TJ Full Music 300B/n Data?

[Alex Kitic]

The EH300B box states I.e. 55mA, and on the bottom it states that it was measured at 300V and -61V. This is basically the same data you have, and should mean that those tubes are good and normal.

The EH300B is a solid anode tube, with 40W dissipation ratings. The TJ 300B "mesh" plate tubes are 40W types too: the anode does have holes, but it is also larger than the solid type on the EH tubes. Anyway, it is in vacuum, so it does only radiate heat and not behave like a heat-sink cooled by air movement.

That said, I guess 35W is a nice dissipation for 300B types: 400V and 85mA, or 350V and 100mA, to give a few examples. The rating on the cartons and boxes is more like "matching".

[Mike H]

There you are then, I was torkin' rowlocks


I must have been thinking of posts on an American forum I saw a while ago, about certain 300B's not being able to take the full 40W.....

[Greg]

There you are then, I was torkin' rowlocks


I must have been thinking of posts on an American forum I saw a while ago, about certain 300B's not being able to take the full 40W.....

You are right Mike and your memory is good. I explored getting 300B mesh plates for my amp and in email with the German valve supplier I was specifically told that mesh plates are not as robust as solid plates and if run at the standard (or close to) Max dissipation of 40W, their life will be considerably reduced. The recommendation was not to exceed 21W. Even on a solid plate, 40W is harsh and my EH300B gold grids had plate glow as a result. I reduced dissipation to 30W.

[Dave the bass]

It's a new game... '300B Plate dissipation Wattage Roulette'. Pick a number, any number

I don't want to kill 'em (much). Ha!

Ta Alex, MikeH, + Greg, yeah, I guessed the OP at the Measured Performance was for matching purposes but I still haven't seen an Data Sheet from TJ stating that ->

The TJ 300B "mesh" plate tubes are 40W types too:

At the moment it seems like its just 'bloke down the pub says they're 40W'ers!' so thats what they are!!!

Did you find that info specifically for the Hole-y TJ's? Any links? Cos thats what I've been looking for, max parameter values for these Tubes but there doesn't seem to be any data sheets for these variations of the 300B, hence the thread.

Whereas the KR's have a measured performance + a data sheet (though still excluding vital data such as inside leg measurement, political persuasion and an invite to tea with their Great Aunt Agatha) giving you a reasonable chance of success.

Funny ol' game

DTB

[Greg]

At the time I was discussing with http://www.jacmusic.com/html/order/jacm ... celist.pdf

Scroll down to page four and under TJ Full Music they cryptically state alongside the 300B, 'Can NOT run in standard amplifiers'. They appear to be selling off their TJ stock, but it might be worth sending them an email.

[Mike H]

Even on a solid plate, 40W is harsh

IIRC this was the exact problem the Americans were having, the posters were expecting their 300B's to do 40W, but kept failing, you can imagine the expense incurred in some cases. This was followed by a comparison of brands, which will do 40W. Someone may have suggested "why don't you turn it down a bit", but no the O.P.'s were still hung-up on this 40W

[Mike H]

PS: the Western Electric data says 36W "Maximum ratings"

It's possible that there was some other brand copy made that could indeed do 40W, and then suddenly all 300B's should do 40W. But I'm just guessing.

[Mike H]

PPS: going by the WE datasheet then, looks like 30W as a safe maximum.

For mesh plates, say halve it to 15W.

We're back where we were then

[IslandPink]

I notice the EML 300B and EML 300B Mesh are respectively 40W and 28W Maximum dissipation. That's more in line with what I guessed for the derating . They have a lot of operating point suggestions for the standard 300B, from 21W up to 33W , with 36W options given with provisos on lifetime . On the Mesh-plates they recommend 22W as a safe long-term dissipation, in the text blurb at the top . That suggests about 5.5W output .

This is a 30% derating from solid plates, which is what I would have guessed if you asked me.
Where is the figure of 50% derating for the TJ's coming from ?

Edit : I see the 15W comment was from Dave's original post . This looks like the 'test condition' to check transconductance, not the recommended operating point .

[Alex Kitic]

Does anyone actually have first person experience with this issue? It seems to me that we are all speculating.

I am by no means a 300B tube expert, at least when it comes to hands-on experience. Thanks to the generosity of a DIY friend, I have just received some 300B tubes and plan to finalize the RH300B amplifier project. My initial intention was running the tubes at approximately 36W dissipation, but due to currently available transformers, I will probably do the initial breadboard testing at 28-30W.

To me, maximum dissipation is exceeded when red spots start forming on the anode. For instance, EL38 have been reported red-spotting even before 25W, but I am currently playing with a pair in my RH Universal at 28-29W dissipation without any stress appearing on the anodes (I can post pictures taken in the dark). If 300B tubes really cannot handle the expected dissipation, I will post my findings.

JAC music seems to be very unsympathetic towards Chinese 300B tubes in general. Last time I checked, only Chech made tubes seemed to be fair and acceptable?! I have no direct experience, but soon will have and post some findings.

