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Help with tube specs

I will be getting a pair of EML 300b "mesh pate" tubes in a few days.

EML warns that the meshes should be run between 22-28 watts of dissipation with the closer to 22 the better and 28 MAX.

The amp I will be using them in is fine but I have another amp I'm not sure of. It's a Welborne 300b DRD. I was able to find this much:

">>>I have a Welborne manual for the 300B DRD and there are no voltages given in the manual. However, the original owner wrote his voltages on the schematic after he built the amps. He shows 505V on the plate and 190V on the cathode for a plate voltage of 315V. He also shows a cathode current of 65mA. So that means you have a plate dissipation of 20.5W.<<<

I also got this:

" The 300b mesh will not tolerate 500v on the plate. Even with a reduced dissipation on the tube, the tube won't last!"

I also read that with the tube drawing 1.4 amps at 5 volts (7 watts) you would add this to the 20.5W for a total of 27.5W. At least that keeps me in the 22-28 realm.

Can anyone help me sift thru this info? Opinions as to "how safe" it would be would be appreciated.

In the meantime, I will only run it in the safe amp for warranty purposes but would eventually like to try it in the DRD and would hate to eat the money if it's a mismatch.

Thanks.
onemug

Showing 5 responses by onemug

onemug OP
784 posts
 
Al, you are my wish come true. I hoped you would see this thread and respond.

Good call on that "one" builders notes.

If I find the correct numbers for this amp, and let's say they are close to to 500 plate and 190 cathode, is the tube seeing the 500 (as the dealer warns) or do I subtract the cathode to arrive at the volts the tube is receiving?

Also, if I feel like gambling without known specs, do you think I would be safe using them if:

I turn the amp on in a dark room...

Look for any spark or flash at start up...

If so far so good, continue to watch the meshplates as they warm up in the first minutes and beyond to see if there are any signs that they are beginning to red plate and turn it off immediately.

These mono blocks use a 5ar4 for rectifying so I get a little bit of a slow start.
onemug OP
784 posts
 
Al, thanks so much. I take responsibility for whatever happens but armed with your knowledge it feels pretty safe.

Charles, will do.
onemug OP
784 posts
 
Isochronism,

I love the 45 also. I had Fi 2a3 monos that could use the 45 with a rectifier sub but never felt I got the full experience of a true 45 amp. Right now I'm using another 2a3 amp that also can use the 45 tube but use this amp in an active x/o system for the tweeter and with it seeing only 2.8k and above, I don't hear much difference between the 2a3 and 45 so I just use the 2a3 in it.

I have a pair of almost NOS Tung-Sol 45's and a pair of Sophia Meshplate 45's that are gathering dust. If you ever think about letting go of your extra set of RP's, let me know and maybe I could use these 45's as a partial trade for them. I would dust them off first. :-)

btw, I did order a pair of the EML 2a3 meshes along with the 300b's meshes. I figure whatever the mesh does, might as well have the blend at the x/o be as good as possible.

I have tried using 2 300b amps in this bi-amp system (nice on paper having the same type amps) but the 2a3 (and 45) just do the highs better for me.

onemug OP
784 posts
 
Got my tubes. Put 4 hours on them yesterday and about the same today. They were great right out of the box and have continued to improve.

Larryi, I did get them from George. He was a pleasure to do business with.

I didn't expect any issues with my my main amp, I'm easily within the 22 watt dissipation. I went over this with George beforehand. I did get an email back from the Welborne site and they said the DRD was ran at 350 volts and 60 mA bias so that comes out to 21 watts dis. I should be fine if I choose to try them in there.
onemug OP
784 posts
 
Charles, Thanks. Agree, a closer proximity would be nice.

Having 3 systems and having to pick one as your favorite is like having 3 children and picking the best. You could say one child has "achieved" more and that is what I would say about my bi-amp/active crossover system.

With the EML meshes top and bottom, this system has achieved the highest level of enjoyment so far but I still love my other 2 kids. :-)

A tricky thing with bi-amping is getting the "blend" right. I read all over the net about "I use a behemoth ss amp for the woofer and a sweet tube amp for the tweeter". No doubt that system would have a great low end and top end. I would question the middle though, where you are hearing ss and tube producing the same frequencies at the same time (x/o point and its slopes) but if it makes you happy, that's all that counts.
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