Let's Get Technical > Power Amp Tech

ADA Microtube 200

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Skitzo:
Hi all,

I have a microtube 200 amp and it's been great so far!  However, I have no sound now.  When I plug it in, the lights on the front come on indicating power is getting in.  I opened it up and all three fuses are fine.  I also have (believe it or not) an old-school tube tester.  Both tubes are fine.  I don't see any blown capacitors....

Does anyone know of any tricks or known issues on this amp?  (I attached a pic)

rnolan:
Hey Skitzo, only thing I can see from the pic is the tubes (particularly RHS in pic) could be a little better seated in their sockets, although it doesn't look enough to stop them working.
Apart from the usuall (which you may have done already) spray/clean the pots and sockets this topic may help (http://adadepot.com/index.php?topic=138.0).   The MT200 has a protect mode controlled by a neon bulb.  If that doesn't fix it, then it's over to MJMP et al for more serious fault finding.
Cheers Richard

Skitzo:
Tell me more about the protect mode....  Perhaps it's just stuck in this mode?
How do I turn it off and on?

Thanks!

rnolan:
Hey Skitzo, my understanding of it (from this topic which also tells you how to fix it (ADA Microtube - "protect" problems http://adadepot.com/index.php?topic=138.0)) is that when the MT200 warms up, it stays in protect mode (no sound) until the tubes have warmed up.  When the tubes are ready the neon light brings the PSU chip (power supply unit) out of protect mode, you can't switch it yourself.

(From one of Sparkers posts in that topic - "I think when the MT200 PSU startup thing was discussed some time ago, the neon inside the box, NE1 (a NE-2H type) was thought of as a suspect. This neon acts as an under-voltage protection for the PSU chip when the amp is switched on, when the neon strikes on the PSU chip is brought out of shutdown. The neons can degrade over time and the strike voltage can change, also they can show sensitivity to light")

Have a read of that topic (in the Power Amp Tech area), it's where I learnt about it. Cheers R

Skitzo:
Thanks for the info.  A neon bulb eh?  Did you happen to see one in that diagram I posted?
If that is the culprit, where would I get one?

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