I think the real reason we don't see fans on more amps is because not enough new amps are being returned for warranty service with problems that would have been eliminated by a fan.
Is there a reason why more high end amps don't have fans?
- Thread starter gmm52
- Start date
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Wouldn’t accidentally spilling a cold beer on it accomplish the same thing?
I guess it would be ideal to keep the power tubes in their own little world apart from the other components, but how wide would the chassis have to be then? And there’s that hot tempered output transformer that would have to be isolated. I think tube amps are just gonna run
hot. It’s their nature.
Skyhook
Friend of Leo's
The fan is supposed to pull the hot air out, not the other way around.
Depends a bit on the placement but if it's mounted as part of the
outside wall, then yeah, it’s a puller.
Tim S
Friend of Leo's
Ampeg took a different approach with their old flip-top design — an exposed amp head with no shell. The exposed tubes and transformers have nothing above them and room-temperature air surrounding them.Wouldn’t accidentally spilling a cold beer on it accomplish the same thing?
I guess it would be ideal to keep the power tubes in their own little world apart from the other components, but how wide would the chassis have to be then? And there’s that hot tempered output transformer that would have to be isolated. I think tube amps are just gonna run
David PNW
Tele-Holic
It may depend on the size of the cabinet and air flow.
When I had my Mesa Boogie Head, it came with a fan. When I took it to Mesa and had it changed to a combo, they left the fan off. I asked about it, and they explained that it was not necessary, having a larger cabinet with proper air flow. Also this was a full size head and the cabinet was bigger than the short head cabinet.
When I had my Mesa Boogie Head, it came with a fan. When I took it to Mesa and had it changed to a combo, they left the fan off. I asked about it, and they explained that it was not necessary, having a larger cabinet with proper air flow. Also this was a full size head and the cabinet was bigger than the short head cabinet.
That makes me feel much better, as I kick the redundant amp back under the stairs.
Dmelton1955
TDPRI Member
Maybe because I'm an old guy, had what you might call a high end amp I got new in 1977, Mesa Boogie. It had 60/100 watts. Turned out it was too loud no matter what I did, traded for a reissue Fender Bassman in1990. Now I use a Deluxe, 100 watts is way too much, 15-20 watts sounds better and you can just mic it if you need to
Dmelton1955
TDPRI Member
Ha ha on me now I get it, my bad. But on the subject of fans I have an 80 year old Masco combo that gets really hot, I just put a fan, (one that doesn't have exposed blades so no flutter) in front, now cool as a cucumber
tele_jas
Tele-Afflicted
I've had amps without fans for 30+ years, but I've also had a few amps with fans during this period. I currently only have one tube amp (went Kemper 2 years ago), it has a fan with an on/off switch. So, if you're recording and it's bothering you or you can hear it, you can turn it off.
On the amps I've had without fans, I never had any overheating issues, even playing outside in 110 degree heat in direct sunlight. I have, on the other hand, taken a few "mass produced" amps apart and seen warped parts due to the heat, but usually not on any handwired amps. Both still worked fine. Actually, the ONLY amp I've ever had shut down on me from overheating was a solid state/modeling amp around 2004, it was a Line 6 Vetta. We were playing a lake gig, outside, in direct sunlight and it was 110 that day. It got so hot, it busted the LCD screen and it just stopped working. I had to get my Dads 1969 Fender Deluxe out and a couple Tubescreamers to finish the show.
A few years ago, I was playing my AC30 in my "music room"... My wife walked in and dropped a basket full of towels down and asked me to help fold them before we left on a 10 day trip out of town. I sat down my guitar, folded the towels.....I thought "I'm going to keep one towel to cover my amp to keep the dust off it", so I threw a heavy beach towel towel on top of my amp (which covered it almost completely)..... I then put up my guitar and carried out the basket of towels and turned out the light. 10 days later, we get back home and I walk into my "music room" and could smell a hot amp. I never turned it off, or put it on standby before throwing that towel on top of it!?!!??! I changed power tubes and played that amp for 2 more years without any issues, before selling it.
