Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => Tubes and Hybrids => Topic started by: luke24_5 on April 26, 2016, 02:05:27 PM

Title: AC30 VR doesn't produce sound.
Post by: luke24_5 on April 26, 2016, 02:05:27 PM
My Vox AC30 VR hybrid amp's power light comes on but no sound is produced.  I can tap on the chassis and there is some static as if something is loose, of the capacitors one gets hotter than the others but there's no swelling or leaking.  The longer I leave the amp on, the more noise it makes as I turn it off. (a sputtering like sound.)  Tried different guitars but the same results.  Worked great one day and not at all the next.  There was no noticeable static the last day it worked.  We replaced the tube but no change and both the old and new tubes glow as it warms up.  Their are no burned spots on the board.  If I turn it on and turn it off shortly thereafter there is virtually no noise but the warmer it gets the worse we hear the noise as it turns off. 

Turing the potentiometers have no effect.  Strum all you want and nothing comes out the amp.  Any ideas on what to check?
Title: Re: AC30 VR doesn't produce sound.
Post by: Vitrolin on April 27, 2016, 12:42:06 PM
hey

check the supply voltages, both the regulated (used for preamp) and the unregulated (used for poweramp).
unregulated should be around +/-26V measured on diode bridge og C13/C22
and regulated +/-15V measured on C19/C28
Title: Re: AC30 VR doesn't produce sound.
Post by: Vitrolin on April 27, 2016, 12:51:37 PM
after posting i reread your question...

capacitors shouldn't get hot, my guess is that its shorted.
wich capacitor is getting hot?
with your amp turned off, take your meter and measure the resistance or conductivity of the capacitor.

i posted a schematic
Title: Re: AC30 VR doesn't produce sound.
Post by: DrGonz78 on April 28, 2016, 02:36:50 AM
capacitors shouldn't get hot, my guess is that its shorted.
wich capacitor is getting hot?
with your amp turned off, take your meter and measure the resistance or conductivity of the capacitor.

Which capacitor is it in relation to the schematic? Also, please be aware that you want to test the caps for any stored charge before you test any resistances with your meter. You will need to drain the caps first before testing for resistance.
Title: Re: AC30 VR doesn't produce sound.
Post by: TolerBear on May 09, 2016, 08:19:56 PM
I'm guessing your output is good. Try maybe something in the power section?

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