Meshplate Help needed

[papparazzi]

Hi

Would somebody give me some help.

Im running My 300b amp with JeLabs/Waltons style single 6sn7gtb tube cascode driving Standard 300b chinese tube with 395 vdc
and 1k res self-bias through 0,22 uf oil cap -65vdc on grid
Driver section of 6SN7gtb runs 4,2 ma 190 vdc over it.

Ibought Fullmusic Meshplate tubes as direct replacement
Listening music I noticed Lower mids and upper bass was
attenuated quite much
Thanks if someone could give me advise what can cause this?
Mesh runs about 27 watts on plate. Is 6sn7gtb too weak to drive
Mesh?

Thanks for help

Papparazzi4646

[Ciscokid]

Hi Papparazzi4646,

I run the same amps with TJ meshes at 27 watts and they sound great! Mine have 375 on the plate, 62.5 on the cathode and 870 ohm cathode resistor.

When I first put in my TJs, I was running them a little to hot (33 watts) and they sounded fantastic. However, after emailing diysupply, they recommended running them between 25 and 28 watts for long life. So I backed my down to 27 watts and did not notice much, if any difference.

Don't know if this is a big deal or not, but I come up with about 25.6 watts with your numbers. Looks like you are right at the minimum ratings, you might try bumping yours up a bit to see if you get an improvement in sound.

What kind of output transformers are you using? Speakers?

Hope this helps,
Danny

[papparazzi]

Im using unknown manufacturer 2,5 k output trannies.
Speakers are 88db/watt Jordans . Ithought Meshplates are direct replacement for standard WE tubes if not over 28 watts dissipation.
Everything works fine if I use standard Shuguang 98b tubes even
with my Jordans have low sensitivity to handle 8-10 watts.

[papparazzi]

Do Meshplate have different grid capacitances etc.. than WE standard ?
Driver tube 6sn7gbt have 24k on plate 180 over tube and 24 k to ground Plate voltage 380 vdc 4,2 ma .
Enough to drive meshplate through 0,22 uf cap??? I don know

[Ciscokid]

Hi Papparazzi4646,

Originally posted by papparazzi
Do Meshplate have different grid capacitances etc.. than WE standard ?

Hmm, now your past me on this one. Perhaps others might know the answer.

I too have the 98B's and while they performed very well in my amps, the TJ's mids are much better to my ears. As far as bass is concerned, both tubes sounded excellent. However, I am runniing 97.5 db Altec Valencia 846B speakers and that could be why

Regards,
Danny

[Raj1]

Hi,

sounds like a silly question, but I think there are 2 differnt versions of the meshplates, with 2.5v and 5v filaments, perhaps they are the 2.5v version?

Thanks
Raja

[papparazzi]

Hi

No silly question at all. I checked tubes matching report it seems to be 5 volts ,there arent any marks in tube itself.

papparazzi

[Raj1]

Hi,

It was just a hunch, perhaps you were right though, perhaps they need a more gutsy driver to sound best......


Thanks
Raja

[tubemaster]

Originally posted by papparazzi
Im using unknown manufacturer 2,5 k output trannies.
Everything works fine if I use standard Shuguang 98b tubes

Hello,

in my experience the Full Music Mesh Plate tubes do have slightly less bass than the Shuguang tubes. On the other hand they excel in the highs with a very detailed and transparent sound.

It could be that in your circuit with your output transformers and speakers the Shuguangs sound better. Remember a single ended amplifier without negative feedback is a tuned living system and if you change one part the sound of the whole amp can change and you might have to retune it.

So if your setup sounds good with the Shuguangs stick with them - or try a different output transformer.

Best regards
Michael

[papparazzi]

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

Papparazz1