el84 bias...How hot?

[Robert M. Martinelli]

Oops...Chuck, it seems we had a "simulpost" ( Thanks Enzo! ) and the points raised are more or less the same, only, I knew the guitarmate +B to be about 400 V...but this doesn't change the meaning of the points we raised....
Best regards
Bob

[Chuck H]

Also...Keep in mind that my 15 clean watts are cathode biased watts. So I get that cool soft attack. I could certainly bump that up a couple watts by using fixed bias. 400+ plate volts and fixed bias for el84's is a spanky, spikey proposition. Great for modern distortion or crystal clean. But too much for most everything else IMHO.

As I said earlier. I've had my best luck with el84's down around 300 to 320 volts and up around 390 to 400 volts (with screens at 330). El84's are like that. It's like having two completely different tubes to work with. The design just naturally has two sweet spots. I wasn't having any luck running down the middle on voltage until I got tricky with it. But it has really worked out.

Chuck

[clyde1]

Hi Chuck,
Please cover more detail, I'd be very interested as I'm doing a 2xEL84 circuit right now and would like to max it out also. I'm somewhat familiar with the Paul Ruby mod although I don't have the particulars anymore but I don't know the other zener trick. Thanks.

[Chuck H]

First thing is a disclaimer. El84's have that sweet chimey tone at lowish voltages like 305 or 320. So if by "max it out" you mean get the most el84ish tone, then you should build with this criteria. If by "max it out" you mean you want the most power and tightness you should go high volts like 390 with the screens up around 335. You lose all the el84 charm this way and shorten tube life to a couple of months for some brands, but you can really get alot from el84s this way.

I ran down the middle at 350 volts with the screens at about 320. With the circuit I have the el84's sound alot more like the big bottles (el34, 6l6) but at lower output. If that sounds good to you then you will like this.

Plates at 350 with a 130 ohm cathode resistor and a 100uf bpass cap. I'm using a Hammond 270EX PT with a full wave diode rectifier and a 150 ohm 50 watt aluminum housed resistor to drop the B+ and give some "rectifier" sag. The first filter is 80uf. Then a 2.2k 5 watt resistor and a 20uf filter for the screens. Screen resistors are 420 ohms. The next dropping resistor for the PI is 5k and the filter is also 20uf.

I have 9.8 volts on top of the cathode resistor at idle. I chose a "Paul Ruby mod" zener value that would not drop below the voltage rise on the cathode resistor. So I went with 20 volt zeners (cathodes toward ground) and 1n4007's below them (cathodes toward the tubes).

There is now a 13 volt 5 watt zener across the cathode circuit. This gives good clean tones but tightens the power amp into fixed bias when pushed hard. Now that I have the voltage on the cathode regulated to not rise above 13 volts, I (or you) could use 15 volt zeners for the "Paul Ruby mod". Though I don't know if it would add further improvement.

All but the last tiny fraction of crossover and overshoot hash was eliminated with a small conjunctive filter across the OT primary. I'm using an 8k primary OT. Your conjunctive filter resistor should be 1.3x the primary impedance from what I've read so I went with 10k and called it close enough. I used the smallest cap that made a visible improvement on the waveform and an audible improvement to the tone, which was 1500pf. So the conjunctive filter on the OT primary is a 10k 5 watt resistor in series with a 600 volt 1500pf cap.

I'm using plain Jane Sovtek el84's. They are performing well and sounding good.

The PI is a typical LTP type with the standard 1M grid loads. The bias resistor is 820 ohms and the tail is 47k. I'm feeding it through a 2200pf cap and using .022uf decoupling caps to the power tube grids. I'm using 10k grid stoppers but you could probably go lower if you want a brighter spikier sound. The preamp is hitting the PI with a max of 7 volts with the boost switch on. This is giving me generous amounts of overdrive. The PI starts to clip just after the power tubes.

