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Grateful Dead Music Forum

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 #127082  by williamsaut
 Thu Apr 25, 2013 2:11 pm
Hello everyone, I purchased an MC50 and want to disconnect the sentry to hear what the clipping sounds like. When I compared the diagram at Waldo's site to the MC50 it doesn't look the same. There's no PC board in the 50 that looks like the one shown for the 2300. I was able to find the schematic drawings for the 50 online and can't really tell where the sentry is located in the circuit and on what board. Anyone here know what board it's on and what components to lift? Waldo's site shows 4 components to lift and which end of each component to unsolder. If I had this info for the 50, I'd use a 4pole single throw switch and wire the loose components back to the board through the switch thus having an on/off for it. Any help is appreciated.


Thanks,
Williamsaut
 #127249  by williamsaut
 Sun Apr 28, 2013 6:48 am
An update to this post, I found elsewhere on this blog, someone who had sent his MC-50 to Classic Tube Audio to get it modded and checked out, So I contacted Pat Hickman there and he will check it out and mod the power jack as well as the Sentry lift switch and all for a very reasonable price.
 #127253  by Smolder
 Sun Apr 28, 2013 7:17 am
there is a lot of talk about that mod (on macs in general) if you search for it. Seems like Waldo, Brad and others have weighed in regarding whether this was actually done on Jerry's rig. Having read through it a year or two ago, I concluded that it wasn't worth my time or effort and moved on. YMMV. There is also a lot of good mac tech info on some of the older hifi forums. A lot more folks used these mac;s for that than guitar, so the bulk of information about them is there. Best of luck!
 #127278  by Jon S.
 Mon Apr 29, 2013 3:07 am
williamsaut wrote:An update to this post, I found elsewhere on this blog, someone who had sent his MC-50 to Classic Tube Audio to get it modded and checked out, So I contacted Pat Hickman there and he will check it out and mod the power jack as well as the Sentry lift switch and all for a very reasonable price.
You're welcome. :smile:
 #127297  by mgbills
 Mon Apr 29, 2013 11:56 am
Thanks Jon.
I'm forgetting what that toggle switch is doing?

I do feel like Pat is a guy who really understands McIntosh architecture.
M
 #127307  by williamsaut
 Mon Apr 29, 2013 2:23 pm
Thanks, Jon S. for speaking up. I had scanned through so much here that when the FYD MC-50 combo popped up I stopped on that. I too decided on the FYD over the Sarno preamp mainly because I wanted to be as much of a purist as possible and the eyelet wired tube drivin spring reverb preamp appealed to me.

I found that I couldn't run the output of the preamp at max without clipping the MC50 at the peaks, not a nice clipping either. I looked inside the amp and found a small blue pc board with an LS471 OP amp chip on it wired from the input to the preamp board and new that was not original ( IC chips didn't exist in 1970 ). So I'm glad to have found someone who will give my amp the once over so I know I'm starting with 100%. When it comes back I"ll give it another shot. Overall the sound is great but maybe it can sound better. Who knows I may end up getting the Sarno to boot. I've also got a H&K bluesmaster that also sounds great. Perhaps I can send it out to Shakedown amps and have him go through it. Maybe put it all in one rack along with an ADA 2FX and a Lexicon PCM60 and A/B/C them on stage!! No better way to compare.

Thanks,
 #127324  by Jon S.
 Tue Apr 30, 2013 3:09 am
Interesting. I found my FYD - MC50 combo sounds best with the FYD's output dimed. But I have not had to turn my MC50 up above a quarter on the volume knob, it's so damn powerfully loud (admittedly I've not yet gigged with it, though I've used it now at several band practices which were at a small club volume level). Perhaps (if not probably) once Pat updates/services your unit generally, you may find that the "clipping" issue is resolved as a consequence and no more changes are needed.
Last edited by Jon S. on Tue Apr 30, 2013 3:13 am, edited 1 time in total.
 #127325  by Jon S.
 Tue Apr 30, 2013 3:12 am
mgbills wrote:Thanks Jon.
I'm forgetting what that toggle switch is doing?

I do feel like Pat is a guy who really understands McIntosh architecture.
M
The toggle switch is the unit's new off-on switch. Handy!
 #127368  by mgbills
 Wed May 01, 2013 7:57 am
Ooooo. A tantalizing thought! Perhaps he could do a standby switch.

Intriguing.
 #127374  by Jon S.
 Wed May 01, 2013 11:42 am
mgbills wrote:Perhaps he could do a standby switch.
There would be no purpose for one that I could see for a solid state power amp (but maybe I'm missing something ...).
 #154808  by TeeJay
 Mon Dec 05, 2016 9:00 am
I lifted the sentry in a MC50 and I noticed the other day upon power up the speaker sucks in hard for a split sec. Should I not have the speaker attached when I power on? That flex can't be good for a vintage JBL. I was just worried about shorting anything without having the sentry. I made a cable with the spade connectors on one end for the mac terminals that I leave attached and a 1/4 plug on the other end for the speaker cab. Would it be an issue to power on the mac then plug in the 1/4 plug into the cab?
 #154812  by hippieguy1954
 Mon Dec 05, 2016 9:30 am
TeeJay wrote:I lifted the sentry in a MC50 and I noticed the other day upon power up the speaker sucks in hard for a split sec. Should I not have the speaker attached when I power on? That flex can't be good for a vintage JBL. I was just worried about shorting anything without having the sentry. I made a cable with the spade connectors on one end for the mac terminals that I leave attached and a 1/4 plug on the other end for the speaker cab. Would it be an issue to power on the mac then plug in the 1/4 plug into the cab?
It will not hurt the JBL's. I've been doing it for years to K120's with original cones and have had no problems. You should see my JBL's flopping when I play loud!
Also, remember JBL made their speaker black+ and red-.

I almost forgot...I'm pretty sure my speakers flexed when powering up my Mc2100 before I ever lifted the sentry.
 #154813  by Gr8fulCadi
 Mon Dec 05, 2016 11:58 am
hippieguy1954 wrote:
I almost forgot...I'm pretty sure my speakers flexed when powering up my Mc2100 before I ever lifted the sentry.
My mc250 does this too, and it's a completely stock unit. So the sentry mod isn't the cause of this to the best of my knowledge. Not sure what is? Actually taking mine to a tech to look at that and to go over it as well. Will keep y'all posted.