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pcrecord 20 June 2016

Hi guys,

Like the title says, I got one of my two LA-610 who doesn't compress anymore.. the action faded over a few months.
I tried to change the tubes and even exchanged the opto cell with the other LA-610 and it did no good.

So I guess a cap or a resistor failed.. I'd need some guidance and some precise schematics

Thanks in advance.

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Boswell Mon, 10/26/2020 - 08:50

GeryGuitar, post: 465870, member: 52091 wrote: 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?

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.

Boswell Mon, 10/26/2020 - 16:31

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?

GeryGuitar Sun, 11/08/2020 - 00:11

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.

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