I think most tube amps are more resilient than people give them credit for. But, I've also heard of some catching fire or melting knobs....so, there's also that
On the amps I've had without fans, I never had any overheating issues, even playing outside in 110 degree heat in direct sunlight. I have, on the other hand, taken a few "mass produced" amps apart and seen warped parts due to the heat, but usually not on any handwired amps. Both still worked fine. Actually, the ONLY amp I've ever had shut down on me from overheating was a solid state/modeling amp around 2004, it was a Line 6 Vetta. We were playing a lake gig, outside, in direct sunlight and it was 110 that day. It got so hot, it busted the LCD screen and it just stopped working. I had to get my Dads 1969 Fender Deluxe out and a couple Tubescreamers to finish the show.
A few years ago, I was playing my AC30 in my "music room"... My wife walked in and dropped a basket full of towels down and asked me to help fold them before we left on a 10 day trip out of town. I sat down my guitar, folded the towels.....I thought "I'm going to keep one towel to cover my amp to keep the dust off it", so I threw a heavy beach towel towel on top of my amp (which covered it almost completely)..... I then put up my guitar and carried out the basket of towels and turned out the light. 10 days later, we get back home and I walk into my "music room" and could smell a hot amp. I never turned it off, or put it on standby before throwing that towel on top of it!?!!??! I changed power tubes and played that amp for 2 more years without any issues, before selling it.
I think most tube amps are more resilient than people give them credit for. But, I've also heard of some catching fire or melting knobs....so, there's also that
The diode on the underside of the board seems to be the weak point. Not an easy thing sticking in a heatsink onto it but I managed even with the high voltage pins of the transformer sticking out.
Even so it only gave me another couple of watts. Going to try a faster diode.
If I was a betting man I would put all my money on a bet that covering an AC30 and leaving it on for 10 days would result in a blowed up amp!I've had amps without fans for 30+ years, but I've also had a few amps with fans during this period. I currently only have one tube amp (went Kemper 2 years ago), it has a fan with an on/off switch. So, if you're recording and it's bothering you or you can hear it, you can turn it off.
On the amps I've had without fans, I never had any overheating issues, even playing outside in 110 degree heat in direct sunlight. I have, on the other hand, taken a few "mass produced" amps apart and seen warped parts due to the heat, but usually not on any handwired amps. Both still worked fine. Actually, the ONLY amp I've ever had shut down on me from overheating was a solid state/modeling amp around 2004, it was a Line 6 Vetta. We were playing a lake gig, outside, in direct sunlight and it was 110 that day. It got so hot, it busted the LCD screen and it just stopped working. I had to get my Dads 1969 Fender Deluxe out and a couple Tubescreamers to finish the show.
A few years ago, I was playing my AC30 in my "music room"... My wife walked in and dropped a basket full of towels down and asked me to help fold them before we left on a 10 day trip out of town. I sat down my guitar, folded the towels.....I thought "I'm going to keep one towel to cover my amp to keep the dust off it", so I threw a heavy beach towel towel on top of my amp (which covered it almost completely)..... I then put up my guitar and carried out the basket of towels and turned out the light. 10 days later, we get back home and I walk into my "music room" and could smell a hot amp. I never turned it off, or put it on standby before throwing that towel on top of it!?!!??! I changed power tubes and played that amp for 2 more years without any issues, before selling it.
I think most tube amps are more resilient than people give them credit for. But, I've also heard of some catching fire or melting knobs....so, there's also that
Wow!
WRT "need a fan", we do know that some components in particular filter caps are sensitive to heat and deteriorate faster if kept too hot.
The fact that almost all vintage Marshall and Fender amps have been observed to retain original caps and tubes and virtually every original part for decades, still in fine working order, pretty much confirms the fans of fans are just a bunch of nervous nellies.
Unless the amp in question is poorly designed or designed without adequate convection cooling.
