[david62]

My Clarinet is weaker in the right channel where I need to keep the balance control in the 9:00 position to have the sound balanced.It is the same for my three input sources.I have tried different 12au7's which doesn't help.I have lived with this for a long while.When I do put it on the bench,what other than voltages and bad solder joints should I check for?The only test equipment that I have is a volt meter.Thanks,
David

[poty]

First - check the gear following the Clarinet (switching interconnects from one side for example)!
If you have already tried different 12AU7s, then there are 3 places of interest: power supply, input side and output side.
The power system can be checked by measuring the voltages. If the voltages in both channels are identical - then the power supply problem is out of the scope (and I'm in doubt the problem is really here).
The input side - my favorite guess to now - has several weak points:
- input selector (the common lead going to the balance pot can have cold joint or half-broken trace) - this can be checked by your DVM in ohmmeter mode (turn the device OFF!);
- bad balance pot (you can short out both of its "sides" to check);
- bad volume pot (put a jump wire between the sweepers of the volume pot and listen to the equality of the volume);
- bad solder joint for C302, R302, R303 or 2-or-7 pin of the tube socket for V300 (visual inspection and resistance measuring).
At the output side you should sheck a bad solder joint for R311, C303, R312, you can also try the second RCA outputs.
If you can easy spot the circuit's elements on the PCB board you can put a jumper wire between the corresponding left and right channels points beginning from the output and listen the channels volume. For example:
- directly at the center pins of the output RCAs;
- between the R311 leads (of left and right channels) or between 3 and 8 pins of V301;
- between the R303 leads (of left and right channels) or between 2 and 7 pins of V300;
- between sweepers of R301;
- between sweepers of R300...
Do this with great cautions and ONLY when the power of the device is off! Ensure the wire is connected good and not touch anything nearby before switching the device on!
The problem will lie between the point where the volume is equal and the first point where the volume differs.

[david62]

Thanks fro the reply Poty.I will first try switching the output interconnects as well as switching the outputs.

[david62]

When I built the Clarinet,I connected large Russian Teflons in parallel with C303L and C303R.I'm not sure if the Teflons could be a factor.

[poty]

When done properly (soldered to the right points and not touching anything else on the PCB by their metal parts) - the capacitors should not be a factor.

[hagtech]

One thought - the balance pot uses a linear taper, not audio (logarithmic).

jh

[david62]

 The 12au7 filaments seem to glow a bit dim.Which points do I measure filament voltages for the 12au7's?The bipolar LED changes color as it should.I think that the mistake that I made building the Clarinet is that I used separate input and output RCA plugs on the back panel.It is very limited,difficult access to solder the short silver wires from the PC board to the RCA's and I think that the solder joints are good,but it is tough to be sure.Also having the RCA's connected to the board with short wires means that I cant remove and look at the top side of the PC board.Hopefully I will figure this out.
Dave

[poty]

The easiest way to measure the heating voltage is across C304, C305, C306. Or it can be measured between 4 and 9 pins of either tube. The voltage should influence both channels as soon as both tubes serves every channel (so the left channel uses half of V300 and half of V301 and the right channel does the same).
Why do you need to look at the top side? All points of interest are accessible from the bottom.

[david62]

I can't see the solder joints of the balance or volume pots or the selector switch solder joints.I was very careful during the build and lighyly scraped all of the leads and PC board trace pads.I inspected the joints with under magnification.It would be nice to inspect them now that I am having a problem.Some of the voltages that I measured are low,but not that far off.R314L is 270 v,R314R is 272,R107 is 364V,R311L is 123V,R311R is 127V, The heater voltage is 5.92 V.I am using Mundorf silver in oli caps bypassed with Russian Teflons for C303L and 303R,and 301 L and 301 R.I checked around with a ohm meter and did not find and high resistance pathways in the input or output.I did notice that I have the Mundorf silver in oil caps in one direction on the left channel and the opposite direction on the Rt.channel,but I believe that they are not polorized so I don't think that it would make a difference.

