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In Reply to: RE: Careful with NOS and Mesh Plate 45s posted by somejoe on April 12, 2010 at 16:55:32
How would you measure the current and how would you know if NOS or other tubes are a good match?
I was thinking of running some National Union 45s in them; they currently have some RCAs - any advice?
Thanks
Follow Ups:
Measure the voltage across the cathode resistor of the 45 and divide by the resistor value. Make sure you do not include the current drawn by the driver tube. In the ElectraPrint schematic you'd measure across the 10 ohm resistor.
Please remember that voltages and currents inside tube amps can kill. if you're not experienced working with tube ear, please consult a technician.
I noticed that the schematic was from Electraprint - just curious, how do we know that this is the schematic and specs used by Welborne? Are they somehow synonymous? Or maybe "DRD45" was unqiue to both Electraprint and Welborne? Thanks
.
Yada,
Jack at Electroprint either Patented or Copywrited the DRD circuit and term as I understand it. Others will clarify it better.
Jeff
Does that mean that every DRD circuit uses an Electraprint transformer (ie, does every Welborne DRD amp use an Electraprint transformer)? Thanks
AFAIK, all Welborne DRDs use Electrprint OPTs, and the unbranded chokes with the brown paper wrappings would also be E-P.
.
Hi,
Somejoe is giving you some very good advice. The schematic is suggesting 50 mills through the 45, with maybe about 490 VDC on the plate, assuming a 10 VDC (I times R drop) through the output transformer primary.
That is super HOT RODDING the tube, which means it will sound OK for the first 500 to maybe 1,000 hours, and then slowly degrade in sound.
If you run the 45 at 28 or 30 mills, as Somejoe does, (or about 7 watts dissipation of the plate) the 45 tube will easily last 10,000 hours, and give consistent performance over its (long) lifetime. It will also allow you to use ALL type 45s, NOS, EML mesh plates, etc., and NOT have to worry one iota about over-dissipating the tubes, or tube life.
So, YOU can do this easily, VERY CAREFULLY !!!! measure across the 10 Ohm resistor, and adjust the 2K pot so that the VDC across it is 0.30 VDC to 0.28 VDC, which is 30 or 28 mills (Ohms Law). If for some reason, you can not get the adjustment low enough, contact me off line, and I will tell you where to add a resistor, to allow for more conservative tube operation, while retaining the convienience of the 2 K bias adjustment pot.
BE VERY CAREFUL, LETHAL voltages exist under the amp, so if you are inexperienced, use a technician as Somejoe warns you.
If this amp sounds worse at 30 mills than at 50 mills, the problem is NOT because of the lower the op point, but more likely, the general design and construction of the amp's power supply. This amp's two stage actual direct coupled audio circuit is simple and decent, so hopefully, 28 to 30 mA. will give you a nice relaxed, UNSTRESSESED-sounding music presentation.
Let us know how it turns out for you.
Jeff Medwin
Sorry for the basic questions, but are you saying that if the amp is built as per the schematic/spec, that any 45 should run - but that if it happens to be setup for 50 mills that the tube will sound ok, but it will have a relatively shortly life? Or are you saying that it won't sound ok either? (For all I know, the amp could be setup for 50 mills, 40 mills, or 30 mills, or anything else.)
Also, why would Welborne have "super hot rodded" the design? What would be the advantage in doing so? If hot rodding a circuit both accelerates tube life and causes a stressed-out sound, why would anyone do that?
It would seem to me that at some operating spec the amp would sound it's best and at another the tubes might last longer, and in the middle would be pretty good sound and pretty good tube life, or is there some other trade-off going on?
I'd like to get 10k hours from a tube, but I might go for better sound and 1k hours if the sound was noticeably better. What I wouldn't want to do is plug in a tube and cause a tube failure, or worse yet, an amp failure.
I bought the amps from a guy who was really into Welbornes and I'm sure he wouldn't have bought an amp that just ate tubes, and based on how good the amp sounds with the RCA 45s I can't imagine it was backed off from sonics too much just to save tube life either; so I'm really just trying to confirm that I can plug in a couple National Union 45s and safely listen to see if the NUs have any noticeably different sonic characteristics than the RCAs.
