#164655  by Jblue76
 Sat Feb 09, 2019 12:22 pm
Hey all,

First of all Ive got to say a huge thank you to this community. I’m pretty ignorant when it comes to electronics and you all have been so helpful in steering me in the right direction. Thank you for sharing with me your expertise, and especially your patience!

So lucky, I just scored a beauty MC50! And for once i got some gear on the right side of the boarder for me. Shipping to Canada from the States is brutal these days! Anyway, now I’ve got to take the Mac along with my ‘68 twin in to get fixed up and ready to go. The plan is to use the twin’s preamp and speakers, and set it up so I can use either the Twin’s power or the Mac’s. What do I need to tell the tech to do, assuming he’s not familiar with Jerry rigs?

I’m going to get him to do the Cesar Diaz mod so the trem can be in or out of the circuit, so does that mean I get him to drill a new hole in the twin for the preamp tap? Any particular kind of jack needed so I can use either the twin or Mac for power?

Should i have the Mac’s input changed to 1/4” or use an adapter to RCA?

I’m also wondering what to do for the output from the Mac— the Twin’s speakers are connected to a 1/4” plug, so do I get a 1/4”output jack put in to the Mac (at 4ohms I guess)? I definitely do not want to loose the ability to plug the speakers into the twin and use its power section. The cloth wire with the 1/4” plug that connects the twin’s speakers to the amp is short; what’s the proper way to lengthen it so it reaches the Mac?

Beyond all of those connection of pre to power amp issues, what else do I have him do to the Mac? New caps— Any particular kind? Anything else?

Thanks again out there. Almost thirty years in the making and I’m SO close to finally having my Jerry Rig! So Psyched!
lovetoboogie liked this
 #164660  by waldo041
 Sat Feb 09, 2019 4:49 pm
For a McIntosh I prefer the Alembic approach and recommend the Input and Output be 1/4" and Banana.

1/4" is not "wrong" if you choose that route for the output, banana plugs and jack just have a lot more surface area to transfer current.

Image

:oops: Just be sure to solder the Red on the Right when the amp is right side up, and NOT Red on the Right when you are installing them with the amp upside down! :?

~waldo
Jblue76 liked this
 #164662  by Jblue76
 Sat Feb 09, 2019 5:51 pm
waldo041 wrote:For a McIntosh I prefer the Alembic approach and recommend the Input and Output be 1/4" and Banana.

1/4" is not "wrong" if you choose that route for the output, banana plugs and jack just have a lot more surface area to transfer current.

Image

:oops: Just be sure to solder the Red on the Right when the amp is right side up, and NOT Red on the Right when you are installing them with the amp upside down! :?

~waldo
Thanks so much. Seeing that picture is helpful. If you go with the banana plus on the Mac’s output do you loose the ability to easily switch back to using the Twin’s power?
 #164668  by TRG
 Sun Feb 10, 2019 6:30 am
I also just picked up an MC50 in great condition, but feel it could be a bit louder. In terms of having it recapped for guitar amplification is it as simple as sending to someone like Audio Classics and asking for a recap, or should I be more specific in the type of caps that are used?

I’m sure the type of caps play a more important role in the preamp, but wasn’t sure how critical the type of caps are for the power amp.
Jblue76 liked this
 #164670  by Pointclear
 Sun Feb 10, 2019 8:04 am
Congrats on your new Mac. I just went down a similar road: I tapped my twin reverb’s preamp and powered it with a harman kardon citation 16 and it sounds beautiful!! Waldo was a HUGE help. You can look o bee to that thread if you’d like for pointers on where to tap your twin and how to “tune” the output capacitors for specific frequency roll-off.
Some of your issues/questions may be more specific to a mc50, but the discussion of how to optimally pair a tube preamp to a ss power amp was really enlightening for me and my wheels are still turning. Things like input and output impedance were never on my radar before Waldo brought it up.

https://rukind.com/viewtopic.php?f=419&t=19844
Jblue76 liked this
 #164671  by Jblue76
 Sun Feb 10, 2019 8:39 am
Read a bunch of that thread. Man, I think I got myself in way over my head here.... hopefully my amp tech will know how to properly mate the pre and power amps so there’s no ice pickiness or low end issues....
 #164672  by Pointclear
 Sun Feb 10, 2019 8:53 am
Jblue76 wrote:
Sun Feb 10, 2019 8:39 am
Read a bunch of that thread. Man, I think I got myself in way over my head here.... hopefully my amp tech will know how to properly mate the pre and power amps so there’s no ice pickiness or low end issues....

You aren’t in over your head. Once you dive in you’ll find the waters deep but inviting and playful :)
Quick note: McIntosh amps, at least the 2300 and the larger ones I have looked at, have very high input impedance values, and the issues I am dealing with aren’t going to be as much of an issue.
You should tap your twin, per Alembic/Jerry specs, right behind the capicator coming off of v4b (the second half of the reverb return tube. You can drill a hole for a 1/4 in out put jack or two banana plugs, as mike suggested.
Jblue76 liked this
 #164673  by Jblue76
 Sun Feb 10, 2019 9:01 am
Thank you, very helpful to be able to tell the tech the correct location for the preamp tap. I know nothing about any of this electronic stuff (but I do know how to squeeze out a sweet Jerry feel from these fingers of mine!). I’ll convert the input of the Mac to 1/4” and do the preamp tap with the 1/4” jack as well. If that one is a switching jack will that make it easy to switch back to using the twin’s power if I can’t take the Mac with me?
The other thing I’m still not clear on is how to connect the twins speakers to the Mac’s output so I can easily reconnect them to the twins output. Waldo said it’s not “wrong” to give the Mac a 1/4” output, but he also said it won’t have the same surface area for the signal to transmit... the others issue here is the length of the twins speaker wires (which are connected to the 1/4” plug). I don’t know, maybe this is the kind of the all techs just know how to work out and it’s not at all a big deal?
 #164674  by Jblue76
 Sun Feb 10, 2019 9:13 am
A long shot but, any chance anyone out there has a Canadian amp tech associate that is well versed in the Jerry Mod thing??? Someone in the Toronto area maybe???
 #164675  by Jon S.
 Sun Feb 10, 2019 11:23 am
Another possible redesign approach (my MC50):

Image
 #164676  by Jblue76
 Sun Feb 10, 2019 11:49 am
Thanks, that looks interesting. So you have a 1/4” in from the preamp, 1/4” out to speakers, I assume the toggle is power on/off? If so, is the benefit not having to plug and unplug the unit each time you use it? What’s the additional 1/4” jack near the power cord and what kind of changes did you make to the power cord? I’d also be interested in knowing if the 1/4” out brought with it any kind of signal loss.
Thanks so much!