12ax7 triode after the phase inverter?

[HotBluePlates]

... I'm leaning towards a single channel AB763 with reverb ...
I was also looking at the '63 Blonde Twin, for it's lower voltages,,,but I'd like to have reverb

...

Can we do that within the voltage range you want to be?

Ideally, you'd have an existing amp you want to plug this stage into, rather than coming up with a design from scratch. Why? Because you know how the amp sounds now, and so will know what the change did to the amp's performance is the main reason. The other big reason is that out of the hundreds of little things to decide to design a complete amp, we would only need to figure out a few to add the new cathode follower stage.

[SILVERGUN]

OK,
 If you agree that the AB763 is a good base, i'll build it on the breadboard first, as-is, and we'll go from there.....I'm hoping this circuit choice will simplify some things for myself and others who might want to build one and just use a Hoffman board and layout

I'll start with a fresh schematic and incorporate those changes to the circuit that I mentioned, and we'll see where it goes.....

I've got a new Hammond 1760L (4.2K primary) that can't wait to push 2 6L6s around 
With my bench supply, I can start with any ac input voltage up to 480,,,,let me know where you'd like me to be

I also have a separate 230 vac supply (straight off the wall---if that's ok) if you'd like to work the negative supply separately at first...your call
I'll start with the standard fixed bias supply that I build onto the board,,,and get it up and running

I was looking for a reason to build a Deluxe Reverb Plus, and here it is........a close friend just bought a reissue that I have full access to, so I'll let you know just as soon as mine sounds better than his   

The part gathering has already begun and the good news is, I have most of it here 
As long as life co-operates, this shouldn't take long........I'll worry about chassis and cabinet details later

[sluckey]

I look forward to following your progress with this project. Let me know if I can contribute. You may want to start a new thread since there are already 50+ messages in this thread.

[SILVERGUN]

Sounds good,
Here's a glimpse into the future...
This is what the AB763 pre/PI circuit looks like layed out on a fancy piece of plywood  

I'll update again when it's ready, and leave the link to the new thread

Thanks for the inspiration guys

[HotBluePlates]

If you agree that the AB763 is a good base...

... can't wait to push 2 6L6s around ...

I was looking for a reason to build a Deluxe Reverb Plus...

Is your final amp gonna be 2x 6V6 or 2x 6L6? It makes a difference because bias voltages are different.

Also, I'd need to know exactly what PT you'll be using, because obviously any supply voltage created will have to use what's available from the PT (or we'd need to know upfront that an auxiliary transformer is needed).

[SILVERGUN]

2- 6L6 for sure....I want to take advantage of the bigger bottle tone

Also, I'd need to know exactly what PT you'll be using, because obviously any supply voltage created will have to use what's available from the PT (or we'd need to know upfront that an auxiliary transformer is needed).

You had mentioned that lowered voltages might help our cause....
I don't care at all about max. volume from the 6L6's,,,,,,so how low can we go?
I wouldn't be against going as low as possible to give you some cushion,,,,and I wouldn't mind using an aux. xfmr either

This one has  305-0-305 taps : http://www.classictone.net/40-18094.pdf (I like the upright, but not necessary)
OR
This one's got 330-0-330 : http://www.classictone.net/40-18005.html  (this one saves me a couple bucks and loses the 5V tap, but has the higher voltages)
OR
330-0-330 http://www.hammondmfg.com/pdf/EDB290EX.pdf
OR
275-0-275 http://www.hammondmfg.com/pdf/EDB290MX.pdf

Any suggestions?

[PRR]

> including 12AU7

Run the AU up nearer 10mA (use ~~~15K plate loads).

Zout will be lower than the AT (but who hears Zout?).

Voltage gain is poor. Balance is poorer due to lower gain. Low gain means you probably can't get "really significant" NFB.

> maybe why fender chose it?

Maybe he wasn't so dumb?

[SILVERGUN]

2- 6L6 for sure....I want to take advantage of the bigger bottle tone

So more like '65 Super Reverb with ss rect....(sorry, I'm still working on model/feature recognition)
I'm thinking that we might want to go 275-0-275 sec., due to the ss.....right?....or lower?

