geez man, doesn't that suck. what's the ebay name of the guy? i live in germany, if he's in my area i might go and give him a beat-up in the name of our community :twisted:
the grille seems to be original, though. ehm, no sarcasm intended, but an appropriate bye-product, actually :green:
[quote author="Gus"] note the use of feedback bottom of the transformer goes to the cathode and the cathode resistor is not bypassed. To help correct the transformer problems and/or drop the gain a little????[/quote]
gus i have both um57 and m582's. now that you pointed it out, this feedback arrangement isn't really clear to me. at least not a very common one, is it? basically all tube mic circuits i know which are NOT cathode follower do have a bypass cap to ground.
so you mean, the xformer might have a low headroom, and in order not to overload it, they reduce the gain by series feedback? but where does this (to my eyes a little unusual) parallel feedback from xformer to cathode come in? what's the effect exactly? repectively, the effect in combination with the series feedback? :? :?:
for comparison, the m582 has a similar circuit as for the output section, here dc feedback is larger (4k7) but bypassed with 330pF to ground. having a much smaller body, the xformer is smaller, too, and should be even easier to overload - but no ac series feedback here...? hm. :?
while i'm at it, i never quite understood why there's no grid resistor in the m582 circuit. capsule goes straight to grid (polarizing voltage applied to capsule's other side). how's the biasing done? maybe the isolation in the mic is so poor that the resulting parasitic resistance is enough to do the job?
[quote author="Mark Burnley"]I had the M582 schem a while back- I e-mailed Gefell for it. The thin connecting cables running down the side of the assembly are prone to crumbling, through age and heat. A very difficult job! [/quote]
i have the schem here, but can't scan it right now, something seems to be messed up with my scanner
just today i restored one m582, bought in moderate condition, which had just that problem - two of the tiny wires had broken off near the tube socket. i bypassed them by new wires, making two additional groves (correct word?) in the tube socket plastic with my soldering iron just wide enough for the wires to fit between the socket and the housing. maybe that made a small change in wiring capacitance, but i couldn't detect any sound difference when a/b'ing!
[quote author="jensenmann"]By the way a fingerprint an a 220M resistor makes a 50M resitor out of it. Make shure to clean them with alcohol[/quote]
really? never heard of that before, does that happen with all high z resistors, or just with older ones...?
maybe that's an explanation why my um57 got a lil' noisy lately