Thats it...Enjoy

Chuck

[ETR]

And I don't want to bust yours, but I think 25W RMS out of a couple of "normal" EL84s is simply impossible ( I' m talking about RMS, not peak to peak power ). Pushing two EL84s to their SOA limit yields about 17 W ( RMS ), and remember an EL84's maximum plate dissipation is 12 W. Even an AC30, which is known to be pretty rough on the output tubes ( they're biased at 14,5 W ) yields "only" some 33 to 36 W RMS ( with four EL84s ) when fully cranked.

Shifting the working point higher than this would give an EL84 a glorious ( but extremely brief ) life, much like James Dean.

I think your amp's operating conditions are simply too much even for the old, good quality EL84s , let alone the current production ones....

With a bias voltage around -17VDC and a + B of 398 V your bias current is more or less 45 mAmps, so the resulting static plate dissipation would be 17 W.

Are you sure your amp didn't have 7189s in the first place?

I'm asking this because, IMHO, the only way to go that high without shortening the tubes' life is to use 7189s, which are a mil-spec extremely rugged version of the 6BQ5/EL84 and can withstand your amp's operating conditions. Given the voltages present inside your Traynor amp and its mode of operation, I consider it more likely to have been designed with 7189s in mind. ( 440 VDC max. Plate voltage, 400 V max. Screen voltage, 72 mAmps max. Cathode current , 13,2 W max. static Plate diss. ).

BTW, the Philips Databook reads 24 W RMS for two 7189s in AB1 at 400 VDC ( Plate ) and a bias voltage of -15 VDC, which seems to be pretty close to your amp.

Best regards

Bob

Ask anyone that knows Traynor amps. 25 watts RMS out of 2 EL84s (Guitarmate) 90 watts RMS out of 2 EL34s (YBA1A) and yes true RMS watts.

You should read about average power dissipation and push pull operation if you want to understand how this works.

[Chuck H]

25 watts RMS out of 2 EL84s (Guitarmate) 90 watts RMS out of 2 EL34s (YBA1A) and yes true RMS watts.

Hogwash

You should read about average power dissipation and push pull operation if you want to understand how this works.

Indeed

[ETR]

If you ever get one on your bench you would know it's true dude. I didn't believe it at first either when someone told me.

[Robert M. Martinelli]

Ask anyone that knows Traynor amps. 25 watts RMS out of 2 EL84s (Guitarmate) 90 watts RMS out of 2 EL34s (YBA1A) and yes true RMS watts.

You should read about average power dissipation and push pull operation if you want to understand how this works.

Hi ETR,
I' m sorry if I sounded like I wanted to deny what you were saying;
As I was saying, 24W RMS at 400 V are indeed possible with a couple of 7189s.

I was only highlighting that those conditions are very hard on EL84s, this, BTW, has been confirmed by Chuck in one of his posts, and can ( and usually do ) shorten tubes' life.

I am aware of the way push-pulls work, and I know about the average power dissipation thing, but, as I told already, the conditions found inside your amp have most likely been defined with 7189s in mind IMHO. This is also confirmed by looking at some Guitarmate schematics, where the output tubes are indeed 7189s. I still think 17 W static are simply too much for EL84s, especially for the current production ones. You should remember that usually EL34s, ( which have waaaaaay larger plates ), are biased between 18 and 20 W, I don't believe EL84s can withstand such conditions without dying prematurely.

Peace

Bob

[Chuck H]

Ok, I have to concede that there are alot of claims of high wattage from the old Traynor YB1A MKII. Traynor even advertised "twice the power" of the normal Bassmaster. The most outrageous claim I saw was 138 watts RMS from a pair of el34's. 70 to 80 watts are claimed by many and a few 90 watt claims. So...

I have no doubt that these are very loud amps. Enough so that since Traynor said the amps had "twice the power" most people just go with it. But the notion that they are putting out more than about 60 watts is just plain wrong. Here's why.

