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
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
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
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
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.
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.
Hi Papparazzi4646,
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
papparazzi said:
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
papparazzi said:
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 said:
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
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
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 said:
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.
papparazzi said:
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
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
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
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