eHam
eHam Forums => Amplifiers => Topic started by: K1KIM on March 11, 2023, 09:35:42 AM
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How long does anyone wait, if at all, to turn off their tube amp after a long last transmission?
My though is that when the tube is hot and fan is running shouldn't their be a certain amount of time to let the amp sit idle with the cooling fan before shutting it off.
As a precaution I have always been putting it into standby for 5 minutes before shutting down, in lieu of "riding it hard and putting it away wet"
I'd like to hear other's opinions.
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You will not hurt the amplifier by letting it idle to reduce the internal cabinet temperatures but the main internal heat source is no longer operational. Glass tube amps have a small heat source and they will not have much temperature mass. The do relay on the fans to route the heat out of the chassis.
Metal tetrodes run at a much lower temperature, typically below 50 degrees C, and generally have the vent holes right above the tube. Natural heat convection will vent the anode with out the fan running.
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I follow your procedure. Sometimes a bit less if not being pushed to hard. Just to cool off the seals.
73's
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You will not hurt the amplifier by letting it idle to reduce the internal cabinet temperatures but the main internal heat source is no longer operational. Glass tube amps have a small heat source and they will not have much temperature mass. The do relay on the fans to route the heat out of the chassis.
Metal tetrodes run at a much lower temperature, typically below 50 degrees C, and generally have the vent holes right above the tube. Natural heat convection will vent the anode with out the fan running.
My ACOM has a single Svetlana ceramic metal tetrode with the vent holes above it in addition to a built in fan.
It appears to be hotter than 50C when I am long winded even at a modest 400W.
I'll have to check with the temp gun next time.
I'll continue to let it idle a while before shut down since it doesn't hurt anything other than a penny in electric.
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The OM2000+ on my desk, takes the temp down to under 40, then it will begin shutdown, think its another 1 min of fan running.
I try to never get it above about 50 -55max, gives me all the power I need at that level.
Runs noticeably cooler in the spring,autumn, winter February is the worst time.
Hopefully IF an aircon company ever rings us back we get the house a bit cooler.
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I never really thought of it... but my SB-200 will usually run 5-10 mins before I shut it down. That isn't intentional.. usually if I made a QSO I'm putting it in the logbook, maybe look at something related online.. then I get distracted... then "oh, I'm done with the amp.. I guess I'll shut it off". With that amp, I don't think it matters a whole lot.. unless maybe you were on long rag chews or were driving it hard (which I don't). Most of the time I'm using it in CW when chasing DX in a pileup or rarely SSB.
I do plan on upgrading perhaps next year to a newer amp that covers 160-6 and I will certainly follow whatever the manufacturer says to do.
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What you are doing is just fine. I normally just put my had over the air outlet and see if the air feels "cool". By that I mean does the air feel close to the temp of the air at start up. To be honest I probably wait about 10 min if the amp has been used for several contacts. I never have just turned off an amp that has just been used. Better safe than sorry.
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Let it run for a few minutes before shutting down.
On my HB amps, I switch amp to standby, then shut off the B+. Then shut OFF the filament. Then run the blower for several minutes. Those fil terminals are stupid hot.
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I am surprised with all the neat add ons for Heath and other amps (soft start, soft key too name a few) that there is not a time delay circuit to run the blower after power down?
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I am surprised with all the neat add ons for Heath and other amps (soft start, soft key too name a few) that there is not a time delay circuit to run the blower after power down?
The Kenwood TL-922 does just that, called...'fan over run'. We put it in my buddy's hb amp. He used a delay timer module, adjustable from 0-15 mins. It activated after the fil was shut OFF. Ok, everything off...except the blower. Somebody on here posted a SS adjustable timer months ago...tiny thing They were dirt cheap, and would run on either 120 / 240 vac.
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My Collins 3-1000 amp has a plug in relay with a dial on the top. Different time ranges available. You can make the delay anything you want.
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You will not hurt the amplifier by letting it idle to reduce the internal cabinet temperatures but the main internal heat source is no longer operational. Glass tube amps have a small heat source and they will not have much temperature mass. The do relay on the fans to route the heat out of the chassis.
Metal tetrodes run at a much lower temperature, typically below 50 degrees C, and generally have the vent holes right above the tube. Natural heat convection will vent the anode with out the fan running.
My ACOM has a single Svetlana ceramic metal tetrode with the vent holes above it in addition to a built in fan.
It appears to be hotter than 50C when I am long winded even at a modest 400W.
I'll have to check with the temp gun next time.
I'll continue to let it idle a while before shut down since it doesn't hurt anything other than a penny in electric.
My temp runs 60 degrees C after a long QSO via temp gun reading at the chassis vent.
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You will not hurt the amplifier by letting it idle to reduce the internal cabinet temperatures but the main internal heat source is no longer operational. Glass tube amps have a small heat source and they will not have much temperature mass. The do relay on the fans to route the heat out of the chassis.
Metal tetrodes run at a much lower temperature, typically below 50 degrees C, and generally have the vent holes right above the tube. Natural heat convection will vent the anode with out the fan running.
My ACOM has a single Svetlana ceramic metal tetrode with the vent holes above it in addition to a built in fan.
It appears to be hotter than 50C when I am long winded even at a modest 400W.
I'll have to check with the temp gun next time.
I'll continue to let it idle a while before shut down since it doesn't hurt anything other than a penny in electric.
My temp runs 60 degrees C after a long QSO via temp gun reading at the chassis vent.
Buddy's 4x10 grid driven amp runs at 150 F (65 C) exhaust air temp, while blathering away on ssb, using ptt / footswitch. Once released, it takes a full minute to get back down to 90 F (32 C) ...where it remains. The 90 F is coming from the cathode sucking a lot of fil power. I just found it easier on the hb amps, to switch to standby, then kill the B+, then the fil xfmr, then everything is off. Then let blower run for a few minutes, before shutting off the blower.
On RTTY/ FM / DATA modes / AM, average plate current is a lot higher..and so is exhaust temps. Tank coils / band switches will also dissipate more heat, since quadruple the watts is being dumped into them. It's just I squared X R..or in this case, RF current squared X the ESR (rf resistance) of the tank coils. RF current in the tank coil is aprx plate current X input loaded Q of the PI net..+ 10%. I was surprised at just how hot tubing coils got on 15m, with a brief cxr applied, then removed, then touched the 15m tank coil, yikes, fn hot. I would have thought the heat would have migrated into the 20m portion of the same 20-10m tubing coil, but it doesn't. 20m end of same coil runs at ambient room temp. It's all localized heat. Then toss in still more heat from the plate xfmr etc.
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How long does anyone wait, if at all, to turn off their tube amp after a long last transmission?
My though is that when the tube is hot and fan is running shouldn't their be a certain amount of time to let the amp sit idle with the cooling fan before shutting it off.
As a precaution I have always been putting it into standby for 5 minutes before shutting down, in lieu of "riding it hard and putting it away wet"
I'd like to hear other's opinions.
I always let em run a few minutes afterwards.
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I fail to see a provable benefit in forced fan cooling after on air use over letting it cool slower by convection.
Same thing happens, just at a slower rate.
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A lot of this is going to depend on the way your unit is constructed and what space you have to add stuff to it.
If you can shut off the high voltage and filament while the fans continue to run, that is the ideal situation. Problem is most manufactures put the fan circuit and the filament circuit on the same power switch. Which of course leaves the filament (heat source) under power when the fans are running.
The way to do it so you can turn off the power and 'walk away' from it would be install a delay relay that is wired to the fan power that would continue to power the fans for a window of time after the filaments were shut down. I would think five to ten minutes would be more than enough time.
