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The Mighty Bogen MO-200A

Hiya,

Anyone look at the crazy that is the Fisher SA-1000 for ideas how to build a Hi-Fi 8417 based amp. ??

For example the ELL80 Drivers are interesting ..

Frannie
 
buglegirl said:
Hiya,

Anyone look at the crazy that is the Fisher SA-1000 for ideas how to build a Hi-Fi 8417 based amp. ??

For example the ELL80 Drivers are interesting ..

Frannie
Click to expand...

I had one of those once never did get it working correctly a monkey peed in it , the person I traded it to had to strip down to a bare chassis and , and boil the tag strips , to get it clean enough to work . The leakage in the bakelite was keeping it from working ( pun intended ) .
 
"No doubt it would make an absolutely killer guitar amp." It definitely would. Very interesting as well as precise info on the Bogen David, thanks! Makes me want to do the same testing with my buddy Jerry's favourite re-purposed PA amp the HK Galaxy 150. A 4 - 6550 power amp with several built in preamp modules. They have a Freed output transformer in them that, for their size, perform amazingly.
 
gadget73 said:
you know, of all the reasons I've seen cited for damage to a piece of gear, I don't think I've ever heard that one before.
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It was used in a research lab , and the monkey had copper coils embedded in its eyes , the SA 1000 was used to apply a signal to the coils , the position of it's eyes would change the phase of the signal to a second set of coils so they could tell where the monkey was looking .That's why it was close enough to the monkey to get peed on , lots of bad Karma in that amp .
 
The MO-200a can be a very decent hi-fi amp for many applications.

That the amp is a bit weak at both the bottom and top of the frequency range when driven to the limits is not surprising. Getting 200 watts out of a mono amp is not the easiest of tasks. And when Bogen manufactured the unit, the typical output frequency range was limited by the typical PA speakers of the time. Think banks of 6 or 12 heavy duty CTS 12" alnico whizzer-cone coaxials. Supposedly full-range, these types of speakers typical rolled off below 80 Hz and above 7 or 8 kHz.

In actual use, when I've heard near-stock MO-200a's they haven't sounded bad at all. I attributed the results to the more harmonic tube distortion. We have already seen what a redesign with attention to audio detail can do. Bricktop's redesign at 70 WPC with 6CA7's could easily have been 140 Watt mono if he started with two MO0200a's. Seems to me that so long as we stop worrying about pushing 200 watts, we can easily get within 7 dB of 200 watts. Seems the iron is decent for most <100 watt applications, and for me, these days that is most applications.
 
jaymanaa said:
I know, I feel like I need a summary that I can understand. :D All I know is I have one, and I'm using the 8417s, and some of Micahs mods.:yes:
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Yes, I am interested to hear your results and impressions. Hopefully Dave's work in this thread will complement yours - and vice-versa.

I have a pair of the MO-100A amps that I have enjoyed on and off depending on equipment rotation. I also have a bunch of the 120W M120 and 60W MX60A amps, which seem to have better claimed OPT power bandwidth performance and more standard taps, so I might apply anything learned here towards those.
 
Tinkerbelle said:
Yes, I am interested to hear your results and impressions. Hopefully Dave's work in this thread will complement yours - and vice-versa.

I have a pair of the MO-100A amps that I have enjoyed on and off depending on equipment rotation. I also have a bunch of the 120W M120 and 60W MX60A amps, which seem to have better claimed OPT power bandwidth performance and more standard taps, so I might apply anything learned here towards those.
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Not the first example of the smaller ones outshining their beefier sib's. Ran across this runniing down early SS Altec rack amps for a friend.


"To give anything less than the best is to sacrifice the gift - Steve Prefontaine"
BTW I'm pretty sure my younger bro' knew and ran with/against Pre' when he was training for the Olympics. Different world back then, better in some ways.
 
Pio1980 said:
Not the first example of the smaller ones outshining their beefier sib's. Ran across this runniing down early SS Altec rack amps for a friend...
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Some of those Altecs have fine iron, although possibly similar bandwidth designs for the application.

