[John L Stewart]

Here is a great example of someone thinking ouside the box. Refer to the cct. The hookup was suggested by Dave Cuthbert of Boise, ID in 2003 & published in EDN Magazine.

After some blow it out of the water I will post more on it.

Cheers to all, John Stewart

[John L Stewart]

Originally Posted by John L Stewart

Here is a great example of someone thinking ouside the box. Refer to the cct. The hookup was suggested by Dave Cuthbert of Boise, ID in 2003 & published in EDN Magazine.

After some blow it out of the water I will post more on it.

Cheers to all, John Stewart

Oddly, soon as I posted this a reference to a pre-existing thread on this same cct came up. Oh well!

JLS

[Alex Pogossov]

"John L Stewart" wrote in message
...

Here is a great example of someone thinking ouside the box. Refer to the
cct. The hookup was suggested by Dave Cuthbert of Boise, ID in 2003 &
published in EDN Magazine.

After some blow it out of the water I will post more on it.

Cheers to all, John Stewart


+-------------------------------------------------------------------+
|Filename: Boosted Triode B.jpg |
|Download: http://www.audiobanter.com/attachment.php?attachmentid=295|
+-------------------------------------------------------------------+

I think this idea is quite old, but it is extremely inconvenient (floating
supply) and unsafe (running 6L6 at 500Vdc on screen, let alone peaks which
would reach 850V !). No wonder this circuit never took off the ground.

Ultralinear connection is far better. However, with the convention
ultralinear one can not use high B+ (to keep screen grid safe).

To achieve ultimate flexibility with the ultralinear connection, screen grid
should be connected not to a tap of the promary, but through a SEPARATE
winding from a SEPARATE screen power supply. In this case one can use high
plate voltage (say 500V for 807 tube) for high efficiency, and yet quite
sensible screen voltage (250V for safety), and at the same time enjoy the
benefits of triode inherent feedback.

In such configuration though this separate winding would not have 30...40%
of primary turns as common in the conventional ultralinear, but less,
probably 15...20%. This is because plate supply is higher than screen supply
and plate voltage swing is larger.

Regards,
Alex

[flipper]

On Sat, 28 Jul 2012 16:11:06 +0000, John L Stewart
wrote:


Here is a great example of someone thinking ouside the box. Refer to the
cct. The hookup was suggested by Dave Cuthbert of Boise, ID in 2003 &
published in EDN Magazine.

After some blow it out of the water I will post more on it.

Cheers to all, John Stewart


+-------------------------------------------------------------------+
|Filename: Boosted Triode B.jpg |
|Download: http://www.audiobanter.com/attachment.php?attachmentid=295|
+-------------------------------------------------------------------+

Yeah, I've seen it but the author completely ignores screen ratings,
not to mention "simply add a 100V supply" isn't quite 'that' simple.

[John Byrns]

In article ,
John L Stewart wrote:

Here is a great example of someone thinking ouside the box. Refer to the
cct. The hookup was suggested by Dave Cuthbert of Boise, ID in 2003 &
published in EDN Magazine.

After some blow it out of the water I will post more on it.

Cheers to all, John Stewart


+-------------------------------------------------------------------+
|Filename: Boosted Triode B.jpg |
|Download: http://www.audiobanter.com/attachment.php?attachmentid=295|
+-------------------------------------------------------------------+


I have 5 comments on this ³outside the box thinking².

1. Didn't we beat this thing into the ground 3 years ago?

2. Patrick's ³bean counters² wouldn't like those floating screen supplies! Four
would be required in a stereo amplifier using push-pull circuitry.

3. Considerable work is required to analyze the screen dissipation of the
³Boosted Triode² given the limited data available on the commonly available data
sheets. A Tektronix curve tracer would make much it easier, I don't have one
though.

4. Couldn't we achieve similar performance using a 6L6 in the straight triode
connection, without the complication of ³Boosted Triode² operation, by choosing
a different operating point, say Va = 500 volts, Ia = 60 mA, and Rl = 5,000 Ohms?

5. There are large real triodes that will provide better plate efficiency than
the ³Boosted Triode² 6L6. I don't know enough about tube theory to know if this
scales so that it would be possible to build a 6L6 sized pure triode of similar
performance to the large triodes, anyone know how actual tubes scale?

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[John L Stewart]

Originally Posted by John Byrns

In article ,
John L Stewart wrote:

Here is a great example of someone thinking ouside the box. Refer to the
cct. The hookup was suggested by Dave Cuthbert of Boise, ID in 2003 &
published in EDN Magazine.

