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March 28, 2024, 10:23:02 PM

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#81
Amplifier Discussion / Help me troubleshoot my LAB SE...
Last post by rileyismycopilot - March 14, 2024, 06:44:23 PM
Hello gang,

I've just acquired an old Gibson / Moog / Lab Series L3 amp from about 1980. It's the smaller one of the bunch (1x12"). It's a fine amp, buuuuut....

It has 2 problems.

1. The input jack labeled "LOW" does not work. It's not crackly or anything, it just does not work at all. I've sprayed it clean and still, no sound. There's a faint, muted sound when the guitar jack is plugged half way in. Other than that, no sound. The other input jack ("HIGH") works fine.

2. There's a loud hum (low pitched hum) + hiss (white noise type of swooooooosh). This buzzing sound increases when the Master control is turned up, but does not increase significantly when the Volume,TMB and Reverb controls are turned up. Also, I do have a sound when I plug the guitar halfway into the "External Processing" jack (aka FX loop). So I guess the power amp part is fine.


What I have done so far is spray the jacks and chopstick the heck out of the circuit board. But I did not find a bad joint or something with this technique. I'm stumped and do not want to randomly change parts.

Do you have an idea what the problem(s) may be? and could my 2 problems (jack + noise) actually be related?

Your help is greatly appreciated, thank y'all in advance!

#82
Amplifier Discussion / Re: Marshall VS100R transistor...
Last post by g1 - March 14, 2024, 01:21:12 PM
What is the wattage of your bulb?
I doubt that the 33VDC at the output was when speaker connected as that would be over 130 watts and your speaker would surely be toast.

Never try to power anything up on a limiter bulb while a load is connected to the amp.
Power up with no load.  Then, if no DC is present on the output, connect load while unit turned on.
Many amps will not power up properly on a bulb with a load connected.
#83
Amplifier Discussion / Re: Marshall VS100R transistor...
Last post by markorock37 - March 14, 2024, 09:01:19 AM
Looks like I'll have to wait until tomorrow to start testing this entire board.
#84
Amplifier Discussion / Re: Marshall VS100R transistor...
Last post by markorock37 - March 13, 2024, 03:11:39 PM
I replaced the output transistors (TIP 142, TIP 147) and installed with the micas. Also replaced TIP29C and a J111 that were bad. Im getting a low brightness (not really dim) on my bulb limiter and a buzz/hum through the speaker. No guitar signal coming through. Tested for DC at the output jack and it was at 33V! Shut it down and started testing components. All diodes test good, and all capacitors test good. Checked some resistors in areas i felt were critical and haven't found anything off. Do you think one of the TO92 transistors is at fault? Or did I blow an output again?
#85
Amplifier Discussion / Re: Savage Amplifier
Last post by saturated - March 12, 2024, 09:38:27 PM
Thank you sir seems like from what I have read that you enjoy pedals.  Now I understand why because I had gotten away from them as too much trouble but I have a renewed interest in them now I really had fun playing through all of them last night.

I need some help dialing in the delay pedal though I couldn't seem to get happy with my attempt to obtain a good setting.  It also has echo which gets out of hand quickly

 :P
#86
Amplifier Discussion / Re: Savage Amplifier
Last post by Tassieviking - March 11, 2024, 10:42:34 PM
Most pedals will not turn on unless you have the input jack plugged in, and it has to be a mono plug as well.
The input jack is acting like the power switch as well to preserve the battery when you are not using the pedal.
#87
Amplifier Discussion / Re: Savage Amplifier
Last post by saturated - March 11, 2024, 09:14:03 PM
Nm teh dreaded chainsaw liveth  :-X

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It almost knocked me out too

I had it on the lead channel
I wanted to hear what it would do to the clean channel (of my audition chorus )

I made sure to turn all the volume knobs on the amp all of the way off
I'm standing there and I push the channel select button and I'm hit with the loudest noise I have ever heard  :P

So I reached down and turned down the output knob on the pedal which had been fully clockwise....duh 🤣 o

 :P
#88
Amplifier Discussion / Re: Savage Amplifier
Last post by saturated - March 11, 2024, 08:17:27 PM
I was anxious to try them and haven't tried to play through them but the light comes on in three
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And I couldn't get the chainsaw pedal to light up but it hasn't been connected to an amplifier at least since the early 90s

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They are a bunch of old ordinary pedals but I hope they still work.

Thanks again 👍
#89
Amplifier Discussion / Re: Savage Amplifier
Last post by saturated - March 11, 2024, 08:03:12 PM
Man THANK YOU SIR !! for pointing that out.
:)
I was at work all day and when I got home I ransacked the house looking for a wall wart with a terminal matching the one in this pic from last May

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The one I tried to use yesterday had a 90 deg on the end of it.  I chased down a couple desktop lamps...no.
Kept looking and finally found it in the bottom of a drawer under a bunch of stuff.

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What's crazy is I got this from my friend's junk store told him I needed a 9v adapter he had a mountain of them and handed me this one and I can promise you we were not cognizant of polarity.

Unless...and this was almost twenty years ago...it's possible I had a pedal with me and tried one until it worked...idk...

 :P

#90
Amplifier Discussion / Re: Savage Amplifier
Last post by Tassieviking - March 11, 2024, 11:11:46 AM
I am not surprised that the wall wart did not power the pedals, the polarity is wrong on the plug.
The center pin should be minus and the ring should be plus at 9vDC, your power supply is the opposite.
I hope you have not damaged the pedals with the wrong power supply.