First time I ever set foot in an SB-200 and it doesn’t look too complicated. But I want to make sure I have it squared away before returning to its owner. My buddy bought this for $200. It looks clean inside with a pair of Cetron 572Bs that don’t look like they had any abuse. As a matter of this thing looks pristine inside. They did place a Harbach ‘Soft Key’ and the all the filter caps have been replaced with CD’s. The parasitics don’t look as though they suffered any kind of excessive heat.

????????? Here is where it gets interesting: It seems the previous owner said that R15 was always cooking. Lo and behold sure enough the 1.5Ω resistor is fried. Following the lead? up into the base of the 572Bs, I see where somebody replaced one of the 1W 33Ω resistors with what appears to be either a ? watt or ? watt going to the grid. The other has the original carbon comp 1W there. Also, the where the wire connects to the terminal strip, it was cold soldered and moved around freely making continuity intermittently.

????????? So 2 questions: 1) would that intermittent cause that meter shunt R15, to toast like that and 2) do those resistors for the grids have to be 1W or will ? suffice like what is in there?

????????? Also, could it be possible it is suffering from a spike as a result of the relay coil? (ok 3 questions!). Included is a photo.

????????? If it turns out this is all that is wrong with it, my friend scored the deal of the day at $200!

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Mod-U-Lator,

Mike(y)/W3SLK

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PS: I also included a photo where that green wire from R15 comes and the different grid resistors.

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So I feel I found the culprit. I stuffed the on 572B on my tube tester just to see if the filament would light up. Nada! So I took a closer inspection of the tube and found the reason for no filament and why the components were zorched in the grid circuit. A picture is worth a thousand words. BTW the so-called ? watt on the grid was toasted also.

Mod-U-Lator,

Mike(y)/W3SLK

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