Hi:

I have two 8417 beam power tubes, which I would like to use in a
stereo SE amp, but I have some difficulty to find enough data for
the tubes to be able to choose the Ra for the OPT and find the right
point on the line for a given B+. I don't want to run the tube with
100mA idle current but something between 55mA and 60mA maximum.
It is not necessary to drive the tube to its limits.
Will an Ra of 5.2kOhms be OK? But for what B+ and which idle current?
I already looked at Duncan's tube data sheets. Frank's pages have
nothing about 8417.
If I could get some help finding a usable OPT I would really
appreciate it.
If the project turns out to be too ambitious I might just use the
tubes for a small CW transmitter on 40m ;-)

Kind regards, Eike

"Eike Lantzsch, ZP6CGE" schreef in bericht
...

snip
I already looked at Duncan's tube data sheets. Frank's pages have
nothing about 8417.



Did you mistype something?

via Duncan's site, some 8417 operating parameters :
http://hereford.ampr.org/cgi-bin/tube?tube=8417

more operating parameters :
http://tdsl.duncanamps.com/dcigna/tu...a/syl-465g.gif
http://tdsl.duncanamps.com/dcigna/tu...a/syl-466g.gif

triode, ultra-linear and penthode strapped characteristics:
http://www.mclink.it/com/audiomatica/tubes/8417.htm

Rgds,
Jan.

JKoning wrote:
"Eike Lantzsch, ZP6CGE" schreef in bericht
...

snip
I already looked at Duncan's tube data sheets. Frank's pages have
nothing about 8417.



Did you mistype something?

No, but it seems I "had tomatoes on my eyes".

via Duncan's site, some 8417 operating parameters :
http://hereford.ampr.org/cgi-bin/tube?tube=8417

more operating parameters :
http://tdsl.duncanamps.com/dcigna/tu...a/syl-465g.gif
http://tdsl.duncanamps.com/dcigna/tu...a/syl-466g.gif

triode, ultra-linear and penthode strapped characteristics:
http://www.mclink.it/com/audiomatica/tubes/8417.htm

Rgds,
Jan.

Thank you, Jan. I don't know how I missed the data sheets in the
sylvania handbook. Sure I saw the cover on Duncan's site. Maybe it
was pure fatigue ;-)

Kind regards, Eike

"Eike Lantzsch, ZP6CGE" schreef in bericht
...
JKoning wrote:
"Eike Lantzsch, ZP6CGE" schreef in bericht
...

Did you mistype something?

No, but it seems I "had tomatoes on my eyes".

snip

With or without curry?
Katch-up man, tear down the blindfold!


8417's are fine but scarce tubes.
So, to keep them going "forever", reduced plate
current/dissipation might be a good idea.
However, I don't have a clue about Life-expectancy
as a function of %Plate-dissipation.
Can any fellow RAT shed some light please?
What's your aim? Penthode, UL or Triode mode?
At what B+?

Rgds,
Jan.

JKoning wrote:
"Eike Lantzsch, ZP6CGE" schreef in bericht
...
JKoning wrote:
"Eike Lantzsch, ZP6CGE" schreef in bericht
...

Did you mistype something?

No, but it seems I "had tomatoes on my eyes".

snip

With or without curry?
Katch-up man, tear down the blindfold!


Curry-Ketchup en frieten? Smakelijk!
Maar niet de mayonaise vergeten!


8417's are fine but scarce tubes.
So, to keep them going "forever", reduced plate
current/dissipation might be a good idea.
However, I don't have a clue about Life-expectancy
as a function of %Plate-dissipation.
[snip]

I would like UL. About the B+ I'm not yet sure. I want to try anything
between 350V and 500V. With what I'll stay depends on how they sound.
When the 8417 once die I can replace them for 6550 if they will be
around still by then.

Groetjes
Eike (not a native dutch speaker) Lantzsch

"Eike Lantzsch, ZP6CGE" said:

Curry-Ketchup en frieten? Smakelijk!
Maar niet de mayonaise vergeten!

