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Old 8th August 2008, 12:04 AM   #1
GordonW is offline GordonW  United States
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Default Bogen MX-60A- output transformer bandwidth?

Got a pair of Bogen MX-60As courtesy of a very nice person from AudioKarma.

I have found many threads about converting these to guitar amps... but I would like to go a different direction, and convert mine into hi-fi monoblock power amps.

Anyone got a handle on what kind of bandwidth these transformers have... and/or conversely, how much power can I get out of them and still get good bass/highs?

I'm thinking of converting them over to (get ready)... g2 screen drive amps, with 6146B output tubes, 6CS7 diff-amp/cathode followers. 6C4 phase splitter (split-load) and a good pentode for the input (anything from 12BY7 to 6CF6 to EF184/6EJ7). Or, alternatively, if I can get enough voltage swing, a HK Citation II front end, with triple 12BY7s (one input, two in the LTP) driving a 6SN7GTB cathode follower, driving the 6146Bs. (BTW, I'm guessing the first design will be better, since I can probably get more voltage swing out of it, to the output grids... but I haven't been able to get the calculations on how much voltage a 12BY7 LTP could swing, with up to 500V available for B+ if needed).

But, to do that, I need to know if I will have enough bandwidth. I know I can improve bandwidth, by lowering the output impedance of the output tubes... anode-to-anode feedback from the output tubes to the diff amp (in the first design) or LTP (in the second design). That said, if the original transformer has decent power bandwidth in the bass, and HF bandwidth (for stability under feedback), I should be able to get it to work...

So, has anyone worked with one of these, in any manner resembling a hi-fi application?

Thanks!

Regards,
Gordon.
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Old 8th August 2008, 07:23 PM   #2
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I just happened to have picked up a MX-60a at a garage sale myself. They're PA amps so I'm guessing they should do nicely in Hi-Fi service. Just from the size and weight I would expect that you could get just about 50 good clean watts out of them if not more. Makes sense since it was driven by PP 8417's.

I've tried lesser Bogen PA amp for Hi-Fi, and they do pretty well.

Mine is on the "to be repaired" heap so I can't say I've ever kicked the wheels on it yet.
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Old 8th August 2008, 07:48 PM   #3
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I've got a chassis and OPT from a M-100 (IIRC?) here..Same deal,separate 70V and feedback windings..I was planning on building a bass amp with it,someday.
Good info,I'll keep an eye on this thread.

Edit:This amp also used 8417's,a quad in Push-Pull-Parallel,claiming 100W output.
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Old 24th September 2008, 07:15 PM   #4
MI-9448 is offline MI-9448  United States
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Default BANDWIDTH IS GOOD

I remember seeing the specs for all of the Bogen stuff in an old electronics supply catalog and was astounded by them.I can't remember them exactly but the MX and MO series had way better than 20-20Khz response.These were top of the line units and were far better than the general use CHB series. Very pricey too.
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