TJ Full Music 300B/n Data?

[IslandPink]

There's nothing odd about a 300B in this regard .
Every valve data sheet ( OK nearly all ) has a 'Limiting Values' section with max dissipation quoted. The understanding is that running a valve at 100% dissipation will only get you 1000 hrs or so ; it may be stated in more detail on the better (later) datasheets .
That's why the recommended operating points are usually say 85% or max diss or less.
For a Standard 300B it's 40W 'max', so an operating point of 80-85% will be 32-34W , which will net you about 7.5 to 8.5W with the right sort of load ( 2.5k - 3k ) . This is what you expect from a standard 300B , and at this dissipation, the lifetime will be 10,000 hrs or more, with luck .

Presumably when people say the TJ meshplate 'cannot be used in normal 300B amplifiers' , they mean it's just not a 'plug-in replacement' : all that's required is to adjust the cathode resistor ( up ) until you get a current consistent with 22 to 25W approx diss .

[Mike H]

Yes it raises the question, what is 'a normal 300B amplifier'

[Alex Kitic]

Yes it raises the question, what is 'a normal 300B amplifier'

This is the mirror image of my dilemma regarding maximum power dissipation!

And, once you take into account that a tube seller has made the statement, plus he is selling-off his stock, the story does not hold water any longer.

I guess this is another conflict of interest issue: fake mesh tubes look enticing, and prices are relatively low (lower than real mesh alternatives, let's face it, looks are the main motivation to buy mesh plate tubes) - but profits might be in jeopardy since sales of real mesh tubes made by another supplier, perhaps with closer links, or higher margins, are threatened by the sales of fake mesh tubes? The total number of customers is limited, as this is a niche market. When it comes to 300B tubes, we are not talking about FMCG...

Does this explanation look logical, or am I being paranoid?

[Paul Barker]

Are you meaning

Actual Mesh



compared to a solid metal plate which has been punched with holes.

[Mike H]

Yes I understood that the whole point of mesh plate is it's made of wire, which offers an increased surface area. A plate full of holes isn't the same at all. Maybe if the plate was thick...

@ Alex you're probably not paranoid, trouble is 300B's are surrounded by this aura of desirability, so the world and his dog want to cash in. Saying it can do 40W adds to the hype. It likely derived from hearsay rather than actual testing.

[Alex Kitic]

Yes I understood that the whole point of mesh plate is it's made of wire, which offers an increased surface area. A plate full of holes isn't the same at all. Maybe if the plate was thick...

Heat can be dissipated in three ways (basically):
1) conduction (not in vacuum since there is nothing to conduct heat);
2) convection (not without a fluid, thus impossible in vacuum);
3) radiation (in vacuum this is the only possibility).

While vacuum in a tube is not absolute, the particle density is such that there is no relevant difference when it comes to dissipating heat from an anode.

The mesh plate migh have an increased surface compared to solid anode, but since the only way to dissipate heat is radiation, the surface does not play as important a role as it would if conduction or convection were at play.

The problem with mesh plate (wires) is the fact that not being solid as a piece of metal, i.e. solid anode plate - it radiates less efficiently as compared to it's own capability to withstand the heat without melting (red plating means red-hot points... that should lead to melting). Since wire is less massive than solid plate, the dissipation capability of mesh plates is lower.

While I am not quite sure why mesh plates were used in the first place (i.e. old mesh plate rectifiers), and avoiding the discussion whether a mesh plate RGN2004 sounds better than a solid plate RGN2004 - what remains is stunning good looks, as the cathode filament can be seen through the mesh plate.

Now about the fake plate: punching holes through the plate to be used for anodes is relatively easy, and the stunning looks (see-through cathode) are easily achieved. But the fact that the plate has holes does not make it less resistant to heat (melting) nor less capable to radiate (particularly if the surface of the plate is equal or larger - which is the case with those fake mesh plates which are larger than the solid equivalents).

Thus the only reason why a fake mesh plate 300B would not be able to dissipate 36W, or 40W... or what a normal current production solid plate 300B can dissipate on the long run, would be the thickness of the material (that is why it is said "the massive plate of the 307A looks like it could dissipate at least 25W...").

Since it seems that so far no-one of the participants to this thread has used fake mesh 300B tubes, we can only guess whether they can or cannot withstand use in a "normal" 300B amp.

BTW, I think we can define as a normal 300B amp the usual concept of a "6SN7 cascaded into 6SN7 driving a 300B with cathode resistor around 880 ohms, drawing approximately 70mA with a B+ of less than 400V, thus dissipation is probably 350 x .07 = 24.5W, or somewhere around 25W...".

