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HD130 stopped sounding on preamp channel during practice

Hi Music men

My HD130 head model without the preamp tube stopped working the other night. The first channel as in the one with less tone controls still works but thats not the channel i like to use. Ive had a look at the electrolytics and tested their ESR and they are fine. all four tubes are still glowing. What should i test next? im thinking i may change the lm1458N op amp since the first channel bypasses the preamp section right?

edit* by "not working" i mean no sign of the guitar input sound at all on that channel and the only sound is when you turn the preamp volume to 10 where it just makes noise

Thanks for the help

mm210's picture

Just blanket swapping of

Just blanket swapping of parts is no real way to go about it. You MIGHT get lucky but you should really just trace the signal through the circuit and see where it goes "POOF"! A signal tracer with another external amp works good or if you have a scope, that's cool too. I vote for the tracer. It will be obvious where the general spot will be when it disappears. Mike.


Yeah thats true. Ive never

Yeah thats true. Ive never used a signal tracer but im guessing that you inject a signal through the input jack then put a probe down the line of cap/inductor filters (using the schematic) with reference to ground? would that be correct? once youve figured out which filter section is failing then check the resistors etc


would it be true to say that

would it be true to say that given theres no sound at all its most likely to be a major component such as a op amp or resistor in the op amp circuit not a filter ? something that when it goes bad completely will cut the signal

mm210's picture

Could be something as simple

Could be something as simple as a cap shorting in the signal path to ground. Those op amps have cap going to ground and if one shorts completely, it will ground the signal.


Inspect the input jacks

Yes it could be something simple. Before you throw money at it, inspect the input jack wires for breaks and loose solder joints. -mgriffin

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