By now not really many if any of those 60s & 70s hand wired built to tour in broke down vans with bad suspension and no AC do still have all original parts, but us older players remember those amps with 20-30 year old tubes and filter caps, as typical.
When BF Fender amps were kind of the standard bar band amp and sitting cheap in guitar shops all lined up and plentiful, new filter caps was rare.
I bought those amps from 1980 to 2005 and never found a single one had new filter caps.
Same with a dozen vintage Marshalls, not a single one had replaced filter caps and none had fans added either.
So the need for fans in properly designed amps is a myth.
Miniaturized amps crammed into little cabs would be an exception.
Mesa introduced amps that need fans when they crammed 100w guts and 12" EV speakers into 12w Princeton Reverbs.
The AC30 would be a Shaman or Magus among tube amps and is not normal, so should be excluded from the stats!
The fact that almost all vintage Marshall and Fender amps have been observed to retain original caps and tubes and virtually every original part for decades, still in fine working order, pretty much confirms the fans of fans are just a bunch of nervous nellies.
Unless the amp in question is poorly designed or designed without adequate convection cooling.
By now not really many if any of those 60s & 70s hand wired built to tour in broke down vans with bad suspension and no AC do still have all original parts, but us older players remember those amps with 20-30 year old tubes and filter caps, as typical.
When BF Fender amps were kind of the standard bar band amp and sitting cheap in guitar shops all lined up and plentiful, new filter caps was rare.
I bought those amps from 1980 to 2005 and never found a single one had new filter caps.
Same with a dozen vintage Marshalls, not a single one had replaced filter caps and none had fans added either.
So the need for fans in properly designed amps is a myth.
Miniaturized amps crammed into little cabs would be an exception.
Mesa introduced amps that need fans when they crammed 100w guts and 12" EV speakers into 12w Princeton Reverbs.
The AC30 would be a Shaman or Magus among tube amps and is not normal, so should be excluded from the stats!
CoolBlueGlow
Friend of Leo's
re: Leo and Jim didn't do it, so we don't need it
Fan cooling was not introduced by Leo Fender or Jim Marshall because at that time there was no such thing as a DC powered low noise miniature fan. Fan technology has come a very very long way since the 1960's. In my opinion, the argument that "Leo and Jim didn't" is not a valid argument.
From where I stand, they didn't because they coudn't. No such fan existed. In the early 1950's HERE is what the available fans looked like;
These are Tektronix oscilloscopes from the early 1950's era. They had these big expensive clunky AC powered fans because quality engineering design determined that they were an absolute requirement for reliability and durability. This scope cost around $2,000 in 1952 - the heyday of Leo Fender's first amplifier design. FWIW, $2,000 in 1952 dollars is between $20,000 and $100,000 2023 dollars. (depending on the scale you use)
In 1952, the most expensive Fender amplifier made retailed for $203.50... 10% of a typical Tek scope!
So, in 1952, what kind of fan did a $2,000 oscilloscope use? They used the only thing that was available, which you see in these pictures. It looks like this;
Standard 1950's/1960's Tektronix cooling fan motor. This one is from 1962.
This design persisted from 1950 until the early 1970's.
1962 Tektronix 575 cooling fan, restored
The point is this. Leo and Jim didn't use fans because for them such a thing was almost impossible. Besides their rarity, fans cost (big) money, fans were large, ugly and added complexity and noise. Besides, from Jim and Leo's perspective "radios don't have them, and they've worked just fine as an appliance for more than 25 years!".
In 1950-1965, little thought or care or even ways to measure or quantify amplifier thermal issues existed. Neither Mr. Fender or Mr. Marshall or Ken Bran had any particular training in chassis thermodynamics, or the materials sciences of capacitors or transformer winding. I doubt very much if Leo Fender in 1952 could have told you the performance specification of the insulation on the wire in the transformers he was putting into his amps, much less its maximum thermal tolerances. He had only two choices, plain enamel and Formvar®. To determine this would require months of investigation, scores of hand-written letters, and in some cases the information was still a deeply held trade secret (aka "Formvar®")
Besides that, at the beginning - when so many stylistic design decisions were made - neither of these very great men had anything like test gear to even measure things like capacitor or transformer core temperatures and correlate them to things like transformer or capacitor life. Those issues were barely even considered in the 1930's and 40's designs that Jim Marshall and Leo Fender and everybody else in guitar amp wave 1 cut their teeth on.
