EL84 Class AB stereo amplifier chassis  - Page 1
Forum section: electronics / projects

author: Jwillis
author_rank: Super Contributor
timestamp: December 08, 2019, 08:40:57 am
content: So finally gathered all the components and transformers. Now I need to set up a placement so I can order the correct size of stainless steel for the chassis. I'll probably get the metal shop to bend it for I only have a small hand break for bending.Aside from spacing for heat are their any other things I should consider when mapping the chassis diagram.I'd like the power transformer in the middle back and the output transformers on either side. I figure about an inch of spacing for the valves and maybe 2 inches between the transformers should be enough.

author: AllTheGearNoIdea
author_rank: Unknown
timestamp: December 08, 2019, 01:40:51 pm
content: I was only going to say do you really want stainless it’s hard compared with aluminium. Just thinking about drilling and punching out valve bases.

author: TimFox
author_rank: Super Contributor
timestamp: December 08, 2019, 03:16:32 pm
content: Gold chromate ("iridite" or "alodyne") coatings on aluminum keep the conductivity and are attractive finishes for tube equipment. Anodizing leaves an insulating surface that needs to be broken through for chassis ground connections. Stainless steel is a PITA for drilling large holes for the transformers and tube sockets.

author: Yansi
author_rank: Super Contributor
timestamp: December 08, 2019, 03:41:19 pm
content: Stainless steel is not pita, if you think first and let em laser cut the sheet metal first!But I would not use it anyway. Use either steel (powder coated), or some medium-hard aluminium alloy, then anodize. Beware, that harder aluminium alloys are harder/not anodizable, due to the alloy metals in it.

author: andy3055
author_rank: Super Contributor
timestamp: December 08, 2019, 05:21:35 pm
content: Quote from: Jwillis on December 08, 2019, 08:40:57 amMake sure to have the 2 transformers as far as possible with each other and at right angle to each other to minimize magnetic coupling that will introduce mains hum on the OPT transformer. If you have not seen already, check this out from Mr. Carlson's Lab:

author: Jwillis
author_rank: Super Contributor
timestamp: December 08, 2019, 10:15:50 pm
content: I was considering that the metal work shop would do most of the bending and punching since they have the tools for it .Basic sketch below.I was going with a brushed metal look with stained hardwood sides .Also considering polished .Gold chromate looks cool too but Anodizing I can't get done locally .The cost quote is quite reasonable so I may even consider having 2 or 3 different metals finishes made . I wanted a keep a metal look to contrast with the hardwood .The positioning of the transformers were going to be right angles anyway taking into consideration the magnetic fields. Besides it just looks better that way. But I'll might add covers but not sure. Theirs a total of 10 tubes 4 EL84 output pentodes, 2 kenotrons ,2 6N1P input drivers (also have 6N23P, probably go with this one ) ,2 6E1P indicators. All tubes are new old stock.I have the data sheets but they're in Russian . Small set back since I managed to sort of translate most parts of them.Controls in front , inputs / outputs and power socket on the back.Thanks everyone for your valuable input .Cheers.

author: floobydust
author_rank: Super Contributor
timestamp: December 08, 2019, 10:22:58 pm
content: TheHammond 1441 steel chassisapproach is full bends with spot-welds and complex woodwork. The aluminium 1444 chassis can't handle heavy weight though and I've had the spot welds break.It helps to take a sheet of paper and some paper/cardboard cutouts or cutout photocopies of the bigger parts, to do a layout and see if there is enough room.If you're using turret strips, sometimes they'll end up in a tight spot or you need an extra one. Coupling capacitors to EL34's might be large size and can take up more room than expected.I think important is cooling, so the O/P tubes are not too close together 1" spacing seems small. The input and phase-inverter's need metal shields especially if using a tube rectifier. Several hundred volts swing near them and they will pick that up on the plates.The worst part with a power transformer in the middle, is where the RCA jacks are. With both on one corner, one channel will need a long shielded cable run so the extra capacitance can unbalance the two channels and add something to fix that.Stainless steel is hard to work with.

author: Jwillis
author_rank: Super Contributor
timestamp: December 09, 2019, 12:03:18 am
content: I did look at those Hammond chassis so thanks for informing me about the weight limitations. I chose Stainless because of its rigidity. Also I can get 4 different finishes at this local shop. #8 mirror , #4 brushed , #2 brushed , and #2B bright .Others I have to special order at a much higher cost. Other metals include aluminum ,brass and copper. Un-coated aluminum starts to looks crappy after a while . The samples of punching they have show no distortion and are clean . They said they can also recommend the best gauge for the weight . The transformers are the Hammond 1650E output at 3.5 lbs each and the Hammond 370KX power at 8.5 lbs That's 15.5 lbs .So I'm get the professionals to do the metal work.I'm also considering polymide sheeting on the inside.I forgot about the caps. Thanks floobydust

author: floobydust
author_rank: Super Contributor
timestamp: December 09, 2019, 12:58:48 am
content: You could do steel and get chrome plating, ala Dynaco. If you have to drill one hole or file something out, then you realize total agony with SS being so hard.If they'll do all the CNC punching, then I'd lay out the entire chassis, including IEC power entry, output binding posts, RCA jacks, holes under the transformers for leads etc. Don't forget bias/balance pots and a #47 lampFront Panel Expresssoftware is free, I did not check the library of parts, output is DXF. It might be useful.Build the whole amp (layout) with paper and cardboard, I know a few people doing it that way and they enjoy that method.

author: Jwillis
author_rank: Super Contributor
timestamp: December 09, 2019, 08:27:06 am
content: I've worked with stainless before . Sheet SS 304 is nothing compared to hardened stainless 630.Small holes up to a 1/2 inch won't be problem . I have air die grinders and drills and tungsten carbide and diamond drills and grinder bits from my HD mechanic days.Once I have a template made the metal shop will do the rest.