Chinese Tube Mic Repair

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benpasley

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Need help! I have Chinese tube mic, about 4-5 years old, distributed by Cascade Microphones. It is the same or almost the same as the SE Electronics 5600 series from the same year with a big cylinder design, removable tube, 9-point selector switch for patterns on the supply...I believe Cascade simply rebranded the SE models.

It went totally out a few months ago. Then it came back on and worked few weeks and then went out. No noise, microphonics, warnings at all. The tube does not glow (assume it would), power is coming down the cable (tested that), replacing the tube did not help. Don't have a tube tester. Anyone want to repair this thing?

Ben Pasley
 
Have you tried checking voltage going to the Capsule? This would be part of the process of elimination. As you rotate the "polar select switch", the voltage will change. If you're getting voltage from the PSU to the mic, that MIGHT eliminate the PSU. Does the tube get warm?
 
it is on again

thanks for the reply. this is so ridiculous. while i am checking the voltage change--which i do get on one lead while dialing through the patterns--the tube came on, glows, and i have signal. i have no idea. the figure 8 and cardioid patterns work fine, the omni mode still has obvious cancellation nodes, but hey, it is on. the electroharmonix tube in the gear is the original, i think, moving the tube around it seems to be well seated, and there is no significant noise. what is up?

ben pasley
 
This is just a stab, but it sounds like the heater supply to the tube is intermittant. I would investigate the cable for intermittant breaks, the solder joints on the tube socket, and possibly the internals to the power supply. Sounds like something is loose and when you bend the cable/socket/wires a certain way, they make contact and the thing starts mysteriously working again.

Be careful when working on these, there are voltages that can kill you! Even with the device unpowered, there are capacitors in there that hold enough enegry to give a real bad day, and possibly your last day. If you're unsure of what's what inside of there, I'd be VERY cautious about poking around.
 
I used to repair radio and amplifier circuits, and one of the ways to cut costs is to use single-sided circuit boards. The result of this is: Through-hole components are not well-supported, and can crack their solder joints on the soldered side, creating intermittent connections.

You may not even see them, but sometimes these cracks appear as circular rings in the solder around the component legs... especially on heavier or heating/cooling components.

I found this photo online:
http://www.rangerovers.net/repairdetails/electrical/fboxcrackjoint1.jpg

Anyway, if you remove power to the mic (obviously) and re-flow the solder joints on the components with some new solder & flux, you can solve the problem.

- Rickshaw
 
thanks folks

i am going with the connection/solder theory for a bit. i was already headed toward a re-soldering campaign on the most obvious connections. i love this mic and i am glad to get some quality encouragements on a repair plan. i will give it a go. i consider this thread done...thanks!
 
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