Am I safe to assume it's OK to beef-up my first stage filtering up to 220uf?  (my board has these options 220, 100, 50/50, 40/20/20/20)

I figure this is a good place to work out a couple of the initial build details first, and then we'll move the thread to continue the PPICF discussion
Unless I figured wrong  ,,,and we should just move

Thanks again for all the help, and thanks for joining in DL and PRR 

[John]

Am I safe to assume it's OK to beef-up my first stage filtering up to 220uf?  (my board has these options 220, 100, 50/50, 40/20/20/20)

SG, if you wouldn't mind could you do a comparison between the 50||50 (with resistor in between) and the 100 or 220? I've read where it does a better job of smoothing ripple without making it "stiff". If it's a pain (on that fancy schmancy breadboard *drool*) then don't bother. 

[SILVERGUN]

SG, if you wouldn't mind could you do a comparison between the 50||50 (with resistor in between) and the 100 or 220? I've read where it does a better job of smoothing ripple without making it "stiff". If it's a pain (on that fancy schmancy breadboard *drool*) then don't bother. 

Sure John,,,,but, do you mean a scope comparison?...and then feel for "stiffness"?..........I'm not sure I've got the experience to notice a difference

One little hold up on this end is that my Variac started to arc at the first winding (like a tiny little sparkler)  .....so I'm probably just gonna buy the PT that we agree on and wait for that to get here, before I go live

[SILVERGUN]

Guys,
Am I seeing this correctly in the fender schematic,,,,as a bias balance? pot?

What does the hollow circle to the left of the wiper arrow mean?

And while were at it,,,,what's the solid circle above the 400 up against that pot mean?

[John]

SG, if you wouldn't mind could you do a comparison between the 50||50 (with resistor in between) and the 100 or 220? I've read where it does a better job of smoothing ripple without making it "stiff". If it's a pain (on that fancy schmancy breadboard *drool*) then don't bother. 

Sure John,,,,but, do you mean a scope comparison?...and then feel for "stiffness"?..........I'm not sure I've got the experience to notice a difference

One little hold up on this end is that my Variac started to arc at the first winding (like a tiny little sparkler)  .....so I'm probably just gonna buy the PT that we agree on and wait for that to get here, before I go live

Oh, sorry. No, I just meant if you can hear any difference. The "stiff" is a term I've heard used to describe the bass response of an amp, IOW you've taken out some of the "sag" or maybe just "mojo" by using a large 1st stage filter cap. OTOH, I think Marshall (?) used big reservoir caps too. Of course, the main thing is I don't have the time or ambition to try out everything I want to, and well... there you are with that shiny new toy. 

[PRR]

> as a bias balance? pot?

Yes. It is a _4_ terminal part. While you can probably source a replacement somewhere, it only balances, will not adjust for the wide range of biases that you need to "use ANY 6L6".

And if you are generous with the main filter cap, you don't really need "bias balance".

Unless this is a restoration, do a standard bias. Either common for both tubes, or if you obsess about balance then separate.

[rzenc]

SG:

Will you try this dc or ac coupled? Fender did it AC, whilst D, Ampeg and hiwatt went DC coupled.

Best Regards

R.

[SILVERGUN]

Will you try this dc or ac coupled? Fender did it AC, whilst D, Ampeg and hiwatt went DC coupled.

That is totally up to my friends here, and what happens when we start experimenting.......maybe we'll try it both ways?

Picture me as the cheap labor......I'll just throw the parts at it, and hopefully learn something along the way
If you notice,,,, some of my questions are pretty dumbed down for the company I'm sharing   
But if you remember my Wreck thread, I'm not afraid to try anything........in this case it's gonna take a little more finness than I possess

I've got great intentions.......
My main goal would be to not make HBP regret his decision to help 

[Gary_S]

SILVERGUN: Did you get an answer to that Fender schematic question you had?

EDIT:  Ah! i see it's answered above! balance pot. But what about the hollow circles in the schematic?

[sluckey]

But what about the hollow circles in the schematic?

