Need some expert troubleshooting advice

[5thumbs]

Hi Gang,
I just finished wiring up a Weber 6A14 head (Blackface Princeton Reverb). Hooked up I get no sound through the amp. I put my Weber Bias Meter on the power tubes and set the plate voltage to around 275 V and then flipped the meter over to read the cathode current and I am getting around 4-8ma. Rotating the bias pot fully, does not change the cathode reading. I have gone through the wiring 3 times to check for mistakes, I have also changed tubes, but I still can't get it to work. Any suggestions as to how to troubleshoot this or where you think the problem would be would be greatly appreciated!

Thanks,
Tim

[Enzo]

Well, first off, we have no idea if you have wired it all correctly. But assuming for now that you did...

Check the speaker. Does it work connected to something else? Even your stereo.

Does ANY sound come out the speaker at all? A little background hum or hiss, any sign of power to the system? Or is it as silent as a tomb?

Power off, measure resistance from pin 8 of each power tube socket to ground. it should show very low or zero ohms, the cathodes on pin 8 should be grounded.

Power on, and do the heaters come on in ALL the tubes?

Now pull the power tubes and fire up the amp. What DC voltages are at pins 3,4,5 of each power tube socket?

275v sounds awfully low for B+ to me.

[mooreamps]

Hi Gang,
I just finished wiring up a Weber 6A14 head (Blackface Princeton Reverb). Hooked up I get no sound through the amp. I put my Weber Bias Meter on the power tubes and set the plate voltage to around 275 V and then flipped the meter over to read the cathode current and I am getting around 4-8ma. Rotating the bias pot fully, does not change the cathode reading. I have gone through the wiring 3 times to check for mistakes, I have also changed tubes, but I still can't get it to work. Any suggestions as to how to troubleshoot this or where you think the problem would be would be greatly appreciated!

Thanks,
Tim

What is the voltage on screens ?

-g

[Bruce / Mission Amps]

Home built amps are hard for us to help with because the actual construction is not absolute.
Even though you looked at it and confirmed three times it is wired right, unless you have a bad transformer or parts, it must not be wired right Tim.
You aren't too terribly far from me... I'm just south of Brighton, maybe you can pull the chassis and stop by sometime and I'll look at it with you.

[5thumbs]

Thanks Bruce,
I might take you up on that! I found the reason for no output! I had run shielded leads for the input and 1st triode return and the shields were grounding the plates (bruce weber told me to! ha!). But now I am only getting a low distorted output. I actually have that posted in another thread.

Tim

[Amp Kat]

Tim if you live anywhere near Bruce I suggest you let him help you with it. That is the best advice you'll find which is also expert advise !

[5thumbs]

Okay Bruce,
I'm giving you a call tomorrow! I changed the dropping resisters as per another thread suggested and still am not getting enough juice to the tubes!

Thanks for your help,
Tim

[Bruce / Mission Amps]

OK call me Monday sometime and I'll take a look at it with you...

[Bruce / Mission Amps]

Did you get the Princeton Reverb kit/clone back together and running OK?
I'd consider putting the B+ rail 18K dropping resistors back to the correct values... use a 10K, or a couple 15K, or one 12K and a 18K etc., but don't follow just "anyone's" random advice on how to mod the B+ rail in these.

added:
Oh and don't forget what I said last week about:
"Even though you looked at it and confirmed three times it is wired right, unless you have a bad transformer or parts, it must not be wired right Tim."

[5thumbs]

Thanks again Bruce for your help troubleshooting my amp! You really went above and beyond by giving me 1.5hrs of your time! In my defense, I would have had a chance getting the wiring right if I had received a eyelet board from Weber with the right number of eyelets! ;-) Thanks again!


I put it all together and installed it in the Weber head cabinet. I had to build some RCA cables for the reverb tank as none where included in the kit. Then discovered the tank doesn't fit in the head cabinet they sent, nor does the EIC power cord which has the jack blocked by the back panel. I finally got the tank into the cab in front of the 5U4G kind of leaning on the front and bottom and then I got reverb tank feedback! The amp sounds great! I just have to figure out what to do with the reverb tank (I am also getting noise from the PT through the reverb). I may end up putting it into some kind of combo cab.

Thanks again!
Tim