35 Watts from (2) 6BQ5 / EL84s ! How?

[Ronquest]

Was looking at another post about 2-6V6 30 Watt schematic https://el34world.com/Forum/index.php?topic=31321.0
So, down a rabbit trail and found an amp reportedly pushing 35 Watts with (2) EL84s.  Roger A. Modjeski Music Reference RM-10 MK2
I know it's hifi but tubes is tubes. 

How could this be done?   And how much then could we get from the 6V6s?

Link to article, it's the 2nd amplifier.
http://www.6moons.com/audioreviews/musicreference/rm10.html

[sluckey]

Maybe they are expressing the power in peak watts which is 1.414 X RMS watts.

[shooter]

reportedly pushing 35 Watts

one of those things I could never get guitarists to "understand" about my builds
I'd tell em it's a 20W amp they would argue it's LOUDER than my 40W amp
I'd explain

1.414 X RMS watts

They'd look at me like I was from mars
sometimes ya just gotta shake head n smile

[WimWalther]

There's also PEP - Peak Envelope Power. I'm not entirely sure how this is measured / calculated, but it's something you run into dealing with RF amplifiers.

Once again, the PEP figure, like Peak Power, seems to exceed RMS power by a noticeable margin.

[shooter]

if ancient history from an 'ol brain recalls it's something like .707 of peak.  that's the point you'd measure for spec.
and, ya, it's not a guitar amp spec. 

[astronomicum]

Maybe they are expressing the power in peak watts which is 1.414 X RMS watts.

Or they took Univox's approach taking RMS X 2 and calling it Music Power 

[HotBluePlates]

... found an amp reportedly pushing 35 Watts with (2) EL84s.  ...

How could this be done?  ...

We don't know the claim is true.

Even if it is a true claim, do you really need/want 35w from a pair of EL84?

If you really want "35w from a pair of EL84" you could do what MusicMan did:  stack the tubes on top of silicon, and run the amp in Class B.

  - In the MusicMan the tube is not driven, the solid-state between the tube's cathode & ground is what gets driven.
  - The solid-state determines whether any current flows.
  - The tube is pinned to a fixed bias voltage, and a fixed screen voltage.
  - The tube passes additional current when the solid-state allows
  - The tube is just there to handle large plate voltage swings, because the solid-state isn't rated to handle the volts.

Yes, the EL84 amp is only claimed to be 35w, but the 2x 6L6 amp was claimed to make 65-75w so the relative tube-size seems to scale correctly.

[Ronquest]

After doing some more research on Roger A. Modjeski's work and life, I'm more inclined to believe he was a truth seeker in engineering and hifi audio and less inclined to believe he was fudging numbers.  But then again I have bought a few 1000W Pyle amps (way)back in the day.
 
Here is a link to the pdf manual and below is the schematic I found.  This documentation is a good read beyond a standard manual!

https://static1.squarespace.com/static/61d0e00ac8fd8f2d31e7f907/t/6574a8c90370701e64923fe5/1702144201227/RM-10+MKII+Manual.pdf

658V (720V penciled in) on the plates.  Interesting.

[glass54]

Up to about 20 years ago and longer, I repaired a lot of MusicMan 2475-75 and 2275-75 amps. the fault was BLOWN Driver Transistors 95% of the time.
Very rarely a tube and occasionally an IC in the preamp. Not nice amps to work on but usually nice speakers (in the Aussie model).
Funny enough I have just received a 2475-65 in my workshop this week to be checked over for resale.
We do have better high Voltage driver transistors as replacement now, due to lots of high powered solid state amps.
....but give me a Fender or Marshall, etc, with tube phase inverter any day.
Regarding High Power Muso Amps (2 EL34 tubes), Dynacord Eminent 2T was supposed to produce 100W into 8R, running 750V HT and 410V G2 supply. I worked on one in late 1980's. It had VERY NICE iron 

Regards
Mirek

[WimWalther]

After doing some more research on Roger A. Modjeski's work and life, I'm more inclined to believe he was a truth seeker in engineering and hifi audio and less inclined to believe he was fudging numbers. 