On another note, I've heard that the EMLs require a different resistor value than most (all?) other 45s; I can believe that some tubes, such as the EMLs, that don't conform to the standard/orginal 45 spec might need a different resistor or circuit value, but is is non-conforming tube design common among 45s, or are most 45s set up such that if one 45 tube works well with a circuit, others should also?
- all I really want to do is swap out the RCAs with the NUs, not second guess Welborne's factory built design
I'm more into listening to amps than building or modifing them :)
Thanks again
Hi,
You ask some good questions. First of all, Somejoe posted a schematic from Electraprint, who "notoriously" (IMHO) runs tubes WAYYY too hot, and it may not be what you have at all.
This "hot rodding" of finals tubes has been prevalent for decades amongst the tube Manufacturers (to sell more tubes) and the tube amp manufacturers (who sell on specifications to end-users, "my amp is powerful").
It is "numbers"..... over quality .....or sonic beauty.
I find very few amp designers approach the tube amp from the basis of achieving long term reliability, and high performance COMBINED.
So, it becomes incumbent upon the thoughtful individual user, such as Somejoe - (who I don't know), to make changes so as to obtain long tube life AND high performance, and this can be done !!! Myself, and a few others, have talked about this up here.
You can plug whatever you want in there, 45-wise, and it will work, pass a signal. To determine for how long, and how good it will sound, you will have to measure the operating points, compute the dissipation (Ohm's Law), and refer to my original post, .... idealize it by using about 7 watts total plate dissipation.
Do NOT think for one millisecond that the amp "manufacturers" are infallible in their designs. Many experienced DIYers regularly out-do what many manufacturers offer. Cheers.
Jeff Medwin
Jeff, thanks for helping me get a bit of a grip on this.
Question, if a tube could run anywhere from 1k hours to 10k hours, I can easily see the benefit of 10x more tube life. Is there any way to begin to quantify or characterize how much sonic quality is lost (if any) when a tube is run for maximum tube life? What sonic attributes if any are lost when maximizing for tube life? Also, if somehow "hot rodding" makes a tube sound better, what are the sonic attributes of "better"?
Still more questions: I thought Electraprint made transformers, or do they make tubes also? What benefit would a transformer manufacturer or an amp manufacturer have in running a tube hot (thereby minimizing tube life and maybe some customer satisfication) unless they thought it would sound better? Which brings me back to what is the nature of the better sound? And is there a point at which running an amp hotter simply won't make the sound any better? And could it make it sound worse if it's really too "hot"?
Thanks for helping with the learning lessons. I appreciate it.
Relax a moment and just think. Let's say your Boss wants you to take out the garbage everyday at the same time.
Let's say you're a good guy and know what you're doing. Now, think: which way is going to get the best, most harmonious job of having you take out the garbage each day-- a Boss who WHIPS YOU each time before you take it out, OR-- a Boss that simply lets you take it out in the best way?
I think the answer is obvious.
Vacuum tubes do not perform well while being whipped, either.
You ask : "How much sonic quality is lost when a tube is operated for maximum tube life?"
That question is irrelevant because there is no such thing. When a tube is operated at its maximum life rating, it IS SONICALLY SUPERIOR to ALL OTHER operating points, period. VERY, blatantly, and audibly superior.
It is up to the amp designer to let that sonic superiority GET OUT of the amp's circuitry and actually drive a speaker with it.
Some problems arise in doing this, and are dictated by CUSTOMERS and designers who know nothing about amp design except what they study, prove, and read. Simple Common Sense is often left out.
(1) Is WATT RATING. It is ASSUMED that more watts= more power into a speaker. But, it might mean that it's nothing but more watts burned-up and not converted into actual music. In any case, the less power the amp produces, the better the speaker, speaker cables, and amp wiring and layout have to be in order to properly drive the speaker. You can see how this works-- if you want to use cheap, thin copper wiring in an amplifier, then MOST of the power will be burned up in the amp, or delayed musically in such a way that it will produce more heat than music even when it DOES get into the speaker. The bottom line of this is simple: if your amp is cheaply built, simply apply more watts and hope some of it gets through. The customer dictates this approach when he refuses to pay for good amp engineering which costs money, but really works.
(2) Is "tube charts". Customers love to read these things, the assumption being that one should design for a "flat load-line". Well, that's nice. Looks pretty on paper. Even fools a few people. Just one problem: tubes SOUND BEST at the RIGHT OPERATING TEMPERATURE, period. End of discussion. Regardless of "tube charts and curves". Regardless of anything else at all.... . Period.
