Harman Kardon ME 25 Ideas

[duce67us]

So,
I found this HK ME25 PA,
Looks interesting,  Mic, Aux (x2) inputs,

Doubler circuit for the HV power,  Hum Balance, 12AX7, 12au7, Pair of  7591A output tubes.

Installed a 1/4" jack on the Mic input, swapped out an old cap.  Man the chassis is small. 

What to do with this little puppy? Can't seem to locate any info on the unit, much less a schematic.

Most parts date to 1965...  Suggestions?

[sluckey]

That's just a power amp. Plug a guitar preamp into it and you should have a nice rig.

[PRR]

> That's just a power amp.

No, it has a mike input and knob.

I had to look thrice, because I had that identical chassis without mike-stuff, and a monitor speaker in the face.

Seems ready-to-play as is.

Better re-read the power tube type numbers.

[duce67us]

You are correct!
7591A Output Tubes!

[sluckey]

Sorry, I looked too quick. That's a very unusual layout!

[duce67us]

Bass cut, treble cut on switches, cathode bias. 

[PRR]

> cathode bias

Ah, jogs the mush between my ears.

My OT was bigger. Probably to reach that unused hole. "ME25" suggests a 25 Watt rating, I recall mine as more, maybe 40W. With 7591 that needs fix-bias, which sounds right for mine. The PT stack was probably a bit taller also.

Not really worth a both-iron change for a just-obvious increase of power.

I recall the amp as electrically and audibly "very fine", did what a power amp should do and no funny-business. Thermally fine also; ran hot but most of the heat flowed out well. The bad part is the 7 pounds of crap in a 5 pound bag. The over-cramped chassis is a production and maintenance NightMare. I would not go in there except to try to find and replace BAD parts. Tweeks and mods just can't be worth the effort to get in, and to patch what you busted to get in.

If Gain (and lo/hi-cut) is not enough for your guitar style, I too would build an external preamp/control before I would try to sqeeze and more stuff in there.

[duce67us]

"ME25" suggests a 25 Watt rating, I recall mine as more, maybe 40W. With 7591 that needs fix-bias, which sounds right for mine. The PT stack was probably a bit taller also.
 The bad part is the 7 pounds of crap in a 5 pound bag. The over-cramped chassis is a production and maintenance NightMare. I would not go in there except to try to find and replace BAD parts. Tweeks and mods just can't be worth the effort to get in, and to patch what you busted to get in.

If Gain (and lo/hi-cut) is not enough for your guitar style, I too would build an external preamp/control before I would try to sqeeze and more stuff in there.

I totally agree.  This thing is packed, without much real estate to spare.
The only information I could find in my search was a single page magazine ad from 1965.  "Mercury PA" available in 10, 25 and 40 W variations.

Thanks for the advice.