different power valves for my MA !!

[washburn 1]

Hi guys
I need a little advice on biasing,please. I have just aquired two matched T.A.D. el34B-STR for a stupid price so i thought i`d pop them in to see what they can do (supposedly a re-make of Mullard valve). The amp is currently set to 38mv upon recommendation of Marshall tech` dep`t but how can i tell what to bias the new valves to, OR do i still just bias the amp to 38mv still ?? Also if the amp is biased just a little hotter/cooler i`m aware of what it can do to the valves BUT what kind of effect can this have on the sound (quality) ?? is it worth experimenting ? Any help would be much appreciated. Cheers all !! (and how do i put these smilies on, cant get them to work! arghh!!)

[Crunchifyable]

Hey Kev.

I thought the MA50 (assuming thats the one you have - you said 2 tubes) was biased at 35MV/MA (well, measured in MV...but demonstrating MA...). Not that 3 Ma is going to make much of an audible difference.

I've heard that low / cold bias = harsh, sterile, cold, perhaps even bright. Can cause annoying cross over distortion if far too cold (this may sound like a puttering engine, so I've heard, and only occurs at lower volumes).
Warm / hot bias = warm, quicker to distort, possibly louder / more output, but shorter lifespan.

In theory you could set them to 70% of maximum idle dissipation (based on plate voltage). In reality, the number that Steve gave (38 a side on the 100 watt, and 35 for the 50 watt) will probably work fine.

I would bias the amp to that amount (38, 35, whatever :) ), or a hair less (reasoning being that over time, the bias will drift upward).

I think it's worth testing with your ears if you wanted to. Worst thing that will happen is it will sound bad (you increase the bias to fix that, or in rare cases, decrease it) or you will wear out the tubes prematurely.

If I were going to re-tube my again, I might try KT66s just to be different.

But I'm never sure what to do with my MA. Might trade it for another Marshall...

[Phano36]

Hello Washburn
In order to adjust your new tubes perfectly, (nominaly wise) you first need to know what is the max static dissipation wattage that the tubes operate. This info is normaly available within the tube specifications sheet. The rest is a question of tastes. As you know hotter bias current will shorten the tubes life and cooller will longer it but will alterned the sound quality. found attached a link that will provide a good tutorial of "How to bias" a tube amp. Be carefull not to zap yourself ! : ) plate voltage can reach +/- 450 volts

regards

http://www.duncanamps.com/technical/lvbias.html

[washburn 1]

Hi guys
Thanks for your replies, i will try and find the spec` sheet for the tubes and thanks,Phano, for the link info. When i spoke directly to Marshall tech `dep`t regarding the bias value for the `50H` they told me it was 38mv.Presume this was correct. When i re biased the amp, one valve was 41 and the other was 48 and i must say the amp now sounds better to my ears. I cant believe it was that high in the first place!! When SteveD designed the amp, many people thought the design for biasing was very convienient needing only a multimeter to test on the 3 point test pins. I guess hopefully that this is actually accurate enough as there is no need to delve any further into the guts of the amp, ie, valve pins, resistors etc as in `Duncanamps` .I can see the obvious need for this in other amps but SteveD seems to have designed `simplicity`into this amp. Hope this all makes sense and any other thoughts especially from SteveD would be really great. Thanks to all. Kev.

[SteveD]

I usually bias them to 36mV per valve but 38 is fine. It's not critical, as long as they are around that area. One thing to bear in mind for European models is that the Marshall factory biases the amps at 230V commensurate with EU legislation. However, in the world outside the factory the UK is still usually 240 -245 and many parts of Europe are still 220. This still falls within the tolerance of the legislation (which was the convenience of the nominal 230V figure).

Now, if an amp biased at 230V is plugged into 240V, the bias will read higher and vice versa if plugged into 220V. Thus, many people prefer to rebias anyway so the amp is optimised for their territory rather than within tolerance. It's not a requirement to do this as the amps are designed to work within these tolerances but purely a personal preferance and it also explains why you might find your bias to be a little higher than expected.

[Crunchifyable]

Well the test points and trim pot(s) have been sort of standard in many if not most amplifiers since the 80s probably, from what I gather from my tiny bit of research. I'm sure it cuts down on tech time, and thus encourages people to buy them due to reduced cost of ownership. Other methods may be slightly more accurate due to fluctuations in power, but I guess the fluciations in power will occur anywhere anyway., and measuring mv across a 1 ohm resistor (basically how the lest points work) is accurate enough for most people. Basically marshall builds the 1 ohm resistor right into the amp, so you or your tech doesn't have to add one

I'm glad you told me about the 38ma figure. I honestly think mine sounded better around 39 than 34, and I bet that's exactly why.

