I don't know the answer, Harry, but I would caution that the voltages and current marked on the person's schematic may vary significantly depending on the characteristics of the particular type of 300B that is being used. Unless the person was known to be using EML mesh 300B's, I would not count on those numbers as being applicable, especially given how close you would be coming to the 28W absolute maximum rating.
P.S: I note, though, that the 28W absolute maximum rating is for "plate dissipation." That would NOT include the 7W that is dissipated as a result of the filament current, which of course greatly increases the likelihood that the tube will be suitable.
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.
I wouldn't worry about the 500+ volts. The tube just sees the difference between the plate and cathode voltages. I suppose it is possible that there might be a small fraction of a second somewhere during the turn-on process where that difference is significantly greater than the much lower value it subsequently stabilizes at, but I'd be very surprised if that could cause any problems. And I see that the tube is rated to withstand up to 450 volts, provided that the 450V does not persist for a long enough period of time, in combination with high current levels, for the resulting power dissipation to be a problem.
The 450V rating, btw, is the same as the rating of the original Western Electric tube. I can't see any reason why exceeding that number by 10% or 20% or so for a small fraction of a second, if it were to happen at all, might cause a problem.
As far as the second part of your question is concerned, given the precautions you would be taking, and the substantial margin between the 28W absolute maximum rating and the 20.5W someone measured with the same model amplifier but probably with a different type of 300B, and also the margin between the 65 ma he measured and the tube's 80 ma maximum current rating, intuitively it strikes me as a reasonable gamble. But hopefully someone with knowledge and experience that is more directly relevant than mine will chime in.
I hope these mesh plate 300b work out well for you.If that`s the case I`d be interested to read your impressions.I`ve not heard this particular tube but it has a very good reputation for excellent sound quality.This is a true mesh plate design as opposed to a'perforated' plate copy.
Al, thanks so much. I take responsibility for whatever happens but armed with your knowledge it feels pretty safe.
Charles, will do.
I always agree with Al's and Charles's opinions wholeheartedly.
I am also a devote of the 300b as is Charles, and with his take on his Tak's, I believe!!
I currently use a pair of RP's with a secondary pair in the waiting as I got a nice deal on a quad set.
Starting fresh, I would go with your choice of EML true Mesh Plate. Very interesting.
I also have a pair of 45 amps which need more immediate attention on power tube replacement. EML is where I will go.
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.
I recall in past posts of your general system set-up, which I always felt was excellent. In fact, I do plan to do similar as I have a pair of JBL 4550s with original HF driver/fiber horn etc, which I have had for years put away.
I am in a small apartment and will move someday and plan to also employ active xo. Your's must sound really nice!! The 45 amps came with TJs and RCA/Cunningham which I am currently using. The EML Globe limited looks very interesting.
I just switch back and forth from 300B to 45 amps every couple weeks. Sure do like them both. Using Beauhorn Virtuosos, btw.
Mesh on top and bottom!! Very nice indeed!!
I have heard/read nothing but good reports concerning EML.
I run EML meshplate 2a3s in my Audionote Kageki amps. A friend runs meshplate 300bs. We have both found that the EML tubes are reasonably reliable and long lasting, but, they seem to be quite touchy about being pushed beyond specifications. When I tried the meshplates in a different amp (unknown dissipation and plate voltage), I got flashing on the plate and distortion after a few minutes of operation (conditions I did not experience with any other 2a3). I think that EMLs restrictions must be respected.
Operated properly, the meshplates are quite special. They deliver the most enveloping soundstage I have heard. If someone were to characterize this sound as "phasey," I can see why, except that image placement is very specific.
If you have any questions, I suggest contacting George Lenz at TubesUSA (US distributor of EML tubes). He is terrific when it comes to prompt replies and gives very good advice--he will not steer you wrong.
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,That`s excellent news!I`m glad you took the chance and it worked out.I`d like to try these EML meshplates someday.Wished we lived near one another and could swap these with the Takatsuki 300b.
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.