes as it is almost 400 deg. Keep in mind ambient temp is quite low for this test at 70 deg. 20 more deg would would be at almost 420 deg. Front tubes look OK.
The reason for this.. I think is the chassis, is too small for adequate tube ventilation. The 6550's dissipate lots of energy they are big and need more spacing between them for good air circulation. A larger chassis would help this out and would look nice too.
Under most conditions this should not be a serious problem but clearly the tube life can be shortened somewhat, but how much? Who knows most folks change tubes fairly often anyway.

Joe

Interesting stuff.

However, one thing that should probably be avoided is THICK layers of paint. I would think it could act as a barrier to good heat transfer. Again, it is not as significant as temeprature difference.

Just place the unit by your air return for proper flow......

Hi
I just Got a pr of Dynaco MK3s One owner 1960 he put them togather,He played them day in day out. Only one had ever Been Open but one time in over 50 years he took one of the to a shop it stop working,The GZ34 went out an the shop put SS diodes.He sead thay lost there Sweet sound he had love,ed.That why he sold them to me for $100. Now all stock tubes, never open!Black top tube Cage an if you have seen the MK3 tube cage, there is no holes in the sides,not much Air gets in,So i got home pulled the SSdiodes out pop in a GZ34 thay came right on an i have been playing the all day.Now i no the is parts that i well be replacing BUT COME ON you think you amps to hot i am in Fl it 98 here to day,an this Man had no AC.Thay sound Vary good, i felt Bad i could see he like the old tube sound i have now 4 pr of MK3s I told him i had a GZ34 i would sale him a New one for $15.
He sead that Thay would Never be the same as thay had been for 50 year old tubes,he sead take them no one he had talk to even new what TUBES were.

PS. I dont think your Transfourmers well Get To Hot If the bias is right, on these 50year old amps the bias was 1.5 An were only SET one time.

I Am still HIGH on the 1960 AIR that came out of the amps when i open them up before i put the Ac to them.
Stock output tubes were GE6550a an 6AN8 were Dyanco still test Good,Go fig

This Really Works....

https://dynacotubeaudio.forumotion.com/t533p15-pa-060-heatsink

As an experiment, I placed a makeshift heat shield (aluminum foil/cardboard sandwich) in the gap between the tubes and the output transformer at the Left Channel of VTA ST-120 and ran the amplifier for 4 hours.

Now I can feel the Left output transformer has even lower temperature than the one on the Right (without the "heat shield").

Usually the Left output transformer is hotter than the one on the Right due to its proximity to the rectifier tube

So it seems that the "heat shield" is working to shield off heat from the tubes.

Anyone tried similar or different approaches for reducing output transformer temperature? Can you share details?

Sorry I cannot post photo here as a newly joined member.

The output transformers don’t get hot by themselves.

VTA120 temps

Hi corndog71,
Thank you very much for sharing the photo
It looks like you made your own chassis for VTA 120.
Excellent work as there are lot more space amongst the tubes and the transformers. This will take care the heat dissipation problem.
You had also moved the attenuator (probably the input RCA too) and the ON/OFF switch to the back. These made a lot of sense.
I have been thinking along the same path too.
Would that be possible for you to share more details on how you did it?
Thank you.

This is an interesting topic, and somewhat related to discussions that occur in the aircooled Volkswagen forums. (oh - the arguments! )   My thoughts, based on a single class I had in heat transfer, nearly 30-years ago, and some conjecture:

1)  It would seem most of the heat transferred to the Transformers is by radiation.  Better ventilation or a fan probably wouldn't do much to prevent this mode of transfer.

2)  As BillyW found, shielding would help prevent this radiated energy from being absorbed by the transformers  It would be ugly, but perhaps chrome plating, or light paint on just the end-bells facing the tubes would be helpful.  Maybe shiny aluminum tape would work too - especially on just the corner of the power transformer, nearest the rectifier (leave everything else black)

3)  I think removing the cover, or some air current (a fan) would still help with convection, and help cool down the whole assembly.

One more crazy-crazy thought. Drill a few holes on the tops of the end bells. Cool air would be drawn in from the bottom (where the wires are), the air would be heated and rise up through the new holes, drawing in more cool air from the bottom. OK, go ahead and shoot me for even thinking of such a travesty.

I did further experiment.

I placed a fan in front of the amplifier and have it blew away from the latter.

After 8 hours running, the left output transportation was still "touchable".

So the airflow created by the fan was working too.

I am thinking making a connecting to the front bias setting valve socket with the filament 6.3Vac from the power transformer, then through a rectifier bridge to make it a power supply of just below 6V DC.

Then connect an USB fan for ventillation.

However I don't know this will cause any hum/noise, or damage for the power transformer.

I still think the ultimate solution would be to have a larger chassis.

BillyW wrote:I did further experiment.

I placed a fan in front of the amplifier and have it blew away from the latter.

After 8 hours running, the left output transportation was still "touchable".

So the airflow created by the fan was working too.

I am thinking making a connecting to the front bias setting valve socket with the filament 6.3Vac from the power transformer, then through a rectifier bridge to make it a power supply of just below 6V DC.

Then connect an USB fan for ventillation.

However I don't know this will cause any hum/noise, or damage for the power transformer.

I still think the ultimate solution would be to have a larger chassis.

I'd probably just run the fan off it's own power supply. FWIW, PC guys can be sensitive about fan noise, and there's a lot of options for fans that make little to no noise. A large diameter fan, with slow moving blades would might work well - like this: https://www.amazon.com/Thermaltake-200x30mm-Anti-Vibration-Mounting-CL-F015-PL20BL/dp/B00J0NZFIA/ref=sr_1_3?gclid=Cj0KCQiAmsrxBRDaARIsANyiD1r8FK62Zy52BW5m-PnekDRMuIhqj5z_zZhp0ENFbGO1Cw_nnnPP9ZMaAhc2EALw_wcB&hvadid=397260718228&hvdev=c&hvlocphy=9030751&hvnetw=g&hvpos=1t1&hvqmt=e&hvrand=10894357993688874228&hvtargid=kwd-296688082531&hydadcr=24328_11043478&keywords=240mm+pc+fan&qid=1580422185&sr=8-3

You could find a PWM fan controller for PC's too, and turn down the RPM so it's just moving enough air to be effective (and reduce noise even more.)

I tried the other day to make the Intel i7 CPU Cooling Fan (4 leads) work by connecting 12V DC to its +12V and GND leads. Fan turned momentary then stopped.

Goggled the web and got the impression that I may also need to connect the PWM lead to +5V DC to make the fan rotate continuously . Will try that and hopefully this won't fry the fan.

Hi corndog71,

I have just read your other posting on this forum and now I understand how your customized chassis was done.

So please don't bother to answer the question I asked.

Thank you!

This one works!

The fans were running at "H" speed setting, drawing air from the amplifier. Dead quiet!

Today's room temperature 23.5 degree C (74.3 degree F)

The VTA ST-120 has been running for 6 hours
The 2 output transformers are just warm
Power transformer and quadruple capacitor are a bit warmer but you can put your finger on them forever
The chassis is just warm. not hot.

This looks like a solution for those have concern on heat generated by amplifier.