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Newbie Help please - Hartke A25 Bass Amp combo

Started by Psabin8951, May 05, 2017, 09:01:24 AM

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Psabin8951

ok so with Q4 removed the reading was as expected so Q4 now replaced and to be sure d13,14,q2,3,5 also.
I now get a hum when a guitar is plugged in, R97 doesn't get too hot but Q8 catches fire!! It literally glows.
I'm about to give up on this one unless anyone has any final ideas for me.

phatt

Sorry to hear,,, Q, Are you using a limiter? 8|

These are Direct Coupled high current circuits and obviously if the circuit is unstable you can blow transistors before a fuse even has time to get out of bed. :)
To circumvent instant destruction of all your hard work you need to limit the current and the best way to do this is with a very simple electrical trick all details to build a Light Bulb Limiter can be found on this forum.
So before you crucify anymore components you need to build a limiter which allows you to get voltage readings around the circuit to get an idea of where the problem exists. if the current tries to rise the bulb Absorbs the inrush and *Limits* voltage saving the transistors from INSTANT DESTRUCTION. :'( :'(

Light Bulb Limiter circuit and build notes at the top of this page;
https://www.ssguitar.com/index.php?board=2.0

Build that then some of the more savvy tecks can tell you where to take voltage readings and they will guide you through the process of rebuilding the circuit.
Don't give up just yet,, Phil.

Enzo

And maybe we forgot, but I hope we made mention of not connecting a speaker until we know the amp is stable and not producing DC?

Jesse

Greetings, I am having an almost identical problem with a Hartke A35 here:
https://www.ssguitar.com/index.php?topic=5343.0
Thanks for any help with this :)

     - Jesse