VOX | Discussion Forums » VOX Amplifiers » AC30 AC15, Custom Series & Custom Classic
Hello. I have a problem with my AC15C1 - yesterday in the morning everything was fine, but in the evening there was no sound at all. The red pilot light is on, but the tubes are not glowing. When I switch the standby on nothing happens. Before there was no loss in sound quality or anything that would suggest any tube problem. I have found two fuses inside the amp, and they both look ok. There is also a third one for the mains, but since the pilot light is working I assume this one is ok. Does anyone know what may be the cause? This is my first tube amp, and I am not familiar with tube failure symptoms:(
I am not familiar with the C models. Do they have a solid sate rectifier.?
Do not have a schem for this amp.....but I am guessing the 3 fuses are :
1. Mains
2. 6.5 VAC (heaters)
3. High Voltage DC.......B+
Check them all with a meter, or replace them if you do not have a meter.
If you want, you can "assume" the mains fuse is good and just replace the Heater and HV fuses one at a time if you want.
If you do not have a meter, Be Careful. It is POSSIBLE your caps have a charge and it will appear across the HV fuse. Caution would suggest a wooden stick to remove that HV fuse. Just be careful you do not grab the HV fuse with both hands and become a conductor between the metal, fuse holder tabs.
Do you have a meter.?
Can you safely check some things with the amp ON.?
Best
AC15C1 do have a solid state rectifier. The Ohm-meter shows around 1Ohm for both Heater and HV fuse - I believe it means that both conduct and are ok - am I right? I would rather not check anything with the amp ON - I'm not that confident about my skills;) So, besides the fuses, what else could it be? Power amp tubes?
You are correct.....1 Ohm means the fuses are good.
What bothers me is that you cannot see heater glow in ANY of the tubes......is that right.?
SOME tubes have obscured heaters, and it is difficult to see if they are "on" or not.....but we are talking about 5 tubes here I believe.....seems like you should be able to see something in at least ONE of the tubes.......in a dark(end) room perhaps...??
That makes me suspect you are not getting heater voltage to any of your tubes.
It is pretty easy/safe to check. You can take a reading from ground, and check Pin 4 or 5 of preamp and power tubes. To ground, you will see about 3 VAC. You can clip one probe to ground, and check for VAC with just one hand. DO NOT let me talk you into anything you are not comfortable with.......But if you take your time, you should not have a problem. You can even have a helper hold the ground probe if you like......then you can check for heater voltage with one hand.
I assume you have checked all the normal stuff; like guitar and speaker cables.....tubes are seated all the way.......stuff like that.......guitar volume knob.....master knob......things happen.
Best
guys...i had the same problem this weekend with my ac15c1. worked fine...then I shut it down for a day or two...went to turn back on and no sound or "glow from tubes" the red power light is on, but nothing else happening. i would like to know serek if you found the problem with your ac15...by reading your posts its exactly what happened to mine..thx.
