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

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

    Post by Bob Latino on Mon May 30, 2011 4:04 pm

    It seems that almost every year as weather gets warmer in May/June, I get an Email from a someone who built an ST-70 kit or has a relatively new tube amp. Usually comments come about how "really warm" the power transformer gets. Comments like "I can't keep my finger on the power transformer for more than a couple of seconds" etc.. Invariably, this is usually the first tube amp owned by the audiophile.

    Tube amps do get HOT. That power transformer is made to run at 125 - 140 degrees Fahrenheit. And yes - at that temperature you won't be able to keep your finger on the power transformer for more than a second or two.

    1. It's warmer in the house in the summer and it's harder for the amp to get rid of the heat.

    2. The power transformer has hot tubes around it causing a small thermal gradient. (the relative difference between two temperatures). On an ST-70 type amp the power transformer has warm output transformers on the sides and hot tubes to the front. Most of the heat will rise but some will radiate from the rear of the power transformer. (unless you pushed that amp against the back wall)

    3. Tube amp's usually don't have heat sinks like solid state amps. The heat sinks absorb the heat from the solid state amp and air moving between the fins on the heat sinks takes the heat away.

    Below is a photo of an ST-120 amp that is also on another post on the forum here. The ST-120 was being stressed last year under conditions that would cause it to get pretty warm. The amp was driving Tung-Sol KT120 tubes which use more current than any tube you can put into this amp. The Weber WZ68 gives a higher B+ voltage. The amp was played fairly loud in another room for about 3 or 4 hours while I was in my workshop. The infrared thermometer gives the Fahrenheit temperatures on various parts of the amp. I did neglect to take a temperature off the Weber WZ68 solid state rectifier. The Weber also gets pretty warm .. Probably as warm as the power transformer ...

    Bob



    mantha3

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

    Post by mantha3 on Tue May 31, 2011 9:54 am

    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

    j4570

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    Join date : 2010-08-30

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

    Post by j4570 on Tue May 31, 2011 10:45 am

    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!

    joeg9100

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    Temp measurements

    Post by joeg9100 on Thu Jun 02, 2011 1:12 pm

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

    Joe

    Bob Latino
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    Re: Tube amps get pretty warm - especially in the summer (photo)

    Post by Bob Latino on Thu Jun 02, 2011 1:54 pm

    joeg9100 wrote:HI why such a difference in output tube temps? Is it just the position? Or a driver issue?

    Joe

    Hi Joe,

    The LEFT channel is closer to the Weber solid state rectifier which does get pretty hot after a few hours. If you have a tube rectifier in there then pretty much the same thing will happen.

    Bob

    joeg9100

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    St 120

    Post by joeg9100 on Thu Jun 02, 2011 2:43 pm

    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

    Bob Latino
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    Re: Tube amps get pretty warm - especially in the summer (photo)

    Post by Bob Latino on Thu Jun 02, 2011 2:55 pm

    Hi Joe,

    The Weber WZ68 works just fine in the ST-120. The B+ is about 500 - 510 volts with the Weber at 120 volts in and the amp works just fine at that voltage. The Weber has a short 3 to 5 second delay built in until the full B+ comes up. This has proven to be enough. The quad cap is 550 volt rated (600 volt surge) and no one (to my knowledge) has ever lost one of the 550 volt quad caps. The amp is sold only with the power transformer that normally comes with it.

    If you get 120+ volts where you are then you could run the ST-120 amp off a 6 to 10 amp variac and set your variac for 120 volts.

    Bob

    joeg9100

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

    Post by joeg9100 on Thu Jun 02, 2011 3:22 pm

    OK Great that Is what I wanted to hear.

    Thanks
    Joe

    j4570

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

    Post by j4570 on Thu Jun 02, 2011 8:51 pm

    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

    Bob Latino
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    Re: Tube amps get pretty warm - especially in the summer (photo)

    Post by Bob Latino on Fri Jun 03, 2011 6:01 am

    Just to add a little more information here on amplifier heat. I have seen on Audiogon one "rebuilder" of ST-70 amps who sometimes paints his transformers orange, blue and other colors. The color BLACK radiates heat better than any other color. If you paint your transformers any color other than black, they will run somewhat warmer. How much warmer - I can't say. The color black is considered an "open door" to heat. Black allows heat to pass into the object quicker and also out of the object quicker. The color white is considered a mostly "closed door" to heat. White objects are harder to heat up and white objects also hold onto heat longer and do not "dissipate" the heat well. Most auto manufacturers will paint the radiators a black color to keep your engine cool.

    An interesting and true story. Many years ago as a youngster of 12 or 13 I found out the hard way about heat from black objects. I was at Swifts Beach on Cape Cod with my family including my cousin Charlie who was the same age as I was. It was an extremely hot day, probably in the mid '90's. My mother and father and Charlie's mother and father wanted to leave and drive back to our rented cottage about a mile away because they were too hot. Charlie and I were having too much fun in the surf and wanted to stay. They allowed us to stay and we promised that we would walk back to the cottage in a couple of hours. They left and we didn't realize that they also took our shoes. At the appointed time we started walking (barefoot) down the paved BLACKtop road. We took about 2 steps and jumped back. The road was very hot. There was no sidewalk beside this beach road and for the first 3/4 mile or so were sharp reeds along both sides of the road that abutted the blacktop. I sensed that "we are really screwed" until I saw the continuous WHITE LINE down the center of the road. I stepped on the white line and it was hot but the heat was bearable. Charlie and I walked about 3/4 mile on that white line. Every time a car came along we had to scramble to the side of the road and into the reeds. We made it but when we arrived our feet were sightly burned from the road heat and cut from the reeds. Live and learn ...

    Wikipedia info on black body radiation

    Bob


    Last edited by Bob Latino on Tue Sep 01, 2015 12:00 pm; edited 1 time in total

    joeg9100

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    Join date : 2011-06-02

    ST 120 Heat

    Post by joeg9100 on Fri Jun 03, 2011 10:01 am

    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

    j4570

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

    Post by j4570 on Mon Jun 20, 2011 7:40 am

    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......

    we
    Guest

    here HOT

    Post by we on Mon Jun 20, 2011 5:17 pm

    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




    Sled108

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

    Post by Sled108 on Sat Jun 25, 2011 11:58 pm


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