1952 was a far different world electronically than today - and 1966 was not much different than 1952 for consumer electronics in merrie olde England whe Ken Bran and Jim Marshall cloned the Bassman into the first Marshall. They were built from miltary surplus bits bought wholesale or secondhand. NOTHING was custom made for Marshall. (or Fender, until much later).
What became the "industry standard" Gen. 1 fan some of you know as the "Muffin Fan" was not even standardized as a military specification until 1961, under MIL-B-23071. (You can download the spec and review it. I have.) It very clearly defines every concievable aspect of standardized cooling fan design, including physical dimensions, airflow, noise, interference and just about anything you ever wanted to know about fans. That was 1961.
It took fifteen more years before anything like a music-equipment friendly fan appeared. The slightly more familiar to musicians Rotron Whisper Fan - still AC powered, did not appear until 1976. That was eleven years after Leo Fender departed Fender Musical instruments.
D.C. powered permanent magnet low noise computer CPU and PSU fans did not appear until the 1980's, with the invention of high permeability magnetic materials like samarium cobalt and a few years later neodymium. They were not commonly available as surplus until the 1990's.
So - the argument that "Jim and Leo didn't so that means no fan is good enough" is specious. We don't know what Jim and Leo would have done if they would have had inexpensive efficient ultra quiet DC powered computer fans, and CNC machined CPU heat sinks and practical flitering materials, and thermal cameras and digital temperature measuring equipment, etc. I suspect they would have included fans everywhere it made economic and design performance sense. The benefit is too obvious.
But, about those fans and that heat;
The real question is not "why didn't Leo". The real question is a thermodynamics and materials sciences question, specifically "what is the total thermal load of amplifier X when contained in chassis Y", and "Does it keep component groups A, B and C within operating ratings as specified by their various suppliers?" That is the only design question that matters. Some amps succeed at this without fans. Some need fans and get them. Others would be better off with fans, but don't get them for reasons of cheapness, oversight, and bad design or tradition. As many of you know, amplifiers sometimes eventually self-destruct in mysterious ways that operators blame on a dozen other things that are really symptoms. Oh, it was "Bad caps"... Yeah, a capacitor failed but WHY did it fail? Or, "The rectifier tube arc'd over" Yes, but WHY? Did the internals sag because you went 50 degrees beyond the thermal maximum, and thus short out?
Cooling - all amps do it. Some do it well, some do it terribly.
Heat transfer is accomplished by radiation and by conduction. These can be aided by convection, and by forced air movement and by electro-chemical heat transfer combined with forced air movement. (your air conditioner is an example of electro-chemical forced air heat exchange)
It is undeniable that some amp designs do a better job of venting and cooling than others. The wide range of cooling quality in various designs establishes that amplifier cooling is not a settled science among historic manufacturing brands. Frankly, it is not even a consideration for some amplifier manufacturers. And, even if it is, different designers achieve differing degress of success for convection cooling based on budget, skill, and traditions that are unsupported by even basic thermodynamic reality.
An amp may be designed so that convection is deliberate, or it may be an accident or afterthought. Obvious convection opportunities may be blatently overlooked. A 1950's Fender Bassman is an example of an amplifier that misses an obvious opportunity for convection cooling.
A Marshall Combo from the 1960's accomplishes substantial convection cooling by simply including an upper vent panel that Fender didn't see fit to include, and by rethinking the tube and transformer layout a bit.
A 1960's Fender Dual Showman head is an example of an amplifier with poor convection and conduction cooling, and with excessive concentration of heat energy in a confined space. An amp like the 1960's Dual Showman may be designed so that there is poor conduction, poor radiation and little or no convection, and yet "work o.k." according to a consumer mindset.
