Vinyl experts: measuring matched tubes with PC?

[doctorcilantro]

I was wondering if anyone has an opinion on the following:

Measuring input into my PC and using Wavelab, I see a 8db
difference in average RMS when monitoring the moving coil of my Sunfire pre.
The (3) EH 6922s I just got are matched. Should I be seeing a more uniform
average RMS (not talking about the peaks)? I have also looked at the recording
of a 1kHz test tone played back from vinyl and saw a 2db difference; I don't
think this is due to the cartridge alignment/azimuth but as you can see this is another possible variable. The Hi-Fi News Analog Test Record has an azimuth test; you listen in mono and adjust cart until the signal sound matched through speakers/headphones, but how would know if the phono stage was imbalanced with regard to gain on each channel. Is the attribute good or bad for a phono stage simply a question of SNR, or with tubes is there always going to be an issue here due to how closely matched the tubes are?

So is this even feasible? I moved the 3 tubes around and at one point the difference was smaller but still substantial. Would matched tube show a matched RMS "at rest"? Assuming the phono
stage is working properly which would be hard for me to verify, isn't this why we match tubes, to match gain?

I may try take the output from the tonearm's RCA box direct to PC sans phono stage to see what's going on with the cartridge, I could boost the signal in Wavelab and would I expect to see the left and right channel with the same balance.

Or should I be testing average RMS by using unmodulated grooves on my test record.

Probably getting way too anal about this, but the original imbalance was substantial.

dc

[jcmusic]

If the tubes are new you have to wait until they are broken in, there is a degrading in tubes until they are broken in and settle down. this could be what you are expirencing.

Jay

[johnyholiday]

what was it doing before the 3 EH 6922 firercrackers, matched with some of these sellers isn't realy a match

[doctorcilantro]

I was using the MM stage. When I switch off the 6922 (which piggy-back on the MM 12AX7) I can see closely matched average RMS levels. The (2) 12AX7s are from Upscale, but I also trust Jim McShane who sold me the EH 6922s. I moved some tubes around and the levels are closer but now noisier.

When a manufacturer states "noise better than -78db" for a phono stage, can you simply observe something close to that with no input singal? IThe Grado Reference should not be introducing noise to the signal, not this much, something doesn't feel right. I'm going to roll in some various sets of 6922 tonight.

Jon