Tubes and Safety regs

[Structo]

Are there regulations about having hot tubes exposed in the back.
Many older amps simply had a 1/4" thick, tolexed board that is screwed on the back, leaving the chassis exposed for power, speakers, etc.

I've seen some amps that have a cage around the power tubes or a wire mesh across the opening to prevent curious fingers out.

Probably a UL or CE mandate.

It's hard enough to get the heat out of a cab let alone closing up the back.
Then to find something that looks classy.

Expanded metal screen looks pretty good when painted black.
Depending on the type, the way the wire is expanded creates a sort of louver appearance that may help the heat leave.

[img:600:600]http://i00.i.aliimg.com/photo/v0/173697 ... home_b.jpg[/img]


Or the perforated metal screen sometimes used for speaker grill.

Although it may not pass enough air to cool the amp.

[img:414:328]http://www.mechanicalmetals.com/images/ ... _metal.png[/img]

Could always add a computer fan but I tend to keep noise makers out of amps.

I know most of the amps here are probably not sold to the public but eventually these amps
will transfer ownership to either an heir as part of an estate or bequeathed to someone else.

What do you guys use to cover the back, if you do?

[Garthhog]

I have heard wind of recent regulations, but I don't know for sure. I use decorative perforated aluminum from McNicols, usually 40% to 50% open for good airflow.

[dorrisant]

Tom, if you run a DC fan at less than its rated voltage it will work, only slower and quieter. I have used a 12v fan running on 5v just to move the air and you had to have your ear impossibly close to hear it. Very little air movement is actually needed to do the trick. Too much movement might cool the power tube too much... Idk. This worked on a Marshall JTM60, notorious for heat issues. Customer has had no more problems for a couple of years now.

I hope they don't make the protection thing mandatory.

[Leo_Gnardo]

I notice the big manuf's have grown tube cages, guessing OSHA or some such has decided to protect users, kids, dogs, cats, ferrets etc from tube burns. Some amp owners ask me to remove them if they rattle. It's funny to see the back of a new Blues Junior, looks like the tubes are "in jail" with those vertical bars. Another artifact of the nanny state. "Let me out, let me out, I wanna ROCK!"

[Structo]

Thanks Tony!

Forgot about that trick as well.

So you run that fan on 5 V AC?

Or you do you slap a diode and cap in there?

[dorrisant]

5VDC... yeah, rectified and filtered. Can't recall what I did exactly..

[Baddog01]

I run my fan off my 6.3vdc filament...

[IMG1365]http://i1051.photobucket.com/albums/s430/baddog01/CE3698C2-3E14-430B-913F-384808F6228B_zpspdkahsva.jpg[/img]

[elk]

Doesn't aluminum help to dissipate heat? I know it's generally not used in the bbq world because it transfers heat so rapidly.

[pdf64]

Fans are good, see http://www.blueglow.de/FenFan.html
For a little more voltage, an FWB rectifier can be used.

[Structo]

Thanks for the link, good information.

[rp]

Can't say about regulations, but the Soldano way to do cab, wide mesh metal grill front and back, is far and away the best way to keep an amp cool. I don't think you'll need a fan unless you have it against a wall or scrim. You can always do belt and suspenders and add a Vox or Marshall like cut out groove with a grill along the top. Should be able to play in Phoenix in August with the air conditioning broken with that.

[Structo]

It's kind of amazing that the early amps really didn't do that great of a job to get rid of the heat.

Usually the heat just drifts out of the back of the cab.

Some heads have ventilation on the front panel but it is usually covered with
grill cloth which inhibits cross ventilation.

With 100W tube amps, add a couple more power tubes and you could probably
cook your dinner on it.

The idea of a fan is intriguing.

Does it blow or suck air in?:lol:

I have read that you shouldn't blow air directly on the power tubes because
it can cause uneven cooling on the tubes.

[R.G.]

The USA has no federal laws mandating compliance with UL. The EU and many other places outside the USA do have laws mandating compliance with certain safety standards.

CE labeling for instance requires freedom from burn hazards and shock hazards as tested with a "test finger" skinny enough and long enough to be more than any normal human could do. Any accessible surface has to be below a specified temperature.

Some places have criminal penalties for damage to people or property from too-hot surfaces or shock hazards, some only allow civil or litigation penalties. In the USA, you're liable for any amount of money that anyone else can convince a jury that you ought to pay, whether or not you comply with any safety standard or not. But not even trying to comply tends to show that you both caused damage, but were willfully reckless in doing so, and you may get punitive damages too.

OSHA has strict rules about the safety conditions you can force employees to deal with. Some of these rely on safety standards, some rely on ad hoc OSHA thinking that you oughta' not do that.

States, counties, and cities MAY have laws on required compliance with UL standards. Insurance companies may refuse to honor a claim for someone using an non-UL compliant device, and the user may sue the maker for that.

The bottom line is to not sell stuff that has predictable hazards. There's significant legal exposure, in addition to hurting someone.

[guitarmike2107]

EN60065 is the driving design guide in the EU that limits the temperature of parts you can touch, IIRC metal parts can raise 30 deg Celsius.

The standard is not a legal requirement but rather a guideline on an approved way to comply with the directives, in this case the Low Voltage Directive, which states you shall not harm anybody or pet or cause fire /shock etc

So you can come up with your own methods based on sound engineering practice, but if you get sued you need to justify your method. so the valve cage is an easy way to show compliance, IIRC the holes have to be less than 4mm to stop little fingers getting in, maybe need to look that one up?

I believe the EN6005 standard and the UL standard are almost, if not, identical.

[rooster]

Talking about what Fender and Marshall did.....

The newer caps may contain such strange guts that they do not need heat to keep the dielectric molten - I really haven't investigated this. However, the early caps (Mallory, Astron, LCR, and Daily) that Fender and Marshall used actually benefited from the heat because it helped them perform as designed. This is in part why fans were never used. With Marshall heads the vents on top were maybe a good idea because they didn't have much venting, not like a Fender combo or head. Eh, a tube orientation thing mostly. The Vox amps, too, which did/do get very hot.

I think that Mesa was the first company to use a fan? And it probably happened as a result of some customer pointing out that the tubes were getting hot, but not because it was needed.

Seriously, tubes are designed to deal with the heat. I doubt a fan on a tube will give it even one more hour of use. ..But if it makes you feel better, go for it.