[longplates]

Hello, all-- I have had a super busy couple months, but managed to squeeze in enough Sundays to finally complete my Cornet 2 build. What a fantastic kit! Unfortunately, I did not have that magic "worked the first time" experience. I have serious right channel issues with my Cornet2. At first, I thought I had NO right channel output at all. Then I listened to it with a headphone amp connected to the Cornet 2 output and heard a very quiet, distorted signal passing thru the right channel. The left channel functions PERFECTLY.  I should point out that I have the Cornet2 PCB connected to the top plate of my Lansing Enclosure, and also have the chassis side panels installed, but am testing it with the rear panel wiring and the rear panel itself entirely connected ELECTRICALLY... but the rear panel is not physically attached to the rest of the Cornet2. It is grounded to the PCB properly. I built my Cornet2 with the "stock" PCB-mounted RCA jacks, to be changed later to an upgraded RCA jack so I believe it is not RCA jack wiring issues. SO-- here is the issue; great sound from the LEFT channel of the Cornet2 connected to my turntable (Quality VPI table; in perfect order; works perfectly with my Audio Research preamp; so this is not a turntable/cartridge/interconnect issue here) but still has less than 1/20th the output in the right channel of the Cornet2 and even that is with much distortion.  I immediately started troubleshooting. I grounded the negative of my voltmeter to the rear panel (the rear panel is connected to "earth" tab on PCB) I then touched the other probe to the 155 volt test point, which is resistor 219R; To my amazement, the missing right channel immediately came in loud and strong, balanced with the left channel, and producing clean, beautiful sound! I removed the meter probe from resistor 219R and the right channel disappeared again. Then I made contact with the positive meter probe to the screw that attaches Q200R to its heatsink; SAME THING! The right channel comes back in, in full splendor. Grounding issue? Before I forget, my voltages with a 5V4GA are running about 30 VDC HIGHER in the malfuntioning right channel than the left channel. Those left channel voltages are within 7-8 VDC of spec.  At the right channel 155 VDC test point I have almost 190 VDC. At the screws bonding Q200R to the heatsink I also have 30 volts higher in the right channel. MY LED D100 is not functioning at all; I STUPIDLY mounted it to the wrong side of the board after a long build session and had to desolder it, pull it thru the PCB, and reconnect; I either toasted the LED or damaged a trace on the PCB because it appears to be connected but has no functionality. But at every spec point, like the 330 VDC test point, I have 30 volts higher in the right channel than the left. The other anomaly I noticed is that on Q100R I have one leg that has no voltage present while the other legs have 8 volts DC, same as all three legs of Q100L in the left. I din't measure for AC on the Q100L. Sooo... obviously a grounding issue? What is the likely culprit starving the DC from the right channel? I am just beginning my troubleshoot, having only completed the Cornet2 earlier today... but if these symptoms I am having add up to something familiar to another Cornet2 builder... I'd be much obliged to have someone point out my stupidity, (heh.) I have to say that with both channels operating, even though I didn't want to run it for long in an obvious "problem" state, the sound was fantastic!!  WOW! this little "taste" makes me want SO badly to get it righted to start REALLY enjoying the Cornet2! ANY HELP APPRECIATED!!! THANKS! L.P. I will post some pics tomorrow.

[longplates]

BTW--I also should mention that the voltages on both pairs of feedback capacitors,  C 202 L / C202 R.. and C204 L and C204 R is exactly the same. The voltages at the resistors in the physical area on the PCB surrounding the 1st ECC83 tube (V200) are also the same from left to right channel; they are not higher in the right channel like further down the chain in the circuit. I will post again tomorrow as i continue again to poke around. Many thanks to anyone who can indulge/assist me with this vexing issue... I can always return the favor  for a solution to my woes with a great deal on some top end NOS 12AX7s or 12AU7s (I'm not trying to actively SELL anything here; please do not mistake this for a lame attempt to sneak in a mention of tubes for sale! They would be a "thank you" reward for help) Thanks again!

[poty]

... I grounded the negative of my voltmeter to the rear panel ... then touched the other probe to the 155 volt test point, which is resistor 219R; ... the missing right channel immediately came in...  removed the meter probe from resistor 219R and the right channel disappeared again. ...  to the screw that attaches Q200R to its heatsink; SAME THING!

