Single Channel AB763 project

[p2pAmps]

Hey There Amp builders,

Here is a little Diddy I'm playing around with.  It's a single channel AB763, no tremolo, 3 knob reverb, 1/2 power switch, Presence control, 4-8-16Ω, 4 6L6GC just for fun :)

Thanks to Doug for a great turret board.  I am hoping for loud / clean amp for steel guitar players or players that dig using pedals etc.  Thinking this will need to be a 2x12. 

Anyway, here is a link to see all the pics so far if you like that sort of thing.
http://www.p2pamps.com/bad-dawg

[shooter]

 

like the braided grounds !
and that mini tranny 
great workmanship as always!

[tubeswell]

Are you using one of the Allen amp schematics by any chance (Old Flame)?

[p2pAmps]

Are you using one of the Allen amp schematics by any chance (Old Flame)?

I am not Tubeswell, I did buy a PT from D Allen but I've never have seen his schematics.  This is one I put together and had Doug make a board for me from my DIYLC app.  Just kinda doing my own thing on this but I am guessing this has been done many times before :).

[p2pAmps]

like the braided grounds !
and that mini tranny 
great workmanship as always!

Thanks Shooter!  Yeah that little baby PT only weighs 10 lbs!

[sjwood3]

Is there an instructional out there on how to do a similar ground buss?  I looks amazing.  I don't love the idea of grounding to the back of the pot.   I'm at that stage in rebuilding an amp as we speak! 

[p2pAmps]

Is there an instructional out there on how to do a similar ground buss?  I looks amazing.  I don't love the idea of grounding to the back of the pot.   I'm at that stage in rebuilding an amp as we speak!

Check out the Aiken's site on grounding.  Basically that bus connects with a bolt through the chassis directly in front of the inputs.  The only thing I ground on the bus are the pots.  There are also other tabs at that point where the bus is connected for other things like Cathode caps, reverb transformer, filter caps (except #1).  At the other side of the chassis next to your PT is where I ground #1 filter cap, power tube cathodes, artificial center tap, transformer, bias supply.  I ground the AC mains by itself.

So far (knock on wood) it's worked out well for me but I am WIDE open for other thoughts and improvements.

Cheers,

[mresistor]

Very nice..  I did one of these single channel AB763s (DR) too, fun. Mine was flipped upright like a Marshall   I did mine from scratch.   I really like the blue paint on the endbells..   very nice touch. 

[DummyLoad]

there is probably a reason the reverb transformer is turned 45deg. offset from parallel/perpendicular planes on all the blackface and silver face fender combo amps with reverb.     

my thoughts are by rotating the transformer 45deg., fender is keeping the winding window eddy currents from firing directly into the driver tube and recovery tube.



--pete

[mresistor]

Interesting Pete  now I will look at mine to note orientiation of the reverb transformer

[p2pAmps]

there is probably a reason the reverb transformer is turned 45deg. offset from parallel/perpendicular planes on all the blackface and silver face fender combo amps with reverb.     

my thoughts are by rotating the transformer 45deg., fender is keeping the winding window eddy currents from firing directly into the driver tube and recovery tube.



--pete

Hey Pete,

I thought about that aspect but thought I would try it this way and see what happens, kind of an experiment.  When I did research on the subject of verb transformers the consensus was Fender did the angled tranny for space reasons.  Others say they have done what I did without any issues at all.  I think some Marshalls did the same but not 100% sure on that.  This is a sort of journey for me to see what I can and can't do and what is fact and what is speculation.  At the end I want a killer sounding amp for both Steel guitar and standard guitar too.  Filling her full of Jensens is also an experiment as I have to know LOL...

In Progress

[NewYorker]

I couldn't help noticing the solid copper connecting your Reverb Mix pot to the ground bus.  I assume you did that for structural reasons, i.e. to keep the wobbly end of the bus from wobbling?

Ed

[p2pAmps]

I couldn't help noticing the solid copper connecting your Reverb Mix pot to the ground bus.  I assume you did that for structural reasons, i.e. to keep the wobbly end of the bus from wobbling?

Ed

BINGO, looking to keep the bus from moving around...

[NewYorker]

Phew!  I got one right today.

Ed

[Willabe]

Very nice work Mike as always. 

Waiting to hear what you think of the Jensen paper/oil caps.

(Sent you a PM.)

[jojokeo]

Is there an instructional out there on how to do a similar ground buss?  I looks amazing.  I don't love the idea of grounding to the back of the pot.   I'm at that stage in rebuilding an amp as we speak!