Deze man spreekt Nederlands!
Een octetje KT88s waard! :-)

I would like UL. About the B+ I'm not yet sure. I want to try anything
between 350V and 500V. With what I'll stay depends on how they sound.
When the 8417 once die I can replace them for 6550 if they will be
around still by then.

Zou moeten kunnen, alhoewel de instelling dan wel veranderd zal moeten
worden.
Wat voor trafo's gebruik je?

--
Sander deWaal
Vacuum Audio Consultancy

"Eike Lantzsch, ZP6CGE" schreef in bericht
...

[snip]

I would like UL. About the B+ I'm not yet sure. I want to try anything
between 350V and 500V. With what I'll stay depends on how they sound.
When the 8417 once die I can replace them for 6550 if they will be
around still by then.


A supply 350V will be fine for PP-AB, but that's not your aim.
For SE, classA, you'll have to stay well below ½ Va-max, or
below 330V, as, relative to B+, both positive and negative plate
voltage swing is, ideally, the same value.
Plotting a 25W plate-dissipation curve, that's a reduction to 71%
of Pa-max., on the 8417 UL characteristics, found at the
audiomatica site, and the subsequent plot of suitable load-lines
derives values for Ra of 3K5 to 4K5 while B+ is at about 300V,
Ia idle about 80mA and Vg1 at about -9V (notes).
Try plotting it yourself!
Plate characteristics are taken at an UL tap of 43%, the Sylvania
recommendation is slightly lower at 40%.

Please note that the audiomatica curves are NOT average
characteristics, but, obviously, taken "live" from a single 8417
sample using their curve-tracer.
Comparing Sylvania published average penthode characteristics
to the penthode characteristics on the audiomatica site bring
about some doubts about the "average-character" of the the latter.
Sylvania average: Ia = 100mA at Va = 300Vand Vg1 = -12V.
Single sample: Ia = 100mA at Va = 300V and Vg1 = - 5.5V(!).
Sylvania average transconductance 23mA/V.
Audiomatica single sample around 16mA/V.
On the other hand please note that average characteristics are
at Vg2 = 300V and the single sample is taken at Vg2 = 200V.
Vg2 magnitude has significant impact on the characteristics, but,
in my opinion, cannot explain the a.m. differences to full extend.
So, I suspect the presented sample to be partially worn or aged.

If you have rather new samples of 8714, expect the -Vg1 lines
to be steeper than given in the audiomatica UL mode curves.
Thus also expect for Ia = 80mA and Va = 300V a Vg1 |-9V|.
Yet, optimum UL load remains around Ra = 4K with ~ 40% tap.
And that's what you wanted to know, is'nt it?

Groetjes
Eike (not a native dutch speaker) Lantzsch

Native Deutsch speaker?
Du bist ein Berliner?
Ook de groetjes,
Jan.

"Sander deWaal" schreef in bericht
...
"Eike Lantzsch, ZP6CGE" said:

Curry-Ketchup en frieten? Smakelijk!
Maar niet de mayonaise vergeten!

Deze man spreekt Nederlands!
Een octetje KT88s waard! :-)

snip

Zou moeten kunnen, alhoewel de instelling dan wel veranderd zal moeten
worden.

Jouw instelling moet ook veranderen Sander.
Doe je woord gestand en stuur op dat octet!
Compromis, ook een sextetje KT66 verlost je van je schuld.


Wat voor trafo's gebruik je?

Dat was nou juist de vraag.
Dus niet lullen maar lezen.


Sander deWaal
Vacuum Audio Consultancy

Een "Vacuum Audio Consultant", is dat iemand die zich
naast audio met absoluut niets bezig houdt?

Mvg, :-)
Jan.

"JKoning" wrote in message
. nl...
A supply 350V will be fine for PP-AB, but that's not your aim.
For SE, classA, you'll have to stay well below ½ Va-max, or
below 330V, as, relative to B+, both positive and negative plate
voltage swing is, ideally, the same value.

No; the max. rating already takes this into account. Thus, this tube can
handle up to 1320V plate without arcing over. (Even the humble 6V6 is rated
for some 1.5 or 2kV peak in vertical amplifier service.)