The one on the wiper of the bias pot just represents the wiper lug. The solid circle on the bias pot represents a fixed tap at some resistance (maybe center tap in this case).

The circles on the standby switch represent the contact lugs.

[jazbo8]

SG:

Will you try this dc or ac coupled? Fender did it AC, whilst D, Ampeg and hiwatt went DC coupled.

Best Regards

R.

Since this whole idea came from a discussion wrt to SSS, it would be cool to see a properly executed direct-coupled design, and for my own selfish reason, I would like to see a comparison between the various tube types for the PI CF, e.g., 12AX7, 12AT7 & 12BH7 for starters. My money is on the 12BH7 

[Ritchie200]

Just look at any of the Major schemo's.  Cathodyne with 12au7 driver swinging some big current.

Jim

[Gary_S]

But what about the hollow circles in the schematic?

The one on the wiper of the bias pot just represents the wiper lug. The solid circle on the bias pot represents a fixed tap at some resistance (maybe center tap in this case).

The circles on the standby switch represent the contact lugs.

Thanks Sluckey for clearing it up. I wondered about it after reading SG's post and schematic.

[rzenc]

Just look at any of the Major schemo's.  Cathodyne with 12au7 driver swinging some big current.

Jim

It's interesting also, but finals are plate-driven.

With respect,

R.

[SILVERGUN]

Since this whole idea came from a discussion wrt to SSS,

And so now I shall name it....... (insert drumroll here)

the SS

Choose your interpretation:
1) Silvergun Super (my personal favorite)
2) Stevie Special (hopefully, a Super Reverb that Stevie would have enjoyed)
3) '65 Super Sport (as a nod to the Nova we all would have picked if we walked into the showroom in 1965,,,,and then drove to the music store and bought the best new amp money could buy)

Since Dan owns the '65 Amps name,,,,we'll just shorten it to SS

[jbrew73]

was any progress made with this project?  ive been considering an amp build with post pi cathode followers for some time but haven't had time to experiment and i was hoping you guys have this thing  all figured out. 

[SILVERGUN]

I had started a new thread where I did some experimenting and embarrassing myself here:
http://el34world.com/Forum/index.php?topic=15798.msg154716#msg154716
 
If I were you and seriously considering a build like this I would go over to The Amp Garage and read up on Steel String Singer or SSS. Those guys have dedicated way more time to this and seemed to have taken any mystery out of it.
 
Here's a great example of the type of clean tone you can expect from a similar circuit....just a gorgeous tone and build.
https://www.youtube.com/watch?v=TB465GMTsjQ
 
And another:
https://www.youtube.com/watch?v=IIIPTTgR3Kc
 
And another:
https://www.youtube.com/watch?v=QCRTGY5fvxo
 

[Fresh_Start]

was any progress made with this project?  ive been considering an amp build with post pi cathode followers for some time but haven't had time to experiment and i was hoping you guys have this thing  all figured out. 

I stumbled across several discussions involving the use of MOSFETS and other evil sand devices to drive power tubes.  GeoFX maybe?  MOSFET Follies?  AX84?  maybe all 3 and/or more.  That may seem like opening a whole new can of worms, but unless you're looking for some asymetrical compression from those cathode followers I'm not sure why you wouldn't want to look at solid state.

Respectfully,
Chip

P.S. In the Halloween spirit:

[jbrew73]

I had started a new thread where I did some experimenting and embarrassing myself here:
http://el34world.com/Forum/index.php?topic=15798.msg154716#msg154716
 
If I were you and seriously considering a build like this I would go over to The Amp Garage and read up on Steel String Singer or SSS. Those guys have dedicated way more time to this and seemed to have taken any mystery out of it.
 
Here's a great example of the type of clean tone you can expect from a similar circuit....just a gorgeous tone and build.
http://www.youtube.com/watch?v=TB465GMTsjQ
 
And another:
http://www.youtube.com/watch?v=IIIPTTgR3Kc
 
And another:
http://www.youtube.com/watch?v=QCRTGY5fvxo

thanks, I'll do some reading over there.