Check out the Aiken's site on grounding.  Basically that bus connects with a bolt through the chassis directly in front of the inputs.  The only thing I ground on the bus are the pots.  There are also other tabs at that point where the bus is connected for other things like Cathode caps, reverb transformer, filter caps (except #1).  At the other side of the chassis next to your PT is where I ground #1 filter cap, power tube cathodes, artificial center tap, transformer, bias supply.  I ground the AC mains by itself.

So far (knock on wood) it's worked out well for me but I am WIDE open for other thoughts and improvements.

Cheers,

Hi Mike!
I've always paid close attention with my grounding schemes. It really is a learned part of building that people only learn about once they deal with their issues from not understanding it. I draw an analogy to boating (in the ocean, not lakes or rivers) where people just want to focus on the sailing and destination aspects. But once there, they realize that they have to find a way to securely stay somewhere, lol and there's no mooring or docking available nearby. So they need to anchor. There's many books that focus on just this one aspect. I think proper grounding, along with layout, is like a dirty little secret to success most just don't quite get? It's not sexy, doesn't have gain stages and special switching...so with most it's who cares? With all this I'll just say don't mix signal grounds with chassis grounds. Signal grounds are a return path for the signal and leave it at that.
Did you or do you ever use the listening device test when you place your iron (the OT at least)? If I don't place my OT on the other side of the chassis (usually the case) then I always do this before drilling any holes...

[shooter]

PT only weighs 10 lbs!

If you need an 11 lb choke for balance, let me know 

[DummyLoad]

wondering if insulated terminals/standoffs would do a better job of support for you than the lugs of potentiometers. 

https://www.dropbox.com/s/lv69ay14j95rt56/20200429_150017.jpg?dl=0

keystone electronics & cambion mfg. them. available from mouser, et-al. prices range from $4 to $12+

--pete

[p2pAmps]

wondering if insulated terminals/standoffs would do a better job of support for you than the lugs of potentiometers. 

https://www.dropbox.com/s/lv69ay14j95rt56/20200429_150017.jpg?dl=0

keystone electronics & cambion mfg. them. available from mouser, et-al. prices range from $4 to $12+

--pete

Thanks Pete!  I like those stand offs but a little short for my project.  I can certainly make some however.  Good tip - Thanks!

[p2pAmps]

Getting very close now.  Waiting on a few of that last caps I wanted for this and she will be ready to start the startup procedure.  Then on to the table saw for cabinet making.

[p2pAmps]

This is the completed chassis for my latest beast. This amp is based on the famous AB763 with some twists.  One Channel, No Tremolo Circuit, Presence Control, Modified Tone Stack, Reverb (Dwell, Mix, and Tone Controls) 1/2 Power switch, and Multi Impedance.  POI Jensen coupling caps throughout and F&T filter caps. 

First tests are great!  Very quiet and powerful.  The tone through my shop test 12" is big and bold.  I can't wait to hear this through a set of 12" quality speakers.

Next, I will get started on a 2x12 combo cabinet for her.

As always, thank for the interest and thanks to all the great folks on this forum.

Mike

[shooter]

beautiful work of art and function !!
I'm amazed at the number of artists here with an engineering mind 

[Willabe]

Looks great Mike. 

Did you polish/buff the B+ filter caps dog house?

[echuta13]

  VERY nice work!!! 

[pdf64]

Looks great, well done!
Assuming that the presence control is of the standard type, ie in the power amp NFB loop, I'd advise against putting it back there by the vol control. As output circuits close by inputs/early stages can give rise to stability problems.
Hopefully you'll get away with it 

[dude]

That's about the cleanest build I ever seen, you're an artist p2p. Bet your cab will outstanding too.

[p2pAmps]

Looks great Mike. 

Did you polish/buff the B+ filter caps dog house?

I did because I am basically insane LOL

[p2pAmps]

Looks great, well done!
Assuming that the presence control is of the standard type, ie in the power amp NFB loop, I'd advise against putting it back there by the vol control. As output circuits close by inputs/early stages can give rise to stability problems.
Hopefully you'll get away with it 

Thank you.  Yes it is in the NBF loop and apparently I did get away with it as it works perfectly and the amp is VERY quiet (so far).  I appreciate your feedback and I will take a deeper look at what you are suggesting.

Cheers!

