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RossD's 2A3 SET
https://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=4542
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Author:  RossD [ 05 May 2014, 08:28 ]
Post subject:  Re: RossD's 2A3 SET

Well time to revisit my 2A3 build. I was slowed down by the holidays and I wanted to first finish my 4S pre amp with a volume pot so I'd have a volume for the 2A3 amp. Now that I have that done its time to start building since I should already have most of the parts.

I've been contemplating building a 'tombstone' style radio enclosure for the 2A3, but then I realized I have an old desktop radio that I have nothing planned for:
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I dissected the old radio chassis and started playing with 5 xfmrs/chokes I have to place on this thing. It's looking REALLY tight. I am considering adding some more steel to the chassis to either one of the sides or a frame up and over to mount the output transformers to gain some more real estate on the main chassis. One of my initial ideas was to keep the dial and the center knob for 'show', but that would include the gear set behind it to operate the fake dial. With my lack of space this might be a pipe dream, but I could at least keep the dial without the mechanism to turn it.

I might have to abandon this concept and go back building my tombstone.

Author:  mwhouston [ 05 May 2014, 08:48 ]
Post subject:  Re: RossD's 2A3 SET

Old radios can be worth a lot. That looks like a beauty.

Author:  RossD [ 19 May 2014, 21:18 ]
Post subject:  Re: RossD's 2A3 SET

So I was playing with a possible layout for the old radio chassis.
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The chassis is 5.25" by 12" long. I'm concerned that the tubes might be too close for heat. The output transformers are really close too.

Author:  Gio [ 20 May 2014, 18:12 ]
Post subject:  Re: RossD's 2A3 SET

Hi Ross. IMO, I think the spacing is too tight. The OPT will pick up a lot of heat from those big bottles.

Cheers

Author:  RossD [ 18 Aug 2014, 20:25 ]
Post subject:  Re: RossD's 2A3 SET

So, I'm back at! With our first baby arriving in late November, I'll need to finish this so I can lull the baby to sleep with some sweet musical gold!
I was at the local antique mall and come across another old table top radio for cheap. It wasn't in working order and would have been more work to fix than I'd want to deal with, but since it was so cheap, it's now my 2A3 platform.
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The previously pictured table top radio will get life as another stereo tube amp, but with less components or at least less sizable ones.

Here is one of my attempts to layout everything. My other option would be to place the output xfmrs in the middle and the large choke to the back right, while shoving the two smaller chokes into the inside of the box. I might go with the latter. I have a 120v neon lamp (from radio shack) that I've managed to fit into the original bulb location but can I wire in series between the on/off switch and the power xfmr; will the current be to much?

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I also am going to put some new veneer on the top and try to repair some of the other spots.

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The old baffle is an ancient piece of corrugated cardboard and is ugly beneath the old fabric. I've got some speaker fabric from the Fender Champ scratch build that haven't finished ( I'll get there, I swear :angel: ), so I'll be using that with new a 'baffle'. Baffle in quotes because there will be no speaker inside the cabinet but there will still be a hole so that any tube light that may get thought the fabric might be seen. Since the new fabric is a bit easier to see through, I'm replacing the cardboard with a thin piece of plywood that will get a dark coat of stain.

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I'd really like a nice piece of furniture when I'm done and if someone thinks we are using this old radio for decoration, even better when it lights up and makes some beautiful music. My last couple of amps have been less than visually appealing. The 6k6 stereo amp wasn't bad but wasn't as concise of a design as I'd like.

I was hoping to use the original rotary on/off switch that was the volume pot (without using the volume pot) but I was reading a solid 30-70 ohms after being turned on. The shafts are good 2" long, and haven't been able to find a SPST rotary to match... I might just use a toggle hidden on the back of it to keep the original pots/knobs in place and looking pretty.

Author:  mwhouston [ 19 Aug 2014, 01:25 ]
Post subject:  Re: RossD's 2A3 SET

Looking good.

Author:  RossD [ 25 Aug 2014, 12:58 ]
Post subject:  Re: RossD's 2A3 SET

Thanks Mark.

Other than the grid stoppers, is there anything that needs to be placed close to any other component? Reason being, I have a decent terminal board (think turret board for Fender Amps but terminals instead of turrets) that was in the chassis and I'm considering reusing it.

Author:  mwhouston [ 25 Aug 2014, 18:34 ]
Post subject:  Re: RossD's 2A3 SET

RossD wrote:
Thanks Mark.

Other than the grid stoppers, is there anything that needs to be placed close to any other component? Reason being, I have a decent terminal board (think turret board for Fender Amps but terminals instead of turrets) that was in the chassis and I'm considering reusing it.


All components for old tube amps were usually placed on tag boards. It adds to the sound, lol.

Author:  RossD [ 07 Aug 2015, 13:28 ]
Post subject:  Re: RossD's 2A3 SET

I finished up the amp finally. I suppose having a 8 month old son will have that effect. But I'm having a instability in the lower frequencies. It starts at lower volumes when it initially turns on and gets a little better after it's warmed up. The bass is very ... lacking and flubs. I need to check my speakers and interconnects as they are both a bit dodgy, I'm guessing I may have wired something up incorrectly. I did put in an old 6sl7gt rather than the new one, so I'll have to swap those before tearing into the wiring.

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As you can see, I still need to finish the cabinet.

Author:  laurie54 [ 20 Nov 2019, 18:02 ]
Post subject:  Re: RossD's 2A3 SET

That chassis (beautiful by the way) is looking quite tall. Have you considered building the power supply vertical and placing on one side of the cabinet with the 300B's and opt's in another chassis on the other side of the cab? Hammond has chassis like the one you now have which are quite resonable.
Or perhaps stacking one chassis (pwr sply) under a second one with the amp.

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