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Innerstage vs R/C coupling.

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Posted on February 25, 2017 at 10:47:01
Michael Samra
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 I was asked about this three times in the last month by different about which is better and I tell them from my own experience it depends on the application.
My Fisher 50A and 55A amps are fantastic and make a lot of power for being triode connected,mainly because of the way they can go into AB2 without a hard clip.I'm thinking this could be due to the innerstage transformers because I also have a pair of Cary/AES SET amps with IT coupling and those are pretty dynamic as well.The IT trafos in those aren't the greatest but with better ones I think the amps would improve a lot as far as overall definition.
Now as far as detail and musical depth goes,R/C coupling holds an edge IMHO but IT coupling appear to have an edge in dynamics.Now,what I'm saying here is not cold hard fact,it is just from my experience from the amps that I have. I believe Mcintosh used an IT coupling transformer in one of their 1950s odd ball commercial amps.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

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Can you say inTerstage?..., posted on February 25, 2017 at 11:07:45
Steve O
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 ...I knew you could! ;-)

 

To make a comparison shouldn't he be using a 1:1 IT?, posted on February 25, 2017 at 11:17:24
Tre'
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 .
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Innerstage vs R/C coupling., posted on February 25, 2017 at 12:08:38
mqracing
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 You might also want to consider LC coupling as an option.

MSL




Builder of MagneQuest & Peerless transformers since 1989

 

RE: To make a comparison shouldn't he be using a 1:1 IT?, posted on February 25, 2017 at 12:19:27
mqracing
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 Unless the galvanic isolation of the 1:1 has strong value in your circuit I just don't see that this approach has much to recommend it. Especially if it is an airgapped 1:1 interstage.

Most airgapped interstages have a distinct lack of adequate primary inductance to do the job well.

better if you need galvanic isolation to go with a parafeed 1:1 interstage. They can be built on a smaller core (with fewer turns and much less winding capacitance) and have far, far greater primary L. And remember that it is the paralleled reflected and inductive impedances that serves as the "load" for the tube driving the primary of the IT.

And if you don't need the galvanic isolation LC coupling provides even more benefits than IT coupling.

MSL



Builder of MagneQuest & Peerless transformers since 1989

 

Three ways to couple......, posted on February 25, 2017 at 12:31:50
drlowmu
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 Mikey,

Lets talk Class A1 triode amps, for high efficiency speakers.

Think about what the prior stage has to work into, and you can prioritize the three ways of coupling one tube stage to another :

WORST : Cap Couple, tube has to power a cap !!

LESS WORSE : Transformer Couple, not too bad at all

BEST - by FAR : Direct Couple, tube gets connected to next stage grid by a short length of high quality wire.

As far as transferring of the signal, the Direct Couple is many many times superior to ANY Cap Couple, in transferring and driving the next stage, in general terms.

Yes, there are engineering exceptions, but if you have a choice, ( for example, a two stage ONLY triode Class A1 amp ), it is hard to beat a DC !!


Jeff Medwin

 

RE: Innerstage vs R/C coupling., posted on February 25, 2017 at 12:53:45
vinnie2
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 I noticed at the end of his video he says that SE is ok as long as you don't need more than a watt or two. If you are using the speakers you should be using with SE amps, that is more than enough!

 

RE: Three ways to couple......, posted on February 25, 2017 at 12:56:49
mqracing
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 Jeff wrote:

"WORST : Cap Couple, tube has to power a cap !!


LESS WORSE : Transformer Couple, not too bad at all


BEST - by FAR : Direct Couple"


consider that when driving an IT your generator (the tube driving the primary) has to also charge the capacitances of the transformer as well as the tube must drive all of the losses (core and copper losses) of the transformer.

Measure the exciting current necessary to drive the IT you have in mind and then compare it to cap coupling (RC or LC).

And in direct coupling if the power supply is in series your front end tube must drive that reactive impedance.

I'm afraid that there is no fee lunch.