[p2pAmps]

That's about the cleanest build I ever seen, you're an artist p2p. Bet your cab will outstanding too.

Thank you Dude! 

[Willabe]

Mike, how do those paper -n- oil caps sound to you?

[p2pAmps]

Mike, how do those paper -n- oil caps sound to you?

I'll let you know soon as I finish up the cab.  I don't want to make any assumptions till I get her in the cab with decent speakers.  Soon I hope, been spending the last 3 days spring cleaning the shop and boy do I feel old (hurting everywhere hahaha)

[pdf64]

Looks great, well done!
Assuming that the presence control is of the standard type, ie in the power amp NFB loop, I'd advise against putting it back there by the vol control. As output circuits close by inputs/early stages can give rise to stability problems.
Hopefully you'll get away with it 

Thank you.  Yes it is in the NBF loop and apparently I did get away with it as it works perfectly and the amp is VERY quiet (so far).  I appreciate your feedback and I will take a deeper look at what you are suggesting.

Cheers!

I was reminded about RG Keen’s excellent page on the topic (thanks shooter!) http://www.geofex.com/Article_Folders/lead_dress/lead_dress_in_tube_amps.htm

[p2pAmps]

Ok, here is a fun little sound clip.  I'm still working on the cab but this is what she will be like.

[Ed_Chambley]

Great build.  Perfect for one of those jacked up Hawaiian geetars.  What kind of music do you play with one of those steel geetars.  Someone told me it was an outdated instrument and some have 2 necks, but I have never even seen one with even one neck.


I got a buddy named emmons says he can play anything with strings, hell add a couple more and call it Bakersfield.


Really nice and over the top build.  Bout par for the course for P2P amps ain't it.


Just funniness, very nice and clean amp.

[Dave]

Very nice build. I am very envious of those who can keep their builds looking pretty. I have built a lot of great amps, but none have ever looked pretty like that. I also have two cents to throw at the grounding conversation. I have yet to find a fail safe grounding scheme. I have tried them all and have had great success with just doing it like Leo Fender did it. But, occasionally, a ground loop pops up and drives me crazy while I try to figure it out. The last one that I encountered was the cathode resistor/bypass cap of the reverb recovery stage was moaning and groaning. After I tracked it down, I found that I could literally ground it anywhere on the amp except for the place I had it grounded.


Dave

[p2pAmps]

We have twins now :)

[kagliostro]

 

VERY NICE

Franco

[sluckey]

Twins squared. Is hat like a Quad?   

[p2pAmps]

Twins squared. Is hat like a Quad?   

2*2^=x. solve for x hahaha

[brewdude]

I like the ground buss.  I’ve never seen (or noticed) the signal wires being tied to the ground bus.

I am working (painfully slowly) on build where I used a vertical terminal strip to hold the far end of the bus.

[shooter]

2*2^=x. solve for x hahaha

(X = 2 full stacks + AB/Y + amp volume 8) - long term hearing

[SILVERGUN]

Mike, you've created quite a conundrum for me.
I can either spend more time trying to make my amps look and sound as good as yours OR practice playing guitar so I can someday play as well as you or your pedal steel partner.
Either way, It's a steep hill to climb. How am I ever supposed to get a shed built?

 

[p2pAmps]

I like the ground buss.  I’ve never seen (or noticed) the signal wires being tied to the ground bus.

I am working (painfully slowly) on build where I used a vertical terminal strip to hold the far end of the bus.

Nice work Brewdude and good idea on your ground bus for sure. 

Cheers!

[p2pAmps]

Mike, you've created quite a conundrum for me.
I can either spend more time trying to make my amps look and sound as good as yours OR practice playing guitar so I can someday play as well as you or your pedal steel partner.
Either way, It's a steep hill to climb. How am I ever supposed to get a shed built?

 

HAHA, thanks!  If it's a she-shed let she build it :)

[DummyLoad]

thinking about using the method in the attached photo.


--pete

[p2pAmps]

thinking about using the method in the attached photo.


--pete

I like it Pete

[p2pAmps]

Here's the final on this 2x12.  Holy moly is this amp loud!  Should be a big hit with the steel guitar and tele pickers. 

[vampwizzard]

AMAZING. is that p2p illuminated in the front?

Seriously nice build start to finish.

[p2pAmps]

AMAZING. is that p2p illuminated in the front?

Seriously nice build start to finish.

Yeah I lite that logo up for fun LOL...

[p2pAmps]

A little steel guitar sound demo