Premier 16SL with less output volumen on one channel

[phantombox]

Hi guys.
I have a Premier 16SL with output volume slightly lower on one channel. Is there a way to adjust this difference internally? I opened the unit and cannot find a single trimpot inside.
Also, I'm looking for a complete service manual for this preamp.

[admin]

There is no service manual for the 16SL that I am aware of. I don't think you can adjust the internal balance but I would ask, why is the volume not equal between the two channels. If there is a component failure, that should be addressed.

But at the end of the day, you can adjust the channel balance via the remote. So that is a work around I suppose.

[roberto]

Hola phantombox,

That difference in level is due to a one 6922tube. It is not necessary to change all 6 tubes. Having one brand new 6922, just change V1, if it is not, then change V2 and so until you find the culprit. The 6922 is a double triode and one half has lower output and it is bad. It will take some time and effort, but I assure you that you can fix it easily.

Happy listening!

[roberto]

For a shortest way to do it, the un-even numbers of the tubes belongs to the left channel and even number the right channel.

[phantombox]

I have 2 good tubes E88CC Siemens and another good one E88CC Philips, all NOS. I put then in the left channel sockets, and then in the right one and nothing changed. Then I put in the old tubes again at random and suddenly the other channel had lower output. The original tubes are CV2492, and are all bad except one. The originAL owner will have to get some new tubes, no doubt.
Admin mentioned that the balance can be adjusted via the remote... Can you tell me more about that?

[admin]

I have 2 good tubes E88CC Siemens and another good one E88CC Philips, all NOS. I put then in the left channel sockets, and then in the right one and nothing changed. Then I put in the old tubes again at random and suddenly the other channel had lower output. The original tubes are CV2492, and are all bad except one. The originAL owner will have to get some new tubes, no doubt.
Admin mentioned that the balance can be adjusted via the remote... Can you tell me more about that?

Do you not have balance controls on your remote?

It looks like this:

[phantombox]

The owner does have a remote. He took out the batteries and put it into a drawer, years ago, he said.
Today he brought me a bunch of CV2492 tubes, all used. I could find one that measures perfect an another that checks out ok.
But after trying any combination of tubes and slots, I come to the conclusion that the problem is not just a tube issue, because the L channel ALWAYS puts out less than the R channel.
So today I checked the components very close to the tube sockets, and 2x 10pF600V caps (C3 and C5) appear to have drifted out of specs.
I use a DVM that senses capacitors down to nF range, so 10pF should show 0.01nF, 510pF becomes 0.51nF.
However, I'm not exactly sure if this actually works...

[AnotherJohnson]

You probably know these things, but I’ll share them anyway.

1. You can’t get a legitimate capacitance reading across a cap that is installed because you’re measuring the cap in parallel with the rest of the circuit.

2. If the caps aren’t leaking, bubbled, or burned, they’re probably OK. They’re not likely to be electrolytics. Most likely to be plastic of some sort.

3. You know the tubes are twin triodes, so I’m sure you’re checking both sides.

Where’s Roberto when you need him

[roberto]

Hola Chicos, here I am...
You are just right AJ. Reading in circuit caps is not a good thing. Those small caps are for prevent a possible oscillation. You have to desolder one lead and do the measuring. We call those caps a bug killer or a flea killer.

You have to change the tubes one by one, and have a listen. It will take some time, but it is the only way to find the culprit tube, or with an oscilloscope. You can measure the plate output of each tube. Just apply 1KHz sine wave tone to the R & L input of any aux, cd or tuner, tape ,etc, on both channels and you can see the wave length with less output when you do the measurements. Remember that on tubes there are lethal voltages there.

99% is due to one side of the tube with less output. The tubes do not share channels. Every tube belongs to the same channel. Three double tubes per channel.

[phantombox]

Of cause I lifted one side of the 10pF caps from the circuit. I learned this in primary school, döö. No offense taken, no offense intended...
I also know that these are twin triodes with lethal voltages...
One of the 510pF caps has its outer cover wrapping peeling of. I think its due to age, otherwise it looks ok.

[phantombox]

Here I am again. It took a while to get a new set of 6922. Also, I went to Germany for the holidays. Family gathering.
With all 6 tubes replaced with new 6922EH Russian made Electro Harmonics, the problem is still the same. So it must be failure in one component, but which one? I noticed that on the only schematic that is available for the Premier 16SL, the components are not identified with R1 or C2 but only with values.
One tube is shining much brighter than the others, but I guess this is due to the production process, when the heater gets a fraction of millimeter closer to the top than the others. It is not the heater voltage.

[admin]

If it's not the tubes, then this is going to get a lot harder to diagnose. I'm not really familiar with the 16LS inner workings. We have the schematic in our database but I believe it is incomplete (1 sheet out of 3). Do you have the full schematic or is it the one we have here at CJO?

Regardless, I would start by checking the volume control circuits. Maybe you can do output testing right at the volume circuit output to see if the volume discrepancy is pre or post volume control? If you have a good technician, I would probably go that route due to safety concerns.

As for the tube brightness, that can vary from tube to tube. If you think it is related to the socket position, you can just switch it with another tube position and see if the extra glow is tube or tube position dependent.

[AnotherJohnson]

Are there any subtle burn marks on any resistors?

How big is the difference (as measured by your balance correction)?

Are you sure you don’t have a defective interconnect or a problem in another component? Is it present with all sources? Phono cartridges and phono set up are notorious for introducing these sorts of issues.

Are you sure that your twin triodes are all balanced? New ones may not be better than old ones unless you’ve tested them.

[admin]

AJ makes some really good points here.

I would change RCA cables (input and output), change L/R channels. Try all inputs to make sure it is not something related to the input.

[phantombox]

Thank for your replies.
I checked the preamp with 6922 tubes in every position, all different types of RCA cables, and switched L/R channels. I also tried each and every input connector with a tone generator, CD, MP3 or touching with my bare fingers. "R" channel always has a noticeable higher output than "L" channel.

None of the resistors shows any sign of burning.
About the exact difference between output channels, I cannot say (I have no way of measuring dB at this time). But it is noticeable right away.
That leaves the volume control... I will check on this tomorrow.

[AnotherJohnson]

From the blurb on CJ’s web site.
**************
Input selection and level adjustment are handled by an array of relays operating under microprocessor control. Level and balance can be adjusted in 100 steps of approximately .7 dB per step, with levels being set by precision, low noise metal foil resistors. All level setting and source selection functions can be controlled by the hand-held wireless remote control.
*************
Is there no level display for L and R so that you can estimate? It says .7dB per click. Can you balance it with the balance control?