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Old 1st July 2004, 03:40 AM   #1
greggy is offline greggy  United States
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Join Date: Jun 2004
Location: Missouri
Cool BOGEN MX60A Schematic

I need a schematic for a Bogen MX60A if anybody's got one. I'm going to try and turn it into a gtr amp. If anybody's done it before and has any suggestions please let me know. I'm open to all suggestions. (i.e. recommended number of cascaded pre-amp stages, tone control ckt, elimination or limiting of degenerative feedback, speaker configurations that work well with it, cool mods that work well with it etc.) I've never modified old iron before, but I have worked with old tube stuff before. (KWM-2A xcvr, 30L1 rf amp, R390A & other military tube stuff) I know how to make it work when it smokes, but I'm not much on creative engineering.

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Old 12th October 2004, 05:14 PM   #2
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Location: between chicago & chedderland
Have you gotten any info. on mods? I've just gotten an MX60A & have a manual on the way; if it has a schem. I'll let you know. meanwhile, any tone/cascade info. would be appreciated.
-Art Heritis
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Old 12th October 2004, 10:45 PM   #3
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Location: Ann Arbor, MI
I had a pair of these amps. I traded them to a guitar player and got the following report.

Disconnect the NFB winding completely. It is a SE winding, one end grounded, the other to the cathode circuit of one of the gain stages. Removed it and said gain is right on, and tone is good.

the Tnuctipun will return
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Old 12th November 2004, 05:47 PM   #4
greggy is offline greggy  United States
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Location: Missouri
Default Modding Bogen MX60A

I modded the amp. All I did was cascade the first three input stages. I added a DPDT standby switch in the secondary of the plate voltage transformer. I replaced the power on indicator. I added a 1/4 jack on the back of the amp right above the #1 input XLR, close enough to tie to the original wiring. The parts probably cost $10.00 and the amp cost me $60.00 (with shipping).

The mods took me less than two hours the first time (being real careful). I also modded an MX30A amp I have, it took less than 1 hour since I knew what I was doing the second time. I haven't done anything to the feedback circuits yet.

This amp screams!!!!!! The lead player in my band says when he closes his eyes he can't tell the difference between it and his Marshall 100 Watt Lead Amp. With three cascaded input stages it has a lot of crunch. It also has plenty of adjustability for him to get a good clean sound. He seems satisfied with the tone controls. I did a lot of research before I modded the amp. This was the first one that I ever did. Before you try it read all of the online resources available and you shouldn't have any problems. I just picked up another one and I think I am going to mod it with foot-switchable channels, clean and distorted. I think I will tie inputs 1 through 3 together for distorted side and 4 and 5 together for clean. Add a switching circuit and I should be in business.
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Old 13th November 2004, 07:28 AM   #5
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Location: Edmonton
well i got one of these sans guts and 8417's so all was left were the transformers and the power supplies so i'm working on building up a good guitar amp outta it.... any info anyone?
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Old 14th November 2004, 08:59 PM   #6
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Location: between chicago & chedderland
Default Ready-Aim-Fire (I hope no fire)

Well Greggy, you talked me into it. Time to get off my Keister & do it. One question: did you use any compression between stages or just go from each stages out to the next stages in?
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Old 16th November 2004, 06:19 PM   #7
greggy is offline greggy  United States
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Location: Missouri

All I did was take the output of one stage to the input of the next stage. I don't have the amp or schematic in front of me now, so I can't tell you which pins. But, it's really easy to figure out. There's already a coupling capacitor on the output of each stage. I didn't change any components and it sounds great. I didn't have to re-cap anything yet. I probably will disconnect the negative feedback at some point, but I haven't had time lately.

I didn't add any compression circuits. I would think if you compressed a stage you wouldn't get the awesome distortion that I'm getting now. I don't know a whole lot about stock old guitar amps, but I didn't think that they used compression in their gain stages.

There's a lot of variations you could consider with these Bogen amps, it's just up to your imagination.

Good luck, let me know how it goes with yours, and I will keep posting on the results of anything I do to my amps.

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Old 27th June 2006, 08:17 AM   #8
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I'm a performer, but not much of a technical wizard. I'd love to learn more about what you're discussing, but some of the specific information with regard to electronics is a little greek to me.

I would like to turn a stock MX60A into a usable guitar amp. In simple terms, and being fairly explanatory (I apologize in advance), would you be willing to tell me what modifications need done in order to achieve this. I will be using a modeling pre-amp with it, so basically having a power tube unit that provides a little bit of warmth is what I'm trying to achieve.

And as part of this, what are the funky speaker connectors on the back of this and:

A) Can I convert them to something normal
B) Can I find them and what are they called?

Thank you so much for the information you have posted thus far. I will anxiously await a reply.
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