But in general, a great many classic Fender designs show a particular lack of awareness of the need for convection cooling airflow. Meanwhile, many Marshall designs seem to be at least nominally aware of this opportunity, which is why classic Marshall designs have convection grills and classic Fenders by and large don't. Obviously, Leo and Jim didn't think the same way about cooling.
Meanwhile, other manufacturers who cut their teeth in the 1970's (like Mesa Boogie) have routinely installed fans in their amplifiers...because they could and sometimes because they had to. The thermal density of the Mesa Boogie designs (4 6L6 and a massive power transformer in a poorly vented cabinet) made them a requirement for survival at Randall Smith's standard.
Its the tubes that get hot, right? Well...sort of
Yes, tubes get hot - sometimes because of runaway operational parameters - but the primary transformer is the real point of concern for routinely excessive operational temperature issues, followed closely by the primary filter capacitors. Rectifier tubes are next, and then your power tubes. Then preamp tubes, all other capacitors and finally resistors.
Primary transformers are big bundles of hundreds or even thousands of winds of thinly insulated wire wrapped in poorly conductive paper and varnish.
A Hammond AO-44 power transformer (Like the ones Dr. Z used in his first amps) has six layers of #26 wire with 52 winds per layer, covered by 12 more layers of #32 wire with 125 winds per layer, covered by one more layer of #22 wire with 24 winds. There are paper insulating layers between each of these layers. It is all soaked in varnish and then enclosed in end bells and stuffed with EI core pieces. Not a very good recipe for thermal conduction.
This wire insulation in that little transformer has an absolute maximum temperature before failure. Do you know it? It is 221 degrees F, or 105ºC The same as most classic Fenders and Marshalls from the 50's - 70's.
Guitarists may know some insulation types, like enamel, so-called "poly" and Formvar®, which is a proprietary name for a particular resin, because they're used on pickup windings. But there are five common thermal classes of magnet wire insualtion. The stuff from Leo's heyday was typically plain enamel or formvar, both of which fall in the lowest temperature class - 105ºC maximum. The most modern high-performance insulations exceed this performance by 135ºC. Polyamides can handle up to 240º degrees Celsius. That's over 450 degrees Farenheit. Yep, you can put a polyamide wound transformer in your oven and cook it at 375 all day long, no harm done. FWIW, 105ºC is 221ºF.
Now, what do you think most transformer manufacturers use for "guitar transformers"? They use the cheapest thing they can get away with based on 'experience'...just like Leo Fender did!
More to the point, ask yourself - how hot does MY primary transformer get at its core when utilized hard? Do you know? Have you personally measured any transformer temperatures? Do you know how poorly transformers conduct internal temperatures? Have you measured that?
I have done this on my amplifiers.
Call me a worry wart, but as a result, I put fans on virtually every amplifier I build. I add fans to many of my vintage amps. Adding a fan can be done non-destructively, and at the end of the day what's worse for value deduction - an amp with an added fan or an amp with a replacement mains transformer?
Because I pay attention to dumb stuff like transformer temperatures and stuff like that, I understand that 105ºC was the maximum for plain enamel and Formvar® when these units were brand new. Many are now approaching 60 years of age or more. A simple DC powered low speed cooling fan properly installed and directed can reduce transformer temperatures by 20-40º C, depending on the amp. If your transformer is operating at 95ºC at the core, you have a very tiny margin of error. If you reduce the transformer's core temperature by 30ºC, you have more than doubled the margin of safety. If you increase it by 20 degrees, you will release the magic smoke.
Of course, it is speculation, but if Leo Fender was standing in my poor little Muffin Laboratory examining those measurements and the data for insulation breakdown temperatures, I think he would reconsider the idea of forced cooling, as well as his bad convection decisions on classics like the Bassman and others.
But do what you want. Based on careful measurements taken from real world usage scenarios for primary transformer temperatures, I use fans.