For the NOS 45, the right temp. on normal types is reached at 245 volts across the tube, and at 28 ma. plate current. That WILL NOT give you a full two watts, and, if the amp is built efficiently (yes, expensively), then it will drive some tough loads easily, and reproduce the full musical bandwidth.. That doesn't mean you can short it out with a 89 db/watt speaker and expect music. For that, you use 1500 watt Solid-State unit, and forget tubes.
So, as you can see, tubes get Hot-Rodded by many who use them. They do this for several reasons: (1) It's the cheap way to force some output thru the cheaply built amp. (2) It looks good on paper-- they are scared "it won't be linear" if they stray from those tube charts straight-line sections-- but this is baloney. Also, music IS NOT linear, and neither is hearing. (3) It used to sell tubes in the tube-era, and few today realize that those old figures are meaningless today. (4) Customers want more watts/per dollar. That is just STUPID. Today, we have many examples of excellent, uncolored musical speakers that run at under 1/4 watt. Together with the latest studio A/D-D/A converters, it's been the greatest advance in audio in the last 5 years.
---Dennis---
Yada,Well, more good questions.
If an amp sounds better when the tube is run hotter, at or above the Manufacturer's spec, it is usually because that amp is poorly executed internally, as far as transfer function, and design of its power supply.
I find best results are obtained with over-designed power supplies, that have a natural stability, under all types of music playback. In addition to the supply's design being as near perfect as possible, the amplifier's internal transfer function becomes a matter to properly address, proper wiring of components, as to wire types, and lengths, and lay outs, so as to NOT LOSE complex musical information inside the ampfilier!!
Particularly in SE amps, where the power supply is INCLUDED in the audio circuit. !!
Most audio equipment is NOT made this way, it is made to a price point, or by individuals who deem such an approach as unnecessary. So, with poorly conceived and wired amps, the hotter the tube is run, sometimes - the better it may sound, at first. But alas, it is only temporary, as the tube quickly degrades due to the hot rodding.
Consider the "Golden Ratio" in design, things like you car, truck, lawnmower, and your Type 45 tube run BEST and longest when designed at or near that number.
And yes, when thoughtfully designed, the Type 45 at 7 watts dissiaption will sonically outperform the same tube running at its full rated 10 watt dissipation, in a good amp. Its easy to hear.
Your family car runs a lot better at 65 MPH than at 100 MPH, and I say it will probably run a LOT longer at 65 MPH. Others will no doubt disagree with me on this topic, and that is fine.
Jeff Medwin
Edits: 04/12/10
Perfect post, Jeff. Thank you.For those interested in detail/discussion/rants/ravings on this subject: Refer to my old posts on TUBEDIY-- from about 2006 onward. Things got really hot in those days, as usual, I was not always believed, but people who played my amps certainly believed! I laid it all out for you-- to be read years later. Jeff is kind enough to continue mentioning those ideas, and he is also trying to make available power supply parts that will contribute to proper vacuum tube operation in the best ways through better power supply parts. Btavo!
A vacuum tube is nothing special. It's just another piece of Physics. You play with it until it (ITSELF!) is operating happily, comfortably, and really humming along. That automatically guarantees at least 20,000 hours of operation from it, and that insures zero sonic degradation over at least 10,000 hours, something that is TOTALLY NECESSARY in order to fully enjoy music.
After all, once you spend days/weeks/months getting an audio system to really perform, wouldn't you like it to STAY that way? It will, if all of the active and mechanical devices are operated in a non-stressed mode.
Of course, that is just simple Common Sense.
---Dennis---
Edits: 04/12/10
Jeff, Thanks again. I noticed in a couple of your posts the reference to 7 watts dissapation; is that something you have found to be an ideal spec? How is that measured? Thx!
PS, what are your favorite 45 and 300B amps? and tubes?
- Ever hear a Jeff Korneff 45 amp?
Yada,
These are just MY personal opinions:
I was taught to NEVER use a stock 300B by my ultra-smart, superb listening, audio mentor. (B-1925, D-1988). The 2A3 and the Type 45 are generally superior sounding. Stock W.E. 300Bs are for people who don't "get it" with high efficiency speakers.