The "gods are not kind" to us :=)

MSL

MSL





Builder of MagneQuest & Peerless transformers since 1989

 

LC Coupling , posted on February 25, 2017 at 13:06:00
Chip647
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 How would this be implemented? C with a grounded grid choke after it? Isn't this a "tuned tank circuit". Grid chokes are awesome. Are you referring to something different?

 

RE: LC Coupling , posted on February 25, 2017 at 13:32:19
mqracing
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 nope... grid chokes it is :=)



Builder of MagneQuest & Peerless transformers since 1989

 

RE: Can you say inTerstage?..., posted on February 25, 2017 at 18:24:36
Michael Samra
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 I could but I have actually seen it spelled both ways.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Innerstage vs R/C coupling., posted on February 25, 2017 at 19:07:48
dave slagle
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 Interesting video... The big issue I have is I suspect he isn't using a very good interstage transformer and he is loading it. Here is the frequency response and phase of a mediocre stepup transformer and it is interesting to note that when you load the secondary to tame the ringing you also introduce substantial phase shift. It would have been nice to see the same tests preformed without a secondary load and the frequency sweep characteristics for both situations.





While the particular graph above is from a simulation, I based the values for the simulation off of an actual measured transformer and was able to get the measured and simmed behavior to match very closely.

dave

 

Innerstage vs Interstage..., posted on February 25, 2017 at 21:43:36
Steve O
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 From the INTERnet:

Innerstage: A feature of the Elizabethan stage that was used to conceal actors who were then revealed at a certain point during the play..........

Interstage: Occurring or situated between two stages (ex. A transformer situated between the driver stage and the output stage of an amplifier).

 

Ask Kara Chaffe at Dehavilland Electric Amplifier Company, posted on February 26, 2017 at 00:57:48
Frihed89
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 She makes her own (better) copy of the 50A. See the URL I posted

 

RE: Ask Kara Chaffe at Dehavilland Electric Amplifier Company, posted on February 26, 2017 at 01:56:53
Michael Samra
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 I've heard those and they are very nice sounding. Kara gets her wired transformer from Jack Eliano. Anyway,these amps are charming.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

Or combine the two...., posted on February 26, 2017 at 02:46:27
PakProtector
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 In similar fashion as McIntosh used with their bi-, tri-, and up to quin-filar output transformer primaries. Capacitor couple between the wires...:)
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

RE: Innerstage vs R/C coupling., posted on February 26, 2017 at 02:51:12
PakProtector
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 What speakers are these? That can deal with 'a Watt or two'?
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

RE: Innerstage vs R/C coupling., posted on February 26, 2017 at 03:28:44
vinnie2
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 Sensitivity of 98 +. I have run them with a 3/4 watt 76 SE amp to good listening levels for jazz and acoustic music, even classical if you don't get crazy with the volume.Use an amp with 2-3 watts and you can get crazy with the volume if you so desire.

 

RE: Or combine the two...., posted on February 26, 2017 at 03:55:24
Michael Samra
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 Doug
Most of the IT transformers have a coupling capacitor working in conjunction with them.Considering the cap value is very small,it is probably there to reinsert high frequency losses that may occur with the Interstage.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Innerstage vs Interstage..., posted on February 26, 2017 at 08:46:54
Michael Samra
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 Nah. From the Intranet.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

Actually from the interweb...so it can't be fake (nt), posted on February 26, 2017 at 12:20:11
Steve O
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RE: Innerstage vs R/C coupling., posted on February 26, 2017 at 14:20:04
drlowmu
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 Hi Vinnie,

What is the tube line-up on the 76 amp ??

Jeff Medwin

 

RE: Innerstage vs R/C coupling., posted on February 26, 2017 at 15:31:23
Tre'
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 "I noticed at the end of his video he says that SE is ok as long as you don't need more than a watt or two."

and are not playing below 100Hz is what he said.

I agree.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

"Innerstage" sounds so cerebral!, posted on February 26, 2017 at 17:47:06
FenderLover
 Impedance mismatch is like "what happened to that other sox, after I pulled the laundry from the dryer?"