I know of Roger as primarily a hi-end hardware guy. He had his own tube testing / conditioning voodoo going on too, have you ever run into tubes screened "RAM Tube Works" in dark blue? That's Roger as well.

[scstill]

Roger Modjeski 35w design
https://6moons.com/audioreviews/musicreference/rm10_2.html
Roger Modjeski site
https://www.ramtubes.com/rogers-corner

[Ronquest]

I know of Roger as primarily a hi-end hardware guy. He had his own tube testing / conditioning voodoo going on too, have you ever run into tubes screened "RAM Tube Works" in dark blue? That's Roger as well.

I noticed that connection in my research today, but had not heard of, nor seen them. Here's that Ram's link to more of Roger's writings and info.
https://www.ramtubes.com/rogers-corner

[scstill]

BTW - remember RaM is designing HiFi amps and so is seeking linear response. Not generally where we like guitar amps to be. If you run the El84 at double the plate voltage (with his other adjusted parameters) you should be pretty far out on the flat part of the grid curves (ie very linear). Seems that for guitar amps 12w is just fine for two EL84 (or double up on the tubes for more w).

[Ronquest]

BTW - remember RaM is designing HiFi amps and so is seeking linear response. Not generally where we like guitar amps to be. If you run the El84 at double the plate voltage (with his other adjusted parameters) you should be pretty far out on the flat part of the grid curves (ie very linear). Seems that for guitar amps 12w is just fine for two EL84 (or double up on the tubes for more w).

I'm more interested in the how and is it possible and I wanted to hear what you guys thought, not really looking for more power.  Wonder what his output transformer ratio was?  Interesting, though I generally avoid hifi, I don't need another $ hobby.

[HotBluePlates]

658V (720V penciled in) on the plates.  Interesting.

700v on a tube rated for 300v max.  What could possibly go wrong?   

[scstill]

700v on a tube rated for 300v max.  What could possible go wrong?   

The writeup explains how it is done safety for the tube. Claims that it is safe with 10yr longevity to date. Maybe our EL34 experts could determine if this is hot air or not. Of course not good for guitar amp sound and need a super big piece of iron, but it is interesting to say the least.
Roger Modjeski 35w design; https://6moons.com/audioreviews/musicreference/rm10_2.html

[shooter]

run the amp in Class B.

haven't read the links so;
operating Class B or C you can exceed LOTS of "normal operating" specs
 
the smart kids figured out how to get 25KW of power from a 500W tube
the magic key is period time, you still can't exceed dissipation over time, so instead of on all the time, it's only on for 10% of the time


at the end of day though, there is no such thing as a free lunch
 

[WimWalther]

We won't be running any audio amps in class-c.. not even guitar stuff. IME, C is effectively limited to FM radio applications.

[shooter]

 
no kiddin


posted just to "illustrate" how to Squeeze mo' watts from less tube

 

[HotBluePlates]

Here is a link to the pdf manual and below is the schematic I found.  This documentation is a good read beyond a standard manual!

https://static1.squarespace.com/static/61d0e00ac8fd8f2d31e7f907/t/6574a8c90370701e64923fe5/1702144201227/RM-10+MKII+Manual.pdf

658V (720V penciled in) on the plates.

The writeup explains how it is done safety for the tube. Claims that it is safe with 10yr longevity to date. ...

You'll have to point it out for me.  I'm not smart enough to find out how 700+ volts is safe for a "300v tube."

On Page 6 & 10, the author mentions derating the voltages on resistors because they were failing.
On Page 8 the author cautions against "too high voltages" for tubes (twice).

In several places the author mentions "light loading":  this just means the OT primary impedance is high, so the plate voltage swing is large, while the plate current swing is small.

But output tube plate voltages swing up as well as down; the concern for starting at 700v & going up on 9-in miniature sockets is about arcing between pins.

There is a claim of 5,000-10,000 hour tube life, but notes that's just an estimate on Page 9.


Maybe the EL84 maximum plate voltage is rated too conservatively.  I know 12AX7s routinely handle ~450v.  But I'm skeptical about 700v.

