Hi,
I looked through the archives, but didn't see this addressed specifically. Is it feasible to build a tube amp in a completely wooden enclosure or enclosures? This may make more sense for a first-timer like me, for the following reasons:
* It's easier and cheaper to find wooden boxes than Hammond aluminum enclosures. I've seen 6"x9" cigar boxes selling on eBay for under $10, a pair of these should be enough real estate to build a stereo amp (monoblocks or separate PSU/audio sections).
* It's easier and cheaper to find tools that can cut holes in wood. I've seen hole saws on eBay for $10-$20. Granted, these probably wouldn't last beyond the first project, but for now, that's all I'm looking for. If I later decide to get into the hobby more seriously, I'll buy a proper set of tools.
* It'll be cool, and different from everyone else's amps
So I'm thinking of trying this with 2 wooden boxes, one for the PSU and one for the audio circuit. Monoblocks would cost more because I'd have to duplicate the PSU. Also, the only 17" wooden box I could find on eBay was a Smith & Wesson display box, and it was over $100
What would the potential problems with this idea be?
* Shielding. I'm not sure how much RFI there is in my environment. I've picked up talk radio once, when I was trying DIY tonearm cable and hadn't shielded it properly. However, that's a good 60dB below the level of the amp, and other than that I haven't directly experienced RFI, so maybe I'll be OK on that front. Is there any reliable way to find out how much RFI I'm dealing with?
* Heat. This is the next big issue in my mind. I know wood will catch fire at a lower temperature than aluminum Would a tube amp get hot enough to set a wooden chassis on fire? Should I drill ventilation holes around the tubes like I see in some amps? Should I add metal heatsinks for PS or cathode bias resistors?
* Bracing. This depends on how thin the wood is, I guess, but I would think that a cigar box would be able to handle a power transformer and choke, and the 125ESEs don't look too heavy.
* The umbilical. I'm aware of some of the issues involved here, because I built my (SS) phono stage as two boxes. That's a 45V supply, so I wasn't too careful with it, but for a tube amp, I know I'll need decent locking connectors, make sure the end connected to the PS is female to prevent accidental electrocution, shield HT from heater (or maybe even use 2 umbilicals and make sure they can't accidetally be cross-connected), and so on. However, these are issues with having separate PSU and audio boxes, they're not related to the boxes being made of wood, so I can worry about them later.
Anything else I'm missing?
Thanks in advance,
Saurav
I looked through the archives, but didn't see this addressed specifically. Is it feasible to build a tube amp in a completely wooden enclosure or enclosures? This may make more sense for a first-timer like me, for the following reasons:
* It's easier and cheaper to find wooden boxes than Hammond aluminum enclosures. I've seen 6"x9" cigar boxes selling on eBay for under $10, a pair of these should be enough real estate to build a stereo amp (monoblocks or separate PSU/audio sections).
* It's easier and cheaper to find tools that can cut holes in wood. I've seen hole saws on eBay for $10-$20. Granted, these probably wouldn't last beyond the first project, but for now, that's all I'm looking for. If I later decide to get into the hobby more seriously, I'll buy a proper set of tools.
* It'll be cool, and different from everyone else's amps
So I'm thinking of trying this with 2 wooden boxes, one for the PSU and one for the audio circuit. Monoblocks would cost more because I'd have to duplicate the PSU. Also, the only 17" wooden box I could find on eBay was a Smith & Wesson display box, and it was over $100
What would the potential problems with this idea be?
* Shielding. I'm not sure how much RFI there is in my environment. I've picked up talk radio once, when I was trying DIY tonearm cable and hadn't shielded it properly. However, that's a good 60dB below the level of the amp, and other than that I haven't directly experienced RFI, so maybe I'll be OK on that front. Is there any reliable way to find out how much RFI I'm dealing with?
* Heat. This is the next big issue in my mind. I know wood will catch fire at a lower temperature than aluminum
Would a tube amp get hot enough to set a wooden chassis on fire? Should I drill ventilation holes around the tubes like I see in some amps? Should I add metal heatsinks for PS or cathode bias resistors?* Bracing. This depends on how thin the wood is, I guess, but I would think that a cigar box would be able to handle a power transformer and choke, and the 125ESEs don't look too heavy.
* The umbilical. I'm aware of some of the issues involved here, because I built my (SS) phono stage as two boxes. That's a 45V supply, so I wasn't too careful with it, but for a tube amp, I know I'll need decent locking connectors, make sure the end connected to the PS is female to prevent accidental electrocution, shield HT from heater (or maybe even use 2 umbilicals and make sure they can't accidetally be cross-connected), and so on. However, these are issues with having separate PSU and audio boxes, they're not related to the boxes being made of wood, so I can worry about them later.