Or something...

8^)

 

RE: Innerstage vs R/C coupling., posted on February 26, 2017 at 18:14:28
vinnie2
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 Don't have it anymore. I used the parts for another build. I think I got the schematic off of Joseph Esmilla's web site.

 

RE: Innerstage vs R/C coupling., posted on February 26, 2017 at 18:16:01
vinnie2
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 I think that is a bit high.

 

Cerebral? Not so much. More like a mondegreen (nt), posted on February 26, 2017 at 20:31:09
Steve O
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I prefer a coupling cap to a cathode bypass cap, posted on February 27, 2017 at 07:53:29
andy evans
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 The problem with direct coupling is that you commonly end up using a cathode bypass cap on the second stage because of the larger cathode resistor.

Because I use DHTs like 26, 01A and 4P1L which can all be used in filament bias with no cathode bypass cap, I prefer using a small teflon coupling cap (or an interstage) to a large cathode bypass cap - however fancy it is.

As said, there's no free lunch. A cathode bypass capacitor is a capacitor, period.

 

Other Methods, posted on February 27, 2017 at 08:54:17
Triode_Kingdom
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 It's my opinion that ITs should be avoided in any DIY design unless a thorough electrical analysis of the transformers can be made. The problem is phase shift, and it can be excessive not only at the edges of the passband, but at random frequencies within the passband as well. If the goal is to minimize distortion induced by occasional grid current (and the subsequent recovery time of bias voltage), there are alternatives to transformers. Reactive (choke) coupling is my favorite, in conjunction with a low Rp driver. Resistive coupling also resolves the problem. Both methods usually require one or more negative supplies.

 

That is because people never DO a proper cathode bypass cap implementation, posted on February 27, 2017 at 09:31:24
drlowmu
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 It takes MONEY and brains and listening to execute a proper cathode bypass cap ( a cap bank ). Especially important in SE applications, and in speaker crossovers.

Most everyone I meet is unaware. Dennis Fraker, on the other hand, singularly, is not !! He knows what he wants, and gets it, performance wise.


Jeff Medwin

 

RE: Other Methods IT, posted on February 27, 2017 at 13:52:54
Chip647
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 I have had good success with Interstage Transformers that are run like fairly substantial output transformers. Using a 6L6GC in triode running 35mA current though an IT designed for it to the grid of the power tube creates a very powerful driver. What does not work is doing this with a 12AX7, I grant you that.

 

RE: Innerstage vs R/C coupling., posted on February 27, 2017 at 14:05:40
sser2
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 Thordarson interstage high end? Give me a brake. This transformer was designed way before hi-fi, at the time when frequency response of 80-8,000 Hz was considered excellent. This transformer has one secondary wound over one primary, without sectioning or interleaving.

Transformer is indeed a poor choice for SE coupling, but the king in differential circuits and PP. Especially a good one like UTC HA series, Lundahl, or Tamura.

 

We haven't AB'd the alternatives so frankly, who knows.... , posted on February 27, 2017 at 16:10:14
andy evans
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 I would have to hear an AB comparison with DHTs in filament bias to make my own mind up. Until then there's absolutely no way of telling. I'm not going to believe that any kind of cathode bypass using any kind of combination is superior unless I actually hear it. I tried several combinations of good caps myself and they were all worse, and by a significant margin. I haven't heard your solution but I'm not going to just take your word for it, I'm afraid.

 

RE: Other Methods, posted on February 27, 2017 at 18:44:53
Michael Samra
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 Jack
The only advantage I see with IT coupling is the fact you can run the driver stage harder to get more dynamics and power from the output stage.
The fact that Fisher 55a can make 55 watts with Triode connected PP 6550s,that's pretty good HP.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: We haven't AB'd the alternatives so frankly, who knows.... , posted on February 27, 2017 at 23:14:45
drlowmu
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 My friend, Dennis Fraker knows how to do all of this, and he's singularly, the best there is, in taste and experience, to implement this. His amps, since 1989,
always out perform all other SETs I hear at shows, on an A-B, so I am pretty sure he knows what he is doing, and knows how to get it done.