Pio1980 said:
"To give anything less than the best is to sacrifice the gift - Steve Prefontaine"
BTW I'm pretty sure my younger bro' knew and ran with/against Pre' when he was training for the Olympics. Different world back then, better in some ways.
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I used to do a lot of running back then and was pretty good at long distances. I had oudles of stamina for distance but not the speed. I loved watching the mile, 1500, 5K, 10K races back then. I am more than a little envious of your brother.
 
Tinkerbelle said:
Some of those Altecs have fine iron, although possibly similar bandwidth designs for the application.


I used to do a lot of running back then and was pretty good at long distances. I had oudles of stamina for distance but not the speed. I loved watching the mile, 1500, 5K, 10K races back then. I am more than a little envious of your brother.
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The Altecs in question were 200W 1590C 1st-gen quasi-comp solid-state transformer-coupled amps, the 50W versions were supposed to be much nicer sounding amps with better sorted-out OPTs. I ended up subbing an Adcom GFA-535 for the domestic app for which the malfunctioning Altecs were vastly overqualified powerwise, also with a simple passive control between the CD player and the amps replacing a malfunctioning McIntosh MX-110 and Soundcraftsman EQ. Guy loves the sound, 'simple' is better IMHO.

An OT sidebar;
My Bro' met and ran distance with some fine folks, he never made it to the big 'O' as something alway seemed to 'let go' during training (which is an inevitable part of the winnowing-down process and the luck of the draw/day), and as it turned out the boycotted Moscow games were his last window of opportunity. He ran recreationally as well as competitively for years afterward but MS has finally recently ended even that. I also ran a bit recreationally thanks to his and Paul Klipsch's influence until arthritis ended it for me and put me on a bike running sitting down (what's not to like about that?:yes::D).
Best! Steve
 
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battradio said:
It was used in a research lab , and the monkey had copper coils embedded in its eyes , the SA 1000 was used to apply a signal to the coils , the position of it's eyes would change the phase of the signal to a second set of coils so they could tell where the monkey was looking .That's why it was close enough to the monkey to get peed on , lots of bad Karma in that amp .
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There was another thread with cat barf in a tube amp, white vinegar may have been a possibility neutralizing the pee tho' just replacing the tag strips and sockets if practical would be better.
Dunno tho', you had it and I didn't.
 
battradio said:
It was used in a research lab , and the monkey had copper coils embedded in its eyes , the SA 1000 was used to apply a signal to the coils , the position of it's eyes would change the phase of the signal to a second set of coils so they could tell where the monkey was looking .That's why it was close enough to the monkey to get peed on , lots of bad Karma in that amp .
Click to expand...

The capacity of man continues to astonish me.
 
OK, so this thread may not die just yet. After some back and forth with Rpampt, I sensed he wasn't ready to roll over on these yet, so I suggested we go forward and split the channels, and make this sucker be the best it can be with the transformers its got -- which is the agreement at hand. Afterall, if we start improving it to the quality of the Dynacos, then he basically just ends up with more Dynacos, which is really silly because he already has those. So, we'll go after these things as they are, to make them the best of what they are -- but with a re-purpose in mind for home stereo use -- and, knowing what we're starting from to begin with.

Stay tuned!

Dave
 
Once split an no longer "sharing" outputs, up the current, maybe drop some voltage
and power output, it would be interesting to see where the specs are at that point.

Meaning quick tweaking it to be the best it can be in "stock" form for HIFI use then.
We know that low current is hurting it, we know paralleling the outputs is as well to.

So taking away some of the known limitations an maybe tweaking feedback it might
improve the performance a fair amount just to get another handle on it's capabilities.

I would be Interested to see the issues we "know about" addressed then the results.
Just to give the best chance in "stock" form to be the best HIFI amp it could of been.

We know with all kinds of mods done it could be much better, but I am curious of just
the obvious HIFI purpose issues addressed how it would perform from that stand point.
(we know the output trannies will still be the limiting factor, but how much was other)

Anyway just my ramblings.. :)
 
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