Knotty

CA-1582 Limiter Crackle Issues
« on: March 06, 2019, 06:07:26 PM »
I've got two CA-1581 limiters and minus the hiss, they're pretty quiet as far as old tube goes. A friend of mine was having issues with his, so I decided to go through it and see if I could get her running great.

Issue:

When limiter has no signal applied, there is an intermittent crackle that occurs. My first thoughts were; dirty connectors, bad tube, failing plate resistor, dirty pot, etc.

1. I've ruled out bad tubes, they test great. Slightly microphonic but that not a huge issue. I swapped another set of 6AU6 into its place and No Change.

2. I've never personally run into a scratchy plate resistor, so I'm not fully sure what to expect. Should I get more noise by tapping it? Is it usually a mechanical failure within the resistor? Could be it, Just not fully sure how to diagnose that fully.

3. I did a pretty intense clean on all of the tube sockets to get built up grime off (I mean this thing is so old and they've probably never been cleaned). After multiple steps of cleaning, I re-tensioned all of the sockets.  No Change with the crackle, but it sonically did change. The limiter clamps down more than it did before, making me think it is a dirty connection issue.

4. The crackling does react to physical pressure when it happens. Ex. when it is crackling, I can tap the input tube (V1 or V2, changes between those two tubes) and the crackle can stop some times. Making me think that it is a dirty connection issue.

So, my thoughts are that I may just need to add new tube sockets for the first two tubes and see if that helps the issue. Maybe the sockets are so old that even an intense scrubbing can't help them without dunking the whole thing in a sonic cleaner haha

Does anybody else have any thoughts on where to search? Thanks!

I've attached a schematic. It's not fully accurate for this unit as it has been modded over the years. But, all components are in the same spots except one capacitor is gone and some values are different.
Knotty


iampoor1

Re: CA-1582 Limiter Crackle Issues
« Reply #1 on: March 08, 2019, 08:27:54 PM »
I have seen similar problems with both dirty tube sockets, and broken plate resistors. The broken plate resistors usually have small cracks in them but break apart with force applied.

Does it crackle even with both of the input tubes removed? May give you a good idea of the problem area aswell. :)

EmRR

Re: CA-1582 Limiter Crackle Issues
« Reply #2 on: March 08, 2019, 09:23:57 PM »
cathode or plate resistor very likely.  Sometimes freeze spray will help diagnose that. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

Knotty

Re: CA-1582 Limiter Crackle Issues
« Reply #3 on: March 11, 2019, 02:24:59 PM »
I have seen similar problems with both dirty tube sockets, and broken plate resistors. The broken plate resistors usually have small cracks in them but break apart with force applied.

Does it crackle even with both of the input tubes removed? May give you a good idea of the problem area aswell. :)

It stops when either input tube is removed. So, I haven't been able to pin it that way. Seems to only crackle when both are installed. Which just could be the added gain makes it noticeable maybe?
Knotty

Knotty

Re: CA-1582 Limiter Crackle Issues
« Reply #4 on: March 11, 2019, 02:26:25 PM »
cathode or plate resistor very likely.  Sometimes freeze spray will help diagnose that.

Oh sweet! Never tried that before. I've seen guys use freeze spray before, but never knew the objective. Will it respond by not crackling anymore? or making more noise?
Knotty


 

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