Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Carlsoti on September 13, 2023, 08:38:21 pm
-
I'm the new owner of the 60's Maggie M10 that I worked on for a friend. I really missed this amp after giving it back, so I've done a handful of various repairs for him to call it mine. Since it's not in the greatest cosmetic shape nor entirely original, and going to be played by me at home, I'd like to tweak a few things. First and foremost, I'd like to slow the trem just a hair.
The oscillator circuit doesn't seem unusual, so I'd guess I'm looking at replacing the two .01 caps hanging off the grid with a pair of .02, correct?
I say guess because I'm not 100% certain EXACTLY how the rest of the trem circuit works, or rather, I'm apprehensive because I've never tweaked a Maggie trem circuit. I have a general understanding of how the varistor trem works, but not a lot of experience with them and I feel like there's intricacies I'm not even aware of. It doesn't look too terribly different from other trem circuits, save for the varistors and the extra caps around them. I'm inclined to say I'd also like to increase the intensity, but I'll do one thing at a time and listen, and also learn a bit more about the circuit before I do more than the rate mod.
Once I get it opened back up, I'll get a fresh voltage chart and put it on the scope just to ease my curiosity.
I'm also interested in learning a bit more about how a fixed-bias input tube reacts with different inputs; straight guitar vs. Fuzz Face vs. unreasonably loud clean boost, etc. Not just the sound, but if it's more or less likely to go "kah-blooey" when tortured for tone. I've got Merlin's books at hand, and a few hundred gigs of the most oft cited reference materials. If anyone could suggest something on that, I'm ready for the deep dive.
Another mod(s) I'm considering is using the previously deleted antihum positions for NFB defeat and nfbd+cathode bypass cap for the last driver stage. I'm sure I'll have to shore up the PI to make that one work, but not beyond my ability. I'll have to dig into the switching again to see if that's even feasible.
I'm contemplating a speaker upgrade, too, but that's $$, and I've no good way around that.
All tips, tricks, cheat codes, etc welcome.
T.I.A.
-
The LFO part of the maggie vibrato is nothing special. You may get away with adding just one .02 cap to slow it down to your liking. You may want to check out sluckey's modded circuit which allows for a slower and faster switch. Congrats on your new amp!
-
Nice project! Please post your progress and any questions. I'm pulling up a chair!
I restored a M10-A several years ago and still have the amp. You can see my amp on my website...
http://sluckeyamps.com/magnatone/magnatone.htm
There may be something there you can use, but keep in mind... The M10 and M10-A are two quite different amps, lot's of common circuits but enough differences to mess you up.
-
That amp has true pitch shift vibrato, not trem. Nothing sounds like it, nothing!
I bought one of the reissues just for the vibrato and I love it! :blob8:
On yours, the vibrato is mono, they did also make a stereo vibrato, it had/has more of a 'watery/ flutter' sound as the sound flips back and forth from speaker to speaker. Mine has a switch for either, I stick with the stereo vib for that watery flutter.
The monos still sound really great, but the stereo with that flutter, man! :happy1:
-
That amp has true pitch shift vibrato, not trem. Nothing sounds like it, nothing! ...
I blame Leo for my incorrect terminology. :laugh: