6L6 tubes

[bsco]

Question.....I have to replace a set of 6L6's in a Fender Bassman...the originals are the short stubby type....the set I have are longer...meaning that there is only about half inch of space between the top of the tube and the wooden cabinet.....isn't this too close for the heat which would be generated by the tubes?? Don't want to catch anything on fire.....the tubes have spring retainers on them as well.....
Cheers

[gui_tarzan]

I wouldn't worry about it too much, heat rises so there's a good chance it won't bother anything. Most of the heat seems to come out the sides anyway.

[Tom Phillips]

I have often found such amps with 6L6 tubes so tall that it was barely possible to change them with the chassis in the cab. I never saw a problem with overheated cabinet wood.
Tom

[bsco]

I have often found such amps with 6L6 tubes so tall that it was barely possible to change them with the chassis in the cab. I never saw a problem with overheated cabinet wood.
Tom

Ok. That was what I wanted to know.....I will go ahead and install these new tubes...his old ones are way out of wack...one is drawing twice as much current as the other...the new ones are dead on....thanks for the clarification.....
Cheers

[Chuck H]

I wouldn't worry about it too much, heat rises so there's a good chance it won't bother anything. Most of the heat seems to come out the sides anyway.

Off topic. And a bit of nit picking, but...

Heat doesn't rise. Hot air rises. Hot water rises. But heat in a non soluble or non amorphous object only adheres to the criteria of moving to an area of less heat no matter the direction. I'm not just trying to be contrary. I think in a case like this it's important to consider. If the tubes are hot, close to the cabinet and there is no venting then there is a paucity of air to heat and rise. Sure, the wood gets hot and is exposed to the air. So some small amount of heat will dissipate from the surface of the heated wood, but not much.

It shouldn't be too tough to determine if there is a fire hazard. Just run the amp for awhile and see how hot things get Not very scientific, but one would almost certainly know if some measures need to be taken with venting or a fan.

Before I earn the A-hole award for this correction I just want to say that there have been many amp designs that suffer from a lack of heat dissipation because the designer assumed that "heat rises". It's common knowledge. And it's actually, technically wrong. And this is a good thing to know when designing an amp. So this is in the spirit of better design and understanding.

[bsco]

Off topic. And a bit of nit picking, but...

Heat doesn't rise. Hot air rises. Hot water rises. But heat in a non soluble or non amorphous object only adheres to the criteria of moving to an area of less heat no matter the direction. I'm not just trying to be contrary. I think in a case like this it's important to consider. If the tubes are hot, close to the cabinet and there is no venting then there is a paucity of air to heat and rise. Sure, the wood gets hot and is exposed to the air. So some small amount of heat will dissipate from the surface of the heated wood, but not much.

It shouldn't be too tough to determine if there is a fire hazard. Just run the amp for awhile and see how hot things get Not very scientific, but one would almost certainly know if some measures need to be taken with venting or a fan.

Before I earn the A-hole award for this correction I just want to say that there have been many amp designs that suffer from a lack of heat dissipation because the designer assumed that "heat rises". It's common knowledge. And it's actually, technically wrong. And this is a good thing to know when designing an amp. So this is in the spirit of better design and understanding.

No my friend....You will not get the A hole award from me.....Actually you raise a few good points....this cabinet is very small and there is not a lot of room inside for heat venting....and with a cabinet like this (60's Bassman Head) you would not want to install a fan in there....and I want to make sure that there is no way something can happen after I work on it...and come back on me.....That is why I asked....and you guys have more experience at this sort of thing.....so...any comments I will gladly accept......Thanks for the reply...
Cheers
P.S. Both Tom and gui_tarzan mentioned that they have never seen a problem...and they might be right....I am going to run the tubes in the amp for a few days....and see if there is any dis-coloration in the wood...I guess I could install a piece of metal on the bottom so that it will help re-distribute any heat that might be there....but I am going to see if I can find a set of 6L6's that are shorter...then there would be no issues......but the music store here don't have them and apparently can't get them.....
Cheers

[TomCarlos]

Ok.. I volunteer to play the role of "Village Idiot" and ask the idiot question... here we go...

