Integrated Amp: Mark III & PAS

[ChrisK]

Hello all,

Being squeezed for living room space by my better half, I've decided to design and build an integrated tube amp from scratch using a bunch of Dynaco parts I've accumulated over the years.

I've got A-431 and P-782 trannies, a couple of Sheldon's cap upgrade boards from Triode, the Poseidon PCB's (yet to be stuffed), and all the Curcio upgrade stuff for the PAS3 (bought already assembled on eBay).

The nice thing here is that I can design the chassis/layout/panel from the ground up, but that's the easy part. Integrating all the electronics is somewhat difficult because they assume a stock Mark or PAS. So, my first job is to draw up a comprehensive schematic, starting with the power supply.

Since this project may be of interest to others, and since I would surely appreciate any critique and advice, I'd like to post my first PDF file to this board. All the information has been pulled from publicly available sources so there shouldn't be any copyright issues.

If there's any interest, please let me know and, especially, explain to me how to post PDF files properly to this board. I don't think you'd want me to insert an 8/12x11 pdf file into this text (if that even works?).

Regards, ChrisK

[TerrySmith]

That sounds like a neat project!

Instead of two seperate P-782 trannies, I would use one toroid such as the Antek 4TK-400, it'll power all of it with no problem. Plus you won't need a forklift to move it around.

You will need a GOOD chassis, Tom Mcnally uses one on his ST70/ Heathkit project.

[ChrisK]

Thanks Terry,

That's a very good idea. I kept thinking something along the same lines, but was timid about trying to spec a substitution. I'll certainly take a look at the Antek toroid which sounds like a much better way to go for several technical reasons, not to mention the significant weight/space reduction.

I'll take a look at Tom's project also.

Regards,

ChrisK

[TerrySmith]

I can't remember where Tom got that chassis. It's like 16"x12", and maybe 1/8 thick aluminum deck.

I like to lay everything out on a piece of cardboard the size of a chassis I'm thinking of to make sure it will all fit.

[ChrisK]

Those dimensions sound about right.

I do my layout work in the Visio drawing program and came up with 19 x 14 inches, but that's with two power trannies. Using the toroid will bring it down to 15x14 or thereabouts. Then, when I'm ready to build, I make a full-sized print of the layout drawing and fix my mistakes.

You got me really "amped up" about the AN-4TK400. Checked their web site and it sounds perfect. There's a new one for sale on eBay for 50 bucks + 10 shipping.

There's an itch I have to scratch, methinks.

[TomMcNally]

You can see my stuff at http://tmamps.com the chassis
is from http://www.yaegeraudio.com/default.tpl it's a
pretty good deal at $ 119. When I built that amp with the
old Heathkit AA-100 transformers, it was the first time I'd
ever used the Dremel tool with cut off wheels and I was amazed
how easy it went.

... tom

[Blair]

Those dimensions sound about right.

I do my layout work in the Visio drawing program and came up with 19 x 14 inches, but that's with two power trannies. Using the toroid will bring it down to 15x14 or thereabouts. Then, when I'm ready to build, I make a full-sized print of the layout drawing and fix my mistakes.

You got me really "amped up" about the AN-4TK400. Checked their web site and it sounds perfect. There's a new one for sale on eBay for 50 bucks + 10 shipping.

There's an itch I have to scratch, methinks.

Buy your Antek tranny direct and save yourself a few bucks. IIRC, it is a $10 difference. That is at least a cap pr two

I used it for a stereo Poseidon amp and it barely gets warm from a tube tranny perspective. You can lay the back of your hand on it for a minute or so after extended operation.

Blair

[ChrisK]

Thanks, everyone, for the sound advice.

Having decided to use the Antek toroid power trans, I see that there seem to be minor differences between the Dynaco P-782 and the Antek AN-4TK400. This probably means that I'll have to learn how to make adjustments to the component values in the power supply. Yeah, life-long learning is good....

Stock bias taps are 55v, Antek is 70v. Stock heater taps are 6.3 and 5v, Antek is 6.3 and 6.3 volts. Not sure about the stock B+ voltage, but the Antek supplies two taps at 400v each (one for each Mark III channel).

