Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Sesh on July 16, 2021, 06:31:27 am
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Hi everyone
So I'm this close to picking up an empty Dynacord Twen that's been raided for tubes and some components. It still has the original alnico speaker and the transformers, though. If the transformers work, it's a very good price, and even if they don't, just the cabinet and chassis would cost me more than three times what I'd pay at say TubeTown. I also like the fact that it's vintage, has some history and wear.
Schematic of the Twen: https://manualmachine.com/html/10/1019/1019c35bf38da312260d6803825a98238efd389cd89c22a0286d35e48f5dcacf/img-1-WDPVa7kjAK.png
Anyways, the Twen is said to be close to a brownface Princeton. The transformers are thus made for a pair of 6v6 push-pull for output, two 12ax7 (ECC83) - one for the preamp and one for the split-load PI and tremolo respectively.
Since most guts have been ripped out, I thought I might as well start over.
I was in the middle of making a Rob Robinette Blackvibe (https://robrobinette.com/RR763_BLACKVIBE.htm) on a turretboard, anyway, when I eyed this one and thought it'd be a perfect donor.
The BlackVibe is a blackface Vibroverb (I'm making it with 6v6's for a more Deluxe-ish amount of watts), but without reverb or tremolo for simplicity/less components. So while it doen't need tubes for the effects, it's a long tailed pair PI and thus need to use the two halves of the 12AT7 for that.
First two questions:
Can I simply just use the one half of the tube that the Twen uses on the tremolo to instead make the LTP? Will the transformers work for the Blackvibe circuit, too, assuming everything's in order?
Next question: Space. The chassis is quite small on the Twen. How do you suggest I build it?
I had already mounted the components on a turretboard, but I doubt it'll fit in there:
(https://i.imgur.com/ZJYk0DV.jpg)
(https://i.imgur.com/D8UYfIp.jpg)
As I'm a first time amp builder, I honestly want to a avoid rat's nest like in the original:
(https://images.reverb.com/image/upload/s--laulnxPa--/a_exif,c_limit,e_unsharp_mask:80,f_auto,fl_progressive,g_south,h_620,q_90,w_620/v1510717152/ryg98k9jbjfrmq6qwdxj.jpg)
and instead follow Rob Robinette's layout as closely...
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The tube layout on that chassis will make using a turret board very difficult. True point to point would work much better. Sure, you can drop the tremolo and use both halves to make a LTP. Fender uses a 12AT7.
I highly recommend don't run the component leads all the way through the turrets and bend the leads on the bottom. It will be nearly impossible to remove a component later. Just stick the leads about 1/4" into the turret works fine and you will be able to easily remove components. Those transformers will work fine.
You may be interested in this layout. It's exactly what you describe. The board is 3-1/8" x 5". May fit on your chassis. You could cut a piece of cardboard to move around on your chassis to see if it would fit.
http://sluckeyamps.com/misc/AB_Lite_II.pdf
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The tube layout on that chassis will make using a turret board very difficult. True point to point would work much better. Sure, you can drop the tremolo and use both halves to make a LTP. Fender uses a 12AT7.
I highly recommend don't run the component leads all the way through the turrets and bend the leads on the bottom. It will be nearly impossible to remove a component later. Just stick the leads about 1/4" into the turret works fine and you will be able to easily remove components. Those transformers will work fine.
You may be interested in this layout. It's exactly what you describe. The board is 3-1/8" x 5". May fit on your chassis. You could cut a piece of cardboard to move around on your chassis to see if it would fit.
http://sluckeyamps.com/misc/AB_Lite_II.pdf
Thanks for the tip! Good to know - it's my first time using turretboards.
I think I'll pass on the amp, I thankfully didn't commit to anything. And I already have one of these guys for the amp: https://www.tube-town.net/ttstore/tt-chassis-fender-style-blackface-deluxe-reverb-bare.html that would go on the shelf if I bought it.