Hi,
I have just owned an secondhand Mastersound Compact 300b but the seller told that the renewal time for power tubes has come .
So i havent used 300b tubes before and have limited funds for them .
Originally stock tubes are EH 300b gold pin .
Here are the options for me ;
- Same Stock Tubes
-Genalex Px300b
-TJ Full music 300b
Bias is set to 15V
Thank you
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I have just owned an secondhand Mastersound Compact 300b but the seller told that the renewal time for power tubes has come .
So i havent used 300b tubes before and have limited funds for them .
Originally stock tubes are EH 300b gold pin .
Here are the options for me ;
- Same Stock Tubes
-Genalex Px300b
-TJ Full music 300b
Bias is set to 15V
Thank you
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190volts , 180mA
Before jumping to conclusions first check the anode voltage and cathode voltage + cathode resistor to see the tube current and grid voltage.Or bias voltage and cathode current in case of fix bias.
Compare with the tube data, if it's realy low change the tube.
Mona
EH 300B Gold: The quality is still unpredictable. I thought they had got it right about 2012 year, but even a pair bought then both failed, at less than 1000 hours. They sounded OK, but the cost/hour is not good enough.
Failure mode was the same as usual, with 300Bs made in this factory (XPO-PUL, Sararatov): the filament disconnects at one end.
Genalex Gold Lion PX300B is also made in the same XPO-PUL factory, and looks like an EH300B. I see no reason to pay more for for the labelling, and the Gold Lion's gold plated pins mean that you MUST use sockets with gold-plated contacts.
I would not be surprised if they failed just as badly. It's just an exercise in "precious brand-name labelling" from what I can see, mixing up Marconi-Osram Valve branding with a Western Electric design. Bizarre.
These failures have affected all models of DHTs from Saratov, Sovtek as well as EH. My first pair of Sovtek 300Bs (1998 year): one failed right away, another is still going, for testing and occasional use.
Beware: the broken filament could end up shorting to A or G (though it never has with mine). Consequent damage might end up costing the price of an OT, among other things.
You can search Google for:
"(EH OR Sovtek) 300B filament breakage"
and get enough hits to know what's happening. George (Tubelab) has reported on breaking a Sovtek open, to analyse the failure.
The old Svetlana SV300B breaks the same way, BTW.
It wouldn't be so bad, if the EH Gold were cheaper, but they were nearly half the cost of EML300Bs in 2015, when my last set failed.
So EML was the choice I made, after discussions with Paul N., here.
The EH is not in the same street as EML, for build quality, and I have more confidence in EML to be better value, once lifetime is taken into account.
The sound of EML 300B is superb, and I don't think the EH would match it (beware that I am not directly comparing, though!).
They are also the first DHTs I have owned which do not make an audible ringing (in the speakers), when you stop loud music suddenly - and I find this very telling.
Failure mode was the same as usual, with 300Bs made in this factory (XPO-PUL, Sararatov): the filament disconnects at one end.
Genalex Gold Lion PX300B is also made in the same XPO-PUL factory, and looks like an EH300B. I see no reason to pay more for for the labelling, and the Gold Lion's gold plated pins mean that you MUST use sockets with gold-plated contacts.
I would not be surprised if they failed just as badly. It's just an exercise in "precious brand-name labelling" from what I can see, mixing up Marconi-Osram Valve branding with a Western Electric design. Bizarre.
These failures have affected all models of DHTs from Saratov, Sovtek as well as EH. My first pair of Sovtek 300Bs (1998 year): one failed right away, another is still going, for testing and occasional use.
Beware: the broken filament could end up shorting to A or G (though it never has with mine). Consequent damage might end up costing the price of an OT, among other things.
You can search Google for:
"(EH OR Sovtek) 300B filament breakage"
and get enough hits to know what's happening. George (Tubelab) has reported on breaking a Sovtek open, to analyse the failure.
The old Svetlana SV300B breaks the same way, BTW.
It wouldn't be so bad, if the EH Gold were cheaper, but they were nearly half the cost of EML300Bs in 2015, when my last set failed.
So EML was the choice I made, after discussions with Paul N., here.
The EH is not in the same street as EML, for build quality, and I have more confidence in EML to be better value, once lifetime is taken into account.
The sound of EML 300B is superb, and I don't think the EH would match it (beware that I am not directly comparing, though!).
They are also the first DHTs I have owned which do not make an audible ringing (in the speakers), when you stop loud music suddenly - and I find this very telling.
Hi Rod, I have installed them for a friend of mine on an amplifier that I built nearly 20 years ago! In the meantime that amp has been running with the Golden Dragon 4-300BLX that was a special version with titanium plate. That was a really good 300B, in my opinion better than the original but was only produced for few years. The amp has used 2 pairs over all these years and has been always in use.
The EML is very good. Honestly I have not found any noticeable difference in sound those few times I have listened to it. Next step will probably be the revision of the PSU to get more power. Aiming to get some 14-15W with 42W plate dissipation which for the XLS should ensure the same service life of normal 300B's running at 28-30W.....
Not exactly cheap, and with thoriated tungsten cathodes, but something special in 300B's is the Elrog.
Manufactured to very high quality standards in Germany.
I would not be surprised when they last three times as long as "normal" 300B's, so maybe the cost/life expectancy rate is not bad at all.