However, other reasons and design considerations do make this (300~350V) a
good starting point in general.

Comparing Sylvania published average penthode characteristics
to the penthode characteristics on the audiomatica site bring
about some doubts about the "average-character" of the the latter.
Sylvania average: Ia = 100mA at Va = 300Vand Vg1 = -12V.
Single sample: Ia = 100mA at Va = 300V and Vg1 = - 5.5V(!).
Sylvania average transconductance 23mA/V.
Audiomatica single sample around 16mA/V.

That's awfully low...

On the other hand please note that average characteristics are
at Vg2 = 300V and the single sample is taken at Vg2 = 200V.

That explains it!

Vg2 magnitude has significant impact on the characteristics, but,
in my opinion, cannot explain the a.m. differences to full extend.

WTF?

...Looks like a nice tube, although precise biasing would indeed be a problem
due to the Gm, as it apparently was originally. Heavy on screen current
though, a 1:20 ratio between idle and peak levels (into a high load
resistance)!
http://tdsl.duncanamps.com/dcigna/tu...a/syl-466g.gif

Tim

--
"That's for the courts to decide." - Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

"JKoning" said:

Jouw instelling moet ook veranderen Sander.
Doe je woord gestand en stuur op dat octet!
Compromis, ook een sextetje KT66 verlost je van je schuld.

Ai...........mijn laatste KT66 GECs hou ik toch liever zelf :-)

Wat voor trafo's gebruik je?

Dat was nou juist de vraag.
Dus niet lullen maar lezen.

Ben een beetje dylsetcishc.

Een "Vacuum Audio Consultant", is dat iemand die zich
naast audio met absoluut niets bezig houdt?

Neenee, ik werk in een absoluut luchtledige kamer.
Doet wonderen voor je concentratie!

--
Sander deWaal
Vacuum Audio Consultancy

"Sander deWaal" schreef in bericht
...
"JKoning" said:

Jouw instelling moet ook veranderen Sander.
Doe je woord gestand en stuur op dat octet!
Compromis, ook een sextetje KT66 verlost je van je schuld.

Ai...........mijn laatste KT66 GECs hou ik toch liever zelf :-)

Welnu, in dat geval dan maar dat octetje.


Een "Vacuum Audio Consultant", is dat iemand die zich
naast audio met absoluut niets bezig houdt?

Neenee, ik werk in een absoluut luchtledige kamer.
Doet wonderen voor je concentratie!

Ben je dan een, tja...hoe moet ik dat noemen, eh... astroaudionaut?
Lijk me toch lastig voor de voortplanting.....
......van geluidsgolven bedoel ik.


--
Sander deWaal
Vacuum Audio Consultancy

Mvg, :-)
Jan

boyz,zasto ne pricate srpski-da vas ceo svet razume?
)
--
--
.................................................. ........................
Choky
Prodanovic Aleksandar
YU

"don't use force, "don't use force,
use a larger hammer" use a larger tube
- Choky and IST"
- ZM
.................................................. ...........................

"JKoning" wrote in message
.nl...

"Sander deWaal" schreef in bericht
...
"JKoning" said:

Jouw instelling moet ook veranderen Sander.
Doe je woord gestand en stuur op dat octet!
Compromis, ook een sextetje KT66 verlost je van je schuld.

Ai...........mijn laatste KT66 GECs hou ik toch liever zelf :-)

Welnu, in dat geval dan maar dat octetje.


Een "Vacuum Audio Consultant", is dat iemand die zich
naast audio met absoluut niets bezig houdt?

Neenee, ik werk in een absoluut luchtledige kamer.
Doet wonderen voor je concentratie!

Ben je dan een, tja...hoe moet ik dat noemen, eh... astroaudionaut?
Lijk me toch lastig voor de voortplanting.....
.....van geluidsgolven bedoel ik.


--
Sander deWaal
Vacuum Audio Consultancy

Mvg, :-)
Jan

"Choky" schreef in bericht
...
boyz,zasto ne pricate srpski-da vas ceo svet razume?
)

Yu backwards?
I guess I know what you mean

..tein redna nee koo tad oed oz , tdeihcseg U tad tliw tein ijg taW
Dutch backwards.