After some blow it out of the water I will post more on it.

Cheers to all, John Stewart


+-------------------------------------------------------------------+
|Filename: Boosted Triode B.jpg |
|Download: http://www.audiobanter.com/attachment.php?attachmentid=295|
+-------------------------------------------------------------------+


I have 5 comments on this ³outside the box thinking².

1. Didn't we beat this thing into the ground 3 years ago?

2. Patrick's ³bean counters² wouldn't like those floating screen supplies! Four
would be required in a stereo amplifier using push-pull circuitry.

3. Considerable work is required to analyze the screen dissipation of the
³Boosted Triode² given the limited data available on the commonly available data
sheets. A Tektronix curve tracer would make much it easier, I don't have one
though.

4. Couldn't we achieve similar performance using a 6L6 in the straight triode
connection, without the complication of ³Boosted Triode² operation, by choosing
a different operating point, say Va = 500 volts, Ia = 60 mA, and Rl = 5,000 Ohms?

5. There are large real triodes that will provide better plate efficiency than
the ³Boosted Triode² 6L6. I don't know enough about tube theory to know if this
scales so that it would be possible to build a 6L6 sized pure triode of similar
performance to the large triodes, anyone know how actual tubes scale?

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

Your comments noted. Su go way & do it. Then report back to us with the results. Cheers, John

[John Byrns]

In article ,
John L Stewart wrote:

John Byrns;960412 Wrote:
In article ,
John L Stewart wrote:
-
Here is a great example of someone thinking ouside the box. Refer to
the
cct. The hookup was suggested by Dave Cuthbert of Boise, ID in 2003 &
published in EDN Magazine.

After some blow it out of the water I will post more on it.

Cheers to all, John Stewart


+-------------------------------------------------------------------+
|Filename: Boosted Triode B.jpg |
|Download:
http://www.audiobanter.com/attachment.php?attachmentid=295|

+-------------------------------------------------------------------+-


I have 5 comments on this ³outside the box thinking².

1. Didn't we beat this thing into the ground 3 years ago?

2. Patrick's ³bean counters² wouldn't like those floating screen
supplies! Four
would be required in a stereo amplifier using push-pull circuitry.

3. Considerable work is required to analyze the screen dissipation of
the
³Boosted Triode² given the limited data available on the commonly
available data
sheets. A Tektronix curve tracer would make much it easier, I don't
have one
though.

4. Couldn't we achieve similar performance using a 6L6 in the straight
triode
connection, without the complication of ³Boosted Triode² operation, by
choosing
a different operating point, say Va = 500 volts, Ia = 60 mA, and Rl =
5,000 Ohms?

5. There are large real triodes that will provide better plate
efficiency than
the ³Boosted Triode² 6L6. I don't know enough about tube theory to know
if this
scales so that it would be possible to build a 6L6 sized pure triode of
similar
performance to the large triodes, anyone know how actual tubes scale?

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

Your comments noted. Su go way & do it. Then report back to us with the
results.

I already did it 3 years ago, at least #4. Add a line to Table 1 in the EDN
article for 6L6 triode at 500 volts with the following parameters:
Amp = Triode with 500 volt Vb
Ip = 60 mA
Vc = -47v
Vdriv = 94vpp
Po = 10 Watts

With respect to #3, we would need extended characteristic charts for the screen
to determine whether the dissipation will exceed the ratings, I read an article
some years back explaining how to extend the existing tube characteristic charts
into areas they don't cover. I'm not going to bother trying to find the article
and attempt the analysis because I have dismissed the whole notion of the
"Boosted Triode" as impractical based on personal prejudices. The only thing
this connection brings to the party is the magic word "Triode". If I were
designing an amplifier of this class and wanted something better than a straight
pentode circuit I would go with cathode feedback. Using the same driver circuit
as with the "Boosted Triode" we could use 10 dB of cathode feedback. 10 dB of
cathode feedback around a 6L6 will give an effective plate resistance of about a
third that of the ³Boosted Triode² connection, a clearly superior result.

I'm working on #5, it's an interesting question, and I have identified the
electrical characteristics that a pure triode would require to provide plate
efficiency equal to or better than the plate efficiency of the ³Boosted Triode².
There's a downside to the required specifications. I am investigating what it
would take to build such a 6L6 class triode; I may choose to keep my results on
#5 proprietary.