But the other part of it is do you really need it at all. And that is going to depend on how hard you are running the tube and what temperatures you are seeing on that tube. Are you thinking that you are gonna get gabby on 80 or 160 meters running full out on AM for several minutes and then sign off and power down, or are you running SSB at 3/4 power and chasing DX with long pauses and when the band goes quiet listening for a few and then shutting down? Big difference there. But ultimately, it's what ever you want to do. If you want automatic coll down that can be left unattended, the time delay relay is the direction to look. And some amps are gonna have space for such a thing while others will not.
The last thing with making any sort of modification to the amp, are you comfortable with doing the install? Working with line voltages and understand the concepts of high voltage that exists in a tube amplifier and how you can mount things too close to that voltage and have arc over issues without even actually coming into direct contact with that high voltage? If you are not well versed in these matters you need to either seek out someone that is, or simply not bother with it.
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Is it more psychological than else? We just turn our cars/autos off full stop. Heat dissipates through the relevant medium, a bit of air when energy is no longer being supplied, does it imply not enough cooling before?
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Is it more psychological than else? We just turn our cars/autos off full stop. Heat dissipates through the relevant medium, a bit of air when energy is no longer being supplied, does it imply not enough cooling before?
Actually the heat will build in an engine after shut down if the water pump and fan no longer are turning.
We all do it, and the pressurized system is made to take it, but it happens nonetheless.
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Is it more psychological than else? We just turn our cars/autos off full stop. Heat dissipates through the relevant medium, a bit of air when energy is no longer being supplied, does it imply not enough cooling before?
Actually the heat will build in an engine after shut down if the water pump and fan no longer are turning.
We all do it, and the pressurized system is made to take it, but it happens nonetheless.
The heat doesn't build up in the engine. The water temperature goes up because the engine oil temperature and block temperature were already higher.
Or, that's my story anyway.
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Car analogies: I’ve always heard that turbocharged engines should be idled for a bit before shutdown, as it maintains the flow of cooling oil to the turbo bearings as it spins down. Running hard with a quick shutdown supposedly cooks the oil, leaving deposits which lead to premature repairs.
My Dad (KE6AR, SK Feb 21st) always taught me to run the slide projector cooling fan after shutting off the lamp. Supposedly to make the bulb last longer, but it also keeps plastic bits cooler. And have you ever seen film in a movie projector cook if it doesn’t keep moving and cooling?
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Car analogies: I’ve always heard that turbocharged engines should be idled for a bit before shutdown, as it maintains the flow of cooling oil to the turbo bearings as it spins down. Running hard with a quick shutdown supposedly cooks the oil, leaving deposits which lead to premature repairs.
My Dad (KE6AR, SK Feb 21st) always taught me to run the slide projector cooling fan after shutting off the lamp. Supposedly to make the bulb last longer, but it also keeps plastic bits cooler. And have you ever seen film in a movie projector cook if it doesn’t keep moving and cooling?
Yeah, but that has nothing to do with this.
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Car analogies: I’ve always heard that turbocharged engines should be idled for a bit before shutdown, as it maintains the flow of cooling oil to the turbo bearings as it spins down. Running hard with a quick shutdown supposedly cooks the oil, leaving deposits which lead to premature repairs.
My Dad (KE6AR, SK Feb 21st) always taught me to run the slide projector cooling fan after shutting off the lamp. Supposedly to make the bulb last longer, but it also keeps plastic bits cooler. And have you ever seen film in a movie projector cook if it doesn’t keep moving and cooling?
This is the same thought process with a tube. Any device that has multiple layers and a heat source internally is going to obviously hotter in the center than the outside. With active cooling (a fan running) the heat that is in the middle is transferred through the parts of the device to the exterior and then finally carried away by the flow of air around the device.
When you stop the internal heating of the device, the heat source is gone, but the heat remains until convection can move that heat to a surface it can be dissipated from. And we need to consider that a vacuum is a pretty good thermal insulator. So the heat will need to move through the vacuum of the tube, unless it's a ceramic tube where the anode is also the heatsink, and even with those, if you are actively removing the heat and then stop the temperature of the anode will INCREASE due to the heat internally that is hotter than the anode heatsink will continue to transfer to it increasing the temperature.