[scstill]

But output tube plate voltages swing up as well as down; the concern for starting at 700v & going up on 9-in miniature sockets is about arcing between pins.

here is that 700v EL84 from RAM. Says it's the great Yugo vacuum, which might prevent that arcing
https://www.ramtubes.com/store/p/yugoei-6bq5el-84

[scstill]

looks like we will never be able to ask Roger directly about the 700v EL84
https://www.ramtubes.com/about

[HotBluePlates]

But output tube plate voltages swing up as well as down; the concern for starting at 700v & going up on 9-in miniature sockets is about arcing between pins.

here is that 700v EL84 from RAM. Says it's the great Yugo vacuum, which might prevent that arcing
https://www.ramtubes.com/store/p/yugoei-6bq5el-84

That's not "proof" because it's the same "source" making the claim:  RAM.

But the tube they champion was made by Ei in Yugoslavia.  So does Ei claim their EL84's plate can handle 700v?
Nope (Scroll to the last page:  Va is "max plate voltage" while Vao is "maximum plate supply voltage" on the other side of the OT)

[Ronquest]

On Page 6 & 10, the author mentions derating the voltages on resistors because they were failing.
On Page 8 the author cautions against "too high voltages" for tubes (twice).

Context here?

HBP, I definitely question the 700V plate voltage too, I'm afraid of my el84s running at 400V cathode biased. 

On page 20 of the manual, it states,   " With the meter positive on the red wire at the most
positive main filter capacitor (caution 700 volts!) measure with the negative first to the blue and
then to the brown on pin 7 of each output tube. We purposely leave the top of this socket pin with
an open hole so a mini-grabber hook can be a`ached. These hooks are strongly recommended as
they prevent slipping and shorting the 700 V plate to something else. "

I would say the RM-10 better be 700V or every other buyer will be calling for repairs when their voltages are off on their first bias and tube roll.  Audiophile guys do test/check specs, have you been on their forums?, just like here, but more pretentious.  Not that this proves anything, but he is stating the plate voltage here too.

So we have yet to see an actual verification of watts in RMS, but I'm tempted to to see one of you throw down 700V on some el84s!

What I also find interesting, is his output transformer.  He states it's rated for 250 Watts.

[acheld]

Pardon my skepticism, but I grew up during the time of snake oil sales for audio gear, though I suppose you could argue that era never ends.

Irrespective of "some" truth in the hype, it remains hype. 

There's no free path to performance.   

How many runs does a top fuel drag engine get before a rebuild? 

[shooter]

How many runs does a top fuel drag engine get before a rebuild?

[sluckey]

I suspect a schematic would be quite revealing.

[Ronquest]

I suspect a schematic would be quite revealing.

Post #7

[shooter]

from a quick look the 600vdc drops thru a 22k yielding 420vdc at plate with 140vdc at cathode leaving 280vdc across the tube, guessing that keeps it "inside" the safe zone?

[HotBluePlates]

from a quick look the 600vdc drops thru a 22k yielding 420vdc at plate with 140vdc at cathode leaving 280vdc across the tube, guessing that keeps it "inside" the safe zone?

That's the phase inverter.

V3 and V5 are the EL84 output tubes for one side, V4 and V6 for the other.  "658" is shown at the plates, but the cathode voltage is not indicated.  There appears to be a cathode-load-winding (Yellow wires) whose center-tap (White wire) goes to the 10Ω shared cathode resistor.

The cathode load (if similar to the plate load & not merely for feedback) only reduces the voltage across the tube when signal is applied & for half of the cycle.  The other half will increase the voltage across the tube.

[shooter]

 
I said it was a quick look 
edit:
the PA tubes looked like the core  of the OT

[PRR]

> a quick look the 600vdc drops thru a 22k

{as HBP wrote while I was napping} I see the 22k feeding the driver, and the OT/power_plates fed 720V or 665V from C301 C302.

This plan has been around for many years. RAM was around until recently. I've never understood it. The ratings, the abuse, the surely very high impedance, or the point (EL84 is as cheap as it gets, use more).

I do doubt it could stand stage-amp duty.