Anything else I'm missing?
Thanks in advance,
Saurav
I build my amps on wooden chassis for exactly the same reasons you mentioned.
http://home.zonnet.nl/horneman/se6c41cpics.htm
I have no problems with RFI.. But you could solve an eventual rfi problem by shielding components..like caps and chokes.
An added benefit is that the rca plugs are not grounded on the chassis but everything is grounded via star earthing...no ground loops in my wooden amps.
At the back of my amp i just have a whole slot so there is natural convection..i.e. not heat problems.
Bracing..depending on the thickness of the wood...speaks for itself really...I use plywood just because it is easy to get...plywood does not have the same good looks as real wood.
Dhaen has some very good options for an umbilical. Sure he'll chip in.
Cheers,
Bas
http://home.zonnet.nl/horneman/se6c41cpics.htm
I have no problems with RFI.. But you could solve an eventual rfi problem by shielding components..like caps and chokes.
An added benefit is that the rca plugs are not grounded on the chassis but everything is grounded via star earthing...no ground loops in my wooden amps.
At the back of my amp i just have a whole slot so there is natural convection..i.e. not heat problems.
Bracing..depending on the thickness of the wood...speaks for itself really...I use plywood just because it is easy to get...plywood does not have the same good looks as real wood.
Dhaen has some very good options for an umbilical. Sure he'll chip in.
Cheers,
Bas
Wow, that's a great looking enclosure! Did you build it yourself, or did you put a pair of old boxes together?
> At the back of my amp i just have a whole slot so there is natural convection..i.e. not heat problems.
Could you explain that please, I couldn't see that in the pictures. I'll probably leave the bottom open like you have, that should help too, especially if I drill holes on the top surface for convection.
> At the back of my amp i just have a whole slot so there is natural convection..i.e. not heat problems.
Could you explain that please, I couldn't see that in the pictures. I'll probably leave the bottom open like you have, that should help too, especially if I drill holes on the top surface for convection.
Hi Saurav,
Built it myself. Just glued them all together nothing fancy...yet ;-)
See the third photo from the bottom...there is a slot stretching almost from the one side to the other.(actually quite hard to see ) .....at the bottom of that " transformer box" there are a couple of holes (you can see a couple of them" that let the heat "out" from the "bottom" part..
Cheers,
Bas
Built it myself. Just glued them all together nothing fancy...yet ;-)
See the third photo from the bottom...there is a slot stretching almost from the one side to the other.(actually quite hard to see ) .....at the bottom of that " transformer box" there are a couple of holes (you can see a couple of them" that let the heat "out" from the "bottom" part..
yes good idea..no way the kids can lift it..can't even lift it myself..
Cheers,
Bas
Here is another one just posted at the Audio Asylum..
http://www.audioasylum.com/forums/tubediy/messages/30979.html
http://www.audioasylum.com/forums/tubediy/messages/30979.html
You're in the states right?
Apparently Bombay Company is quite good for getting a nice wooden box..
http://www.bombaycompany.com
Nice box on a special
http://www.bombaycompany.com/webapp...rId=-2000&storeId=10051&langId=-1&siteId=core
$29
Apparently Bombay Company is quite good for getting a nice wooden box..
http://www.bombaycompany.com
Nice box on a special
http://www.bombaycompany.com/webapp...rId=-2000&storeId=10051&langId=-1&siteId=core
$29
I'd seen that AA thread, didn't realize it was you. Thanks for the Bombay Company link (yes, I'm in the USA), I hadn't considered buying a box from a store because I'd assumed they'd all be too expensive. I've been looking around at thrift stores too for a while, but haven't seen anything promising.
This is the kind of stuff I was loking at:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2533066176&category=12
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3225080789&category=11673
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3225081097&category=11673
This is the kind of stuff I was loking at:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2533066176&category=12
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3225080789&category=11673
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3225081097&category=11673
Didn't even think about wine boxes, that's a great idea. Though I'm not sure how much the snooty wineries up here would want for their boxes
I found an archived thread with Dhaen's posts about umbilicals. There's some good advice in there, and connectors I didn't know existed. Thanks for letting me know.
I found an archived thread with Dhaen's posts about umbilicals. There's some good advice in there, and connectors I didn't know existed. Thanks for letting me know.
Hi Saurav;
I had a lot of the same concerns you've expressed when I got serious about scratchbuilding valve amps.