So now lets consider the operational expectations of transmitter tubes. NO ONE makes a 'ham radio' tube. Other than maybe the glass envelope 3-500. Anything that is ceramic was designed to be sitting in a commercial transmitter that is run 24/7 for months at a time. Used by folks that don't get a hoot about a power bill because their transmitter EARNS them money or is otherwise funded by a company or the government. The guy that has the ability to 'turn it off' simply doesn't bother. So it's kept hot, and the fans run all the time. And the tube is designed for that type of operation, not fired up in the evening for a couple hour's. Then shut off to cool manually when the switch is thrown. And even back in the day for AM stations that were daytime only operation, the tubes were glass (833's 811's and 572's). Filament current wasn't the crap that was present in the 500KW transmitter at WLW (4500 amps) so the HV was turned off and the active cooling was left running with the tubes left hot.
Now, a guy is NOT gonna want to leave his tubes hot and just pay the power bill in most cases. BUT, that's when a filament will typically fail is on startup. This is even present in incandescent light bulbs. They 'burn out' when power is applied to them. Leave them on all the time and they never fail. But current limiting the filament power, bringing up a tube slow (which no one actually bothers with) would significantly increase the life of the filament. But properly cooling it after it's shut off is certainly NOT going to hurt it and may also increase it's life. Of course running it as it was designed to be run would be better, but that isn't in the cards for most ham operators and their electric bills.
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So, we turn the power off and the tube gets hotter. I can envision a perpetual motion machine.
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So, we turn the power off and the tube gets hotter. I can envision a perpetual motion machine.
The principle is pretty simple and is called "Heat Soak".
Essentially, when forced cooling stops in a machine, be it a liquid cooled car engine/turbocharger or tube amp cooled by air, thermal energy is still flowing from the hotter points in the system to the cooler, but the cooler bits are getting warmer because there is no more forced cooling and so parts of the path get hotter than they normally do. Sometimes MUCH hotter. With tube amps, those with glass tubes/frit pin seals are most vulnerable. They can deform/crack and leak.
High output car engines have the same problem and they often have fan run-on thermostats to keep the cooling fluid temperature low and promote liquid convection cooling withinn the engine/turbocharger.
If this is NOT done, "wet" cylinder liner seals can fail or oil in turbo bearings can "coke up" due to excessive after-run heating.
No perpetual motion is required for this phenomena.
Brian - K6BRN
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Just go back to low school basics.. There is a fundamental principle of 'Conservation of Energy' (and Mass). We talk of 'power' rather loosely.
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Well, the heat does not build up is my point. It may move around.
Conservation of energy always applies.
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Well, the heat does not build up is my point. It may move around. Conservation of energy always applies.
Regardless - allowing an amp with forced air cooling to idle and cool for a while after being run hard is usually a good idea. Which is the point of the original post.
As to how long? SS amps usually have a temp readout and I let them settle to below 30C. For tube amps its usually just 3-5 minutes. Longer does not hurt - so when in doubt, stretch it out. (cooling time, that is).
Brian - K6BRN
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Regardless of conservation of energy. I love it..
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You know, it just boggles the mind that as we sit here discussing a hobby that is technical in nature, based on a TON of scientific principals that we get the comments on here I have read.
Perpetual Motion? Really? I have to ask if you are trying to shine people on with that or you are serious.
Lets look at this from a different perspective. Heat up a rock to 200 degrees. Now remove the rock from the heat and put it in a metal can that is 70 degrees. The can will get hotter because the rock inside of it is hotter than the can when you placed the rock it the can. How does that happen? THe heat from the rock leaves the rock and transfers to the can. Simple enough.
Tube guts. Fire up your 3-500 and lay down on the key on FM. The Anode gets GLOWING hot. The filament is glowing hot. Glowing hot is over 1000 degrees for most objects. So where doe that heat go? Outer space, another dimension, how about into the glass envelope surrounding the tube and physically connected to the hot parts. Now when the fan is running, laws of thermodynamics tell us that air can act as a medium to transfer heat to.
