[sdiy] Looking for wisdom - Klein & Hummel UE-100

[René Schmitz]

Hi Mark,


Am 17.10.2022 um 11:16 schrieb mark verbos via Synth-diy:

> Second, how should I power this up safely? I assume that the power caps are dead, but any advice?

Looking at this here:

https://www.gyraf.dk/schematics/KH_UE100_equalizer.pdf


If any of the tubes has lost the metal shine on the inside of the glass, 
but is white instead then they have lost vacuum, and need to be replaced.

The rectifiers are selenium rectifiers if I'm not mistaken. These can 
let out some bad smelling toxic smoke. Consider replacing them with 
something modern first.

(Si Diodes and a resistor, to simulate the higher drop a selenium 
recfier has.)

You could try tickle the caps with a current limited bench PSU, say 
20-30V. That should indicate shorts in the caps. Likely they've dried 
up, and need to be replaced, as you say.

If you feel ready to bring it to mains, an old trick is to put a larger 
lightbulb in series, to delimit the current.


> I have read about people powering these and caps exploding, is there any way to prevent that?

When this was built the wall voltage was 220. So the supply voltage is 
going to be higher than back in the day.

Maybe that is why the caps are blowing up?! A sure way for fireworks is 
to set it to 110V, and run it on 230V. :) What you've read could be an 
account of that...

> If I replace these 16uF electrolytics, the trimming is gonna be out, there appears to be just a few trims, so they can’t be for all these caps.


The trims are gain adjustments. To trim out gain variations because 
tubes age, and they have higher unit to unit variations. You'd adjust 
them if you swapped a tube.

Given the origin story, I would not be surprised, if the rest of the 
unit is actually working.


Best,

  René