Then again, tube amps always seem to sound different on different days.




And to get smiles and what not to work , I think you have to uncheck "disable smiles."

And glad to hear Steve's recommendation of 36.

Guess I'm always a bit late to these things :).

[washburn 1]

`ello chaps
Thanks for all your help. So far i have googled TAD el34B-STR data sheet and looked at the figures but to me they might as well be in vulcan (perhaps Spock could understand them!!) . Basically i am unsure as to what figures to use, to calculate the bias voltage to set these valves at. Was just wondering if anyone can help me with that figure or can indicate how to arrive at it as i have never dealt with `valve tech` before, and it seems pointless just chucking them in without proper adjustment if i am to try them for sound quality.Have also googled the =c= data sheet and although some specs are the same or very similar, some appear totally different. Sorry to be a pain!!!

Crunchi, already have smiles `enabled` and the side panel does state that they are on but when i click on one i just get the smile description word on screen . sorry to appear a dunce but this is the only forum i have ever registered on.

Please can anyone help? Ta. Kev.

[Crunchifyable]

Not really sure about the STRs. My guess is to just treat them like a real EL-34. It might be fine that you didn't understand the specs of the tube, because I think the manufacturers tend to exaggerate the capabilities of the tubes.

From my brief research, it seems like they are just relabed Chinese El-34s. Are the STRs supposed to be a long plate / higher headroom version?

My thought is warmer biases tend to sound better and break up earlier. Yes, they wear out tubes faster, but given that JJs, TAD, etc. tubes tend to be mildly inexpensive, and also given that I don't really crank mine fully or play it for many hours a month, I figure a warm bias setting is good for things. I guess by warm I mean 37-38 mA to start, and assuming the number will creep up in time.

I'm just glad EL-34s are in production and inexpensive (relatively, but I only intend to have / use 50 watters). Certainly a much better situation than it was 20 years ago.

[washburn 1]

Hi Crunchi
Yes i also understand that they are of Chinese origin but manuf` to higher grade. I really only got them as they came up SO cheap on ebay that i thought i would keep them as spares but seeing some good comments about them i thought i could give them a blast. (only been out of the box for testing,EVIDENTLY, for a project that never happened). Yeah, don`t know of the physical properties of their make-up. Think they`re just supposed to be good. When you say to treat them just as a normal el34 i don`t quite understand, they ARE only normal .Did you mean that el34`s are all set the same , bias-wise? I thought all valves needed they`re own bias ajustment . One thing i dont understand is the effect that a valve and an amp circuit have upon each other and which influences which. By that i mean does the amp circuitry and values determine how the valve will behave and what bias it will need OR is that immaterial and means that the valve actually imposes its own stamp on the amp how the amp behaves and determines what the valve will`draw` and therefor how it needs to be biased ?? WOW sorry . Steve , if you read this an can enlighten us i`m sure it would be very interesting. From you guys out there`s experience is a bias of say 35 - 40mv quite average and would most valves be happy within that (or another) certain tolerance or can you not generalise like that ??!! ME CONFUSED !! Give us a clue chaps! All the best, Kev. p.s. still no smilies!! me sad !!

[Crunchifyable]

Yes, I would say that all EL34s would be set about the same bias wise.

It's true all valves are slightly different and need to be biased to an even and accepable amount, and this is more or less what a person does when they set them to 38ma.

Now what I do not understand is exactly why each tube is different. Sort of a mystery.

In reality, I suppose different tubes might be able to take different stresses. The problem of course is never being able to know if the manufacturers are inflating their numbers, interms of how much these things can take. In the spec sheets, it will list maximum static or idle dissipation, of which about 70-72% would be the highest recommended figure
(I forget the exact reason why 2% or so gets added to the 70% figure, but it has to do with a particular inexactness in bias readings).

But to deal with that sort of thing requires more work than simply measuring across a 1ohm resistor (which is basically what happens with the test points - to figure for the tube, you'd have to check the plate voltage, probably in the procedure outlined in the duncanamps site or in other places. Never done it myself, in part because the data from tube manufacters might be off, and partly because the platevoltage will vary based on how close the outlet is to its rated power.).

I wasn't sure of those ones you bought were standard EL34s or a modified / hybrid version, like the JJ EL34B (never tried it nor really care to, it's supposed to be a mix of EL34 and 6L6 - sounds good on paper, but I like my tubes to crunch up asap, and 6L6s don't really do that.).

Yea, Chinese seems okay too. If you can get em cheap, thats great and more incentive to really make those tubes scream for mercy

I'm really liking 37-38 mA for mine. Not as mushy as it was before when I guess the bias rose, but much better than the 34 mA figure I used briefly.