Fan cooling was not introduced by Leo Fender or Jim Marshall because at that time there was no such thing as a DC powered low noise miniature fan. Fan technology has come a very very long way since the 1960's. In my opinion, the argument that "Leo and Jim didn't" is not a valid argument.
From where I stand, they didn't because they coudn't. No such fan existed. In the early 1950's HERE is what the available fans looked like;
These are Tektronix oscilloscopes from the early 1950's era. They had these big expensive clunky AC powered fans because quality engineering design determined that they were an absolute requirement for reliability and durability. This scope cost around $2,000 in 1952 - the heyday of Leo Fender's first amplifier design. FWIW, $2,000 in 1952 dollars is between $20,000 and $100,000 2023 dollars. (depending on the scale you use)
In 1952, the most expensive Fender amplifier made retailed for $203.50... 10% of a typical Tek scope!
So, in 1952, what kind of fan did a $2,000 oscilloscope use? They used the only thing that was available, which you see in these pictures. It looks like this;
Standard 1950's/1960's Tektronix cooling fan motor. This one is from 1962.
This design persisted from 1950 until the early 1970's.
1962 Tektronix 575 cooling fan, restored
The point is this. Leo and Jim didn't use fans because for them such a thing was almost impossible. Besides their rarity, fans cost (big) money, fans were large, ugly and added complexity and noise. Besides, from Jim and Leo's perspective "radios don't have them, and they've worked just fine as an appliance for more than 25 years!".
In 1950-1965, little thought or care or even ways to measure or quantify amplifier thermal issues existed. Neither Mr. Fender or Mr. Marshall or Ken Bran had any particular training in chassis thermodynamics, or the materials sciences of capacitors or transformer winding. I doubt very much if Leo Fender in 1952 could have told you the performance specification of the insulation on the wire in the transformers he was putting into his amps, much less its maximum thermal tolerances. He had only two choices, plain enamel and Formvar®. To determine this would require months of investigation, scores of hand-written letters, and in some cases the information was still a deeply held trade secret (aka "Formvar®")
Besides that, at the beginning - when so many stylistic design decisions were made - neither of these very great men had anything like test gear to even measure things like capacitor or transformer core temperatures and correlate them to things like transformer or capacitor life. Those issues were barely even considered in the 1930's and 40's designs that Jim Marshall and Leo Fender and everybody else in guitar amp wave 1 cut their teeth on.
1952 was a far different world electronically than today - and 1966 was not much different than 1952 for consumer electronics in merrie olde England whe Ken Bran and Jim Marshall cloned the Bassman into the first Marshall. They were built from miltary surplus bits bought wholesale or secondhand. NOTHING was custom made for Marshall. (or Fender, until much later).
What became the "industry standard" Gen. 1 fan some of you know as the "Muffin Fan" was not even standardized as a military specification until 1961, under MIL-B-23071. (You can download the spec and review it. I have.) It very clearly defines every concievable aspect of standardized cooling fan design, including physical dimensions, airflow, noise, interference and just about anything you ever wanted to know about fans. That was 1961.
It took fifteen more years before anything like a music-equipment friendly fan appeared. The slightly more familiar to musicians Rotron Whisper Fan - still AC powered, did not appear until 1976. That was eleven years after Leo Fender departed Fender Musical instruments.
D.C. powered permanent magnet low noise computer CPU and PSU fans did not appear until the 1980's, with the invention of high permeability magnetic materials like samarium cobalt and a few years later neodymium. They were not commonly available as surplus until the 1990's.
So - the argument that "Jim and Leo didn't so that means no fan is good enough" is specious. We don't know what Jim and Leo would have done if they would have had inexpensive efficient ultra quiet DC powered computer fans, and CNC machined CPU heat sinks and practical flitering materials, and thermal cameras and digital temperature measuring equipment, etc. I suspect they would have included fans everywhere it made economic and design performance sense. The benefit is too obvious.
