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AB763 circuit Master Volume Mod Reverb/Delay Processors (HW)
Old 4 weeks ago
  #1
Gear Head
 

AB763 circuit Master Volume Mod

Hi,

I'd like to add a master volume to my 64 Deluxe Reverb. I found this site a few months ago:

AB763 Mods by Robinette, Master Volume Mod

I sent the author of the site an email asking for help, but I've yet to hear back from him. So I come to you experts now.

I'm confident with a soldering iron, I'm sure I can tackle the project. I have some questions tho, I want to make sure I do this right before I go destroying a great amp.

1. I'm familiar with schematic symbols and signal flow, but I still struggle relating a specific area of a schematic to it's real-world physical location. In other words, if y'all could describe (or even have a picture on hand) where exactly the two wires reside in the amp for this mod, that would be super helpful.

2. The most convenient place for the pot is the space where the old auxiliary 2-prong outlet resides, I'm sure y'all know that. If I were to rip out the power outlet, what do I do with the leads that terminate at the outlet? Is it dangerous to just put a threaded cap on them (individually of course, not joined)?

3. Related to the previous question, it seems the outlet space is located directly above a transformer. The site suggests coax wire to elminate possibility of interference. I would want to use coax anyways to be safe, but I'm a bit confused where it says to only ground it at signal input. Does that mean only connect it to ground where the leads join the factory circuit? Leave the bare wire disconnected at the pot?

I appreciate any answers at all, thanks ahead for your time
Old 4 weeks ago
  #2
Lives for gear
 

Quote:
Originally Posted by BrassElephant View Post
Hi,

I'd like to add a master volume to my 64 Deluxe Reverb. I found this site a few months ago:

AB763 Mods by Robinette, Master Volume Mod

I sent the author of the site an email asking for help, but I've yet to hear back from him. So I come to you experts now.

I'm confident with a soldering iron, I'm sure I can tackle the project. I have some questions tho, I want to make sure I do this right before I go destroying a great amp.

1. I'm familiar with schematic symbols and signal flow, but I still struggle relating a specific area of a schematic to it's real-world physical location. In other words, if y'all could describe (or even have a picture on hand) where exactly the two wires reside in the amp for this mod, that would be super helpful.

2. The most convenient place for the pot is the space where the old auxiliary 2-prong outlet resides, I'm sure y'all know that. If I were to rip out the power outlet, what do I do with the leads that terminate at the outlet? Is it dangerous to just put a threaded cap on them (individually of course, not joined)?

3. Related to the previous question, it seems the outlet space is located directly above a transformer. The site suggests coax wire to elminate possibility of interference. I would want to use coax anyways to be safe, but I'm a bit confused where it says to only ground it at signal input. Does that mean only connect it to ground where the leads join the factory circuit? Leave the bare wire disconnected at the pot?

I appreciate any answers at all, thanks ahead for your time
I can tell by your questions that you have no business working on this amp.

Pack the amp up and take it to a tech and describe what you want to do....
Old 4 weeks ago
  #3
Gear Head
 

Quote:
Originally Posted by UKMK00 View Post
I can tell by your questions that you have no business working on this amp.

Pack the amp up and take it to a tech and describe what you want to do....
Its two wires and a pot, it's stupid simple, I just wanna make sure I'm putting the wires in the right place, and choosing a good spot for the pot to reside.

But thanks for your encouragement!
Old 4 weeks ago
  #4
Lives for gear
 

Quote:
Originally Posted by BrassElephant View Post
Its two wires and a pot, it's stupid simple, I just wanna make sure I'm putting the wires in the right place, and choosing a good spot for the pot to reside.

But thanks for your encouragement!

And another thing...Mr Robinette was nice enough to include a wiring diagram which shows exactly how to wire this mod. It could not be more precise and direct.


Do yourself a favor and take the amp to a tech.

High voltage is no place for hubris...
Old 4 weeks ago
  #5
Lives for gear
 
Radardoug's Avatar
 

It might look stupid simple, but it probably isn't.
Old 4 weeks ago
  #6
It is very simple. You lift the cap before the 12AT7 driver tube and wire in a 250k volume pot between it and the junction of the two 220k mix resistors.
Old 1 week ago
  #7
Here for the gear
 

64 deluxe

are you nuts it don't need a MV don't drill holes in it go buy a 5 watt amp anything but a MV in your vintage amp crazy fool
Old 1 week ago
  #8
You don't need to drill a hole or permanently modify the amp. Some use input jack #2 to fit it. Is it a tool or an investment?
Old 1 week ago
  #9
Gear Head
 

Quote:
Originally Posted by Jim Williams View Post
You don't need to drill a hole or permanently modify the amp. Some use input jack #2 to fit it. Is it a tool or an investment?
This is the most helpful post here so far...

Yes, its just a tool.

Quote:
Originally Posted by Bobtec View Post
are you nuts it don't need a MV don't drill holes in it go buy a 5 watt amp anything but a MV in your vintage amp crazy fool
I understand its a piece of history, an icon, blah blah blah

To me, its just (an awesome sounding) piece of electronic equipment and I'd like to mod it to fit my needs. Its MY amp, not yours.

I came here to ask how to do something...
not to ask if I should do it...

Jim, thank you for your level-headed input.

I'm no tube-amp-expert-technician, but I figured this mod was simple enough to handle, and to get my foot in the door towards becoming confident with this kinda stuff.

I (errantly) came here for some encouragement and some specific guidance because I'm a very visual person, and not good (yet) at matching schematics to real world physical locations

I came here to learn, but everyone (not you Jim) just decided they know what's best for me and my gear haha. Classic slutz I guess.
Old 1 week ago
  #10
Gear Head
 

Hate to tell you this, but that guy's master volume mod/add ins are incorrect.

That's probably why you don't hear from him.
Old 3 days ago
  #11
Lives for gear
The Master Volume is actually implemented the same way it is done in the Matchless DC-30 amps, and it does work through cancellation of the two signals that are opposite/inverted to each other.
Old 1 day ago
  #12
Lives for gear
 

Quote:
Originally Posted by audiospecific View Post
Hate to tell you this, but that guy's master volume mod/add ins are incorrect.

That's probably why you don't hear from him.
Why is it incorrect? Looks like it will work.
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