Help Please~!!

[Mike]

Hey all, OI finished my A1a build and have some serious problems with it.
First I fired it up and I had 2 of the filter caps backwards so I kept blowing fuses.Now I have that straightened out and the tubes light up but I get no sound.
I checked for voltages and I'm only getting 3.2 on the pins where the power is connected. 12AX7's too.
MNaybe I'm not checking them correctly or maybe the caps are dead??

I hope that I didn't hurt my trannies~!! How do I check a tranny to see if it's OK?? I have heard that you should Ohm them out but what readings should I get?? And if you say INFINITE what does that mean that my meter should show?? Nothing, zeros,or??

I am at a loss here and very nervous because I can't afford to buy new trannies. I can barely afford new caps.

Any and all help is welcomed and I would very much appreciate it~!!!

Thank you all~!!

Mike

[Robert]

Hi Mike,

Try reading www.paulrubyamps.com/info.html. Also, you should recheck EVERYTHING against the reference schematic. Posting some pictures would be helpful as well.

Robert

[Chris G]

Hey all, OI finished my A1a build and have some serious problems with it.
First I fired it up and I had 2 of the filter caps backwards so I kept blowing fuses.Now I have that straightened out and the tubes light up but I get no sound.
I checked for voltages and I'm only getting 3.2 on the pins where the power is connected. 12AX7's too.
MNaybe I'm not checking them correctly or maybe the caps are dead??

I hope that I didn't hurt my trannies~!! How do I check a tranny to see if it's OK?? I have heard that you should Ohm them out but what readings should I get?? And if you say INFINITE what does that mean that my meter should show?? Nothing, zeros,or??

I am at a loss here and very nervous because I can't afford to buy new trannies. I can barely afford new caps.

Any and all help is welcomed and I would very much appreciate it~!!!

Thank you all~!!


Hi Mike,
I would remove those caps......chances are there dead.Once those are replaced.......check for high voltage in the power supply.Set your meter to dc voltage............put the black lead to ground and the red lead to each of the b+ spots in the power supply(..........BE VERY CAREFUL WHILE DOING THIS AS YOU ARE WORKING IN THE AREA OF THE AMP WERE THE HIGHEST VOLTAGE IS PRESENT..................If you could post a picture or drawing of what you have, we may be able to help you more. I wouldn't worry about the pre-amp until we straighten out the power supply,Your trannies are also probabley fine, the fuse did it's job! Again be careful..Keep us posted
Chris



Mike

[Mike]

OK, I disconnected my red leads from the rectifier diodes and got 300+ volts from them. So that ois good. I reconnected them to the diodes and disconnected the lead from the cathode end of the diodes and got 600+volts. I got 600 to the standby switch and to the other side of the switch but tghen when it hit the first 160uF cap it read 900+ volts~!!
I quickly checked the last end of the 160uF caps and the voltage came down to 400+. I checked the voltage at the cap can which is my 40,20,20,20,20uF caps and they went from 900 to 700.

What in thre world could make the voltage jump so high??
I disconnected the OT lead from the 160uF cap.
I am using the RED lead from the Hammond 1645 OT I am using to connect to the 160uF cap. Does anyomne know if this is correct??
Of course brown and blue are for the power tubes.

Any help would be greatly appreciated~!!

Thanks
Mike

[tubedogsmith]

Make sure you are changing your meter from AC to DC as appropriate and that you have a good battery in it.

[ampdoc1]

I'm not sure what you meant by quickly checking the last end of the 160uf cap and you got 400V. I'd check the polarity and connections of those 160uF caps and divider resistors, as well as the ground connection to the stack. If everything is installed correctly and the parts are good, you should get almost exactly half the B+1 voltage at the mid point of the caps, and obviously 0 volts on the ground connection to the bottom.