80 watts?!?

[marshman]

I was reading a review of the Bogner Shiva in Guitarist UK (I think) and it says that an el34 loaded amp produces 80 watts? Are we still talking 'clean watts' here? Are 34s really capable of that sort of power?

http://www.bogneramplification.com/

Check the Shiva, it's right there. Is it a question of seriously over-building the OT? My inner bass player wants to know.

[markh]

You can get 100 "stereo hi fi" watts out of a pair of EL34s with the right B+ and OT, but it's pushing them a little, dissipation wise.

--mark

[zaphod_phil]

Forget about stereo hifi watts. You can get a good 100W RMS clean out of a pair of EL34s running somewhere around 700V. One or two more conservative Traynor amps get 90W out of a pir of EL34s. Even running at lower voltages, a typical "50W" marshall with EL34s will produce 60W RMS clean, and similarly a "100W" Marshall with EL34s will produce 125W RMS clean.

[veets]

I've got one of those YBA1A's as well. Use it for bass with a JBL E140. I fully believe it can easily produce the 90 Watts RMS they say it's good for. Even more with todays wall voltage, and still more if modded for 6550's, 807's or 6146's. Absolutely paint peeling loud with a guitar. I think you'd hear it OVER an 8" naval gun. All from a pair of fat bottle 6CA7's. Prices have kinda skyrocketed in recent years on these Traynor's though.

[martinw]

Pah, that's nothing. I have a copy of the GEC book, "An Approach to Audio Frequency Amplifier Design" from 1957.
In there is discussed an amp which uses a pair of EL84's, a pair of KT66's, THREE output stage transformers, and a pair of GEC V1505 output valves, in class AB2.
The V1505 uses a plate voltage of 2500V to produce a plate dissipation of 275w per valve.
Overall the amp kicks out 1100w clean.

[Snakeman]

Even more with todays wall voltage, and still more if modded for 6550's, 807's or 6146's. Absolutely paint peeling loud with a guitar. I think you'd hear it OVER an 8" naval gun.

I'd like to shoehorn a pair of 807s into my YBA-1, but the screen voltage is limited to 300V(?). How would you reconcile this?[/quote]

[zaphod_phil]

AFAIK, 807s will give less power out, not more. 807s are basically similar to 5881s in a coke bottle, with a top cap anode connector for RF use. Both the EL34 and 807 are rated for a max dissipation of 25W. However, VaMax for EL34s is 800V, but only 600V for the 807. With higher voltages you can deliver more power output, provided you chose the load impedance and bias to stay within the25W max dissipation rating.

The other thing to bear in mind that EL34s are true pentodes, and have a lower damping factor than beam tetrodes like 6L6/807s, 6551s, etc. I have read that given similar operating conditions (DC voltage, grid drive, etc), the EL34s will therefore swing higher output power, which is supposedly why similar amps which with a pair of 6L6s will produce 50W, will give 60W with EL34s. To really get more power out with 6551s or other big tetrodes, you would need to up the power supply voltage and grid drive level.

[clobo]

Hi,

I had two industrial pa's (Marsland RA-75D) that I used as "test bench" for my prototype builds. A pair of EL34's delivered well over 80W of clean power with 880V Plate Supply, 470V Screen supply, and a class-B McIntosh style design (OT splits load between plate and cathode circuits).

Claude

[veets]

zp's right-the 807's will give you a bit less than the EL34's-but only at the upper reaches of their ratings. I'm fairly confident that a YBA1A could be modded for 807's--and still produce around 80-100 watts of clean power. MUCH cheaper tube to buy too--I think that is the saving grace of using 807's.

[zaphod_phil]

You might get 80W out. I doubt you would get much more than that. Remember they'll only handle 600v - "only" he says And they're beam tetrodes, so they have a higher damping factor. An 807 is basically just a 6L6 in a different bottle.

[veets]

Ok, so how about using 6146's, zp? Can they exceed the 6CA7's for clean power output in a YBA1A?

[zaphod_phil]

With any of these tubes, the bottom line is that you would need to put in bigger transformers to give more voltage and current. Then maybe also tweak the PI to provide increased drive. Not too trivial.

[marshman]

I had heard somewhere that the hardcore 100w Plexis were usually making something like 150 watts (flat out, full bore, NOT CLEAN tone), but was a bit dubious about 80 watts of clean from a pair of EL34s. I take it that it IS possible, just not normal in some way. Unfortunately, I don't have the background to really understand the jargon.

Thanks

[jnewman]

To get rid of as much jargon as possible and sum up:

Tubes operate with a DC high voltage supply.

The higher the DC high voltage supply, the more power you can coax out of your tubes.

Many amplifiers run around 300-450V as the DC high voltage supply.

If you increase the DC high voltage supply to 550-700V, you can get a lot more juice out of your tubes, but increasing the supply voltage this much causes some problems (or at least necessitates some design decisions) of its own.

[zaphod_phil]

Basically, if you run them at higher voltages you can get more power out, and still stay completely within the tubes' specs.

IIRC Plexi/Richie tested a 100W Plexi and measured 125W RMS *clean* coming out of it! This is why some of those old 100W Plexis had a habit of blowing up 4X12s. Similarly many 50W Marshalls actually out around 60W clean. And we have the Traynor YBA1A producing 90W. People don't seem to realize what powerful tubes EL34s are!

[dotfret]

Rating is all down to the distortion (or as Charlie Watkins used to politely call it, "coloration"). Yer Marshall plexi 100 puts out 100W RMS at the BS spec. distortion level for valve amps -at full crank it puts out 147W+ at about 14% coloration. I am too old to accurately remember all the numbers -I am only quoting those I know are reasonably right.
Working the B+ numbers is not necessarily a good guide - it is possible to work a valve over its max voltage, but starve it in other ways so that it survives - there were, for example, Accoustic designs which did just that. OTOH there were designs which underestimated how far you could push this concept, which is why the Dan Armstrong Graphic amps are so hard to come by these days....

[zaphod_phil]

Rating is all down to the distortion (or as Charlie Watkins used to politely call it, "coloration"). Yer Marshall plexi 100 puts out 100W RMS at the BS spec. distortion level for valve amps -at full crank it puts out 147W+ at about 14% coloration. I am too old to accurately remember all the numbers -I am only quoting those I know are reasonably right.

The 125W that Richie measured was *clean* RMS - maybe not quite hifi, but clean by guitar amp standards. Heavens knows what the power output would have been distorted. And he isn't the only one to report these very high power levels from Marshall amps with EL34s.

Working the B+ numbers is not necessarily a good guide - it is possible to work a valve over its max voltage, but starve it in other ways so that it survives - there were, for example, Accoustic designs which did just that...

The EL34 specs allow you to get up to 100W out of a pair at 5% THD, without doing anything you shouldn't - see http://tdsl.duncanamps.com/show.php?des=EL34 All completely kosher and within spec.

[dotfret]

Stop taunting me because I can't remember the THD level for the measurement, Phil!
We should remember that not all EL34 are the same ( some are 6CA7) - while it is possible to do the 100W at 5%THD, You cannot guarantee that from some examples of the Bantam design, but with fat boys it is a lot easier. Whatever, one would like them to have a useful lifespan, not drive them rapidly to destruction.