Where does one begin to troubleshoot for a lack of volume??

[playonit]

Finished my Ceriatone DC30 build and am lacking full volume in ch.2 and still have some hum...I just fixed another issue in ch. 2 where volume only worked when the knob was at the zero position... I am a novice and look forward to any ideas I can get... my initial thought is a bad ef86?? ch. 1 appears fine and dandy..

Thanks

[Phil_S]

It is hard to know. If this were mine, I'd start with the layout and a highlighter [1]. Start at one end and work your way methodically to the other end. As you check each part for correct value and wiring, mark it off. Eventually, you should find the problem. I know this will be tedious, but it will force you to break out of the mold where you continue to miss what's not right about it.

[1] The real truth is that I'd put a meter on all the tubes first and look for where there is inappropriate voltage (too high, too low). Then, I'd put a scope on it to see where the signal is not right. You probably don't have a scope, but do the voltage check, record all the DC voltages at the various tube pins and post the results here. Skip the heater pins...we'll assume they are OK, and they are AC volts anyway. Then, do the highlighter thing. Remember to discharge caps for your safety.

[playonit]

Thanks Phil...... I did highlight the layout before startup.. and everything follows the layout... and looks good. I will double check to verify my initial check.. Since I am a novice can you or someone explain how to check voltages at the pins?? DMM ground to frame probe to??? what pins on the sockets do I check? tubes in or out ???....Do I check pre-amp,power and rectifier pins?? I am very safe and take no chances... always drain the caps and keep a hand in a pocket when the powers on. Thanks for the help...

[Structo]

Anything before the rectifier is AC, after the rectifier is DC.
Of course the heater wires are AC.

I attached a 12ax7 voltage chart.

I also included a EL84 chart.
Print these out and write down your voltages.

Set your meter to DC volts, if it isn't an auto ranger meter you will have to set it for 500v for the pins 1 & 6.

Clip your black probe to chassis ground and with one hand in your pocket power up the amp, touch the red probe to the pins listed.
Don't worry about pin 9 or 4 & 5 since those are AC heater voltage.

[playonit]

Thanks Tom.... Tubes in or out??? I will post my findings tonight or tomorrow

[ChrisM]

Tubes in

[dehughes]

Nice voltage chart, Structo! Where did you find those, and do you have some for other tubes?

[Sonny ReVerb]

Wow! Look at these pinout charts:

http://www.bustedgear.com/res_Tube_pinouts.pdf

[playonit]

I got the voltages tonight and there looks to be some issues... the ef86 is sick and is probably the lack of volume issue in ch.2 . 5751 #1 also looks to be having a problem and 5751 #3 plate has that high 305v reading that is confusing to me.... ef86 bad tube?? or other??

Thanks all

[Structo]

Yes the link that Sonny provided is what I used for those charts.

A real handy file.

[Structo]

I got the voltages tonight and there looks to be some issues... the ef86 is sick and is probably the lack of volume issue in ch.2 . 5751 #1 also looks to be having a problem and 5751 #3 plate has that high 305v reading that is confusing to me.... ef86 bad tube?? or other??

Thanks all

How did you measure the cathode voltage on the 5751?

[playonit]

I got the voltages tonight and there looks to be some issues... the ef86 is sick and is probably the lack of volume issue in ch.2 . 5751 #1 also looks to be having a problem and 5751 #3 plate has that high 305v reading that is confusing to me.... ef86 bad tube?? or other??

Thanks all

How did you measure the cathode voltage on the 5751?

By measuring pins 3&8 with my DMM set V autorange?

[Structo]

Is that measured to ground? DC voltage right?

Just seems real high.

Although I don't know this amp, typically on a 12ax7 you would get between .75 to 2 volts.

[playonit]

Is that measured to ground? DC voltage right?

Just seems real high.

Although I don't know this amp, typically on a 12ax7 you would get between .75 to 2 volts.

By Ground you mean black lead to chassis??? Wow, if it should be .75 - 2 ??

I wish I knew what the volts are supposed to be for this amp but am having trouble gathering that benchmark... The el84 section seems well matched? Looking at the ef86 volts would you think bad tube.. I traced and checked wire accuracy and continuity and it checks out with the layout.. what about the 305v plate voltage on tube 3??

THANKS Tom

[Structo]

99% of the time when you measure DC voltage on a tube amp, you ground your black lead to the chassis.
This also allows you to probe the amp with one hand on the red probe.
That way you don't take the risk of getting a lethal shock through both hands with your heart in between.