Upside down tubes

[ruffrecords]

I am still rethinking the Poor Man's Tube Mixer enclosure. The best looking, reasonably price, readily available,d not stupidly small one I can find is a one of the Hammond 1456 series:

It is about 10 inches wide, 9 and bit deep and just under 4 inches high. It has a nice 30 degree sloping front panel, a flat top and nice wooden cheeks.

The thing is, learning from the first prototype where the main board was on the floor and the front panel PCB was behind the front panel and the connectors were on a third rear panel, having those three separate is a wiring, assembly and servicing nightmare. So if I use the Hammond enclosure I would like to get everything, with the possible exception of output transformers, to fit on a single panel where it can be built and tested.

The top panel is shown in side view on the middle left of the above picture. Connectors mount on the back, the front panel PCB mounts on the sloping part which means the active electronics i.e. tubes would need to be mounted under the flat top. That way all interconnects are on that one panel. The thing is this means all the tubes will be pointing downwards so their heat will flow up over the PCB before exiting through the rear ventilation grill.

So my question is, will this be OK or is it just too risky?

Cheers

Ian

 

[scott2000]

Interesting....


LMB Heeger has some similar enclosures as well....

https://lmbheeger.com/modulardesktopconsole.aspx

Maybe some way to secure the tubes if it is ok to install them upside down...Like on those old decade counters?? Or are you asking because of heat?

 

[ruffrecords]

Interesting....


LMB Heeger has some similar enclosures as well....

https://lmbheeger.com/modulardesktopconsole.aspx

Maybe some way to secure the tubes if it is ok to install the

I am asking because of heat. I am not concerned about them falling out.

Cheers

Ian

 

[john12ax7]

Guitar amps have been doing this for decades without much issue.  Though the tubes are outside the chassis which insulates the components somewhat.

My guess is with low power preamp tubes it wouldn't be too large of a temperature rise.  Using AEC-Q200 qualified parts would help as well.

 

[Bo Deadly]

How are you going to do engravings / silkscreen on that thing?

Since you're asking for opinions, I'll give you one. Make it like all the old rack-mount tube test and measurement lab equipment from the 40's and 50's like Pultec, HP, Gertsch, Boonton Radio, Ling, etc (just not 10 feet deep). That would be the right look IMO (and I would not underestimate the importance of it's appearance). Ideally this would mean a really thick steel panel with some matte black finish, high quality silk screen and Bakelite General Radio / Raytheon style knobs. But 4mm aluminum black or natural anodized with engravings and the phenolic Davies knobs would be the obvious cost-effective alternative. Sorry for always poohing your ideas (still "no" to builtin digital effects) but I wouldn't bother if you're circuits weren't nice. Hammond stuff isn't that nice. And it's overpriced for what it is.

If it's supposed to be a small desktop / portable device, then make it look like this:

Anything that looks like this will sound awesome.

 

[PRR]

> all the tubes will be pointing downwards

The sound will fall out. Make a mess in the bottom of the box. Sour Salsa. Petrified Polka. Rotten Rock.

You don't say what tubes. HOT 13W-30W power tubes have been mounted upside down. You are only using few-Watt bottles?

But the lasting examples are P2P. Tube PCB amps in general do NOT last. How long do you expect to support this product? Leo Fender leveraged his health into a major sell-out. But Jim Marshall stayed in the game and even roped his daughter into it.

I suspect your fine product will mostly go to 100 hour/year mini-studios. Bah, it won't be "cooked" until you and your customers move on. But if it gets into one of Pucho's 23/7 busy-studios you may want a fast-swap overhaul kit.

 

[CJ]

you can cheat the heaters,  6 volts will run cooler than 6.5 volts, a tad cooler than 6.3 volts,

 

[shabtek]

I would wager they also have an enclosure that could be used for a meter bridge/ tube cage atop that sloped enclosure. the wooden ends would not be as elegant  though. 
A similar sloped profile could be attained with separate enclosures and piano hinges--DaveP could make it happen!

