5E3 Normal Channel not working

[mebond11]

Cheers everyone, hoping to rely on the kindness of strangers for some help on a 5E3 clone.

I recently completed the 5E3 build (my first) and to my utter amazement it worked the first time when I plugged into the bright channel, and sounded great with little noise.  However, when I plug into the normal channel, I get no sound.  I think I have a problem in the tube or socket, because I am showing the following voltages in the first preamp tube:

Bright (working) channel cathode voltage:  1.4V
Bright channel Plate voltage: 112V
Normal (non-working) channel cathode voltage:  9V
Normal channel plate voltage: 274V

grid voltages in both cases are small millivolt numbers.

The normal channel voltages seem way high.  When I tap the grid pin on the non-working normal channel with a chopstick, I get a small pop out of the speaker, and all the pots are functioning.  So it seems that everything downstream is working.  I checked the cathode resister and it is reading 820 ohms, consistent with its rating, the cathode voltage at pin 8 is 1.4 volts, but by the time the jumper gets it to pin 3, it's 9 volts.  The input jacks look to be wired correctly, as does the rest of the signal path.

I ordered a spare tube to see if a switch will cure it, but curious if more experienced folks can suggest where they think the problem lies in case that doesn't work.

I appreciate all the feedback.  Thank you!

[uki]

Welcome to the forum!

If you can provide the schematic used in your build that help others to help you.
Recheck all connections on that channel, solders joints, voltage readings. Post here, the more info you give easier to track down the problem !

[sluckey]

the cathode voltage at pin 8 is 1.4 volts, but by the time the jumper gets it to pin 3, it's 9 volts.

Bad jumper or solder job on one or both ends of the jumper. Resolder the jumper first. If no go, replace the jumper. Still no go, replace the socket.

Still no go? Post some hi-rez pics of that end of the amp.

[mebond11]

Thank you for the replies...I will try reworking the tube socket and see if I can get it up and running.   a bad solder connection would increase the voltage because the current flow is restricted?  And that would also drive up the plate voltage?

[Papa Jim]

I may be wrong but wouldn't it take a constant current source in order for a bad solder joint to drive up the voltage. Hmmm I gotta think about that one though.

[mebond11]

As requested, a schematic.  The normal channel signal starts at the jack, runs through one side of the 12ay7 preamp, then up to the volume caps.  The bright channel runs through the other side of the 12ay7, and up to the volume caps.   Since the bright channel and volume caps are functioning normally all the way to the speaker, i figure the problem is somewhere in the input path, tube or tube assembly, probably the latter because the voltages are abnormal at the pins of one half of the 12ay7.

But I’m a newbie making guesses here.   BTW, despite my problems I enjoyed the experience immensely and felt I learned a lot.   I’m delighted it is at least half working, even if I never get the other half working.

[sluckey]

Thank you for the replies...I will try reworking the tube socket and see if I can get it up and running.   a bad solder connection would increase the voltage because the current flow is restricted?  And that would also drive up the plate voltage?

A bad solder connection or bad jumper would look like a resistor and would decrease the current flowing through the tube. With reduced current flowing through the tube less voltage is dropped across the plate resistor. This allows the plate voltage to "float" higher toward the supply voltage. There's no driving it up taking place.

If that jumper were completely open then the current flow through the tube would be totally cut off just as if you had opened a switch. In this case, the plate voltage would float all the way up to the value of the B+ feeding the tube.

[mebond11]

Thx, very useful information.

[mebond11]

Turns out it was a bad solder joint on the cathode jumper that I could only see with a magnifier.  Five minutes work and I’ve got a beautiful amp.   Thanks so much for the useful help and suggestions...good karma to you all!