What transistor do you use for Q200R? The stock 2SC3942 has plastic case - so it is isolated from the heatsink and the screw. In the Cornet 2 the heatsinks are not connected to anything either. So... touching the parts should not change anything. In your case it do change, so the first obvious things - check if there is a solder bridge somewhere near the heatsink.
In case you use some non-isolated transistor (like TIP50) the abovementioned troubleshooting won't help.
The whole behaviour IMHO can be explained by the lack of connectivity of the cathode of V202 (in right channel) to ground. Your multimeter has finite resistance which is enough to close the circuit of the cathode follower in place of the intended circuit (R217, Q200, R218). So your steps should include:
- (power off your device!!!!) check resistance from the cathode pin of the V202 (for the right channel) to the collector of Q200 (220 Ohm);
- resistance from the emitter of Q200 to ground (should be 910 Ohm).
If both resistances are OK, check the voltage on the base of Q200 (while the Cornet 2 is on of course) - should be around 6.2V. If OK - most likely the Q200 is out of order.

... voltages with a 5V4GA are running about 30 VDC HIGHER in the malfuntioning right channel than the left channel.

It can be the result of open circuit for the last stage (what I described earlier). The last stage drain about 6,5mA and if the current doesn't flow the voltage drop on the R220-R221 is lower and the resulting voltage is higher. I'm slightly surprised that the voltages on C202s and C204s are the same, but it may be just coincidence.

MY LED D100 is not functioning at all; ... The other anomaly I noticed is that on Q100R I have one leg that has no voltage present while the other legs have 8 volts DC, same as all three legs of Q100L in the left. I din't measure for AC on the Q100L.

What are the Q100L and Q100R? Q100 and Q101?

[longplates]

Poty-- thanks so much for your assistance!

I did indeed use a TIP50; bad choice, I guess, but that is the only equivalent that digikey HAD. ( IF I had I known the disadvantages of using TIP 50... I'd have added another supplier to the list for my build and sourced something else for Q200R and Q200L!)

 I misquoted on the "Q100L and Q100R" You are correct, they are indeed Q100 and Q101 on the schematic, and Q101 was device I measured as having one leg with no voltage present. It was a hectic night... ;0)

I'll admit upfront here that as far as anything to do with solid state devices... I am at beginner knowledge level.. but I measure exactly what you quote for Q200R: The cathode of V202 to the collector of Q200R measures 221 ohms. The Q200R emitter to ground is 913 ohms.

HOWEVER, I measure only around 3VDC on the base of Q200R to ground.  On Q200L it is 6.2.

BTW--- as far as V202 is concerned: ( I do wish I knew what the DC on the tubes should be, roughly,  on each pin, but here are the measurements and my basic observations)

 The ECC82/12AU7 (V202) at least APPEARS to be operating/drawing current; it's seemingly PROPERLY functional in triode one, for the left channel, (produces normal audio; DC voltages present) and has high tension on the elements associated with triode 2, the right channel, also... just 20-30 volts higher in triode 2 than triode one; I have no idea what the various voltages on the 9 pins of ANY of the tubes SHOULD be, (they are not in the Cornet2 manual) but here are the voltages on V202 that I measured: Pin 1: 345VDC (This is anode ONE, for the functional left channel, as I read it) Pin 2, (grid one): 141 VDC Pin 3 (K one): 158 VDC Pin 4 (fil. one): 6 VDC Pin 5 (fil. 2): 6 VDC Pin 7 (g2): 155VDC  Pin 8 (K2): 180 VDC  Pin 9: No voltage

So the only anomaly from your thoughtfully provided spec resistances/voltages is the base of Q200R, which is 3 VDC rather than 6.2 VDC

I have to attend to something-- I'll return ASAP with voltage measurements from the resistors where the spec voltage is printed on the PCB (helpful!!) And I do apologize for my ignorance!

POTY-- THANKS SO MUCH!!!

 L.P.

[longplates]

Poty-- I have to go to my mother's house to assist here with some daily health regimen activities...

I will return and post other DC and resistance readings including those from Q200L and V200 and V201,

when my mother is... all set... for today, bless her.

THANKS AGAIN

[longplates]

OK-- It's not 3 pm Eastern yet; so I have time for one more quick question--

Poty-- What do you make of the fact that just touching the positive meter probe to resistor 219R (as well as resistor 211R) made the silent, non-operating  right channel come in sounding perfect? Just like touching the meter probe to the attachment screw of TIP50? (both with the negative probe of the meter grounded to the "earth" terminal of the PCB... via the rear panel ground which is wired to the "earth" tab)

Could this indicate high AC ripple at 219R? ( just A Shot In The Dark)  (classic movie, that!)

