Vox AD50VT Repair for Loud Thump or Pulse.mpg 

I’m glad that 12 years later, these are now easy to find lol. Love the vid still

Hey, thanks so much for this video! My amp developed the same problem, so I used your link and ordered a replacement pot from Hong Kong. This afternoon I finally got around to soldering it in, and my amp is now working fine again!

nice work. funny as soon as the video started, I thought 2 things, a short, or a bad pot. when you started to rotate the pot on the rear power level, I knew it was the pot, its that sound, ive heard it before :-) when ever you cant find a pot, open the pot up and do surgery man..lol. ive done it. rebuild the pot by prying the 4 clips on the back of the pot. ive only rebuild a few (older guitars/amps, because replacement is easier but in older guitars+amps, those pots are highly sought after, the only time you'll have trouble rebuilding is when the inside of the pot has a short / worn a spot where there is a break, even then conductive paint can be used. but its a steady hand operation. most times though, its just oxidized, dirty. finding an entrance and exiting the dirt is key. by the way @ 5:56 get yourself a chop stick, poking around with a screw driver is a bad habit :-) nice of you to share your experiences with others. again, nice work. thumbs up.

Yep, one of the weaknesses of the design: The Valve Reactor circuit depends on two anti-parallel opamps; the product of their gain must always be exactly one. The pots are chained into this circuit. The thumping comes from a weak point on the potentiometer which comes on and off. This, as a consequence, causes the Valve Reactor circuit to oscillate.

Thanks man, I got the similar problem but only the loud thump at a certain point of the power control knob (around 11 o'clock or 40% of the max power) and absolutely no guitar sound when plugged in. With WD40 on the back of the power control knob, although the thumbing is still there at the exact same place, I got the clean guitar sound back. I'm sure changing the potentiometer would have solved the problem completely like you said, but since I don't plan to turn the power control down that low anyway (I usually set the knob at around 3-4 o'clock or 70-80% of the max), all is good for now, at least. Thank you very much for the hint. It really helps.

I love these amps. I own 3 of them. I removed the ugly chrome grille and spray painted them black. HUGE improvement and was super inexpensive.

I needed a similar pot for a vox ad120vt. Studio sound electronics (amp repair parts) had a pc mount dual 100k, linear taper pot! here in a couple of days. Great resource, especially for tube amp repairs.

Great video, very informative.

i like the chrome grille - some people just can't stand change

Long cool woman in a black dress.! Nice video, cheers Rob

hi there, I need help. I have a danelectro honeytone miniamp, and, something's definitely gone wrong with it. When I power it up, there is this kind of "pulsing" sound coming from the speaker. power light goes on and off simultaneously with that pulse. then after quite a while pulsing stops, power stays on and when I plug my instrument, I get no sound. is it dying or something? thanks in advance!

what model pot was it you said you got it off eBay my AD50Vt Vox is doing the same thing I can't find the part

Hi! I own a Laney IRT Studio and it tends to pop when I turn it off... I assume that's because it lacks a standby switch... but then I notice it also pops when I change from lead to clean channel using the footswitch and also using the amp switch on the frontal panel, although It seems to me that it is more noticeable when using the onboard switch... I've read several forums and there's a lot of people with the same issue with differend tube amps: Mesa, Orange, Marshall... What do you think? do you think this is normal? do you think this could be fixed? and if so... would you explain me how to do fix this issue? Thank you, looking forward to read you! great videos you upload!

good tutorial, I have an AD30 VT that squeals , and have zeroed in on the small 3 wire cable that goes between the input jack and the top circuit board, any suggestions?

First comprehensive video I have seen involving a vox repair. Great stuff! My AD50vt has a horrible scream on the hi-gain settings, more so when the treble is past 12 0'clock position... Now I sent it in for repairs when I originally bought it (no sound problem) and then it came back and slowly developed a hi pitch scream, it doesn't sound like any feed back I have heard of... Do you know what the problem could be?

the vol on these amps i think is part of a feedback loop,though that sound with the power control sounds like an intermitant solder joint,i had to replace one of the dual gang pots on one of these amps,as the control shaft had been snapped off which ruined the pot tracks etc. I prefer tube amps,they sound waaaay better anyway,and the tube inside these amps does not run at the proper plate voltage to bring the tubes plate curve to be in the proper region,i bought the pots for this amp easy and cheap.The parts come from china anyway,remember the amp is made in china,Vox and marshall and fender stick it up your arse on parts and the amp too,way too expensive for a shite sounding amp.

What about the 100KA dual ganged pot from RS wired off the board?

My ad50vt switches channels (amp mods) and effects randomly all by itself. Have searched forever to try to find a fix. Haven't found anyone else who's had that problem.

Thanks for the video. My brother brought his ad50vt to me for me to repair it. I can sometimes locate and fix problems in various electronic, but with this I really don't know where to start. The amp powers on but there is no sound. Can you give me some guidance?

Hope this does not happen to mine. Love this amp

My amp (AD30VT) has exactly the same problem. Where can I find the replacement pot?

You ordered those parts from China based on "a guess"...? Did you not remove the old dual pot and then check it to confirm it was u/s before ordering..!?

OH KOREA MASS PRODUCTION

aliexpress WH148 B100k, yep?

man i hope this never happens to mine :)

You get what you pay for.

7815 7915

My ad50vt switches channels (amp mods) and effects randomly all by itself. Have searched forever to try to find a fix. Haven't found anyone else who's had that problem.