The max dissapation of an el34 tube is published at 25 watts. That is the max safe dissapation according to the MFG. Can you push it beyond that? Sure. Sometimes with some brands. Some brands of el34 will go to 30 or even 35 watts max. But not most. This would require running them at near max plate and screen voltage. The YBA1A MKII has 525 plate volts. With modern wall voltages you can bump that to 550 plate volts. Thats still 250 volts below the max. You would need to bump that up to get to even 60 watts of clean power. The other issue is the operating class. The YBA1A MKII is a class AB1 amp. To go beyond AB1 the amp would need to have a power tube grid circuit capable of at least SOME current. But it uses a standard AC coupled LTP inverter so no current can be drawn by the grids. If you fed the power tube grids through a pair of cathode followers you could get into AB2 and MAYBE get 70 watts from a pair of el34's. If you really want watts from your el34's you'd have to move to class B. Class B is not used in tube guitar amps because you would not be able to overdrive it without the consequence of substantial crossover distortion. You may even get crossover distortion clean. And from the el34 data I saw only Phillips published high voltage class B data. According to which the only way to get 90 watts from a pair of el34's is to run them in class B with the plates at 775 volts. Class B requires that the power tube grids draw substantial current that the YBA1A MKII circuit simply can't provide. You would litterally need to be feeding the power tube grids with a cathode coupled 6v6 or some similar arrangement.

So, Being as the YBA1A MKII is locked into AB1 by it's circuit limitations, and can't supply any grid current, it simply can't be putting out more than about 60 watts.

[ETR]

Hi ETR,
I' m sorry if I sounded like I wanted to deny what you were saying;
As I was saying, 24W RMS at 400 V are indeed possible with a couple of 7189s.

I was only highlighting that those conditions are very hard on EL84s, this, BTW, has been confirmed by Chuck in one of his posts, and can ( and usually do ) shorten tubes' life.

I am aware of the way push-pulls work, and I know about the average power dissipation thing, but, as I told already, the conditions found inside your amp have most likely been defined with 7189s in mind IMHO. This is also confirmed by looking at some Guitarmate schematics, where the output tubes are indeed 7189s. I still think 17 W static are simply too much for EL84s, especially for the current production ones. You should remember that usually EL34s, ( which have waaaaaay larger plates ), are biased between 18 and 20 W, I don't believe EL84s can withstand such conditions without dying prematurely.

Peace

Bob

Guitarmates are EL84 powertubed amps see here: http://www.lynx.bc.ca/~jc/661128_YGM2.gif

I owned one for a few years and measuerd 25 watts unclipped sinewave many times out of it. They are fixed bias and are usually biased at about 5-6 watts/tube.

I have also owned YBA1A's and have measured 90 watts unclipped sinewave many times as well. Both amps still had what appeared to be the original power tubes in them and I have worked on many of these with original power tubes over 30 years old. They connect the supressor grids to the negative bias supply and do have some unconventional circuitry but work great and are very reliable.

Most the reason these amps produce fairly high power with relatively low power tubes is that the transformers can supply a lot of current. It's not just about the voltage.

[ETR]

Ok, I have to concede that there are alot of claims of high wattage from the old Traynor YB1A MKII. Traynor even advertised "twice the power" of the normal Bassmaster. The most outrageous claim I saw was 138 watts RMS from a pair of el34's. 70 to 80 watts are claimed by many and a few 90 watt claims. So...

I have no doubt that these are very loud amps. Enough so that since Traynor said the amps had "twice the power" most people just go with it. But the notion that they are putting out more than about 60 watts is just plain wrong. Here's why.