 

RE: Other Methods, posted on February 28, 2017 at 04:44:08
dave slagle
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 Hey,

Isn't the phase shift directly tied to the frequency response? In other words excessive phase shift = poor frequency response independent of the coupling method?

and... while we are on the subject of the "evils" o phase shift.. If phase shift is so awful, how can we ever use any sort of a filter due to the phase shift directly tied to the transition from passband to stopband?

dave

 

RE: Other Methods, posted on February 28, 2017 at 08:06:20
Tre'
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 " If phase shift is so awful, how can we ever use any sort of a filter due to the phase shift directly tied to the transition from passband to stopband?"

Isn't that the point of the "one amp, no tone controls, no crossover, one full range speaker per channel" crowd?

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Other Methods, posted on February 28, 2017 at 09:13:26
megasat16
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 Quoting Tre - "Isn't that the point of the "one amp, no tone controls, no crossover, one full range speaker per channel" crowd?"


When used with a really good Full Range speakers, a Single phase shift from IT is a lesser evil compared to the multi inductors and caps induced crossover phase shift from a typical 2 or 3 way speakers.

Having said that, the 20Hz bass is not the strongest suite in these SET + FR setup so a sub is useful if you are a bass freak.
.
.
.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

That is your experience and opinion., posted on February 28, 2017 at 12:10:26
91derlust
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 It is not universally accepted.

I think I'd really like Dennis and his amps, but can differentiate between my opinion and Truth.

91.

"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein

 

RE: Innerstage vs R/C coupling., posted on February 28, 2017 at 14:01:22
Gordon Rankin
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 My 2 cents...

IT's can be sound like a built in compressor sometimes. I find the use of these with horn systems can really shine. You also have to watch the build of IT's. Some are bifilar wound which means the polarity in must equal the polarity out or the design looses high end big time!

RC, problem with DHT's is that as you approach the bias point with the input signal, the R increases the voltage as the grid is drawing current. This rebiases the output and causes depleated output.

RC, pentode, problem here is usually R is low and C is high and there are not many good large C's out there for coupling... or they are $$$$

LC, I like grid choke as the Rdc of L is low so grid current is not an issue. Also the AC Z of the inductor is really high so you can use a relatively low C value.

Thanks,
Gordon
J. Gordon Rankin

 

RE: That is your experience and opinion., posted on February 28, 2017 at 16:33:27
drlowmu
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 Of course its my opinion, formed by a lifetime doing audio, and going to RMAF the last nine years -spending much of each three days in the Serious Stereo room.

I know I am experienced enough in audio, and honest enough as a human being, to voice my opinion up here.

Yes, I think you would like Dennis, and his amps, and his GPA 604 MLTL implementation, but Australia is a far way to come from, for an audio show !!

Cheers,

Jeff Medwin

 

RE: That is your experience and opinion., posted on February 28, 2017 at 16:48:41
91derlust
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 Did not mean to question your experience Jeff - just trying to say different strokes for different folks.

Yeah, we can be pretty isolated down here, for both better and worse...

91.

"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein

 

RE: Innerstage vs R/C coupling., posted on February 28, 2017 at 18:12:44
Tre'
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 "I like grid choke as the Rdc of L is low so grid current is not an issue."

Is it the DCR of the choke or the reactance of the choke that is in play?

The tube is being driven into grid current by a periodic signal, right?

The peaks of the input signal.

The grid is falling in and out of the grid current condition at a rate equal to the rate of the music peaks.

It seem to me that the reactance of the choke, at that frequency, would come into play.

Am I wrong?


