Monday, November 01, 2010

I'm playing a set tonight, and for various reasons I don't want to drag out my full set-up, forcing my hand at a little improvisation. This has me surveying the piles in terms of what relatively compact devices will either produce or pass sound, the forefront contender being a Tektronix 106 square wave generator.

I've determined that the GenRad/Tektronix connectors will take a banana just fine, and since I have a chassis mount banana lug I can ground reference the signal output without resorting to stupidity. I'll consider bastardizing this unit with UHF connectors since they occupy the same sort of space and I can probably pull it off cleanly, otherwise I'll just leave them be. This of course is an eventual plan, and bears no relation to what I hope to do today.

Cracking the case to give it a visual reveals a quartet of 7189 tubes living in harmony with a variety of discrete transistors. Two days in a row now I've peeked at the guts of a tube/transistor hybrid, this one won't be getting the knife though, so I'll have to proceed with caution. Thankfully the transistors are socketed, so in the event that B+ has intermingled with the low voltage buss, part replacement will be a breeze.

Of course, it would appear as if I'm getting ahead of myself, since I'm not going to tackle this level of failure a few hours before a show. Evidently those General Electric electrolytics from 1968 have not fared well over the years. Here's a shot that captures the clear corrode through of the negative lead on that cap, and that murky brown glut is an erupting carbon comp resistor.

Once I find a bit of Tektronix silver solder I'll have a go at replacing this section, and all similar electrolytics. For the time being, I'll have to see if I can burn in my SKL 302 variable filter instead.

EDIT: at 80.9 volts AC mains input, the signal leg of output #2 was sitting at roughly +10 volts DC. Meaning we'll be seeing some more in depth gutshot of this unit as well (also meaning no one will be hearing any signal pass through this beast for a while yet). Here's an appetizer:

1 comment:

valis said...

I heard the show was terrific and I'm sorry to of missed it. BTW the blog is looking great! Way to stay on top of it!