Has anyone ever tested the heat being generated from a tube when (A) the chassis down and tube facing up (on top) vs (C) chassis in case and tube facing down (below the chassis)? Depending on the air and air movement in the case, I sometimes wonder about the chassis (being metalic) radiating the heat back to the tube.

Of course, the fair test case would be the same signal level (frequency, amplitude, speaker load, etc) and the measurements taken using something like as IR Laser Infrared Digital Thermometer?

Sorry... I had to ask... I have always been curious about this.

[Enzo]

No, the warm chassis is not going to heat the tube, but could slow the radiation from the tube some. If you are concerned over the wood, glue some aluminum foil on the cab floor under the tubes.

[Chuck H]

I think the reason gui_tarzan and Tom mention that they've never seen any problem from heat in these amps with bigger tubes may be (They have more experience with this model than I do. And...) it's a class AB1 amp and the tubes don't get that damn hot. The thermal limit spec'd for tubes is pretty obscene IIRC. The amps I'm aware of that have trouble with heat are Class A. When a tube sits idling all the watts it's making need to go somewhere and so they turn into heat. A class AB1 amp idles between, say, 40% and 75% dissipation. A class A amp idles at or slightly above 100%. So, a lot more heat.

Fender didn't change much AFAICT WRT clearance and venting between two and four tube versions. I don't know which one you have but if they were prone to catch fire we would probably know by now. There's pretty good clearance between the tubes and the front of the cab and a big, oval hole right where the tubes are. So some air can convect and move heat from the cab. I wouldn't worry about it (but I also wouldn't take my word for it ). Go with gui_tarzan and Tom's experience on this.

[Pdavis68]

You could staple maybe 2 layers of heavy duty tinfoil to the surface of the wood. A lot of the tinfoil would actually not be in direct contact with the wood and because of this, the tinfoil would act as a bit of an insulator between the tubes and the wood. It would also help dissipate the heat since the heat would move to the sides of the tinfoil furthest from the tube heat and dissipate. Just a thought.

[Chuck H]

You could staple maybe 2 layers of heavy duty tinfoil to the surface of the wood. A lot of the tinfoil would actually not be in direct contact with the wood and because of this, the tinfoil would act as a bit of an insulator between the tubes and the wood. It would also help dissipate the heat since the heat would move to the sides of the tinfoil furthest from the tube heat and dissipate. Just a thought.

That seems like decent reasoning to me. But I don't think even heavy duty tin foil (actually aluminum foil) would be durable enough if not glued. Most walk in hardware stores carry some sort of aluminum sheet product that could be used. I think I cut up an aluminum roof flashing once. I keep a roll of 8" aluminum flashing around now because I got tired of Macgyver-ing projects. Probably still thin enough and eminently less problematic with staples and time. You can still cut the stuff with regular household scissors too

[Pdavis68]

Sorry, I've been calling it "tin foil" my whole life. I realize it's aluminum... Just what they always called it when I was a kid...

[Chuck H]

I still say "tinfoil" all the time. It's only in circumstances like this where I think to differentiate. I don't even know if one can buy tin foil anymore so it would be tough to get it wrong anyway.

[Jazz P Bass]

They make aluminized duct tape.

I use it all the time to repair ripped up Fender Hot Rod's


Aluminum Foil Tapes :: HVAC :: Venture Tape

[eschertron]

They make aluminized duct tape.

I use it all the time to repair ripped up Fender Hot Rod's


Aluminum Foil Tapes*::*HVAC*::*Venture Tape

[ATTACH=CONFIG]34846[/ATTACH]

Hey! That would make a d*mn big capacitor!

...back on topic: is there enough foil on that tape to really be effective for either shielding or heat transfer?