Tre'




Have Fun and Enjoy the Music
"Still Working the Problem"

 

let me tell you something..., posted on March 1, 2017 at 09:09:26
PakProtector
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 I have met God, and when I brought up cathode bypass caps, he gently told me to use fixed bias.
cheers,
Douglas


Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

RE: let me tell you something..., posted on March 1, 2017 at 09:47:45
TomWh
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 But Douglas when you talked to God what did he say about SE vs Push Pull??? I am staying out of these theory debates. My phono stage a lone has 6 interstage trans with some of Dave's lcr riaa inductors.

I just have to suffer with my phase shifted, band limited, shit riaa curve phono stage. Someone has to keep these iron guys in business.

Enjoy the ride
Tom

 

RE: let me tell you something..., posted on March 1, 2017 at 09:56:37
drlowmu
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 If you were able to hear his amps, then you would understand exactly where he comes from. Theory doesn't matter much, listening results do !!

Jeff Medwin

 

RE: let me tell you something..., posted on March 1, 2017 at 11:16:59
megasat16
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 I only have like 6 IT in my 845/211 LV amp. The more IT I add, the better it sounded. It must be the earwax that is masking all the phase shift in my amp while adding the high extensions with the more immediate bass that had my tin ears fooled.
.
.
.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: let me tell you something..., posted on March 1, 2017 at 12:20:59
TomWh
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 Jeff met you and Dennis at Denver about 5 years ago. You and Dennis were a pleasure to talk to. The amps were good but magical well you did not have a turntable and quad speakers in the room. I know the quads will not do polka music as well but a tenor sax.

Just having some fun. You pick your speakers 1st. Then you build modular so you can change everything then you listen change listen etc. Etc. Etc. As far as power coating goes I did that on my 510 Datsun.

Enjoy the ride
Tom

 

RE: let me tell you something..., posted on March 1, 2017 at 12:46:28
drlowmu
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 Thanks !!

At the 2016 RMAF, Dennis had a turntable, first time. Next year, there will be a turntable and plenty of Polka music, fun stuff to experience on high efficiency rigs.

Right on, "speakers dictate the system." I am so happy to be back to ALTECS, after decades of not having them.

Jeff

 

RE: Other Methods IT, posted on March 2, 2017 at 13:06:47
Triode_Kingdom
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 Yes, the driver tube must be able to deliver power, not just voltage, if A2 or AB2 are desired. This is true regardless of the specific type of coupling. Obviously, given this requirement, a 12AX7 might not be the best choice. :)

 

you'll have to ask Him yourself...:), posted on March 3, 2017 at 05:48:15
PakProtector
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 I don't see any point to delivering His side of that discussion...LOL

I have not built many SE amps, and certainly none for any purpose other than to take their part of an instrument's overall performance( as in geetar amps ).

I'll stick with PP when it matters; I have yet to hear a SE amp worth getting up to turn on, save perhaps low level stuff for the wife in the Kitchen...
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

RE: Other Methods IT, posted on March 3, 2017 at 09:48:35
Tre'
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 "..the driver tube must be able to deliver power, not just voltage, if A2 or AB2 are desired. This is true regardless of the specific type of coupling."

Even in A1 the driver tube must be able to deliver power, not just voltage, to satisfy the Miller capacitance (which can be substantial in a DHT).

This also is true regardless of the specific type of coupling.

I just thought that needed to be said.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

Very good point., posted on March 3, 2017 at 14:00:55
sser2
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 Not only power, but insanely low output impedance.

In a typical AB2 tube stage, drivers output impedance should not exceed 500-600 Ohm. This can only be achieved by a combination of low Rp PP driver stage AND a step-down interstage transformer.

 

RE: you'll have to ask Him yourself...:), posted on March 4, 2017 at 14:27:44
vinnie2
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 Then you haven't been listening to the right SE amps.

 

RE: you'll have to ask Him yourself...:), posted on March 4, 2017 at 17:29:35
PakProtector
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 yeah, sure...I have heard *MANY* SE amps, from *MANY* builders. I'll spare you the List, several frequent this board, and none are religious fanatics...just solid, well respected builders.