But we need to understand something here. YOU CAN'T COOL AIR, you can ONLY remove the heat from the air, or anything else with heat in it, and move it somewhere else. Air conditioning in your home or car doesn't cool the air.. It moves the heat outside. Hence the reason the condenser outside gets hot and blows air hotter that the surrounding air, and in the winter, a heat pump will take the heat from outside and bring it inside to warm the house. But the scientific part of it remains the same. You remove heat from air, and transfer that heat to other air with air conditioning or a heat pump.
All that being said. Back to the can. If you put a fan on that can, you remove the heat from it that is being transferred from the rock so it doesn't get as hot as it would if you put the can in some insulation and didn't blow air on it. And that is what you are doing when you shut the fans down on a hot tube. The tube WILL cool off, but the outer envelope will actually get hotter before it gets cooler. Not because of free energy or some mystical nonsense, but because the tube contains things that are MUCH hotter than the envelope of the tube. And that heat will transfer somewhere. The only place it has to go is out of the tube, and to get there it has to go through the envelope.
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You can write a book if you like. But, the heat does not build up in a tube once the power is turned off.
Any part that gets hotter has an associated part that lost that heat.
The water in a car gets hotter, but that heat was lost by the oil and the block.
Don't use the term heat builds up and all will be cool.
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This morning, I read through the cooling section in the 1967 edition of Eimac's "Care and Feeding of Power Grid Tubes." Although operating cooling requirements are given substantial treatment, there's no discussion about cool-down procedure.
At the moment of amp shut-off when forced-air cooling stops, do envelope and seal temperatures momentarily rise above the normal operating temperature with cooling? It would be an interesting exercise to record real-time tube temperatures across amplifier models with a Flir device.
Paul, W9AC
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This morning, I read through the cooling section in the 1967 edition of Eimac's "Care and Feeding of Power Grid Tubes." Although operating cooling requirements are given substantial treatment, there's no discussion about cool-down procedure.
At the moment of amp shut-off when forced-air cooling stops, do envelope and seal temperatures momentarily rise above the normal operating temperature with cooling? It would be an interesting exercise to record real-time tube temperatures across amplifier models with a Flir device.
Paul, W9AC
Hi Paul (W9AC):
Yes - measurement of tube pin/seal temperature over time after amplifier shutdown with a good FLIR would be interesting, but would also likely be different for different tubes and amps due to different thermal paths.
But there IS some official guidance on this. The CPI data sheet for the Eimac YC-179/YC-179A power triode states:
"Airflow must be applied before or simultaneously with the application of power, including the tube heater, and should normally be maintained for several minutes after power is removed for tube cool-down."
https://mgs4u.com/wp-content/uploads/2018/01/Eimac-YC-179-PDF.pdf
Eimac Application Bulletin #20 titled "TEMPERATURE MEASUREMENTS WITH EIMAC TUBES" might be helpful as well, if you can find it. This bulletin is mentioned in many Eimac power tube data sheets.
Brian - K6BRN
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:)I have often thought about this , and where the heating of envelopes and pins that unsolder themselves like in the TL-922 I was wondering about a mod that will cure this problem.
Having a circuit, run off mains that will run fan and have a run on timer circuit, much like run on circuit for automotive radiator fans.
OR.. Having an Bi-metallic clickson temperature switch, like the ones used in microwaves to sense the exhaust air, and not turn off unless the air Temp is below 55 or 60 Degrees C.
The problem we face in South Africa is that the power utility can be turned off without warning and Having an TL-922 with 3-500Z tubes, this is a huge problem. If power goes off in the middle of an QSO and tubes are hot, the pins unsolder themselves.
Still working on an ups or battery backup for the Fan on this issue.
73 De William , ZS4L / ZS5WC
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"Airflow must be applied before or simultaneously with the application of power, including the tube heater, and should normally be maintained for several minutes after power is removed for tube cool-down."
The above is good enough for me.