The max dissapation of an el34 tube is published at 25 watts. That is the max safe dissapation according to the MFG. Can you push it beyond that? Sure. Sometimes with some brands. Some brands of el34 will go to 30 or even 35 watts max. But not most. This would require running them at near max plate and screen voltage. The YBA1A MKII has 525 plate volts. With modern wall voltages you can bump that to 550 plate volts. Thats still 250 volts below the max. You would need to bump that up to get to even 60 watts of clean power. The other issue is the operating class. The YBA1A MKII is a class AB1 amp. To go beyond AB1 the amp would need to have a power tube grid circuit capable of at least SOME current. But it uses a standard AC coupled LTP inverter so no current can be drawn by the grids. If you fed the power tube grids through a pair of cathode followers you could get into AB2 and MAYBE get 70 watts from a pair of el34's. If you really want watts from your el34's you'd have to move to class B. Class B is not used in tube guitar amps because you would not be able to overdrive it without the consequence of substantial crossover distortion. You may even get crossover distortion clean. And from the el34 data I saw only Phillips published high voltage class B data. According to which the only way to get 90 watts from a pair of el34's is to run them in class B with the plates at 775 volts. Class B requires that the power tube grids draw substantial current that the YBA1A MKII circuit simply can't provide. You would litterally need to be feeding the power tube grids with a cathode coupled 6v6 or some similar arrangement.

So, Being as the YBA1A MKII is locked into AB1 by it's circuit limitations, and can't supply any grid current, it simply can't be putting out more than about 60 watts.

Like I said you should read about average power dissipation and push pull operation. A 25 watt rated tube can dissipate 50 watts half the time and still have an average dissipatin of 25 watts. Two 25 watt tubes in push pull can do this and put out 100 watts quite easily with no undue strain. That's usually done in class B operation. You can have two 25 watt tubes do 90 watts in push pull class AB which is what Traynor did with the YBA1A. There's plenty of info on the net if you care to look for it.

[Robert M. Martinelli]

Chuck,
I'm glad you pointed that out in detail; it often amazes me how often manufacturers mislead people with their over-confident blurb ( often knowing what they're stating it's not true ).

It would take only a little time to take a look at datasheets ( I have some old and valuable ones, but for the ones who don't have them at hand, plenty of data can be tracked down on the internet with a simple click ) to understand what's true and what's not.

The same applies to operating classes as well....some people talks about them without knowing what they're all about, so I' ll try to make some points clear for them in a nutshell, at least for the classes of our interest.

1 - First of all the class of operation is ALWAYS stated under working conditions ( with signal flowing ).

2 - Class "A" - The device is always on ( 360 degrees ). One device can suffice in reproducing the input waveform. Theoretical efficiency 50% ( in practice much less than that ).

3 - Class "B" - The devices are on for half a cycle ( 180 degrees ). At least two devices are needed to reproduce the input waveform. Class "B" is inherently prone to zero-crossing distortion (a.k.a. cross-over distortion ).
Theoretical efficiency 78 %, in practice around 70%.

4 - Class "AB1" ( first variation on class "B" ) - The devices are on for more than half a cycle ( >180 degrees ) but less than 360 degrees; a little current flows at all times ( this is why it is often said class "AB1" amps work in class "A" at very low volumes ) to keep the tubes away from cross-over distortion. As seen in class "B", at least two devices are needed to reproduce the input waveform.

5 - Class "AB2" ( second variation on class "B" ) - Same as above, but with the ( control ) grids drawing some current.

6 - Most ( if not all ) push-pulls amps on the market are AB1 designs ( even if some of them are said to be class "A" by the manufacturer, e.g. Vox AC30 ).

7 - Doubling the power yields only a 3dB gain, so the difference is barely audible to the ear ( 3 dB are set as the standard for the minimum audible difference the human ear can perceive ).

But... for a minute.....let's assume we run a couple of EL34s at 50 W each in class "B", this means, being the practical efficiency 70%, you only get 70 W out of that, then you have to add the losses in the OT's iron and copper ( 10 % ) so what you would get at the speaker would be around 60 W, but with cross over distortion. You would then need to "sacrifice" some of the power to go "AB1" and kill the cross over distortion, and that brings us in the 50 to 55 W area ( RMS ).

So....
It only takes the knowledge of a certain amp's operating conditions and a datasheet ( together with little mathematical skills ) to determine the real
( RMS ) power that amp can put out ( The "loudness" of an amp involves other factors, like the speakers' efficiency ).