And I'll hand that one right back to you, you have not heard the right PP amps.
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

RE: Very good point., posted on March 4, 2017 at 18:28:36
Triode_Kingdom
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"In a typical AB2 tube stage, drivers output impedance should not exceed 500-600 Ohm. This can only be achieved by a combination of low Rp PP driver stage AND a step-down interstage transformer."

It can also be accomplished using cathode followers reactively coupled to the output stage with chokes (or a center-tapped choke). Altec did this in the 1570B, and I used it for my A2 211s.










 

RE: Other Methods IT, posted on March 4, 2017 at 18:42:25
Triode_Kingdom
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 "Even in A1 the driver tube must be able to deliver power, not just voltage, to satisfy the Miller capacitance"

The need for a low-Z driver regarding Miller capacitance has to do with dissipation in the driver, not the need to deliver power to the load. Like any pure reactance, Miller capacitance doesn't consume power. Rather, the circuit's dissipation results from the resistance of the driver in series with the Miller capacitance. Current into the Miller capacitance causes power to be dissipated in the driver's series resistance. Reducing that resistance serves to reduce the dissipation (and the frequency-sensitive voltage drop). No power is delivered to the load in any case.

 

Interesting circuit., posted on March 4, 2017 at 23:40:34
sser2
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 Thanks for posting this. A very specialized case.

The output stage works in pure class B2. 811 tubes (not very linear, to put it mildly) are biased at about zero volt. Although cathode follower has low output impedance, 6W6 triode connected, at 25 mA cathode current, will have difficult time delivering the calculated 42 mA peak grid driving signal current and 1.5 W driving power required for full output power of this amp. Tons of power, but a lot of distortion. Probably was intended as PA amplifier for sporting events, like Daytona 500 races.

 

RE: Interesting circuit., posted on March 5, 2017 at 08:41:16
Triode_Kingdom
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Joined: September 24, 2006
 Not to get into a long-winded discussion about this, but ... :)

I have to disagree regarding the 811A. I used them for years as linear amplifiers in audio-modulated RF service (single sideband). Their IM and THD are not significantly different than other tubes. As for the 6W6, I haven't used them myself as power drivers, but they do have huge peak current capability due to the robust heater design. That's the same reason I used a parallel-connected 6BL7 follower to drive each of my 211s. Can't speak for the Altec, but in my case, distortion measurements indicate no perceptible change as the output tubes enter A2. Distortion goes up gradually with increasing power, but there's no "step" at A2. That tells me the low output Z and power delivery of the followers is at least the equal of an IT.

 

RE: Other Methods IT, posted on March 5, 2017 at 09:01:45
Tre'
Industry Professional

Posts: 17294
Location: So. Cal.
Joined: February 9, 2002
 You said "Current into the Miller capacitance" but then you said "No power is delivered to the load"

If the driver stage has to deliver current to the Miller capacitance then isn't the Miller capacitance a load for the driver tube?

Maybe I'm not understanding what you mean by "the load" or maybe I don't understand what you mean by "consume power".


by Thorsten Loesch

"In addition, a directly heated triode (and any similar triode) has a quite substantial Input Capacitance comprising mostly the miller amplified Anode to Grid Capacitance.

The input Capacitance of a given Valve is (Cga + Cstray) * Mu + Cgk. This capacitance must be driven from somewhere, not only with respect to the frequency response, but also concerning the current draw at higher frequencies.

For a 300B Valve the input capacitance is usually around 70pF, a little more in reality due to stray capacitance's from the wiring or pcb. If we take 80pF Input Capacitance and a Bias of 70V for our above mentioned operating point we must be able to supply the current drawn by this capacitance up to at least 100kHz (usually a much higher frequency is strongly advisable) at full voltage swing.

The impedance of the 80pF Capacitance at 100kHz is around 20kOhm, the peak current drawn by this capacitance at full signal is 3.5mA."




70v times 3.5ma of current is .245 watts of power that needs to be sourced from the driver stage to satisfy the Miller.

