DIY AC15 Tremolo not working
Hey There!
Just builded a Vox AC15 with Normal channel (EF86) and top boost channel of AC30.. Shmeatic:havazli's Library | Photobucket
The amp is working and the sound is amazing,but the tremolo (it's from Vox Pacemaker) not working.When tremolo is "on" there's near 70v drop on the overall amp voltage..The signal is somewhat blocking distorted ..😡.I've checket several times for mistakes..
Any advice and suggestions will be greatly appreciated..
Hey There!
Just builded a Vox AC15 with Normal channel (EF86) and top boost channel of AC30.. Shmeatic:havazli's Library | Photobucket
The amp is working and the sound is amazing,but the tremolo (it's from Vox Pacemaker) not working.When tremolo is "on" there's near 70v drop on the overall amp voltage..The signal is somewhat blocking distorted ..😡.I've checket several times for mistakes..
Any advice and suggestions will be greatly appreciated..
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Hi Havazli,
If you have a scope, I would look at the output of your trem circuit at the wiper of the depth pot. This will give you an idea if the trem is working. If you don't have a scope, try a voltmeter here, the numbers should be changing indicating some varying voltage at the very least.
If it's working and still problems, try connecting the trem ouput to the output tubes bias circuit. Ground the grid resistors of course.
If you have a scope, I would look at the output of your trem circuit at the wiper of the depth pot. This will give you an idea if the trem is working. If you don't have a scope, try a voltmeter here, the numbers should be changing indicating some varying voltage at the very least.
If it's working and still problems, try connecting the trem ouput to the output tubes bias circuit. Ground the grid resistors of course.
The way the wiper is on the trem (and I know this because it was pointed out in my own design), if you have it turned all the way toward ground and the trem turned on, you've basically got a 220K to ground for your signal (whereas it's 470K [220K + 250K] to ground with the wiper the at the other extreme). If you have one side of the pot go to ground, one go to the red dot in the power amp and then the wiper go to the tremolo, then it's always 470K to ground.
I don't think that would be enough to suck your 70V, though.
I don't think that would be enough to suck your 70V, though.
Hi Poacher,
Thank you for the reply...Yes ,I measured the voltage,even I hooked a red diode (in place of cathode resistor and bypass cap)from cathode to ground.Obviously it's oscilating.When the deep pot's wiper is in short with the ground i.e. in 0 position everyrthing is OK,but when İ try to turn it a bit suddenly the overall voltage reduces,the volume is going out and the signal is creshes (a kind of block distortion).BTW I build three different circuits.The result is the same..😡
Hı pdavis68,
As I pointed above,I builded few different circuits (every one with new components) The result is the same..😕
Havazli, something is going on crazy here when you don't have the grid resistors to ground. So, you're saying that as soon as you start lifting the grid resistors from ground with your depth pot, these problems occur. If you're dropping 70 volts, perhaps your amp is oscillating. To simulate this, how about you connect a 470k resistor to the grid resistors and ground. If the amp is still stable then the source of the problem is coming from the trem circuit. Pdavis suggestion regarding the pot is similar idea, but I would leave the trem output disconnected from the wiper at the moment.
Have you tried applying the trem output to the output tube cathodes as I suggested in my previous post? This way, we leave the grid resistors to ground and vary the bias another way.
Perhaps you have DC on the trem output, but if you built 3 separate circuits with same results then probably the coupling cap is good, unless you used the same cap 3 times and it's a leaky cap.
Of course, scoping it would tell you more about what's happening. You could see the oscillation if that's what it is.
Good luck,
Have you tried applying the trem output to the output tube cathodes as I suggested in my previous post? This way, we leave the grid resistors to ground and vary the bias another way.
Perhaps you have DC on the trem output, but if you built 3 separate circuits with same results then probably the coupling cap is good, unless you used the same cap 3 times and it's a leaky cap.
Of course, scoping it would tell you more about what's happening. You could see the oscillation if that's what it is.
Good luck,
Exactly Poacher..When I disconnect my grid resistor from fround,the amp starts to crashe -odd crackling noise and when strumming the gitar it only distorted with way low volume..Anyway,i'll try it applying to the cathodes,as you suggested..
Thank you!
Thank you!
Hi again!It been a long time.
I tried all the suggestions above.
1-Dosconnected the tremolo from grids and wired 470k resistor from grids to ground.The result was the same - block distorted sound.
2-Wired the wiper of intensity pot to the tremolo output and the grids to the hot side - no difference.
3-Connected the tremolo output to the PA tubes cathode - no oscilation..
Meanwhile I forgot to tel you that my PA tubes cathode resistor is 150 Ohm instead of 130 Ohm..Is it possible that difference to cause this problem?
I tried all the suggestions above.
1-Dosconnected the tremolo from grids and wired 470k resistor from grids to ground.The result was the same - block distorted sound.
2-Wired the wiper of intensity pot to the tremolo output and the grids to the hot side - no difference.
3-Connected the tremolo output to the PA tubes cathode - no oscilation..
Meanwhile I forgot to tel you that my PA tubes cathode resistor is 150 Ohm instead of 130 Ohm..Is it possible that difference to cause this problem?
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