Fixing UA La-610 Compressor (need schematics with voltage points)

I will try a 22k to see if it doesnt get that hot.

BTW does one know where to buy these on-off-on switches. I found a lot on the web but no type with these angled legs. Thanks!

 

22k gets hot as hell as well ;-) Next thing I try is to use a different 6005.

Any ideas besides this? Maybe bias is misadjusted?

Does anybody have a schematics of the LA-610 (not MKII). I searched the web, but all links I found were blocked by my anti-virus software.

 

i've read that Universal Audio has a strict no schematics in public policy.. they will not allow schematics for their products to be published for public use. i suppose this is to prevent cloning.

 

What's the voltage across the replacement 22K? If the tube is taking excessive current, that's likely to be the reason the original 22K burnt out.

 

It's 207,4V on 22k = 1,95W

The metal foil resistor i use has 3W

 

This gets more and more difficult without the schematic.

My feeling is that around 9mA standing current through that valve is too much, although it's pushing the dissipation into the resistor rather than in the valve itself. If this is a conventional self-biased stage, maybe the cathode decoupling capacitor is going leaky?

Is this tube the one that drives the T4 opto device?

 

>> Is this tube the one that drives the T4 opto device?
Yes

 

I tested with a different 6005 tube, just the same heat and voltage. The other resistors are in range.
So I think the heat is "normal" since the compression works again.

 

Interesting. I returned the LA-610 with the new 22k resistor and the original 6005 tube to my friend for testing. He told me the compression knob is way more sensitive and the compression is more „sluggish“ than before. He can hear this and see it on the „lazy“ meter needle. So I swapped the 6005 with the new one, we tested again. He told me with a wide grin that the LA610 is working perfect now. Indeed I could see the needle reacts faster now. Maybe the old tube had suffered by the open resistor and had too much gain for the T4 opto coppler. Thanks again for your help.