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help troubleshooting an HD130 212 combo!

Hi I am having trouble I was hoping someone could help me troubleshoot this musicman HD130 212 combo,(version without the 12ax7 preamp tube) I have 2 of them I wanted to use in stereo, so it is possible for me to compare

Symptoms timeline:

* started with I believe one or both of the speakers crapped out on me,

* replace speakers with hi wattage correct impedance speakers (not sure if speakers were ever the problem)

* at the end of a loud practice, amp blew a fuse.

* changed fuse correctly, now amp is loud humming, controls do nothing, 2 tubes are "redplating"

* new set of tubes, same loud humming, controls do nothing, 2 tubes are "redplating"

* swap out large electrolytic capacitors, same loud humming, controls do nothing,

* locate transistors on one of the power boards,
JE1692 & ECG377 looks bad to me, JE1692 has turned brown

JE1692 measures:
hFE = 48
Uf = 521mV

ECG377 doesnt register on parts tester, is "damaged or unknown part"

I read I can swap those with matched pair of 2N6488

both 2N6488s measure:
hFE = 181
Uf = 496mV

solder those in, turn the amp on, doesnt redplate, all 4 tubes are lighting up as normal, however it is still no controls and it is only humming, but the hum is much quieter this time.

* any ideas?


oop! I got it! I think I had

oop! I got it! I think I had the right idea for the most part, on a whim I tossed in a fresh LM1458 because 'why not?' and it was in fact the final piece to this entire equation.

Nice! ooh yea so glorious, loud clean amp perfect mid range and sense of compression, everything my ears are missing from the JC-120(which I also love just different flavor), it is so much sweeter when you have to work to get it.

In retrospect I might not have needed to change all the electrolytic caps but OK a recap will have to happen at some point right?


Good work

You done good!

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