@jean-paul what exactly is the imperfection? Having an amp with a closed case in which the parts can easily stand whatever temp is in the case? 27W idle is not at all unusual for a 300B in SE class A (and "only" 75% of the rated max).
Of course cooling in as much as necessary and reasonable is good thing. No one questions that.
Of course cooling in as much as necessary and reasonable is good thing. No one questions that.
BTW... to cool the components inside the amp, my guess would be that holes above those parts would be much better.
Exactly, everything will collect dust and obviously I clean my amps from the outside occasionally. If possible I would like avoid having to clean the inside.
Funny you say you wouldn't work on TVs because of dust but suggest to me drilling holes even if not necessary.
Work and hobby are different items. Many techs were not too fond of repairing TVs, certainly not those of dog owners. Videorecorders were also not favorite (as cockroaches loved them).
Your conclusions are not really based on the excellent replies you got. If you want to do things a predecided way and want justification that is OK.
Yes minimum 4 mm holes around tubes and around hot parts both in bottom and upper cover. Where there is air flow there is cooling, where there is air flow there will be dust. Dust that could have been vacuumed in a daily routine. A routine not very popular with audio hobbyists I dare to say.
Your conclusions are not really based on the excellent replies you got. If you want to do things a predecided way and want justification that is OK.
Yes minimum 4 mm holes around tubes and around hot parts both in bottom and upper cover. Where there is air flow there is cooling, where there is air flow there will be dust. Dust that could have been vacuumed in a daily routine. A routine not very popular with audio hobbyists I dare to say.
Last edited:
90% of the answers were about if this helps cooling the inside, which I do not argue at all.
My original question was just meant about the tube, which I made not clear enough it seems.
And of course work and hobby is different. But cleaning the internals of stuff I once built is not my favourite part.
And I am not predecided when I ask. I have a preference here to keep the case close if possible, yes, and wanted to clarify if the tube really would benefit it I added these holes.
My original question was just meant about the tube, which I made not clear enough it seems.
And of course work and hobby is different. But cleaning the internals of stuff I once built is not my favourite part.
And I am not predecided when I ask. I have a preference here to keep the case close if possible, yes, and wanted to clarify if the tube really would benefit it I added these holes.
Cleaning internals is what we all have to do as it can not be avoided with hot electronics that needs air flow for, ironically, getting rid of its own generated heat and possibly desired longevity. It is a defect by choice. You can not make a cake without breaking eggs.
My best advice is to buy a fully closed class D amplifier. No dust, excellent sound, no heat, high damping factor, no trouble with difficult loudspeakers and lower power consumption. Only once a month a moist cotton cloth over it and fertig 🙂
My best advice is to buy a fully closed class D amplifier. No dust, excellent sound, no heat, high damping factor, no trouble with difficult loudspeakers and lower power consumption. Only once a month a moist cotton cloth over it and fertig 🙂
Well then, the answer is clearly this. Any increased cooling helps.
As for TVs, they accumulate a MASSIVE amount of dust. I'm talking about the older tube types. Well in excess of audio equipment, unless in a bar or similar. So yes, I would drill holes around the tube, or buy the chassis with the holes punched. Got a compressor? I do, and I use it. I don't recommend you clean out cassette decks with it though! lol! You can blow the belts off (seen it done more than once).
The minor bother of occasionally blowing out the chassis more than pays for the cooling it provides. The secret is air flow as many have said and I agree.
Here is a true statistic for you to consider. The failure rate for any electronic component doubles for every 10°C rise in temperature. Doesn't matter 300B, 12AX7, transistors or passive components. This is physics at work, you aren't going to win that argument.
As for TVs, they accumulate a MASSIVE amount of dust. I'm talking about the older tube types. Well in excess of audio equipment, unless in a bar or similar. So yes, I would drill holes around the tube, or buy the chassis with the holes punched. Got a compressor? I do, and I use it. I don't recommend you clean out cassette decks with it though! lol! You can blow the belts off (seen it done more than once).
The minor bother of occasionally blowing out the chassis more than pays for the cooling it provides. The secret is air flow as many have said and I agree.
Here is a true statistic for you to consider. The failure rate for any electronic component doubles for every 10°C rise in temperature. Doesn't matter 300B, 12AX7, transistors or passive components. This is physics at work, you aren't going to win that argument.
Not sure why you keep posting that statement everywhere over and over on a DIY forum. This about having fun building stuff that then even sounds good.
Last edited:
Firstly, heat isn't what makes air move. Air pressure does that, or rather a differential in air pressure and the movement will always be from high pressure to low pressure. Unless you are fixed bias, the cathode resistor sitting under the 300b's base is probably going to dissipate a lot of heat (~80v multiplied by ~70mA) and locally that'll make for a higher pressure pocket of air. The air will move. To restrict air movement will be inviting all components inside the box to heat up excessively. Since the OP is interested in the bulk of the heat generation which is above the board, I'd suggest that even warm air movement from below board via the holes is better than no air movement, so the answer is that the tube does more easily dissipate heat from having holes in the chassis - it just isn't as efficient as forced air cooling since the additional air which is moving is already partially pre-warmed.