On one of my hb 2 x 4-400 amps, with bottom lid off...and rf deck pushed back on the desk, with just enough overhang, such that I could take some V measurements at the sockets, I put my finger on pin #1..... and just about took my finger prints off. It was fn hot...and then some. Those pins run stupid hot.
On my hb 3CX-3000A7 amp, initially I was using a SK-306 chimney, made for a YC-156 / 4CX-5000 tube...with their 4.94" OD anode cooler. The 3CX-3000A7 tube anode is only 4.125" OD, so used layers of 1/8" thick silicone rubber and a SS hose clamp, to plug the gap. We had the blower + heater on ( 7.5 vac @ exactly 50 amps, using a clamp on ac ammeter around one leg of the fil cable going to the next shelf below).
Ran it for like 10 mins, then shut down the fil and blower...and removed tube.... so I could tweak the silicone rubber down a bit on the anode, which required 1st loosening up the SS hose clamp.
I was sitting in my office chair, with tube vertical, and base of tube between my crotch, and a nut driver, tweaking the hose clamp etc. Tube base inner + outer collets were good and warm. But after 1 min, it was getting hotter and hotter + HOTTER. It was ready to burn my gonads, so lifted tube up...and gotta outa the chair asap. Then felt the inner / outer collets..and indeed they are hot..... but cooled off fairly soon.
And I had loads of air, with a pair of dayton 4C4006B blowers running, and also a magnehelic gauge installed, which read 1.15" pressure. 70 cfm airflow...and a helluva lot of pressure.
On all this hb stuff, with expensive tubes, when done for the night, amp in standby, B+ shut off, fil shut off.... but blower stays on for 5-10 mins. Depending on what u were doing beforehand, that anode can get stupid hot...with the requisite airflow.
Tubes cost too much, even to rebuild, so I leave the blower on for a while. I also use the small Variac to bring up the fil V slowly to 7.5 vac. I have a fil V meter...and also a fil ammeter. Fil current comes up from 0-5-10-15-20.....50 amps, over a 20 second period...by hand. Same deal when done for the night..and reducing fil V back to zero. That's my..'new way' of doing 'step start' on directly heated metal tubes. Cold resistance of these tubes is like only 1/10 of the hot resistance, and I was using a surplus fil xfmr, rated for 8.25 vac @ 79 amps. It has a 208 vac input, so the variac has to be used, to make it work. Just about all of the fil xmrs, ( except henry radio 8k ultra) are capable of one helluva lot of peak current, when u lay essentially a dead short on em...like > triple rated current. I'm 90% convinced that's where a lot of grid to fil shorts come from.
On the L4B 2 x 3-500Z amps, I just let the amp sit on standby for a few mins, then shut it down..which shuts everything off, no blower over run used, but that may well change on my next round of mods.... more of an experiment.
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:)I have often thought about this , and where the heating of envelopes and pins that unsolder themselves like in the TL-922 I was wondering about a mod that will cure this problem.
Having a circuit, run off mains that will run fan and have a run on timer circuit, much like run on circuit for automotive radiator fans.
OR.. Having an Bi-metallic clickson temperature switch, like the ones used in microwaves to sense the exhaust air, and not turn off unless the air Temp is below 55 or 60 Degrees C.
The problem we face in South Africa is that the power utility can be turned off without warning and Having an TL-922 with 3-500Z tubes, this is a huge problem. If power goes off in the middle of an QSO and tubes are hot, the pins unsolder themselves.
Still working on an ups or battery backup for the Fan on this issue.
73 De William , ZS4L / ZS5WC
The TL-922, already has fan over run built into it. I think it runs for like 5-10 mins. For frequent power outages, I would replace the fan with a 12 vdc unit.... and power it externally from a battery/ charger setup.
I have experimented with the Klixon ( fixed temp) sensors / spst-NO switches...which close on a temp rise. Problem is, u cant' adjust em. Recently, I bought a few german, fully adjustable types, that also close on a temp rise when temp exceeds the dialed up level. It's just a T stat..that is used for cooling, and trips on a temp rise. They are designed to fit a standard DIN rail setup, and they came with mating short DIN rails. Din rail mounted 1st...the the T stat just snaps into the Din rail. I use that on the HB B+ supply, with it's pair of 10" slowed down fans.
