| Author | Message | ||
| rhclam |
I just recently purchased a MM RD100 100 watt head with all SS pre-amp and 2 6L6s for output, it has 4 inputs 1. High gain 2. Low gain 3 300mV input- bypass part of the pre amp 4. 3 V line input- bypass all pre amp and goes directly to the op amp driving the phase splitter ) The Amp has the following problem: Every once in a while, the volume will fad away until it is completely gone. This will be the case on inputs 1,2 & 3. As on 4, it will still have a very very very soft tone In order to get it work back to normal: I have tried the following : 1. Flipping the Hi, stand by , low switch a few times 2. Flipping the GND switch a few time 3 . Flipping the impedance switch ( 4 or 8 ohms) a few times. I am not really sure which of the above actually fixes it. but it did. Again , this problem does not happen often , I have probed all voltages on the tube pins when it is working and is currently still waiting for it to break down to measure the difference. This is an annoying problem which resulting in me keeping the chassis outside all the time. Any suggestion ? Thanks | ||
| Langley |
Here's some general 'no math' procedures that I use, before calling the Amp Doctor. It might be overkill, but I find more problems this way than with a signal injector and a scope. Verify the viability of the speaker cable. Try a different speaker, observing impedance. Jiggle test chassis wiring (use a plastic probe). Jiggle test components (use a plastic probe). Run amp in the dark, observing for arcing. Visibly inspect electrolytics for leaks,bulges... Clean jacks, contacts, grounds... (I've seen dirty effect loop jack's cause problems like this.) Re-tension tube contacts. Replace the phase splitter op amp (LM1458 ?). Discharge Caps, as necessary, for safety. If this doesn't do it, then it's time for the Amp Doctor. Remember, there's danger inside any amp. Nobody want's "Probable User Error" written on their tombstone. Some of the procedures above expose one to potentially lethal voltages, even if the amp is Off. I get the feeling from your statements about probing the tube pin voltages that you've got balls. Sorry if I'm preaching to the choir. "Give a man a fish, and he'll eat for a day. Teach a man to fish, and he'll have enough Mercury to start a thermometer factory.". | ||
| rhclam |
Thanks, Langley, however, since it last happened, I am still waiting to it to happen again. It is hard to fix something when it is not broken ! Have another question regarding reverb. On my RD 100 when reverb is enable, a hum starting at reverb dial 2 and increases with the dial. Reverb effect itself is working fine. it that normal or there are ways of improving it. BTW , thanks for the warning about high voltage, I am doing everything I can to do it safely. I do know a a little bit about electronic but of course Tube is new to me, I have to read up on this subject simply because they didn't teach that stuff any more when I was going to school even though it was 20+ years ago. | ||
| Langley |
Re. the reverb, check the condition of the wiring that goes from the chassis to the reverb tank and back. Check the footswitch and it's wiring too. Clean and re-tension the RCA plugs, male and fem. If the connection maintenance is a miss, check the reverb pan I/O mpedances. Pull the pan out and look for the part #. (On my 210-65 the Accutronics part # is 4FB3D1B. Your # ought to be something similar.) Link to http://www.tubesandmore.com/images/AES04 -059.pdf There do a find on your reverb pan's part #. At the respective entry, input and output impedances can be found. Grab your VOM and check it out. If, after all the applied maintanance, it's still noisy - and that's unacceptable, and you don't want to use an external reverb stomp box, then it's Tech time. Enjoy. |
Tue, 03/25/2014 - 09:58
#1