Best regards

Bob

[Robert M. Martinelli]

Guitarmates are EL84 powertubed amps see here: http://www.lynx.bc.ca/~jc/661128_YGM2.gif

I owned one for a few years and measuerd 25 watts unclipped sinewave many times out of it. They are fixed bias and are usually biased at about 5-6 watts/tube.

I have also owned YBA1A's and have measured 90 watts unclipped sinewave many times as well. Both amps still had what appeared to be the original power tubes in them and I have worked on many of these with original power tubes over 30 years old. They connect the supressor grids to the negative bias supply and do have some unconventional circuitry but work great and are very reliable.

Most the reason these amps produce fairly high power with relatively low power tubes is that the transformers can supply a lot of current. It's not just about the voltage.

Hi again ETR,

The primary ( or each half of it ) is a current ring, the current flows from the +B to GND through the tube(s), this means whatever current flows from the PT in the OT has to flow in the tube(s), they can never be treated independently....if the PT and the OT can handle a lot of current, this doesn't mean the tubes can do the same.

As to the schematic, I've seen other Guitarmate schematics with 7189s, though I don't have the link at hand...

You're stating you measured many times 25 W unclipped, so, at this point, as Chuck already asked, I would like to ask you about the method you used for your measurements.

Best regards

Bob

[Chuck H]

Ok. Just for giggles I looked at a bunch of Traynor schems. Two of them were for the yba1a mkII with over 500 volts on the plates ('69 and '70). Both of them had the supressor tied to 0V rail (ground). But this is not to say that a later model didn't use the supressor grid differently. I had a later model Bassmaster that did have the supressors wired the way you describe. For what it's worth it was a great amp. I still have it though it's circuitry no longer resembles the schematic in any way. This amp was a mod test platform for many years. But don't worry. It's not a real collectible. It's one of the later models with the over/under channel inputs seperated by the controls.

Anyway, I also looked up a Musicman 150 schem. These are widely regarded as the most efficient tube instrument amps. They run the power tube grids from what appears to be a source follower (provides the grids with a limited current path) and run the plates of four 6L6 tubes at 700 volts. By the schem I would say these are AB2 amps. Each 6L6 is good for 37.5 watts in this amp. Musicman also made a "75" with two tubes. Let me state for the record that you would not want to overdrive one of these amps. Aside from hearing loss there would be substantial crossover distortion. These were not designed to be pushed into overdrive conditions. They ran substantially more plate voltage and a different class of operation than the yba1a and still only got a meager 75 watts from a pair of big bottles.

Now I'm going to say what I really think. Not because I'm mean. It's because I'm an obsessive truth pounding a$$ho!e that most people eventually learn to dislike.

Your repeated use of the "sine" indication and the wattages of 25 for the guitarmate and 90 for the Bassmaster are spot on with the vintage literature on the Yorkville website. I believe that you have no direct knowledge of the actual output of these amps and are instead just reprinting what you've read from what you believe to be a responsible source of information. It's not. Stop doing it. Or you could answer my first question on this subject. How did you measure the output of these amps? Please include details.

Chuck

[Robert M. Martinelli]

Now I'm going to say what I really think. Not because I'm mean. It's because I'm an obsessive truth pounding a$$ho!e that most people eventually learn to dislike.

Your repeated use of the "sine" indication and the wattages of 25 for the guitarmate and 90 for the Bassmaster are spot on with the vintage literature on the Yorkville website. I believe that you have no direct knowledge of the actual output of these amps and are instead just reprinting what you've read from what you believe to be a responsible source of information. It's not. Stop doing it. Or you could answer my first question on this subject. How did you measure the output of these amps? Please include details.
Chuck

+1 on both, Chuck!

As to the first point, glad to learn I'm not alone

As to the second point , it confirms the idea I already expressed that some manufacturers ( even reputable ones ) are often offering blurb instead of truthful info. And, yes, I'd like to learn about ETR's measuring methodologies too.

Best regards

Bob