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I repaired a TL922 a couple of weeks ago that lost the solder in one of the filament sockets in spite of a working time delay fan shut off. The problem with many 3-500Z amps is the fan blows across the tubes rather than up through the sockets as they were designed to be operated. Eventually the filament pin connections get higher resistance from age and corrosion and melt the solder. Very common.
Sometimes the only permanent cure is replace the socket.
I let my amps run a considerable amount of time before I turn them off. Just out of habit.
I have a 3-1000Z amp and the tube is visible through a screen covered glass as was the style back in the day. I would ask you to look at a glass tube and see how quickly it looses color either after a transmission or when the filaments are turned off. A few seconds... the color is gone.
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But there IS some official guidance on this. The CPI data sheet for the Eimac YC-179/YC-179A power triode states:
"Airflow must be applied before or simultaneously with the application of power, including the tube heater, and should normally be maintained for several minutes after power is removed for tube cool-down."
Brian - K6BRN
I found a similar requirement under the seal cooling heading in an early 1950s issue of the Eimac tube catalog, courtesy of W9ADM who is long SK by now. See p. 36:
https://worldradiohistory.com/Archive-Catalogs/EIMAC/Eimac-Tubes-Catalog-1950-1953.pdf (https://worldradiohistory.com/Archive-Catalogs/EIMAC/Eimac-Tubes-Catalog-1950-1953.pdf)
"Air and water flow must be started before filament and cathode power are applied and maintained for at least two minutes after the filament
and cathode power have been removed..."
Paul, W9AC
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VE7RF said:
I have experimented with the Klixon ( fixed temp) sensors / spst-NO switches...which close on a temp rise. Problem is, u cant' adjust em. Recently, I bought a few german, fully adjustable types, that also close on a temp rise when temp exceeds the dialed up level. It's just a T stat..that is used for cooling, and trips on a temp rise. They are designed to fit a standard DIN rail setup, and they came with mating short DIN rails. Din rail mounted 1st...the the T stat just snaps into the Din rail. I use that on the HB B+ supply, with it's pair of 10" slowed down fans.
If air temperature is a premium detail in an amp then install a temp switch with the probe in the airstream. SOR or Ashcroft makes them and they are adjustable. The ones we had at work were a couple hundred dollars but they were for a Class I Div. I environment. I thought they made ones that were cheaper because we had a 'purchasing consultant' that felt we needed to save money not realizing they were being used within 5' of solvent charging.
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I repaired a TL922 a couple of weeks ago that lost the solder in one of the filament sockets in spite of a working time delay fan shut off. The problem with many 3-500Z amps is the fan blows across the tubes rather than up through the sockets as they were designed to be operated. Eventually the filament pin connections get higher resistance from age and corrosion and melt the solder. Very common.
Sometimes the only permanent cure is replace the socket.
I let my amps run a considerable amount of time before I turn them off. Just out of habit.
I have a 3-1000Z amp and the tube is visible through a screen covered glass as was the style back in the day. I would ask you to look at a glass tube and see how quickly it looses color either after a transmission or when the filaments are turned off. A few seconds... the color is gone.
Typ Johnson style 3-500Z sockets all have ...'helper springs' on all their existing contacts, that provide additional tension.
Pins 1+5 are the fil...and pins 2-3-4 are the grid pins. Folks have removed the sockets..and swapped pins 1+5 for pins 2+3. Then you have a good set of contacts for the fil pins. Then tweak the bad contacts before installing into pins 2+3. ..which will be good enough for the grid pins.
