Music Man 130 Tube guitar amp Shorted High Voltage power supply blowing the fuse Locate fault
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- čas přidán 18. 12. 2022
- Interesting tube guitar amp. Leo's last hurrah. The music man is a hybrid. Running OP-amps for the preamp rather than 12AX7's. There is one 12AX7 which serves as the Inverter driving 4-6CA7 tubes. This one arrived dead. Immediately blew the fuse when AC was applied. I knew the problem must exist in the power supply. Filter caps looked nasty, but the primary failure was a shorted diode on the rectifier board. So, I replaced the diode and re-capped the amp (electrolytics only). One of the negative bias caps was open. That more than likely started the sequence of excessive current and finally shorting out the power supply section. After installation of the filter caps, a fresh set of tubes were installed and the amp took off running again. On all of these vintage amps, it is good practice to install new filter caps. There is no need to test them. Replacing a few and crossing your fingers will only prolong the next failure. Save yourself time & expense. Note: The high voltage in these amps hovers around 725vdc! Use caution when inside. Also, to prolong the life of the tubes, lower the idle current. The manual states .5VDC at bias test point. Lowering that will increase tube life.
- Jak na to + styl
I like how the Hioki meter displays Voltage drop in the diode test mode. Incredible how fast it updates, adding one to the tool list for 2023. Merry Christmas D-lab!
Solid state rectifier, blowing fuse, probably the first thing to check is the diode junctions for shorts, low hanging fruit first. I always enjoy the logical methodological troubleshooting methods you embrace Terry. Wise to check current when bringing the PS back to life. Sometimes a shorted electrolytic, or elsewhere, caused the diode to fail, sometimes not.
Thanks Terry. Simple and straight to the point.
Ahhhh nice to see a Music Man amp. I've never owned one, but used one many times, one of my favorite amps of all time.
Nice diagnosis and repair once again!
Another great lesson, thank you so much Terry!
That is a nice amp there.
Thanks D-Lab.
Excellent Terry.
Nice wire management on that amp. Pride in workmanship...
Nice one Young Tel!! Musicman (Leo) amp (A proper quality amp!!)
Laughing at myself. First thing I thought when I read the title.... "Holy cow! How do you build an amp with 130 tubes?"
Nice amplifier sir thanks for sharing video.
Great Vid! thanks for the advice on the meter
Great job
Thanks Terry
Fender generally used 6L6GCs, thse tubes are a version of the EL34. I hope he owner had it rebiased. Also for EL34s, pin1 (g3) should be connected to the cathode, pin8.
Very logical fault finding process :) and at last a use for a standby switch! Hioke meter on xmas present list.
I have two of these!! this is an early one with 12ax7 PI tube!! later years did not have this but added vibrato and reverb! get one if you can find one!!
This was my first "real" amp, bought used in '82. The only amp I know of that had a high/low power switch, which were different taps off the primary of the power transformer. Since it was a primary tap, it lowered everything on the secondary, including the filament and bias. I think in low mode the B+ was around 450V.
Hehee, this is a video for me. I own a Hioki multimeter and a Music man 130 amplifier. The Hioki must be the best and most priceworthy meter on the market and the MM 130...gosh, WHAT an amp. Powerful and solid. Like a friend of mine said, "With a 412 cabinet You can tear down buildings with that thing" :) I am very satisfied with them both.
Hi Frend. What is the price of this Hioki model. Thanks a lot.
@@miguelrichartmellado2834 There are many different models. Mine was 70 bucks, but i do believe You can pick one up for between 40-50 to 200 bucks and be very happy.
@@ralfhedstrom Hi Ralph. Thank you. Kind regards.
I use the same meter. Such a snappy meter. Just wish the backlight would stay illuminated longer. I enjoy working on those amps. Those original electrolytics always puke on their boards.
Thanks! D-Lab
Hi Terry, another good diagnostic video, thank you. What is the model number of your Tenma Variac please?
Meter readout lag is a drag. I’ve only experienced it with cheaper meters. On my old fluke 87 never really noticed it and now use a fluke 87V. Never noticed it on both.
👍👍
Would you have a suggestion for what I can use to replace the diodes on the 2 el-34s? The part number is mr-250-5. I can't seem to find anything like that. The amp I have had two mr250-3 in series.. after a red plating incident they failed on one side..
Were plastic zip ties period correct for this? Almost looks as though it should be lacing string hand tied. Just curious....
Hey Terry. Do you recommend removing the 'death capacitor' from these amps? I am working on a 2100-75 and am not sure if I should just cut it out, leave it, or replace it with a new safety Y2 cap.
No dummy load needed if no tubes are installed?
Hi there i have a music man that just recently lowered in volume and sounds like an octave pedal is connected to it!!
I have brand new tubes if it were the fuse it be completely out correct?
If not can anyone please send your help to me so i may trouble shoot this.
Thamk you
Peace and love to all
Christopher
So the standby switch puts the diodes into the circuit? Why can't you detect a diode short with or without being in standby? I guess I don't understand where you are measuring for the short.
You and me both. Maybe a wiring schematic and a highlight of the diode in question would have helped.
Ok, I stumbled across a diagram pdf online. Standby switch is between transformer and diodes. I don't like the term standby here, he says standby on has a short, why, it should be open to take diodes out of the equation. ?
@@Joetechlincolns Still confusing. Some people have odd ways of explanation, but what bothers me is not answering or clarifying comments. I most likely will not comment on his channel again, even though I do enjoy it.
That was no match for you.