But, about those fans and that heat;
The real question is not "why didn't Leo". The real question is a thermodynamics and materials sciences question, specifically "what is the total thermal load of amplifier X when contained in chassis Y", and "Does it keep component groups A, B and C within operating ratings as specified by their various suppliers?" That is the only design question that matters. Some amps succeed at this without fans. Some need fans and get them. Others would be better off with fans, but don't get them for reasons of cheapness, oversight, and bad design or tradition. As many of you know, amplifiers sometimes eventually self-destruct in mysterious ways that operators blame on a dozen other things that are really symptoms. Oh, it was "Bad caps"... Yeah, a capacitor failed but WHY did it fail? Or, "The rectifier tube arc'd over" Yes, but WHY? Did the internals sag because you went 50 degrees beyond the thermal maximum, and thus short out?
Cooling - all amps do it. Some do it well, some do it terribly.
Heat transfer is accomplished by radiation and by conduction. These can be aided by convection, and by forced air movement and by electro-chemical heat transfer combined with forced air movement. (your air conditioner is an example of electro-chemical forced air heat exchange)
It is undeniable that some amp designs do a better job of venting and cooling than others. The wide range of cooling quality in various designs establishes that amplifier cooling is not a settled science among historic manufacturing brands. Frankly, it is not even a consideration for some amplifier manufacturers. And, even if it is, different designers achieve differing degress of success for convection cooling based on budget, skill, and traditions that are unsupported by even basic thermodynamic reality.
An amp may be designed so that convection is deliberate, or it may be an accident or afterthought. Obvious convection opportunities may be blatently overlooked. A 1950's Fender Bassman is an example of an amplifier that misses an obvious opportunity for convection cooling.
A Marshall Combo from the 1960's accomplishes substantial convection cooling by simply including an upper vent panel that Fender didn't see fit to include, and by rethinking the tube and transformer layout a bit.
A 1960's Fender Dual Showman head is an example of an amplifier with poor convection and conduction cooling, and with excessive concentration of heat energy in a confined space. An amp like the 1960's Dual Showman may be designed so that there is poor conduction, poor radiation and little or no convection, and yet "work o.k." according to a consumer mindset.
But in general, a great many classic Fender designs show a particular lack of awareness of the need for convection cooling airflow. Meanwhile, many Marshall designs seem to be at least nominally aware of this opportunity, which is why classic Marshall designs have convection grills and classic Fenders by and large don't. Obviously, Leo and Jim didn't think the same way about cooling.
Meanwhile, other manufacturers who cut their teeth in the 1970's (like Mesa Boogie) have routinely installed fans in their amplifiers...because they could and sometimes because they had to. The thermal density of the Mesa Boogie designs (4 6L6 and a massive power transformer in a poorly vented cabinet) made them a requirement for survival at Randall Smith's standard.
Its the tubes that get hot, right? Well...sort of
Yes, tubes get hot - sometimes because of runaway operational parameters - but the primary transformer is the real point of concern for routinely excessive operational temperature issues, followed closely by the primary filter capacitors. Rectifier tubes are next, and then your power tubes. Then preamp tubes, all other capacitors and finally resistors.
Primary transformers are big bundles of hundreds or even thousands of winds of thinly insulated wire wrapped in poorly conductive paper and varnish.
A Hammond AO-44 power transformer (Like the ones Dr. Z used in his first amps) has six layers of #26 wire with 52 winds per layer, covered by 12 more layers of #32 wire with 125 winds per layer, covered by one more layer of #22 wire with 24 winds. There are paper insulating layers between each of these layers. It is all soaked in varnish and then enclosed in end bells and stuffed with EI core pieces. Not a very good recipe for thermal conduction.
This wire insulation in that little transformer has an absolute maximum temperature before failure. Do you know it? It is 221 degrees F, or 105ºC The same as most classic Fenders and Marshalls from the 50's - 70's.
