Meshplate Help needed

[tubemaster]

Originally posted by papparazzi
Well I still suppose I have Impedance matching problem with
0,22 cap and 220k grid res to ground???

Papparazz1

Hello,

no, your operating points are perfectly within range.

The low frequency -3dB cutoff point as determind by the coupling cap, grid resistor and output resistance of the driver (assuming the load resistance of the last 6SN7 is 23.5K like in the JE Labs circuit) is at about 3.2 Hz which means that at 20 Hz the attenuation is -0.1dB which is fair enough.

The high frequency -3dB cutoff point - assuming the 300B's Miller capacitance is about 80 pF as indicated in the Western Electric Datasheet - is at approx. 330 KHz which is perfect as well.

If in doubt you could measure the frequency response but the actual dropoff is probably determind by the output transformer and not the driving stage.

Best regards
Michael

[papparazzi]

Hi

Thanks for advise Tubeman . As electrically selftaught i dont understand
output tranny role on this case ?? Trannys lackin low end or not
if i have about same specs tubes ? How can i know which trannies are suitable
I have tried also Krone w32b tubes, they works fine but need ofcourse more voltage and current to get their best. Dont have this kinda trouble
What about coupling cap 100uf for cathode, is value enough I have second pair 100uf Elna should i double value ?

Papparazzi

[papparazzi]

Sorry ! Not tubeman but Tubemaster
More : so is Global feedback through about 4,7k res solution? Or buy new trannies think higher value would be better for impedance ?
Mesh does have really good sound i can hear it allready, if i only get response right

Papparazz1

[tubemaster]

Originally posted by papparazzi

What about coupling cap 100uf for cathode, is value enough I have second pair 100uf Elna should i double value ?

Hello,

no, 100µF is perfect. It gives a -3dB rolloff point at about 4 Hz.

Make sure you have the 47µF cathode cap on the second 6SN7GT in place and that it has a voltage rating above 100V. This gives a corner frequency of about 2.4 Hz btw.

Originally posted by papparazzi
More : so is Global feedback through about 4,7k res solution?

No! Feedback is a problem - it is never a solution!

The easiest solution is to stick with the Shuguang tubes if your amp sounds good with them. Besides if it also sounds good with the Krones I would be suspicious that something may be wrong with the Full Music or that they just don't happen to work in your system. Before making any changes to the amp you should measure the frequency response with the different 300Bs.

If you don't have access to adequate measuring equipment you can use this software which is available as a free demo: www.audiotester.de

Best regards
Michael

[papparazzi]

Hi

Why is commondly used 220 uf in cathode coupling ,if 100 uf is enough?.
I havent found much info ,or users experience using Meshplates
Only basic curves and typical operaring point.Mesh curves seems
different than typical WE tube .At the moment I am running them
with 400 vdc 63ma Looking at curves it doesnt seem good operating point at all?
Normal 6sn7 doesnt seem to be good ,dynamics are limited A/B seems to be better. I also run 6sn7 with two tubes per channel ,I suppose stress tubes less?

Best Regards
Papparazzi