OK, now I'm REALLY behind schedule.

Back this evening.

[poty]

I did indeed use a TIP50; bad choice, I guess

Why? It's OK.

I misquoted on the "Q100L and Q100R" You are correct, they are indeed Q100 and Q101 on the schematic, and Q101 was device I measured as having one leg with no voltage present. It was a hectic night... ;0)

Let me postpone to analyze LED problem. I hope it doesn't have any relation to the right channel silence.

The cathode of V202 to the collector of Q200R measures 221 ohms. The Q200R emitter to ground is 913 ohms.

OK.

HOWEVER, I measure only around 3VDC on the base of Q200R to ground.  On Q200L it is 6.2.

Then - time to check R215R, C205R, base of Q200R (connectivity and working order). The source of the 6.2V voltage is one point for both channels, so the only suspicious parts are those mentioned.
I'm busy now, so several questions I'll answer soon, but not now.

[longplates]

Poty-- Thanks again for your time and knowledge

[poty]

MY LED D100 is not functioning at all; I ... had to desolder it, pull it thru the PCB, and reconnect; I either toasted the LED or damaged a trace on the PCB because it appears to be connected but has no functionality.

Having multimeter you can easily check continuity between the LEDs legs and the places they are supposed to be connected (cathodes - to ground, anodes - to respective collectors of Q100 and Q101). If something is wrong you always can use a piece of wire to mend the connection.

on Q101 I have one leg that has no voltage present while the other legs have 8 volts DC, same as all three legs of Q100...

Do I understand correctly: you have 8V on all three legs of Q100? It seems very strange... The emitter point can show 8V, but the base readings should be (6.8/(10+6.)*8=3.2V then, collector - around 2.6V. So you should carefully check solder bridges around the Q100 and the transistor itself. The fact that on Q101 you do not have voltage on one leg can be related with the problem of Q100, but it can be related to other problems too (check if R107 is soldered right for example). The D100 can be tested with help of multimeter (Cornet 2 should be powered off!!!): in one direction the resistances should be low, in the other - high.

I do wish I knew what the DC on the tubes should be, roughly,  on each pin

I hope I'll not reveal any secret if I write the values of the pins (counted from the schematic, actual values could be in the margins of 10%):
V200, V201:
pin 1&6: 150V
pin 2&7: 0V
pin 3&8: 0,9V
pin 4&5: 6,2V
pin 9: 0V
V202:
pin 1&6: 328,5V
pin 2&7: 150V
pin 3&8: 155V
pin 4&5: 6,2V
pin 9: 0V

What do you make of the fact that just touching the positive meter probe to resistor 219R (as well as resistor 211R) made the silent, non-operating  right channel come in sounding perfect? Just like touching the meter probe to the attachment screw of TIP50? (both with the negative probe of the meter grounded to the "earth" terminal of the PCB... via the rear panel ground which is wired to the "earth" tab)

As you can see: left channel part of V202 has 141-158= -17V grid-cathode, right channel part - 155-180=-25V grid-cathode. While -17V on the left side is also much in my opinion, the -25V on the right side is definitely made the triode stop conducting. The tiny grid AC signal can't "open" the tube, so it is not "transfered" further to the output. The offset (-25V) is defined by constant current sink of Q200 which "controls" the grid-cathode voltage to such value that the current through the tube is 6mA ( (6.2V-0.7V)/910Ohm=6mA). You have only 3V on the base of the transistor which gives us (3-0,7)/910=2.5mA through the tube. Your multimeter has finite resistance which you "connect" between the ground line and the cathode (all the three point you have mentioned are connected to the cathode) and made another "way" of current flow. The current through the tube increases and allows the grid AC to be amplified. It was my initial thoughts. But... In the other thread you mentioned R107 ... The resistor is not connected in any way to the cathode, so I cannot explain the resurrection of the right channel by the initial theory. The only thought arrived to my head - some continuity problems which mend themself by applying force to the PCB (tiny crack on a trace or faulty soldered joint). In this case the right channel should go alive even if you touch the places by any isolated thing.

[hagtech]

Sounds like maybe the value of base resistor on the TIP50 is wrong?  I think CCS problem.  Can you post photo?  Often a problem is very easy to spot that way.  Perhaps the 470uF electrolytic on that CCS is installed backwards.  That would produce the symptoms you see.  It's the probe experiment that is bothering me.  If touching something made it operated, then perhaps a bad solder joint?

jh