Guitarists may know some insulation types, like enamel, so-called "poly" and Formvar®, which is a proprietary name for a particular resin, because they're used on pickup windings. But there are five common thermal classes of magnet wire insualtion. The stuff from Leo's heyday was typically plain enamel or formvar, both of which fall in the lowest temperature class - 105ºC maximum. The most modern high-performance insulations exceed this performance by 135ºC. Polyamides can handle up to 240º degrees Celsius. That's over 450 degrees Farenheit. Yep, you can put a polyamide wound transformer in your oven and cook it at 375 all day long, no harm done. FWIW, 105ºC is 221ºF.
Now, what do you think most transformer manufacturers use for "guitar transformers"? They use the cheapest thing they can get away with based on 'experience'...just like Leo Fender did!
More to the point, ask yourself - how hot does MY primary transformer get at its core when utilized hard? Do you know? Have you personally measured any transformer temperatures? Do you know how poorly transformers conduct internal temperatures? Have you measured that?
I have done this on my amplifiers.
Call me a worry wart, but as a result, I put fans on virtually every amplifier I build. I add fans to many of my vintage amps. Adding a fan can be done non-destructively, and at the end of the day what's worse for value deduction - an amp with an added fan or an amp with a replacement mains transformer?
Because I pay attention to dumb stuff like transformer temperatures and stuff like that, I understand that 105ºC was the maximum for plain enamel and Formvar® when these units were brand new. Many are now approaching 60 years of age or more. A simple DC powered low speed cooling fan properly installed and directed can reduce transformer temperatures by 20-40º C, depending on the amp. If your transformer is operating at 95ºC at the core, you have a very tiny margin of error. If you reduce the transformer's core temperature by 30ºC, you have more than doubled the margin of safety. If you increase it by 20 degrees, you will release the magic smoke.
Of course, it is speculation, but if Leo Fender was standing in my poor little Muffin Laboratory examining those measurements and the data for insulation breakdown temperatures, I think he would reconsider the idea of forced cooling, as well as his bad convection decisions on classics like the Bassman and others.
But do what you want. Based on careful measurements taken from real world usage scenarios for primary transformer temperatures, I use fans.
It doesn’t matter that much whether it’s pulling or pushing. There still needs to be an inlet for that air, and that’s where the dust comes in.
And a cheap air filter would keep the majority of the dust out. But then you would have to clean it when it gets loaded up. Really not that much of an inconvenience.
I don't think they're really bothered by heat. Tubes can handle heat, and wires too. My guess is that old style tube amps, which is what I have, just don't need them. And they may introduce some oscillation or other mechanical sounds. Maybe a computer based modeling amp would need one if it has a CPU and circuitry?
sinecrafter
Tele-Meister
Because they don't need them for cooling and the noise plays havoc with recording.
Stratocast
Tele-Holic
I have a 600 watt....or so it states ...solid state amp... I do not use it much because I prefer tube amps...it is a Fender... and it Never gets warm...
if your Tubes on your Tube amp are getting extremely warm it could be they need to be set for frequency... tubes need to be in sync with each other... I did not know this until.. one of my tubes got so red that it looked like it was on fire.. inside the glass... and then it blew up.. the tube splattered every where.. luckily it did not cause a fire just a lot of smoke...
I would take your amp in for a "tune-up".. and see what the amp tech says....
it could be your "hot tubes".. either need to be replaced.. or re tuned... it has something to do with wavelengths and frequencies.. and radio waves is all I know or understand about it..
when your amp is tuned.. it should not run hot enough to need a fan,...
Too bad they couldn't have fit a dust filter in there too...
chris m.
Doctor of Teleocity
This is why I keep coming back to TDPRI. Every once in a while you get schooled by someone who really knows what they are talking about! I love it when I get facts instead of opinion. Complete with archival photos of old fan technology. Wow.
Here's a thought-- if someone has a tube amp head where the tubes are mounted below a PCB, would it make sense to turn it upside down? That way the tubes would be above the PCB and the heat would tend to dissipate upwards. Yes, all the knobs would be upside down, but it wouldn't be that hard to deal with....
