Let's Get Technical > Power Amp Tech
ADA Microtube 200 Help Needed
rnolan:
Excellent, here come the experts :whoohoo!: . They'll get you sorted :thumb-up: . And as mike says have a good check around the neon. My gut feel (for what it's worth) is this isn't the issue but rule it out as it could be and that's what you've changed.
@ Dante, they are good pics :thumb-up: , MJMP also takes some good ones though LoL.
@MJMP, is the brown ring/tarnish on the resistor a cause for concern ?
MarshallJMP:
Well those resistors that are used with zener diodes can get hot.So not really a concern but it's best to check it out anyway.
davec69:
Thanks Rodan. The marks on top of the caps were made by me with a orange highlighter, when I replaced the caps. It was my way of keeping track of which caps I had already replaced.
I haven't checked whether the tubes light up, I can do that tonight, and report back.
--- Quote from: rnolan on January 22, 2017, 05:26:31 AM ---Hey davec69, Something is not right (obviously LoL), there's also brown colouration on top of some of the caps :dunno: . MJMP will have a better idea than me. The output transistors look ok. Do the tubes light up ok when you power on ?
--- End quote ---
davec69:
Another question for the experts. When working on the PSU board, do you remove it, or just tilt it up for access? I could not find an easy way to remove the board, which made it difficult to replace the lamp. It's entirely possible that the solder was not good.
davec69:
Ok. Here's what I found, from a little further testing tonight.
Firstly, the neon lamp appears to be blinking when the amp is on, with or without stand by.
Yes. The tubes appear to be glowing, though the glow is very faint.
Voltage measurements
D25 - 23.36/ on side nearest transformer - 14.86v other side
D26 - (-14.78v)
R34 - (177.8v)
Voltages for the red plugs going to the preamp boards were pretty much the same for both channels.
Of the 4 wires Both the outside wires read roughly 11.5v. The two inner wires both fluctuated in the 5mv range.
Below are a few video links, in case it helps. (Sorry for the phone ringing)
1. General Overview of the inside of the MT200 - http://www.tandemmedia.com/images/mt200/adamt200.mp4
2. Faint Glowing Preamp tubes - http://www.tandemmedia.com/images/mt200/adamt2001.mp4
3. Blinking neon lamp - http://www.tandemmedia.com/images/mt200/adamt2002.mp4
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