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[Patrick Turner]

On Sunday, 29 July 2012 02:11:06 UTC+10, John L Stewart wrote:
Here is a great example of someone thinking ouside the box. Refer to the cct. The hookup was suggested by Dave Cuthbert of Boise, ID in 2003 & published in EDN Magazine. After some blow it out of the water I will post more on it. Cheers to all, John Stewart +-------------------------------------------------------------------+ |Filename: Boosted Triode B.jpg | |Download: http://www.audiobanter.com/attachment.php?attachmentid=295| +-------------------------------------------------------------------+ -- John L Stewart

I see schematic (c) has a 100Vdc floating supply placing Eg2 at +500Vdc. YUK.
Plus you then have to apply more Eg1 bias.

In replies below, 'tis said that Patrick's bean counters woodknot like the idea of so many floating Vdc sources. They are unable to dislike them or like them because they are not employed here to grumble and whinge about everything I do.

I'm not a huge fan of triode amps although my kitchen radio has an EL34 SET amp with 12dB NFB and its 6 Watts is ample for by sensitive old 1953 speaker with 1974 tweeter. I could never see any reason to add just one a 100V supply to allow the EL34 to perhaps make 8 Watts instead of 6. UL would be easiest with a tap at 50%, but the OPT I used in the radio is ex-surplus from an ancient tape recoder-player. No available UL taps.

Just about anything is better than SE pentoad. But king of them all for SE operation is to have 20% of primary turns in a cathode winding for OP tube, and THEN have Eg2 at a fixed voltage wherever you want it and all nice and safe at say 300Vdc for a 6L6. Ea can be almost anything you want between 300Vdc and 500Vdc with appropriate Ia to give a wide range of RLa values which can be used.
The cathode NFB will straighten out the mess that tetrodes and pentodes make and typically 20% CFB allows same PO as pentode/tetrode, but effective Ra is typically 1/2 triode Ra. If Pda at idle = 22W, expect up to 10W output at anode. THD is typically 2% at 9.5W. At the same 6W as a triode can make, expect THD 1%. The action of CFB works to make the tube operate as if set up with 20% UL tap, but ALSO with series CFB, so you end up with an output stage that has closed loop gain less than a 300B, maybe 3.0, which is in fact plenty if you only want Va-k = 200Vrms, and Vk = 40V, and Vgk = 20V. So about 60V drive is needed, but its at very low current change so a decent driver SET
is easily arranged to give far less THD than the OP stage.

But hey, about nobody bothers travelling the extra country mile to get the sort of performance I demand from multigrids. But the CFB is the best way I know to apply NFB when don't have real triodes around, such as 300B, 2A3, 45, or want to rely on plain old triode strapping of multigrids. The triode connection is merely allying the anode voltage to apply its NFB action that happens in every triode ever made. UL is a not to bad compromise because screen has a foot in both camps, and useful NFB is applied, but Ra is not lowered quite enough, so additional global loop FB is always needed, but nowhere near as much as in a pure tetrode/pentode connection.

Of course, the simplest way to extract more PO from 6L6 in triode is to use fixed bias, and use 1/2 a 6SN7 as a CF driver direct coupled to g1 and then use class A2,and PO will rise from about 6W to maybe 9W. The first few Watts are in A1. For 6L6 triode or UL connection, Ea = Eg2 up to 400Vdc is OK, and for 6L6GC, up to 450V is OK. The Vac acting on the screen lowers its Pd and its unlikely to cook, hence one doesn't have to worry about keeping Eg2 350V.

Patrick Turner.

[Patrick Turner]

On Sunday, 29 July 2012 02:11:06 UTC+10, John L Stewart wrote:
Here is a great example of someone thinking ouside the box. Refer to the cct. The hookup was suggested by Dave Cuthbert of Boise, ID in 2003 & published in EDN Magazine. After some blow it out of the water I will post more on it. Cheers to all, John Stewart +-------------------------------------------------------------------+ |Filename: Boosted Triode B.jpg | |Download: http://www.audiobanter.com/attachment.php?attachmentid=295| +-------------------------------------------------------------------+ -- John L Stewart

I like thinking outside the box. I'm currently working on an EM84 circuit to give tuning indication on my revised kitchen radio. I thought maybe Mitt Romney could fit one to his mormon forehead so thet when he gets a good idea that's good for the people not just the ferken rich, it'd light up. Maybe no need to have another to light up when he gets a bad idea because it'd wear out too quick.

Now I gotta figure why Google new system has introduced me as "me" not my real name. Of course, last time I looked, I was indeed myself, and hence me, but pharkin Google sees things differently......
Patrick Turner.