Bugara 333

[soulman25]

I need s schematic for a Bugara 333. I have no B+ on any of thr 12AX7 pre amp tubes. I have -14 volts on pin 3 of V7 . i should habe 300 volts to the plates and 180 volts there about to the heaters. There is no B+ anywhere to the pre amp tubes. Please . If anyone has this schematic , please post. Thanks one and all.

 

[Lingwendil]

In a zip file on here-

Schematics

Might want to move this to the instruments/amps forum though

 

[soulman25]

Found problem with 12AX7s A+, was a broken wire on a two prong plug. But now i have a new problem with my EL34s, the EL34 valve furthest away from the phase inverter valve, is glowing red hot when I take it off stand by. I have replaced D1 and D2 both 1N4007s also replaced D3 and D4, Both are, R2000Fs diodes and the furthest EL34 tube
from phase inverter still gets hot, I dont know if is valve 1 or valve 4 thats getting hot as they are not marked. I thought by chance that the diodes may be bad under power even tho they checked fine with my diode checker. But was not the case. C4v and C5 are 100p ceramic disk caps which normally dont go bad. There is also some 680 ohm resisters along with some 10 ohm resisters that are used as the Grid and plate resisters but the resistince in them are all fine. ???? Theres not much left on that board to change out . Could the problem be coming from else where ? If anyone on this site can offer any ideas please feel free to do so. What can it be ?

 

[soulman25]

In a zip file on here-

Schematics

Might want to move this to the instruments/amps forum though

That is a really nice build . Did you design it yourself ? Thats really awesome !!

 

[llwhtt]

Remove all of the output tubes and measure the voltage on pin 5 of the output sockets, you should have a -VDC even in stby.

Craig

 

[soulman25]

Thank you Craig I will try that. I will look on the schematic to see where that voltage comes from if i dont see it on pin 5 of the tube sockets.

 

[llwhtt]

No or low -VDC on pin 5 equals red plates.

Craig

 

[soulman25]

Bugara 333.

I have a Bugara 333XL on my bench. I have one of the EL 34s furthest away from the 12ax7 phase inverter tube that starts plating red. I have replaced D1 thru D4 on the same board. Even tho they checked out good with my diode checker. I thought they may be failing under power so i replaced those as well. Customer needs amp by next week. Ive checked all the 12ax7s and EL34s in my tube checker . All tubes checked out fine. If anyone has any ideas on this problem , please feel free to elaborate. Thanks one and all.

 

[soulman25]

Just right off hand do know the value of that negetive voltage on pin 5 ?? As im not at the shop right now.

 

[soulman25]

Right off hand , do you know the - voltage rating on pin 5 of the EL34s ? Im not at the shop right now.

 

[llwhtt]

Probably anywhere from -30VDC to -50VDC. This is the bias voltage so it all depends on the tubes, the plate voltage and the desired idle current.

Craig

 

[Printer2]

I have replaced D1 and D2 both 1N4007s

Why? Might be good to check for the right polarity.

 

[rayma]

I have one of the EL 34s furthest away from the 12ax7 phase inverter tube that starts plating red.

Try replacing the associated grid coupling capacitor, which could be leaking positive voltage to the grid.

 

[kevinkr]

Threads merged, please do not start multiple threads on the same topic.

 

[soulman25]

Found problem with red plateing it was a sliver of solder that came out of my solder extracer and landed in between a small resistor and pin 5 of the EL 34s . No more red plateing just have to get it to pass signal now.

 

[soulman25]

I now have my -47 volts on pin 5 of the EL34s.

 

[soulman25]

Thank you Craig for all your input.

 

[soulman25]

Found problem with Bugara 333XL. was a problem in the bias circuit. A piece of solder from my solder extracter fell in between pins5 of the output tubes and a resister pad. which took my bias voltage to ground causing tubes to plate red.