20 Most Recent VOX Amplification Vox Valvetronix VT50 Modeling Combo Amp Questions & Answers

bulbs have tolerance, that means it can work with + or - 6.3v just use the 7.6v which a diffrence of 1.is ok for it to work.

Firstly check all valves are glowing, if they all glowing, check speaker cone isn't blown

Yes you could blow the speaker. There is either a problem in the power supply or possibly the power amp chip has shorted to one of the power rails. Some of the vox stuff uses th LM3886 chip as the power amp. While these are supposedly protected, they can go bad. Download A schematic that MIGHT be close to your unit... it is for the VT30 but probably is similar:

http://elektrotanya.com/vox_ad15-30vt_sch.pdf/download.html

Scroll down to "Get Manual" and click on it to download the schematic. Do this test: Adjust the power level control. IF it doesn't vary the level significantly, then check the voltage across the speaker... IF it isn't less than 1 volt DC (bias) replace the LM3886 chip. Use thermal grease and any insulators they are using. Chip about $8 from Digikey.com. Note these come with two different pre-bent leads... make sure to get right ones. IF the output bias is with 1 volt DC of ground, check for bad filter caps and rectifiers.

Is this it? https://www.google.com/search?q=VOX+VT15+guitar+amplifier+need+a+input+PCB+BOARD ..

If your amp isn't producing signal, your best bet is to take it into a local Vox autorized repair shop. There are leathel voltages involved and if you're not an experienced tech, you can get hurt, not to mention screwing to amp up worse. Here's a link to the Vox contact page http://www.voxamps.com/contactus And one to find the list of Vox repair shops. Korg USA Musical Instruments

The most likely case is that one of the main output transistors (if which there are many) is shorted. When the protect circuit senses DC on the final output, it will not allow the output relay to come on to protect the speakers from raw DC. With the power removed, you can check between each outputs Emitter and Collector and you will probably find close to zero ohms. From that point you need to unsolder each of the pins of the bad channel until you find the shorted device(s) and replace them.

'pianoforte'

BREV. N. 838420

See page 22 troubleshooting of this manual. It may help you. dd501 (yamaha.com)