Question about adjusting the balance

@carlsbad2

So the question is, how is your tube bias set? I prefer manual tube bias adjustment so I can match any 2 tubes. Theoretically, an auto bias circuit should do this also, but if you’re getting different voltages, then maybe it isn’t.

the bias for my amp is set manually, but I can only bias the left bank of six output tubes and then the right bank of six output tubes (and I have them within a couple of mA, (I believe the last time I checked on bank was about 268 and the other was about 270) and I cannot adjust the bias of the individual tubes.

However, when I was referring to checking AC volts at the speaker terminals (per the instructions on the test CD) and I said the voltage discrepancy was following the tubes in the left and right balanced input sockets (when I switched them back and forth from left to right) I was referring to the preamp. And I assume you swere referring to the amp? I don’t have much of a handle on the circuit topology or circuit functions of components, so does a preamp need to auto bias its tubes? Except for volume and the left and right "input levels" (which was what I was using to adjust for the voltage discrepancy at my speaker terminals) there is NO adjustments whatsoever for bias on my preamp (Cary SLP05 and the tubes are 6SN7s).

But my original question was this:

I put a 20Hz to 20 kHz pink noise in and put my sound level meter where my head is and used the "input level" knobs to get the meter to show that the speakers were at the same level. Then I put in the 315 Hz test tone (which is the one that the instructions said to measure VAC at the terminals with) and using the sound level meter, the settings I achieved with the pink noise tone to adjust the balance with were way off.

I can understand that the meter would show different dbs for the different tones, but I would have thought that once it was balanced with one tone it would be still balanced with the other tone.

And I was just wondering why that would be. That’s all.

I never thought of thinking deeper on it. Not a problem if you want to.

Thanks, @ghdprentice  , I think I am probably getting ready not to worry about it anymore.  I was just wondering if there was an easy explanation to why I could use the SLM to balance the out put of each speaker with one test tone, but then with the 315 kHz tone to have the speakers no longer reading equal on the sound level meter.

That was all.

So what you data is telling you, as you described it above.  Is that you have a probem with either one of your highs or one of your mids.  My first thought was that it would likely be a driver or a crossover component in your speakers.  

Ahhhh, thanks, @carlsbad2  , that would make sense. 

but you said the voltage discrepancies followed the tubes.  Does the discrepancy at different frequencies follow the tubes?

I didn't actually go that far.  I do have a couple of pairs of 6sn7s that meausre almost dead nuts even, so I could spend some time and what the sound level meter said with them in there at the two different frequencies.

I know my question was probably confusing, although I tyed to spell it out as best I could, but what I did first was to use the AC vm to adjust the "input level" knobs until I was reading equal AC volts at the speaker terminals (with the 315 Hz tone).  It was then that I had the bright idea to see what the actual speaker output at my listening position, from each spaker, was.

Thanks.

@carlsbad2 , sincere thanks for your input. I did not play with different input tubes, but I do actually have a HT center channl version of the 805 Matrix that I have not used for years, so, even though I figured it was a fool’s errand, and therefore I was the right man for the job, I did play musical tweeters (actually with both speakers). To not make a short story long, I am pretty sure my wacky readings with 315 Hz were due to operator error.

I discovered that the readings with 315 kHz would change, for example, depending on where I was standing when I was trying to read the meter, and even depending upon where my head was when I was trying to read the meter. I won’t go on & on about how I tryed and failed to establish a reference point for myself and the meter at 315 Hz, but I did discover that the meter was way more stable (less subject to fluctuations due to my own positioning) at 20Hz to 20kHz and with the "input level" knob adjusted to compensate for the weaker preamp balanced input tube AC voltage at the speaker terminal, using pretty stable readings with the 20Hz to 20 kHz tone, the speakers had basically  the same readings from my listening position.  Meaning, that with the "input level" knob adjusted down (on the side I have the stronger tube on) to achieve equal AC voltage at the speaker terminals of both speakers, I also got nearly equal readings with the sound level meter.

So, much to do about nothing, but thank you for your input.