Why do most amp manufacturers mount the valves pointing down

Rog · Post by **Rog** » Fri Jul 16, 2004 8:27 am

I mean, this seems to go against at least two common-sense design criteria.

Firstly - there is a constant gravitational force trying to pull them out of their sockets - compounded by vibration when playing which is also trying to loosen the socket's hold on them.

Secondly - as heat rises and as thermionic valves are a heat producer in operation, or even when quiescent, why mount the bottles so that most of the heat is directed exactly where it would be best to keep it cool? The base of the valve is its most fragile part and heat/cool cycles do not do nice things to sliding connections.

I know there are exceptions to this rule - and I realise that having the controls at the top of the amp makes it difficult to do otherwise, but damn!

Bluesbird · Post by **Bluesbird** » Fri Jul 16, 2004 9:02 am

There's far better airflow there. If you have them horizontal (with top-rear mounted controls), the heat would build up in the area between the baffle, top of the cabinet, and the chassis at the rear. In many cases, this may also leave inadequate room to mount the bulky transformers.

Rog · Post by **Rog** » Fri Jul 16, 2004 9:14 am

Couldn't they mount the chassis with the valves and transformers at the bottom of the amp unit and the controls at the top?

Post by **GrantB** » Fri Jul 16, 2004 9:58 am

Dr Rog - i too have pondered that question. I'd say that the design elements for a combo mean they need to have the controls on top so access, and the pots and switches should be as close to the PC board, or chassis as possible. I have two amps that shun this however. The Trace Elliot Velocette is a comba and has the valves at the bottom along with of the knobs n stuff at the back. This thing gets so hot its helping peel the vynyl covering off...BUT, it would be way hotter if it were upside down! The other amp is the Sovtek Mig Fighter Jet 50 which is really a Fender Bassman in Russian spy costume - that is a head though and can easily have the guts facing upwards because the way heads are used (on stacks)...anyway, intersting thought.

I say simply set your "fav" settings, turn your combo upside down (knobs against the floor) and begin reaping the massive benefits of a slightly cooler valve amp

Rog · Post by **Rog** » Fri Jul 16, 2004 10:04 am

>I say simply set your "fav" settings, turn your combo upside down (knobs against the floor) and begin reaping the massive benefits of a slightly cooler valve amp

ROTFL - great idea. mate!!!

B45-12 · Post by **B45-12** » Fri Jul 16, 2004 12:02 pm

I allways understood this upisde-down valve design was for servicing - you can undo the holding bolts/screws then slide the chassis half out on the slides, reach all the controls, most of the 'innards' and the valves for measurements/repair.

Mind you it's probably really because amp makers are truly bastards/swines etc. but there you go.

TMG 03 · Post by **TMG 03** » Fri Jul 16, 2004 12:33 pm

My amp has little spring caps that hold them in place as so they don't fall out when moving the amp.

Marshall Heads have them on the bottom facing upwards. Like someone said it is about heat and airflow around them

Rog · Post by **Rog** » Fri Jul 16, 2004 12:46 pm

As far as servicing - I had a Jansen Bassman 50 with point to point wiring. I was servicing it and pulled the chassis out - unfortunately, the hot rail was about 3/4 of an inch behind the front panel - just enough so that one got a good grip on the rail with the meat of one's hand nicely earthed on the chassis... bastards!!!

Post by Bg » Fri Jul 16, 2004 1:04 pm

you pulled the chassis out when it was live? Murphys law would dictate that you were going to get a belt....

Rog · Post by **Rog** » Fri Jul 16, 2004 1:11 pm

LOL - it was turned off and unplugged, but those caps....

Post by **GrantB** » Sat Jul 17, 2004 10:13 am

Oh yeah - actually caps can kill ya...if you've a dodgy heart. I have had wicked cap belt when playing the aforementioned Sovtek Mig. Fackin near pooed me pants...

ash · Post by **ash** » Sat Jul 17, 2004 10:37 am

I think I still have a scar on my hand from 600 Volts of Jansen Juice!! The amp was unplugged and I touched the cap as I was tearing the guts out of it to rebuild it as a Marshall clone.
I was quite confused for a while there, trying to work out what just happened

Ended up being a wicked sounding amp...

ash · Post by **ash** » Sat Jul 17, 2004 10:45 am

Anyway, back to the question...

The reasons have been mostly covered: You need to have the knobs at the top of a combo, so its easiest to have the tube pointing down from the chassis, even if you have to fit retainers to stop them vibrating out.

Marshall just turned the whole get-up upside down in his early heads, even having the inputs on the other side too. This makes sense when the head is going to be on top of two cabs - the knobs will be at the right height anyway.

Plus you don't have to do some balancing act to slide the chassis into place.

The reason you can't really put the knobs at the top and the valves at the bottom is because then you'd need three sheilded wires for each control carrying up to 400 Volts back and forth along the sides of the cab.

If thats not an invitation for death by beer spillage, then it will at least hum like a two-buck-slut....

Rog · Post by **Rog** » Sun Jul 18, 2004 11:42 am

> hum like a two-buck-slut

ROTFL

And you'd know this because.....

ash · Post by **ash** » Sun Jul 18, 2004 4:12 pm

Aaaahhh, something I heard some grown-ups talking about once