Manufactured to very high quality standards in Germany.
I would not be surprised when they last three times as long as "normal" 300B's, so maybe the cost/life expectancy rate is not bad at all.
I am currently enjoying the EML 320B-XLS tubes in my SE amp. I really can't imagine a better tube: they sound outstanding. I have a pair of JJ 300Bs I have had for a decade. They still sound good and after all sorts of testing anomalies that resulted in massive over voltage and over current they still bias up perfectly.
I have used EH, Valve Art, JJ, and Svetlana. I also had a pair of Full Music with perforated plates.
One of the Full Music started drawing excessive grid current.
I never believed that they would stand up to full ratings, but i did not use them that way.
One Svetlana's I had gave up, because the DC on the filaments caused the filament to touch the grid (it electromagnetically was attracted to the closest side of the plate).
I think this can be a problem for any 300B if it does not space the filament exactly in the middle of the 2 sides of the plate (and if the filament is not centered exactly in the grid).
These dimensions are critical, and if you overheat any tube, the elements may warp, compounding the problem.
Valve Arts, JJs, and EH are still working.
It may be of interest, the JJs are the only one that strings the filament in series.
All the other 300Bs tap the filament in the center, and parallel the outside ends of the filaments.
All of my amplifiers that used 300Bs were self biased, except for a pair that was battery biased. They were all used very conservatively within their voltage, current, and plate watt ratings.
One of the Full Music started drawing excessive grid current.
I never believed that they would stand up to full ratings, but i did not use them that way.
One Svetlana's I had gave up, because the DC on the filaments caused the filament to touch the grid (it electromagnetically was attracted to the closest side of the plate).
I think this can be a problem for any 300B if it does not space the filament exactly in the middle of the 2 sides of the plate (and if the filament is not centered exactly in the grid).
These dimensions are critical, and if you overheat any tube, the elements may warp, compounding the problem.
Valve Arts, JJs, and EH are still working.
It may be of interest, the JJs are the only one that strings the filament in series.
All the other 300Bs tap the filament in the center, and parallel the outside ends of the filaments.
All of my amplifiers that used 300Bs were self biased, except for a pair that was battery biased. They were all used very conservatively within their voltage, current, and plate watt ratings.
Only pic i have found is attached , actually i dont undertand too much about these valves .
İ am seeking for the best sound , dealer showed me the bias settings and the company mastersound set them to 15V , there is only bias for powers . I guess EH are set to 15V
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Filament to Grid Bias for a 300B would more likely be 50 to 80 or 90V.
15V bias would have to have a Very Low B+, and there would be very low power out.
Even into an infinite load, 15V times u, 15 x 3.85 = 57.75V peak swing.
Into a 2.5k Ohm load (too low for low distortion), that would be less than 0.7 Watts (actually it would be even less, because you do not get u for gain, you get u x (RL/(RL + rp)).
with rp at 800 Ohms, you get gain of u x (2500/(2500 + 800)) = 2.92.
2.92 x 15 = only 44V peak swing; 0.4Watts in round numbers.
A higher RL impedance will get more peak swing, but not more watts.
5000 Ohm RL would get 49.8V peak swing, and 0.25Watts.
15V bias would have to have a Very Low B+, and there would be very low power out.
Even into an infinite load, 15V times u, 15 x 3.85 = 57.75V peak swing.
Into a 2.5k Ohm load (too low for low distortion), that would be less than 0.7 Watts (actually it would be even less, because you do not get u for gain, you get u x (RL/(RL + rp)).
with rp at 800 Ohms, you get gain of u x (2500/(2500 + 800)) = 2.92.
2.92 x 15 = only 44V peak swing; 0.4Watts in round numbers.
A higher RL impedance will get more peak swing, but not more watts.
5000 Ohm RL would get 49.8V peak swing, and 0.25Watts.
Unless someone has this amp a pops in to tell you how to do it properly it is better if you don't guess and ask Mastersound directly. 15V bias doesn't make any sense for a 300B.
I would think that your amp has a mixed bias or self bias made with two resistors in series and only read the voltage across one (200-220 ohm I would guess for typical 300B operation to get 15V).
However, as Mastersound is still in the business, and from what I can see also doing well, it is better if you ask them directly by e-mail.
cihansatar,
The Mastersound instructions for the Mastersound 300B amplifier you emailed to me mentions setting bias to 15V, by adjusting the potentiometers that are in front of the 845 tubes.
Does your amp have 845 tubes?
If it has both 845 and 300B tubes, I am guessing that the 300B tubes are self biased,
and the 845 tubes are mixed biased.
Any way, it sounds like whatever tube is being biased, it is Mixed Bias, as was previously mentioned by someone else in this thread (part of the voltage coming from (adjustable) fixed bias, and part of the voltage coming from self bias).
The Mastersound instructions for the Mastersound 300B amplifier you emailed to me mentions setting bias to 15V, by adjusting the potentiometers that are in front of the 845 tubes.
Does your amp have 845 tubes?
If it has both 845 and 300B tubes, I am guessing that the 300B tubes are self biased,
and the 845 tubes are mixed biased.
Any way, it sounds like whatever tube is being biased, it is Mixed Bias, as was previously mentioned by someone else in this thread (part of the voltage coming from (adjustable) fixed bias, and part of the voltage coming from self bias).
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