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Hi there,
I'm looking to re-tube my WPA3.5, and am thinking of a "premium tube".
I've been running both the stock Sovteks and the the Shuguang 2A3C
Has anyone tried the JJ/Tesla 2A3-40 the the WPA3.5?
Are they drop -in replacements for the 2A3?
Thanks!
Follow Ups:
I tried the JJ 2A3-40 briefly last year in the Wright WPA3.5. Compared to the Shuguang 2A3C, the JJ had a somewhat darker, warmer sound. It was only a brief test, but I thought the JJ was a very good tube. It might be a matter of taste and system balance between it and the Shuguang tube. Both are IMO significantly better than the Sovtek, which itself is by no means bad.
There should be no technical problems using the JJ 2A3 in the WPA3.5. As noted in this and the other recent thread on this amp, the amp is designed to use NOS 2A3 operating points, so the JJ should be running well within its safety margins, which are much wider than for NOS 2A3s. The JJ spec sheet indicates this tube has similar plate resistance and gain to NOS, so there should be no unpleasant surprises.
Thanks - I appreciate the "tasting notes" of the JJ2A3-40 compared with the Shu 2A3C, and also the note that teh operating points accommodated NOS 2A3s - I'm thinking that should accommodate the EML 2A3 meshies, assuming they don't turn on too quickly.
"Are they drop -in replacements for the 2A3?"
Yes
nt
I think you will enjoy the JJs. Allow a little break in time. Only other one is more expensive EML 2A3s, also very nice.
Jeff Medwin
Thanks for the suggesting the EML 2A3.
I was interested in trying the mesh version, but wasn't sure if it was a good match for the WPL3.5
My understanding is that the WPL3.5 was designed around the Sovtek 2A3, and that the WPL3.5 drives it pretty hard.
I've seem to recall various posts on discussion forums (including this one?) that indicate the EML 2A3 mesh might not last too long in some amps, if they are driven too hard.
I've attached an info sheet from EML
If you could clarify this for me, I really appreciate it!
> > > My understanding is that the WPL3.5 was designed around the Sovtek 2A3, and that the WPL3.5 drives it pretty hard. < < <
I don't think so.
I was one of the earlier buyers of the 3.5s. They came with sino 2A3s. I don't think the Sovteks were even out yet.
Jack
The Sino 2A3s of those days were pretty tough; I know several people (including myself) who operated them at 18 watts dissipation.
The cathode-follower grid drive enables the WPA3.5 to handle instantaneous peaks of greater power than the steady-state maximum; I believe George based his "8-watt" rating on this effect. However, this is pushing the tube into Class A2 with grid current, even if it's only occasionally. On the plus side, the cathode follower also prevents a 2A3 positive grid voltage spike at turn-on. You'll have to ask Jac about EML tubes; I know he is usually opposed to A2 but would approve the slow turn-on of the cathode follower.
IIRC, the early WPA3.5s had Magnequest DS-025 outputs with 2.5K primary. Combined with the 750 ohm cathode resistor, it seems very likely the operating point was the book value, 250v/60mA/15watts plate dissipation. The extra resistance in the power supply is probably there to adjust the plate voltage, and to limit the rectifier current and extend its life. I'm pretty sure the CCS shown in the schematic is an error, since it would prevent any drive voltage getting to the 2A3!
Output tansformers on the early ones were the tiny MQ TFA-204, not DS-025 (later switched to Onetics). As you said, George used resistors on the rectifier cathode in all his designs, mainly to extend rectifier life, but for the WPA 3.5 he had to drop the voltage some due to the crappy Hammond 200 series power transformer he used in the early ones (poor regulation, ran real hot and often ended up buzzing). On later ones he used custom power transformers made by DeYoung.
There's a 522K resistor from pin 2 to pin 6 of the 6SN7. I asked George about it and he said he always used it in that type of circuit (direct-coupled) for sonic reasons. Do you know what it does?
On the WPA 3.5 I looked at, the choke was in the ground leg
Thanks for that, my memory was faulty. I SHOULD have remembered, we were all falling in love with the TFA-204 when that amp originated, and George was quite active in the VALVE club at the time.
Fascinating about the 522K. It looks like it's there to adjust the first stage bias according to the local power line voltage, to stabilize the operating point. What a clever (not to say sneaky...) guy George was!
~!
The Mind has No Firewall~ U.S. Army War College.
Interesting - I have read that the WPA3.5 get 8 watts out of the Sovtek, though, instead of the usual 3.5W, which also made me wonder if the tubes are driven quite hard.
But, I have found a 2003 post on the EML jac site from Michael Klementovich saying he used the EML 2A3 in his WPA3.5, and they worked very well: "the improvement was not slight but massive". No indication as to how long they lasted, but no sign of an immediate flame-out!
I suppose the fact that the WPA3.5 is NOT on the EML list of amplifiers that need special attention is encouraging.
A call to George at TubesUSA might also be helpful
I would guess the solid plates may take more abuse than the meshies..
YMMV
Willie
I think you are right - the solid plates would probably work - but, the meshies get such high praise as "the best of the best", I'd like to give them a try.
Can't remember whre I read it, but I recall one listener - perhaps a tube reseller - stating that they thought the EML 2A3-S (solid plate) was their favourite sounding 2A3... ahead of the mesh plates. My guess is that they sound different (not better or worse) and preferences will differ.
Cheers.
“As long as we have any intention to be right… we should be wary. So long as words have the slightest ego attachment, they are dishonest.” Charlotte Joko Beck
"I've attached an info sheet from EML"
You need to attach a schematic for your amp or measure the plate voltage and plate current. Without that info there is nothing to go on.
that I can find, which may not even be a the exact schematic of my particular unit - given that George seemed to tweak his designs on the fly!
While am sure that is a fine schematic, that is not even remotely close to the George Wright WPA 3.5 schematic dated 1/26/98 from Wright sound Company. The one I hold is hand drawn by George himself give to me by Roger Hug from Seattle, Washington. Out of respect I will not post that schemo here. There are numerous differences and the one you hold is not even remotely close.
Kind Regards,
Ken
The Mind has No Firewall~ U.S. Army War College.
With no voltages, we can not answer your question. If you want to document yours, using this schematic as a reference, then we can compute dissipations and suggest a conservative 2A3 op point, if needed. The 750 Ohm Rk will likely get increased in value some, but that depends upon the entire amp.
The power supply filter to the finals is quite poor in design, why anyone would add 480 Ohms of resistances there, is beyond rational thought. I'd mod the supply before I would spend penny one on a EML meshie. I can PSUD that for you if you get the VACs and VDCs documented.
Jeff Medwin
Thanks very much for looking at this so closely.
I think you've answered my initial question; namely, that I should not invest in EML meshies at this point.
As to modding the power supply, learning DIY is on my bucket list, but I wouldn't be able to mod the power supply myself at this stage, or even measure the voltages, so that will have to be project for another day.
Thanks again.
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