Has anyone done this before and is willing to advise? Otherwise, I'll break out the reference books and try to evaluate from scratch.

Thanks, ChrisK

[Blair]

You should be able to change the pot value (higher) from the original bias schematic for more adjustment and maybe place a dropping resistor in series with the bias voltage, but that is no big deal.

If you use SS rectification, you can eliminate the need for the 5v winding and use the 6.3 for your filaments.

I found that once the bias, and the rest of the amp is properly set up, you simply have 20v more B+ which any KT88 will take. Mine runs around 520v B+. Of course, there are fixes for that as well such as higher DCR chokes, etc.

Have fun!

Blair

[battradio]

If your hart is set on a 5AR4 by ,a 5 volt toroid to go with the large one .

Mark

[ChrisK]

You should be able to change the pot value (higher) from the original bias schematic for more adjustment and maybe place a dropping resistor in series with the bias voltage, but that is no big deal.

If you use SS rectification, you can eliminate the need for the 5v winding and use the 6.3 for your filaments.

I found that once the bias, and the rest of the amp is properly set up, you simply have 20v more B+ which any KT88 will take. Mine runs around 520v B+. Of course, there are fixes for that as well such as higher DCR chokes, etc.

Have fun!

Blair

Thanks, Blair. That's all good news.

As far as SS rectification is concerned, I've read mixed reviews over the years in the forums. You know, the subjective "listening test" stuff. So my approach was to use the GZ34 but change it out with a Weber Coppertop if I want SS, but still be able to go back to the tube.

The post from battradio (Mark) made me think, though. Is my heart set on tube rectification? Not really. SS has many benefits and maybe I should just make the decision to go with it. When increasing capacitance, it's a natural to install some fast/soft recovery diodes in full wave.

Hmmmm.....

[ChrisK]

If your hart is set on a 5AR4 by ,a 5 volt toroid to go with the large one .

Mark

Makes a lot of common sense, thanks. But, my heart is'nt set on tube rectification, especially since I'm not doing a refurb here but a new system from the ground up yet trying to stay true to the Masters.

Shoot, Dynaco started using SS rectification in their tube amps...

Thanks for helping me reconsider this.

ChrisK

[Blair]

I have heard both, and I prefer SS rectification personally. It is all subjective. Here is the amps I keep referring to even though it is before the 70v bias tap was available. It is the AN-4T400. I used a separate tranny to get my bias, but your tranny will be fine.

http://img.villagephotos.com/p/2005-12/1115293/CannonCamera197.jpg

http://img.villagephotos.com/p/2005-12/1115293/CannonCamera200.jpg

http://img.villagephotos.com/p/2005-12/1115293/CannonCamera182.jpg

http://img.villagephotos.com/p/2005-12/1115293/CannonCamera191.jpg

Blair

[ChrisK]

You can see my stuff at http://tmamps.com the chassis
is from http://www.yaegeraudio.com/default.tpl it's a
pretty good deal at $ 119. When I built that amp with the
old Heathkit AA-100 transformers, it was the first time I'd
ever used the Dremel tool with cut off wheels and I was amazed
how easy it went.

... tom

Tom, you are one prolific amp builder!

Oh yeah, the Dremel tool! It's sweet for detail work but I keep breaking those thin little cutoff disks...not on the chassis but on the bench when I move the tool around.

Chris

[ChrisK]

I have heard both, and I prefer SS rectification personally. It is all subjective. Here is the amps I keep referring to even though it is before the 70v bias tap was available. It is the AN-4T400. I used a separate tranny to get my bias, but your tranny will be fine.

Blair

Whoa, that's a beautiful job! Between the oak, cherry trim (?), aluminum plate and build quality that's a keeper, for sure. Pride in craftsmanship shows in all the details...

I like the way you extended the wooden rail to support the iron. Funny, when I looked at your pictures I immediately saw a lot of the design elements that have been in my mind: Nicely finished oak rails, using .1" alum plate (so much easier to work), simple, clean lines....

Oh yeah, I'm going "green" and reducing my carbon footprint: The GZ34's are out of the picture and SS is in. Less power, less heat, less space...thanks for helping me make that decision.

Good stuff, yeah.

Chris