As I said, if any 300B is not capable to dissipate 25W on the long run, it should not be considered as "fake something" but simply a bad, not performing tube.

[Alex Kitic]

Pardon my intrusion one more time - I remembered that someone mentioned the Sophia Electric mesh 300B are actually the same as TJ Full Music mesh 300B (made in the same factory, it seems).

Looking at the pictures on the web, and comparing with the pair I have just received from a generous DIY friend, I am can only say they look identical.

Well, the Sophia Electric website (you can easily Google it, I am not, nor think of advertising for them - so I will not include a link) shows a specification with a little picture showing the curves... it clearly states 40W maximum dissipation.

To me, all the data shown look like copied from the WE datasheet, but than again, if it is a 300B it is logical the same or similar performance... is it not?

The issue here is only trying to show that stated characteristics are not missing, as some imply - but until it is tested, we cannot say whether the tubes are compliant with those characteristics.

[Mike H]

Heat can be dissipated in three ways (basically):

It has nothing to do with heat dissipation. It's about how the electrons land on the anode, but nobody knows what really happens, IIRC

[Mike H]

Sorry if that sounded terse, it wasn't meant to.

I read about all this must 2 years ago or more, can't remember the details but there were some theories about how having a mesh of wires affects electron behaviour. Whatever it is, plates with holes in aren't the same. IIRC

[Alex Kitic]

Sorry if that sounded terse, it wasn't meant to.

...some theories about how having a mesh of wires affects electron behaviour. Whatever it is, plates with holes in aren't the same. IIRC

No problem, I am not at all snappy

You are right about that, a plate with holes is not the same as wire mesh - and it probably has influence on the "sound" the tube produces (actually, the intrinsic character of the tube, if we may call it that way).

Actually, I am trying to avoid the "sound quality" issue of solid vs. mesh vs. holes in the plate - I am only concerned here with the heat dissipation, as many consider that mesh plate 300Bs cannot dissipate 40W, and that mesh and holes in the plate types are limited to 15-20W dissipation.

Thus, the story is about dissipation and reliability - the discussion about sound would require a get-together of sorts with tube rolling ... the latter is improbable in my case, but maybe some would like to build the RH300B once it is finalized and thus give opinions both on the sound of the amp, and the sound of the various 300B versions?

[Greg]

The reason why I explored buying TJ mesh plates was because, following a tube rolling session here, the mesh plates came out as the best in terms of sound. However, following the research I did, I was not prepared to compromise power to such an extent in the interest of preserving valve life. The seriously lower dissipation at 21W suggested for the mesh plates to perform with longevity was too much a loss of power for me. To run them at 36W may have sounded fantastic but my wallet and budget would not tolerate the cost of frequent replacement.

[JamesD]

Since some are nit-picking so will I

Conduction through air is throughly disrupted by convection and has minimal effect.

However conduction is quite effective in a vacuum tube - through the support structure and down into the valve base - it is responsible for more valve base heating than radiation from the anode to the valve base...

Nit-pick over

James

[Mike H]

Which explains chassis heating up in the immediate vicinity.

I think Greg's summed it up, and is the same direction I was thinking, you have to choose between the sound, or the power.

[Alex Kitic]

The seriously lower dissipation at 21W suggested for the mesh plates to perform with longevity was too much a loss of power for me. To run them at 36W may have sounded fantastic but my wallet and budget would not tolerate the cost of frequent replacement.

Where did this info come from?
1) You used the tubes, or your friends did, and they died prematurely (the tubes) due to 36W dissipation?
2) Information found in some forum?
3) You guess the data based on pieces of paper showing the current tubes would draw at a given operating point (i.e. tube matching)?
4) Tube seller recommendation?

Also, did the tubes show red spots at 36W dissipation?

[Greg]

The seriously lower dissipation at 21W suggested for the mesh plates to perform with longevity was too much a loss of power for me. To run them at 36W may have sounded fantastic but my wallet and budget would not tolerate the cost of frequent replacement.

Where did this info come from?
1) You used the tubes, or your friends, and they died prematurely due to 36W dissipation?
2) Information found in some forum?
3) You guess the data based on pieces of paper showing the current tubes would draw at a given operating point (i.e. tube matching)?
4) Tube seller recommendation?

Also, did the tubes show red spots at 36W dissipation?

It was a minifest and we tried about five different types of 300B. The mesh plates did not die but were run at about 36-40W dissipation. We were not looking for red spots on the plate and all was done in daylight. No plate glow was noticed. This was several years ago. The advice to run mesh plates not exceeding 22W dissipation came from Jac Music when they were selling a full range of Full Music TJ valves.