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VE7RF said:I have experimented with the Klixon ( fixed temp) sensors / spst-NO switches...which close on a temp rise. Problem is, u cant' adjust em. Recently, I bought a few german, fully adjustable types, that also close on a temp rise when temp exceeds the dialed up level. It's just a T stat..that is used for cooling, and trips on a temp rise. They are designed to fit a standard DIN rail setup, and they came with mating short DIN rails. Din rail mounted 1st...the the T stat just snaps into the Din rail. I use that on the HB B+ supply, with it's pair of 10" slowed down fans.
If air temperature is a premium detail in an amp then install a temp switch with the probe in the airstream. SOR or Ashcroft makes them and they are adjustable. The ones we had at work were a couple hundred dollars but they were for a Class I Div. I environment. I thought they made ones that were cheaper because we had a 'purchasing consultant' that felt we needed to save money not realizing they were being used within 5' of solvent charging.
I looked at that method, and at the time, was too expensive, and also required dcv to operate it. I wanted a dead simple T stat, that's bullet proof, and the german Din rail T-stats were cheap, and bombproof. No DCV required to operate em, and contacts rated for 300 vac @ 20 amps. The T stat could be used to turn on a fan (or blower), or could be used to shunt out a resistor... to speed up a fan.
I have since tried yet another method for cooling on the hb B+ supply, and simply wired the 2 x 115 vac fans in series, and ran em on 118 vac....so each fan gets 59 vac. The pair of 9" diam fans gets 59 vac..and fans on all the time. Beyond dead quiet. When bigger diam fans are slowed down, the noise level drops a bunch...and also the PITCH drops in freq a bunch. Low level, low freq fan noise is something one can easily tolerate. I also tested each fan individually with a small 0-130 vac variac, and found they would turn on with just 15 vac applied. I also tried both fans wired in series, and used the small variac to turn them on. They both start spinning with 30 vac applied ( 15 vac dropped across each fan).
Don't ever operate identical 120 vac blower's in series.....and apply 240 vac to the mess....esp if they have the usual start / run caps installed. When T=0, at initial turn on, the V drop across each blower is vastly different, like 200 vac across 1st blower...and just 40 vac across the 2nd blower. Scott tried just that, using a pair of identical 120 vac Kooltronics blowers...and his line V was on the high side, like 250. Smoked one of the blowers.
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AB-20...and all the application bulletins are on eimacs website.
https://www.cpii.com/library.cfm/1#22
It's the 3rd item up from the bottom of the huge list. Scroll right to the bottom....then u will see it.
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For a pair of 3-500z, my theory is that you want the ENTIRE tube to cool as evenly as you can. If the amp is shut down soon after a long transmission is the cooling un-even? Meaning, if the base is cooled at a different rate than the glass envelope, that can't be good for the seal. This is just my thoughts, no scientific tests made.
Opinions?
On my 922, in addition to a stronger factory fan installed, I have holes below the tubes with fans that are mounted on the outside/bottom below which blow air up from outside air to the bottom of the tubes. This has gotta help. I leave them on for a while after use. Time will tell.
Bob
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VE7RF said:
I looked at that method, and at the time, was too expensive, and also required dcv to operate it. I wanted a dead simple T stat, that's bullet proof, and the german Din rail T-stats were cheap, and bombproof. No DCV required to operate em, and contacts rated for 300 vac @ 20 amps. The T stat could be used to turn on a fan (or blower), or could be used to shunt out a resistor... to speed up a fan
I don't know what you mean by expensive but an Ashcroft temp. switch is nothing but a sealed capillary filled with a thermo-active fluid, (usually glycol). As the temp goes up, the fluid expands and pushes a plunger that activates a 10A micro-switch. No power whatsoever is required.
Edit: Jim I know you are a 'motorhead', here's a dirt cheap one for $24 from Amazon. Same as on a HVAC system. https://www.amazon.com/American-Volt-Adjustable-Thermostat-Temperature/dp/B01E52O5DG/ref=asc_df_B01E52O5DG?tag=bngsmtphsnus-20&linkCode=df0&hvadid=80195746824459&hvnetw=s&hvqmt=e&hvbmt=be&hvdev=c&hvlocint=&hvlocphy=&hvtargid=pla-4583795273577896&psc=1