Here goes:
1. Shielding: not an issue. FWIW I always use shielded microphone wire for my signal leads from the RCA jacks to the source selector (or vol control if no selector) and that works fine.
2. Heat (and fire): most woods kindle (IIRC about 400F or 200C) at a temp higher than a correctly functioning trafo should operate at. However, fire is a risk, particularly if you are using old "non fire resistant" carbon comp resistors in a PS - thus I'd limit myself to wirewounds, metal oxide, and other power resistors that are fire retardant for that app. As far as heatsinking is concerned, it really depends on the amount of power that the resistor dissipates. My little wood chassis'd "Gnat" MK II has a PS resistor that dissipates an honest 10.4 watts and it gets HOT - and it thus got a heatsink AND a vent placed in the chassis to help out.
3. Bracing: you can always add a bit more if you need it. I'd do a test fit with just the heavy components before I finalised the layout. FWIW, I had to add bracing following initial construction and testing of load carrying on my 2A3's oak chassis. The best way to get a feel for this is to build it and find out; sorry but there are some things that are best learned by direct experience....
4. Umbilical: I don't have a specific recommendation here, but I know that I've seen decent milspec high voltage connectors at surplus houses from time to time.
Frankly, of the issues you raise, IMHO heating is the biggest issue, but not quite the way I read it in your post. The problem with wood chassis and heat is due to the "mobile" character of natural hardwoods (i.e. they change their shape and size with environmental changes). The fact is that if wood is not dried correctly and completely it will have a tendency to split, "cup" (a kind of warpage), or shrink (it shrinks perpendicular to the grain). Thus, you should make CERTAIN that any wood you're using in this app is thoroughly dried and from a reputable dealer in hardwoods. You may also want to consider adding a thin sheet of plywood under the hardwood decking.
The other heating issue is with the valves themselves - the fact is that the metal mounting plate for the valves acts as a heat sink. Without this you will encounter higher temps on the valves and sockets. You might consider mounting the valves on a metal plate that could be either atop or recessed under the wooden decking, and allow a generous clearance hole for the glass envelopes of the valves. BTW, if the wood is too thick, it may be difficult for you to access the underside of the sockets - when laying out an amp, you should consider the order of assembly with an eye to how much room there is to work, so that you are not getting in your own way.
If heat buildup inside the chassis remains a problem, you can always add a 'computer type' cooling fan for $3-$20 USD and run it off the 6.3V windings of your PS trafo. Some fans run quieter than others, so that's also an issue.
Good luck with your project!!
All the best,
Morse
I had a lot of the same concerns you've expressed when I got serious about scratchbuilding valve amps.
Here goes:
1. Shielding: not an issue. FWIW I always use shielded microphone wire for my signal leads from the RCA jacks to the source selector (or vol control if no selector) and that works fine.
2. Heat (and fire): most woods kindle (IIRC about 400F or 200C) at a temp higher than a correctly functioning trafo should operate at. However, fire is a risk, particularly if you are using old "non fire resistant" carbon comp resistors in a PS - thus I'd limit myself to wirewounds, metal oxide, and other power resistors that are fire retardant for that app. As far as heatsinking is concerned, it really depends on the amount of power that the resistor dissipates. My little wood chassis'd "Gnat" MK II has a PS resistor that dissipates an honest 10.4 watts and it gets HOT - and it thus got a heatsink AND a vent placed in the chassis to help out.
3. Bracing: you can always add a bit more if you need it. I'd do a test fit with just the heavy components before I finalised the layout. FWIW, I had to add bracing following initial construction and testing of load carrying on my 2A3's oak chassis. The best way to get a feel for this is to build it and find out; sorry but there are some things that are best learned by direct experience....
4. Umbilical: I don't have a specific recommendation here, but I know that I've seen decent milspec high voltage connectors at surplus houses from time to time.
Frankly, of the issues you raise, IMHO heating is the biggest issue, but not quite the way I read it in your post. The problem with wood chassis and heat is due to the "mobile" character of natural hardwoods (i.e. they change their shape and size with environmental changes). The fact is that if wood is not dried correctly and completely it will have a tendency to split, "cup" (a kind of warpage), or shrink (it shrinks perpendicular to the grain). Thus, you should make CERTAIN that any wood you're using in this app is thoroughly dried and from a reputable dealer in hardwoods. You may also want to consider adding a thin sheet of plywood under the hardwood decking.