 

[tony hunt]

Ian,

my first thought was no way, the thermals will make it unstable and prone to failure sooner than later.

But then I went back over your other thread to understand your aims and have made a sketch.  I think you need to get the valves towards the back as much as possible, like on old rack gear, but still on the board. Hope the sketch loads ok. Use taller feet on the base to help the convection.

I have found these Hammy enclosures to be rather flimsy. Perhaps this one is OK, but the guage of metal seems to be awfully thin. I usually fold this kind of thing in 2mm on my small brake press. I like to get the panels laser cut in advance to save time.

Cheers, t

 

[scott2000]

Ouch....These are pricey

https://www.newark.com/bud-industries/c-1555/cabinet-prestige-10-5in-steel/dp/10M5140

It'll be interesting to see how you decide to finish it. Maybe there is a possibility that some people will end up veering off into other ways of mounting these things regardless of how it turns out if there is wiggle room to do that?

I've even seen some pretty heavy duty sloped enclosures from electrical supply surplus houses that could be useful....

 

[abbey road d enfer]

Well, I have a 1970's Ampeg VT22; it has 4 big bottles (7027) mounted upside-down on a phenolic PCB.
The PCB has swelled, but there is no electrical issue.
I would expect FR4 to be more stable.
Considering you don't have power tubes in your mixer, I wouldn't worry about electrical/structural issues.
However I would not neglect the possible effects of heat build-up on the tactile sensation. Maybe consider fan cooling...

 

[emrr]

Well, I have a 1970's Ampeg VT22; it has 4 big bottles (7027) mounted upside-down on a phenolic PCB.
The PCB has swelled, but there is no electrical issue.
I would expect FR4 to be more stable.
Considering you don't have power tubes in your mixer, I wouldn't worry about electrical/structural issues.
However I would not neglect the possible effects of heat build-up on the tactile sensation. Maybe consider fan cooling...

Agreed.    Have one too, same experience. 

 

[ruffrecords]

Thank you everybody for your input, especially those who took the time to include links or even a sketch of their suggestions. To help clarify things:

1. The tubes are all low power double triodes. Most are 6922/E88CC.6DJ8 plus the occasional 12AX7 so they are nt great producers of heat but not zero either.

2. This is meant to be more  a DIY project than a product (although I will probably end up building some if there is demand) so an enclosure that is readily available almost anywhere is an important consideration along with how easy the thing as a whole is to assemble/test and trouble shoot.

3. Appearance is important and the big problem with off the shelf enclosures is drilling the holes and making the legend look half decent.

4. The only way I know so far of achieving 2 & 3 is to use regular 3U 19 inch mount  Eurorack kits by Schroff, Fischer or SRS. Then I can use the normal Eurocard size EZTubeMixer PCBs and front panels are easy from Schaeffer et al. But this already exists in the form of the lunch box project from a few years ago. The problem with that is there is not enough panel space for things like faders (rotary or otherwise) and a nice stand alone desktop option is not available.

The ideal answer would be a Eurorack based console shape with a near horizontal space for faders and a near upright section that would take EZTubeMixer modules and doesn't cost the earth - something which I am  working on - but it would be even better to find something off the shelf.

Cheers

Ian

 

[PRR]

> 1970's Ampeg VT22

Forgot that. Agree. My VT-40 had problems but not PCB toast.

 

[abbey road d enfer]

> 1970's Ampeg VT22

Forgot that. Agree. My VT-40 had problems but not PCB toast.

For those who may wonder, VT22(2x12" combo), VT40 (4x10" combo), V4 (head) share the same chassis.

 

[CJ]

you know those communion crackers they give out in church? that's what Ampeg used for pc boards.

G10 boards should take the heat all day long,

use as much copper as you can fit for the traces,

without arcage of course,

 

[PRR]

I said I forgot.

> the same chassis.

IIRC(!!), -22 is four 7027 tubes, -40 is two 7027 tubes; but it is clear where two more would go.

 

[BluegrassDan]

I looked into those Hammond mixer cases a while back, but it seems like they're too flimsy and would be trouble should you need to get in and repair/service something.