It would be useful to know what the intended plate voltage is (nominal or for a certain wall voltage...e.g. exactly 240 or exactly 120 in the US). I don't think most cheap DMM can handle the plate voltage found in guitar amps anyway.

[jagermike66]

Now, if an amp biased at 230V is plugged into 240V, the bias will read higher and vice versa if plugged into 220V. Thus, many people prefer to rebias anyway so the amp is optimised for their territory rather than within tolerance. It's not a requirement to do this as the amps are designed to work within these tolerances but purely a personal preferance and it also explains why you might find your bias to be a little higher than expected.

Explains why my MA50H was up at 40ma when I bought it lol cheers steve

[Crunchifyable]

Guess what I learned today... I think.

These tubes you just installed may have been the stock tubes in my Marshall MA (or similar). I thought Stock was Svetlana, but apparently not on the MA.

VLVE-00087 EL34B Shuguang Graded Anode Current White Logo

Means my spares are actually the Chinese tube, if all the info floating around on the net is true.
And all along I thought the originals were Winged =C=s.

Minor disappointment, but not surprising given the cost of Winged =C=s. If / when I go for a retube, have to decide whether I want to use the Marshall branded ones or get more JJs.

Be interesting to see if you like the Chinese ones over what you had in there before.

Granted I have no idea if STR is any different from EL-34b. I think STR = Special tube request, meaning TAD custom ordered them and who knows what they changed or improved.

[washburn 1]

Hi Crunchi
Hi mate, just googled your valve code, (00087 el34b)very interesting! Its amazing what you can find if you google! My new valves arrived today but have not had chance to fit them yet. Will let you know what i find. Am surprised to to hear that your valves may not be =c=`s , pretty sure that mine are as, looking at the make up of various brands of el34 it seems that the c`s are the only ones that have a sort of metal `tang` inside the bottle to support the valve innards, one on each `corner` top and bottom of the bottle/plates (if that makes any sense) and have the brown base, and mine have the dimple inside the top of the bottle, although my new TAD are also brown but without the `tangs`. I guess any further info or findings from other guys would be cool !! Steve, what d`you reckon? Cheers, Kev.

[Crunchifyable]

Well I compared mine visually with Chinese tubes for sale and Winged =C= for sale, and visually, it looked exactly like the Chinese one. Kind of hard to explain it, not really knowing what is inside them, but the angled metal plates on the top of the attenna looking things give it away as being Chinese. Winged =C= looked different.

So I'm pretty sure they are Shugang. It must have been a decision at some point. I do know my head was an old model from 2009 that didn't end up being sold into 2011. My guess is maybe the revoiced ones got better tubes as well.

At anyrate, the JJs I have should last me a while I hope.

[washburn 1]

Hi Crunchi
Got my TAD`s in today and err WOW!!!! these things open up the soundstage and just seem to make the amp sound `bigger` . Better bass response, i now have the bass and resonance set lower, without loosing any depth. Bass sounds tighter and more promenant without being too forceful, and not loose. Mids and top has opened up just like taking a towel away from the front of the cab, without becoming harsh or brash and the amp sounds like it can `breath` easier and at full volume they saturate SOOO beautifully the amp takes on a georgious thick midrange without becoming clogged up or overcoocked as if it cant handle it, (which i thought it did before, as if the amp just couldn`t handle being up full , not so now!). Treble is not at all harsh, AND i can stand about four feet away without any feedback on any guitars(with strings deadand). I realise its easy to think that sometimes we perceive different to be better but i did a blind test with my son (bassist, i know!) but he has a good ear and he genuinely thought the TAD were better in ways i `ve just described. If you remember i, like you went back to the Marshall/Shug`s preamp valves after a more `considered` trial. I love `em!! Svets may be good,reliable valves but it doesen`t hurt to try others, you might strike gold!! (in my opinion). They seem to be chinese and MAY BE specially selected and relabelled but i really think that there is NOTHING wrong with chinese tubes these days . It appears that Shuguang have really invested A LOT of money into the production of their tubes , and i for one think it has paid off!! It seems that some folks on the Marshallforum really like the Shug`s and we should not be embarressed to admit to using them. I`m guessing your chinese tubes sound good also. Nice one Shuguang!! still no bloody smiles !! what to do? p.s. my amp is also a 2009 model and the guy i bought it from only bought it new in July 2010, after the revoiced models appeared BUT speaking to Marshall Tech dept it appears that mine thas been revoiced, due to the mods i found inside that they told me about.I`m guessing POSSIBLY Marshall offered a mod recall on unsold stock at that time.