The EML line, available today, is probably the best sounding audio tubes ever made.
They will outperform all NOS 45s and 2A3s, due to their superior design, linear filament structures, etc.
Actually Yada, in 2010, for some low efficiency bookshelf speakers I own, I am building a DC SE VAIC AV-32B amp. That VAIC tube is the circa 2001 predecessor of EML's very nice 300B-XLS, which is probably the only other non 45 or 2A3 tube I would use. Oh, the NOS 2A3 does well at 10 or 10.5 watts dissipation. Just my tastes and prejudices !! The 2A3 is my favorite all-around tube.
Jeff
Hi, Thanks for the thoughtful reply but I'm not sure I could find the 10 ohm resistor or the 2k pot, much less add a resistor. I can solder and run a volt meter but the chances of me making an error here is moderately high; I might not shock myself but I might put a well operating amp into a less well condition.
I guess it's hard to know what the value is for an off the shelf Welborne DRD-45 amp? (these amps were made at the factory).
I'm still trying to figure out what happens if I plug in a NU45? Is it likely that the National Union tube is going to behave circuitry-wise in a manner that is differen that the RCA tube?
Thanks for trying to help without me being able to give much/any circuit specs.
====
So, YOU can do this easily, VERY CAREFULLY !!!! measure across the 10 Ohm resistor, and adjust the 2K pot so that the VDC across it is 0.30 VDC to 0.28 VDC, which is 30 or 28 mills (Ohms Law). If for some reason, you can not get the adjustment low enough, contact me off line, and I will tell you where to add a resistor, to allow for more conservative tube operation, while retaining the convienience of the 2 K bias adjustment pot.
BE VERY CAREFUL, LETHAL voltages exist under the amp, so if you are inexperienced, use a technician as Somejoe warns you.
If this amp sounds worse at 30 mills than at 50 mills, the problem is NOT because of the lower the op point, but more likely, the general design and construction of the amp's power supply. This amp's two stage actual direct coupled audio circuit is simple and decent, so hopefully, 28 to 30 mA. will give you a nice relaxed, UNSTRESSESED-sounding music presentation.
Let us know how it turns out for you.
Jeff Medwin
I see no problem TRYING to run a NU, aside from my comments, both 2A3s meet the same 2A3 spec from their manufacturers. Optimizing for either is what I was discussing, best sound, longest life.
Jeff Medwin
Thanks very much for the schmetic and the info; I appreciate - but I think it's probably a bit beyond my skill. What are the chances of being able to plug in a National Union 45 and have it work without problems? If it doesn't work, what's the likely downside?
Also, just out of curiousity, let's say I made the measurement - I'd get some specific value; then how would I know if it would be ok to use the NU 45s?
Thanks again.
Yada, tube BRAND has nothing to do with what the tube IS-- when you are talking NOS (New Old Stock).
Back in the Day, tube factories made tons of tubes of one type-- at a time, then switched over to a run of something else. Some factories made only one or two types, also.
A certain design, made by one factory, could have anything from RCA, Sylvania, Motorola, Zenith, Raytheon, G.E., N.U., Tung-Sol, and at least a dozen more-- names stamped on it, and every one could be the SAME TUBE--or maybe NOT.
For instance, you might get two Sylvania 45 tubes in Sylvania boxes. One tube could be G.E. origin, the other could be RCA. A third might be a Sylvania. Depending on batch, the filaments might be hung from mica insulators, from flat-wire springs, from coiled-wire springs, or a whole lot more.
As you can see-- with old tubes, BRAND means NOTHING. TUBE CONSTRUCTION and MATERIALS USED determines the tube's characteristics.
Can you plunk-in the NOS N.U. instead of the NOS RCA? Of course! The N.U. probably IS an RCA-- or maybe Sylvania, or maybe Raytheon, or maybe Tung-Sol, or maybe G.E., maybe Sears, maybe Zenith, maybe Philco, etc. Of course, for two amps, you use two identical tubes. This DOES NOT necessarily mean the same brand-- just the same TUBES. LOOK at them! INSIDE THEM. Use magnifying glass-- pick two that are alike in every way.
So, put it in. Observe what it does. If it runs cool, sounds clean, and doesn't do anything radical, it will probably run.
---Dennis---
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