Screeching Vox AC15 C1 repair.
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- čas přidán 30. 04. 2020
- With volume knobs all the way down, it still was screeching! Old tubes go micro-phonic and can destroy your transformer. The fix was to replace the 6 year old tubes. Here is how it is done. Note tubes are like strings, they sound like crap after they get old. High get dull and lows get flubby sounding.
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Even though it hasn't been plugged in in awhile, capacitors can hold a charge for a LONG time. You already know this -- make sure your viewers do too!
15 minutes
Hello i have the same amp ac15 i bought in guitar center used but very good condition i like to know when do i replace the valves is there a sign when my valves go bad?
I hear Rush, I press like!
Are these Chinese Vox amps built to last or should I look into the handwired ones? I would like the EF86 channel on the Heritage Head but they are pretty expensive.
It was rock solid. However hand wired is worth more.
Glen, I just picked up a used VOX AC15-C1 112 Combo and it seems to be very "touchy" with LOUD Popping noises whenever I flip a switch on guitar, or when I flip from standby mode to ON. I already installed all new JJ tubes and it didn't help much. I already checked the boards, and everything looks very clean, no burnt or oozing resistors, etc.. Any suggestions would be appreciated.
See if any caps are swollen.
Thanks Glen but already checked for that - The boards look very clean.@@GlenHyden
@@A.WebbAndFriends My last thought would be the JJs are suspicious even new.
YOU ARE MORE RIGHT THAN YOU KNOW GLEN - I installed new JJ's into a vintage Ampeg Jet II 112 Combo and when I turned up the reverb past "6" the amp would howl and it turned out the new JJ was highly microphonic. I've been a tube amp collector since 2005 back when CRATE amps were popular. Hate to say this but its become obvious that the new era JJ's are garbage. I've heard the same from others too. @@GlenHyden
The general problem is an oscillation. Many factors can contribute. Many high gain amps use a tiny little ceramic cap to clamp down oscillations on the plate signal path. Change tubes first, then a scope of the speaker output load, verify oscillation riding on the signal. Then narrow it down to which plate 'starts' the oscillation. BTW> Self biasing is kinda a way manufactures say they don't care if they overdrive their tubes causing short life and brittle usueable tone. You can bias a self bias amp, but you should really know the electronic theory before getting into such things. :)
So the input gain and impedence is usually too high on modern combo amps. Fender blues Jr have a fixed bias so you have to change the resistor. I'm assuming a vox is the same idk. I'm having hum issues on my NEWISH 2 year old ac15c1x. A stellar amp but Mt God already malfunctioning? Change the resistor and the tubes will last decades!
Get one that's 1 Meg or lower
The cool thing about tube amps is, besides the sound, is that the most common issue is a tube and the user can simply replace the tube to fix the problem. The cool thing about solid state amps is that the part of the amp that equivalent to the tube seldom fails. ;)
It would have been nice to see you show the squeel and then once you determined the issue was a tube, swap them out one at a time to figure out which on was the offender. It's unlikely that all the tubes were shot. You also could have taken a pencil or chopstick and tapped on the tubes to see if you got a noise in the amp. It's an easy way to find a microphonic tube. The only caution is that tapping on a good tube could transmit the vibration to the bad tube, making more than one tube be suspect. The bonus of finding the bad tube, even if you wanted all new tubes, is you can toss the known bad tube out and you now have a supply for that rainy day when another tube goes bad.
I should have added the original owner said he's never done maintenance on this amp. The tubes must have been a good ten or fifteen years old. So new tubes is the path I took.
@@GlenHyden I just bought the same amp used and much to my surprise, it has a complete set of pristine tung-sol's. I was certain that I'd be replacing the tubes.
@@merwinjm that amp with a strat single coil is pure gold chime sound.
Do you have another issues with that amp?
No other issues. I'm not a strat blues player but this is absolutely perfect for that. You can even get good rock sounds out of it but forget heavy metal. The amp should work flawless for another 5 years until the tubes give up. again.
What are the exact tubes you got?
J J Electric ECC83S and EL84 from tube depot.
wanna hear squeeeeal man
These amps are always biased too hot, like 100 to 110% max rating, plus the screen resistors need to be of greater resistance and watt rating.
How much did you pay for the amp? I'm looking at used ones at the moment.
Thanks for the video!
$250 US. After I had it perfected I sold it for $360.