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Cornet2 Issues

post #1 of 5
Thread Starter 

Hi there,
Just finished building the Cornet2. Thanks Jim for the awesome piece of electronics. Everything works okay, but not perfect.
Unfortunately, the right channel is low, not by much, but noticeably lower to shift the balance to left side.
I swapped the 12AX7's and it doesn't solve the problem, but alters the levels making right channel worse off.
These are my voltage readings - 
B+ - 366 (should be 365)
R211L - 338 and 311 (should be 330 and 300)
R211R - 339 and 314 (should be 330 and 300)
R219L - 175 (should be 155)
R219R - 193 (should be 155)
V200 Pin 1,6 Left - 185 and right - 203 (should be 150 each)
V201 Pin 1,6 Left 168 and right 185 (should be 150)

If I swap the tubes, the values become:
B+ - 364 (should be 365)
R211L - 337 and 310 (should be 330 and 300)
R211R - 338 and 313 (should be 330 and 300)
R219L - 190 (should be 155)
R219R - 209 (should be 155)
V200 Pin 1,6 Left - 168 and right - 187 (should be 150 each)
V201 Pin 1,6 Left 185 and right 203 (should be 150)

As you can see, Pin1,6 voltages also get swapped when changing the tube. Also the R219 voltage gets increased by 15 in both channels by swapping.

To me it seems like a tube problem, but I don't know jack about such complicated circuits.

There is also a hum/buzz (dont know the difference) in the sound. Both channels. Have properly grounded everything. 
Please help!! 

post #2 of 5

Have you measured DCR of all the resistors and inspected for solder bridges? 


Have you tried a totally different tube? 


Have you engaged the "mono" switch? 


Do you have an "inverse RIAA" circuit to test?

post #3 of 5
Thread Starter 

Thanks for all the help!


I have not measured the DCR. I am not an expert, so I don't even know how to go about it. What will it achieve? Do you want me to check whether the resistance is symmetric on both channels?


I haven't tried a completely different tube. I just ordered a matched pair. 

I do not have a RIAA equalizer. I will get one, it's too cheap to even bother building one.


A couple of questions. Should i measure voltages without the tubes? Is that going to help in knowing whether the voltages are distorted by the tubes.

What voltages should I measure in addition to the one I measured? Also I noticed that the resistor had a lot of variance, nothing beyond 5%, but could that be a reason?



post #4 of 5
He wants to be sure that you used the right resistors in the right spots.
post #5 of 5
Thread Starter 

I just checked all the resistors again. Everything at the right spot. But I see other voltage issues.


So I am not getting 6.2 V at the pins. Instead the readings are 4.5V. Pin 4,5 and transistor all have 4.5V
I back tracked the readings to the input to the diode rectifier circuit and the input is 6.1V. The two green wires have a reading of 3.15 V each. Is that a good voltage from the transformer? That seems to be in line with what that winding should give. But what i dont understand is that if the voltage at the pins are also supposed to be 6.2, that would effectively mean that the 1.8 resistor should be bypassed ?!
The line AC is 119 V so that is good. I rechecked all the connections and tranny configs. They are as per the color code.
Thanks Dsavitsk and Nikongod.

Edited by mucool - 6/12/14 at 10:22am
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