I refer to that, rightly or wrongly, as the driver stage delivering power.

and my point was, regardless of the type of coupling the Miller capacitance current requirement still needs to be satisfied.


Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Other Methods IT, posted on March 5, 2017 at 09:42:22
cpotl
Audiophile

Posts: 1002
Location: Texas
Joined: December 6, 2009
 "You said "Current into the Miller capacitance" but then you said "No power is delivered to the load"

If the driver stage has to deliver current to the Miller capacitance then isn't the Miller capacitance a load for the driver tube?

Maybe I'm not understanding what you mean by "the load" or maybe I don't understand what you mean by "consume power"."

Perhaps he was making the point that no power is delivered into a purely capacitive load, since the voltage and the current are 90 degrees out of phase. In your example of 70v times 3.5ma of current, if that were into a resistive load it would indeed represent a power dissipation of 0.245W, but if the load is pure capacitive, the power dissipated into it would be zero.

Whether that is a relevant issue as far as demands on the driver is concerned is another question.

Chris

 

RE: Other Methods IT, posted on March 5, 2017 at 10:33:09
Tre'
Industry Professional

Posts: 17294
Location: So. Cal.
Joined: February 9, 2002
 "if that were into a resistive load it would indeed represent a power dissipation of 0.245W, but if the load is pure capacitive, the power dissipated into it would be zero."

That's the part I don't understand.

"We know that in Pure capacitive circuit, current is leading by 90 degree from voltage ( in other words, Voltage is lagging 90 Degree from current) i.e the phase difference between current and voltage is 90 degree.
So If Current and Voltage are 90 Degree Out of Phase, Then The Power (P) will be zero."

So "power" is the wrong word for me to use. It seem like a matter of semantics. Current still needs to be delivered from the driver stage even if it causes no heat in the tube (load).

am I on the right track?

Thanks.



Tre'


Have Fun and Enjoy the Music
"Still Working the Problem"

 

Miller, posted on March 5, 2017 at 11:05:44
elblanco
Audiophile

Posts: 3486
Joined: August 20, 2004
 .

 

RE: Other Methods IT, posted on March 5, 2017 at 11:15:04
cpotl
Audiophile

Posts: 1002
Location: Texas
Joined: December 6, 2009
 "So "power" is the wrong word for me to use. It seem like a matter of semantics. Current still needs to be delivered from the driver stage even if it causes no heat in the tube (load)."

Yes, I would agree that in the context of discussing the requirements for the driver to be able to supply the necessary voltage and current signal to the output stage, the fact that the power dissipated into a capacitative load is zero is probably hardly relevant.

I haven't thought much about it, but on the face of it I would suppose that the design criteria for a driver that can supply the voltage and supply the current are not really that much affected by whether the voltage and the current are 90 degrees out of phase or not. What matters should be that the driver can provide the necessary current, at the required voltage, without significant voltage drop at the higher frequencies where the capacitance matters more.

Chris

 

RE: Other Methods IT, posted on March 5, 2017 at 15:26:11
Triode_Kingdom
Audiophile

Posts: 10042
Location: Central Texas
Joined: September 24, 2006
 Yes, that's what I meant, but it's not just a matter of semantics. The fact that the load doesn't consume power, and that there's a significant power factor involved, might affect the topology and tube type selected for the driver. I admit that I haven't needed to deal with this apparent contradiction as a mathematical problem, but that's not to say the principles can simply be ignored. In any event, I just wanted to clarify the operation. My comments weren't intended to nitpick your post. :)


 

I think I got it. Thanks (nt), posted on March 5, 2017 at 17:46:12
Tre'
Industry Professional

Posts: 17294
Location: So. Cal.
Joined: February 9, 2002
 .
Have Fun and Enjoy the Music
"Still Working the Problem"

 

LMAO....that explains it, posted on March 6, 2017 at 18:03:14
PakProtector
Audiophile

Posts: 12363
Joined: May 14, 2002
 I have speakers that are at minimum +3 dB over yours, and it is now quite plain our definition of 'crazy' is quite different.
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

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