The other heating issue is with the valves themselves - the fact is that the metal mounting plate for the valves acts as a heat sink. Without this you will encounter higher temps on the valves and sockets. You might consider mounting the valves on a metal plate that could be either atop or recessed under the wooden decking, and allow a generous clearance hole for the glass envelopes of the valves. BTW, if the wood is too thick, it may be difficult for you to access the underside of the sockets - when laying out an amp, you should consider the order of assembly with an eye to how much room there is to work, so that you are not getting in your own way.
If heat buildup inside the chassis remains a problem, you can always add a 'computer type' cooling fan for $3-$20 USD and run it off the 6.3V windings of your PS trafo. Some fans run quieter than others, so that's also an issue.
Good luck with your project!!
All the best,
Morse
check it out Hi Saurav;
You have 2 choices on the heat sinking - one is to use a wirewound that's in an aluminium housing that's got mounting holes for heat sinking (this is the better way IMHO) and the other is to use a ceramic potted wirewound and couple it radiatively to the heat sink (i.e. use a "wrap around" sheet of aluminium that stands off the resistor by 3 or 4 mm which is tied to a much larger heat sink). The obvious danger here is that the aluminium MUST NOT be allowed any way of making contact with (or worse, between) the leads of the resistor!! Careful measurement and mounting of the pieces is absolutely required.
In the case of the Gnat MK II I used the bottom plate of the chassis as the heat sink and mounted the resistor 4mm above it (this way any flexing of the bottom plate in handling would not be able to flex the leads to the resistor). There's also a sheet of the same aluminium that I bolted in that goes up alongside the resistor. It's got to be dumping it's heat pretty efficiently, since the bottom plate directly underneath and alongside the resistor heats up pretty quickly! As an additional safety measure, I used a 25w rated NTE made resistor (I compared the NTE to the Philips ECG and the ECG was a bit smaller - thus had less surface area and a smaller thermal mass, even though both resistors were rated at 25w) - better than a 100% overdesign for the power dissipation involved.
Frankly I would have preferred to use a 50w aluminium potted wirewound (Michael Percy has 'em the last time I checked) but I used what I had on hand.....
Fans are a bit funny - I've got some that are really noisy and some that are really quiet - but you're right, it's not that hard to make one work in this application. I'm surprised that more people don't use 'em. The last fans I bought were $3 each and dead quiet at 6.3V!
All the best,
Morse
You have 2 choices on the heat sinking - one is to use a wirewound that's in an aluminium housing that's got mounting holes for heat sinking (this is the better way IMHO) and the other is to use a ceramic potted wirewound and couple it radiatively to the heat sink (i.e. use a "wrap around" sheet of aluminium that stands off the resistor by 3 or 4 mm which is tied to a much larger heat sink). The obvious danger here is that the aluminium MUST NOT be allowed any way of making contact with (or worse, between) the leads of the resistor!! Careful measurement and mounting of the pieces is absolutely required.
In the case of the Gnat MK II I used the bottom plate of the chassis as the heat sink and mounted the resistor 4mm above it (this way any flexing of the bottom plate in handling would not be able to flex the leads to the resistor). There's also a sheet of the same aluminium that I bolted in that goes up alongside the resistor. It's got to be dumping it's heat pretty efficiently, since the bottom plate directly underneath and alongside the resistor heats up pretty quickly! As an additional safety measure, I used a 25w rated NTE made resistor (I compared the NTE to the Philips ECG and the ECG was a bit smaller - thus had less surface area and a smaller thermal mass, even though both resistors were rated at 25w) - better than a 100% overdesign for the power dissipation involved.
Frankly I would have preferred to use a 50w aluminium potted wirewound (Michael Percy has 'em the last time I checked) but I used what I had on hand.....
Fans are a bit funny - I've got some that are really noisy and some that are really quiet - but you're right, it's not that hard to make one work in this application. I'm surprised that more people don't use 'em. The last fans I bought were $3 each and dead quiet at 6.3V!
All the best,
Morse
Hi,
I hate to point this out...
Does fire hazard mean anything to you at all??
Personnally, I'd rather use a metal topplate to attach anything that could possibly inflame...
That would surely help me sleep better at night.
Never forget that wood, when moist, conducts surprisingly well...not that I'd want to experience the proof.
Hate to spoil the fun,
I hate to point this out...
Does fire hazard mean anything to you at all??
Personnally, I'd rather use a metal topplate to attach anything that could possibly inflame...
That would surely help me sleep better at night.
Never forget that wood, when moist, conducts surprisingly well...not that I'd want to experience the proof.
Hate to spoil the fun,
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