If the 300B tubes are not capable of 35W dissipation on the long run, it is disputable whether they are worth the fuss, compared, for instance, with 307A (in my RH307A), particularly if the latter can be run at up to 30W dissipation, like some claim. At 15W dissipation, the 307A is already capable of at least 8W output power, in pentode mode, of course.

[Greg]

Alex, please read or reread my post above. Yes, in general 300B terms I am not speculating but telling you what I found. Certain modern production 300B's do not tolerate (at least, not for long) dissipation at 36-40W. By expressing 'plate glow' in my previous post I was of course referring to (in your terminology) red spots forming on the anode.

The problem with modern equivalent valve production is the tendency to rely on original performance specs, in this case based on Western Electric 300B. It is clear that many subsequent copies of the WE 300B do not perform to the same standard and therefore compromises have to be made to ensure valve life longevity. This is what I have done. One could of course argue that in consequence, my EH300B Goldgrids are not true 300B's which rather returns to the points being raised by DTB in his original post.

In terms of 'mesh-plate' designs, all I've done is pass on the advise I have received, with a link on how DTB could explore this further if he wishes. If TJ Full Music do not publish a spec sheet for their 300B, what else is to be done other than rely on the knowledgable advise of others, including in this case, a respected supplier of audio valves?

[Dave the bass]

Ta for al the replies and the references everyone.

Yeah, just to back-track the 15W figure came from the OP the TJ's were tested at and their 'measured performance' checked + noted on the little card supplied with the valve. I'll use 22W as a max anode disp for now when using the TJ's on this project.

DTB

[Mike H]

Seems reasonable!

EDIT: BTW on the American topic they also had trouble getting exact inforamtion. Case of 'try it and see', unfortunately depending on brand some 300B's can be expensive guinea pigs.

[thomas]

Seems reasonable!

That was the umm 'scientific basis' for my dissipation choice....

[Alex Kitic]

Greg, I did not quite understand that you do own some EH300B tubes and have done some "testing" i.e. use in your own amp. Of course, if yours were developing red spots at 36 to 40W in a long run, that is disappointing, but not that much, since I did somehow expect that new production tubes will most likely be slightly inferior to old production both in longevity and reliability (i.e. lower dissipation). But I guess they can still be operated at 30+ W (400V at 83mA = 33.5W approx)?

The 300B is a much hyped tube, and replicas or current production tubes are made because there is a constant demand. Quality does not necessarily follow...

Someone wrote about 36W dissipation as maximum value in the WE datasheet - but that is not the Absolute Maximum, rather Design Center value: thus a further 10% at lest should be considered as absolute, i.e. WE would declare them (and probably has in some other datasheet) as 40W Absolute Maximum.

What actually remains to be seen is the behavior of "mesh" tubes, and this is something that has not been exactly reported in this thread or elsewhere.

1) The reputable seller is by no means sympathetic of TJ (now sold as Sofia?), and is selling-off his stock. This might be a two-way thing, as usually is in trade. I would like to avoid speculating, but am not inclined to believe everything this seller has to say. Maybe because I am from the same country that used to have Ei (RR Zavodi) and thus I know first hand whether everything the seller states is really true. Confidence is easily lost. Don't get me wrong, I am just not inclined to believe everything people say, particularly when they make money out of it, and are "sharing confidential info". That's typical merchant talk, just as I am used to hear in other fields...

2) The problem with mesh and "mesh" tubes is whether a perforated anode can be considered as mesh, i.e. plate made out of wires. It is more than obvious that a plate made of wires cannot have the same dissipation of a solid plate, but punching holes is not mesh either way, both as not being "true mesh" and not having the same loss in possible dissipation. The holes punched in the plate allow a similar aesthetic effect, but the loss in surface or mass is not equal. Thus I am inclined to believe that while true mesh plates mean less dissipation capability, that is not necessarily the case with "punched-true holes fake mesh" anodes.
And it is a fact that the fake mesh anodes are well larger than the solid anodes on the EH300B. While it does not necessarily mean a compensation, it could be: whichever it is, I look forward to finding out myself.

3) The reputable seller has made a statement that the nice papers with plotted curves are actually fakes... thus if we are to believe his words, it should imply that the nice papers do not mean 22W dissipation rating.

4) Last but not least, the reputable seller states TJ tubes are not adequate for use in standard 300B amps. But what is a standard 300B amp? I guess most commercial amps are, and if you reconsider a little what is inside those amps, they seem to be built around one or two schematics... and by assuming values based on what we see on pictures of the interior, or knowing the "expected" schematics values, none of these amps exploits the "full" maximum dissipation, it is mostly in the vicinity of 30W, if I am guessing it right. At 30W approximately, EH300B, Sovteks, etc. should work without fuss... and according to some Australian forums, Chinese tubes seem to be taking the same "usual" dissipation (30W approx, if I am correct).

In the end, what matters is the following: if the 300B solid plate cannot take 30W, and if fake mesh is not able to dissipate 30W, that is a dissapointment. But if those values are more like 22W for solid and 15W for fake mesh and mesh... the 300B is a loss of time. I sincerely hope that is not the case, as it would imply that there is something terribly wrong with audiophiles and DIYers all around the world, beside all that we already know.