This is exactly the same question as whether to run a cooling fan on a sportscar radiator even when it already at speed. The answer is "yes" - the fan always adds to the cooling of the radiator - it just doesn't add much since the bulk is already coming via air through the radiator due the forward motion of the car.
It is the incremental movement of air around the tube which is what needs to be counted and having holes in the chassis adds a bit to total airflow.
kind regards
Marek
This is exactly the same question as whether to run a cooling fan on a sportscar radiator even when it already at speed. The answer is "yes" - the fan always adds to the cooling of the radiator - it just doesn't add much since the bulk is already coming via air through the radiator due the forward motion of the car.
It is the incremental movement of air around the tube which is what needs to be counted and having holes in the chassis adds a bit to total airflow.
kind regards
Marek
Hi Marek,
I think most of us understand what creates air movement. One might say this is blindingly obvious. Hot air happens to be less dense than cooler air.
Basically, excess heat is your enemy. Heat is unavoidable, but you can mitigate the problem if you so desire. This is similar to changing the oil in a car. You don't have to, it won't blow up just past the interval. But sooner or later you're going to have to pay the piper. No point in arguing how long it will run (no one knows for sure), but there is zero argument against the fact it will run longer.
I think most of us understand what creates air movement. One might say this is blindingly obvious. Hot air happens to be less dense than cooler air.
Basically, excess heat is your enemy. Heat is unavoidable, but you can mitigate the problem if you so desire. This is similar to changing the oil in a car. You don't have to, it won't blow up just past the interval. But sooner or later you're going to have to pay the piper. No point in arguing how long it will run (no one knows for sure), but there is zero argument against the fact it will run longer.
And looks good too. If you like a row of holes around the tube socket, then go for it. Personally, I would do it.
Kinda surprised you're getting so much push back on this subject, but then, maybe I shouldn't be. Didn't realize drilling a few holes was so controversial. 😉
jeff
Last edited:
IMHO, the usual ring of holes probably doesn't provide much additional airflow around the tube. It would be interesting to see a flow map of how the air moves from the deck and up over the tube. I can imagine the possibility where the holes actually make it worse! Multiple tubes with holes probably ventilates the inside better, but as said, that's not the discussion.
Any cooling effect of the holes is likely to be microscopic, especially if the chassis is completely enclosed with a bottom cover and has no vent holes anywhere. It certainly won't hurt anything, though, and the holes may add an aesthetic touch to the amplifier.
No, that is not the case. Actually if you look at the EL34 amp, there are two vent screens in the top of the amp specifically over heat producing internal parts (cathode resistor on one end and power supply dropping resistor for the other), along with vent holes specifically placed on the bottom cover to provide this same convection cooling. These perform the same function. On my 300B and KT120 builds I used holes around the tubes instead for the same purpose. On the KT120, the vents in the bottom are at the back to ensure air flows through the entire case. Note on the 300B amp the cathode resistors are mounted to the top of the chassis to keep that heat away from other passive parts that will degrade over time if exposed to heat.
Sealing the case with no vents and relying on part spec to just deal with whatever heat is generated is a bad design philosophy.
Last edited:
Some of the better fancooled devices has filters that filter air pressed into the device, nedding regular filter cleaning but keeping interior clean.
Fans that sucks air out is wrong by two reasons : they allow dust accumaulate and they get less efficiency as worm air is less dens.
Fans that sucks air out is wrong by two reasons : they allow dust accumaulate and they get less efficiency as worm air is less dens.
Know those all too well professionally. Can be very dirty and one needs breathing protection/mask. They work OK when environments are public/industrial and dirty. They are replaced according a maintenance schedule.
For home use the chances are that they are eh.. forgotten. When dirty the air flow is seriously hampered and the fan makes more noise. Both are a nuisance in audio. If one needs a fan in audio a design error is accepted.
Unless it is for medical reasons one is better off without them. Keeping the home clean is simplest.
For home use the chances are that they are eh.. forgotten. When dirty the air flow is seriously hampered and the fan makes more noise. Both are a nuisance in audio. If one needs a fan in audio a design error is accepted.
Unless it is for medical reasons one is better off without them. Keeping the home clean is simplest.
Last edited:
If you have access to a thermistor or thermocouple thermometer instrument, you could attach that to a hot spot on the tube and then do 2 measurements, one with the holes plugged, and one with the holes not plugged. Allow the amp to reach its stable operating temperature before snapping the 2 readings. You will then know the answer to your question with certainty.
Hi Jean-paul,
Just home use? Nope, I'm afraid that in most long term installations, they don't clean the fan filters. Then they simply remove them. "Cost cutting".