[poty]

The voltages seems not very different.
Why you do not want to use "jumper test" to find the place to check first? If you were able to measure the high voltages - then you can "jumper" the abovementioned places (with double precautions) on powered on device. For example, it is easy to connect a wire between the C302s (left and right). If you have the equal volume in the two channels after that - the problem is in the volume or balance pots or with input selector. If not - try to interconnect the C303s and check again. Then you'll have a "big picture" which you can made more detailed after.

[david62]

 So,if I want to eliminate the volume pot and the selector switch,I would jump the C302 's directly to input RCA center pins? That would have the volume at full for both channels?The C303's jumped to the center pins of output RCAs would eliminate bad PC board traces in the output?How about my having the polarity of the Mundorf Supreme Silver In Oil caps dirrerent in Rt.and L channels?Thank you for your help.
David

[poty]

So,if I want to eliminate the volume pot and the selector switch,I would jump the C302 's directly to input RCA center pins? That would have the volume at full for both channels?

While you can do this way too I wrote about different thing. Jumping C302's directly to input RCAs needs 2 jumpers and is problematic, because you will not be able to control volume. I doubt you can listen to the differences at full volume.
I wrote about using only one jumper and connect C302L to C302R. In this case you will present the same signal for the rest of the circuit. If the problem is before the point (of jumping) - you will have the same volume level at both outputs. If the problem is after the point - the difference will stay.

The C303's jumped to the center pins of output RCAs would eliminate bad PC board traces in the output?

The same thoughts are good for this jumping too. While at this point with your method you save the possibility to control volume level (because you are not bypassing the volume control) there is one danger: C303s prevents rather big DC to appear in the output. You should do this ONLY with the "output sides" of the C303s!

How about my having the polarity of the Mundorf Supreme Silver In Oil caps dirrerent in Rt.and L channels?

The polarity does not matter, at least for such degree.

[david62]

Thanks for clearing up the jumping 302L and 302R to have the same signal in L and R. I would place the jumper on the side of the caps connected to the center of the volume pot?
David

[poty]

It is really does not matter and the only difference is the number of parts which will be eliminated in the input side. If you put the jumper on the side to the volume pot - the capacitors will be in "working circuits", otherwise - in "blocked circuits".

[david62]

I just put the Clarinet back on the bench,but can't work on it until later today or this evening.The C302 L and R are jumpers,so it will be very easy for me to connect them together. My balance control works in the opposite direction.the left channel is the stronger channel,so I have to turn the balance control to the left to decrease the left channel.With a ohm meter and the leads of the C303 caps,I know that the outputs are connected to the proper L and Rt. RCA's.Could this balance control issue be the problem?

[poty]

Yes and no. You should check the connection of the pots, because there may be just miswiring.

[david62]

How could I have mis-wired the pots since the pins on the stock pots plugged into the drilled holes in the PC board?Thanks,
Dave

[poty]

How could I have mis-wired the pots since the pins on the stock pots plugged into the drilled holes in the PC board?Thanks,
Dave

Well, it was only my guess. You described wired (not PCB mounted) RCAs and I decided that you have the same connections for pots.
It would be better if you post some pictures of insides - otherwise it is difficult to understand what did you make. The PCB mounted pots (if you bought the right parts for them) cannot be mis-wired, so it (the problem) must be somewhere before them. The only things before them are RCAs. I'd check their connections (with DVM) to the right traces/parts on the PCB.

[david62]

I checked The output RCA's via the C303 cap leads and they are wired correctly as far as right and left goes,but I will check them again.I placed the jumper between the C302 positions and will try it this evening after company leaves and report the results.I wish that I understood how my balance pot works opposite where it decreases the channel when turned toward that channel.
Dave

[poty]

I checked The output RCA's via the C303 cap leads and they are wired correctly as far as right and left goes,but I will check them again.

You continuously mention С303 wirings and the output RCAs. But why do you think the mistake is not on the input side? As far as I understand - the input RCAs are also connected by wires?