Rgds, :-)
Jan.

--
--
.................................................. .......................
Choky
Prodanovic Aleksandar
YU

"don't use force, "don't use force,
use a larger hammer" use a larger tube
- Choky and IST"
- ZM

.................................................. ...........................

JKoning wrote:
"Eike Lantzsch, ZP6CGE" schreef in bericht
...

[snip]

I would like UL. About the B+ I'm not yet sure. I want to try anything
between 350V and 500V. With what I'll stay depends on how they sound.
When the 8417 once die I can replace them for 6550 if they will be
around still by then.


A supply 350V will be fine for PP-AB, but that's not your aim.
For SE, classA, you'll have to stay well below ½ Va-max, or
below 330V, as, relative to B+, both positive and negative plate
voltage swing is, ideally, the same value.
Plotting a 25W plate-dissipation curve, that's a reduction to 71%
of Pa-max., on the 8417 UL characteristics, found at the
audiomatica site, and the subsequent plot of suitable load-lines
derives values for Ra of 3K5 to 4K5 while B+ is at about 300V,
Ia idle about 80mA and Vg1 at about -9V (notes).
Try plotting it yourself!
Plate characteristics are taken at an UL tap of 43%, the Sylvania
recommendation is slightly lower at 40%.

Please note that the audiomatica curves are NOT average
characteristics, but, obviously, taken "live" from a single 8417
sample using their curve-tracer.
Comparing Sylvania published average penthode characteristics
to the penthode characteristics on the audiomatica site bring
about some doubts about the "average-character" of the the latter.
Sylvania average: Ia = 100mA at Va = 300Vand Vg1 = -12V.
Single sample: Ia = 100mA at Va = 300V and Vg1 = - 5.5V(!).
Sylvania average transconductance 23mA/V.
Audiomatica single sample around 16mA/V.
On the other hand please note that average characteristics are
at Vg2 = 300V and the single sample is taken at Vg2 = 200V.
Vg2 magnitude has significant impact on the characteristics, but,
in my opinion, cannot explain the a.m. differences to full extend.
So, I suspect the presented sample to be partially worn or aged.

If you have rather new samples of 8714, expect the -Vg1 lines
to be steeper than given in the audiomatica UL mode curves.
Thus also expect for Ia = 80mA and Va = 300V a Vg1 |-9V|.
Yet, optimum UL load remains around Ra = 4K with ~ 40% tap.
And that's what you wanted to know, is'nt it?

Groetjes
Eike (not a native dutch speaker) Lantzsch

Native Deutsch speaker?
Du bist ein Berliner?
Ook de groetjes,
Jan.

Hartelijk bedankt Jan.
This was a really helpful post. I wasn't aware of the differences
between the Sylvania recommendations and the curves on the
automatica site. My 8417 are labeled RCA; the label is etched into the
bulb, so I think they are genuine. Did Sylvania make 8417 for RCA?
The valves look new and unused but I cannot be sure.
I thought of purchasing transformers from "Ask Jan First" site. He has
some offer of EI84 transformers but now I see that I will not be able
to get the right Ra with those. So it seems to me that I need to use
two of my many transformers, take the windings off and make my own
SE OPTs. That will be a leasure time problem - I have very little of
such thing ;-)
Funny is that although it is impossible to get good tubes or even a
good transformer here in Paraguay it is quite easy to get the material
to make your own OPT. So it is exactly the other way around than in
Europe. We *DO* live here heads down :-))

And no, I'm not a Berliner, I'm a Hamburger - Muahahahahaha! So we are
back to Curry Ketchup en frieten.
My wife and me imigrated into Paraguay 12 years ago to do voluntary
work. About 20 years ago I learned Flemish in Gent and still read it
fairly well but I lack practice and so "words don't come easy". Now
I'm better at Spanish and English.

Hartelijk gegroet, Eike

Tim Williams wrote:
"JKoning" wrote in message
. nl...
A supply 350V will be fine for PP-AB, but that's not your aim.
For SE, classA, you'll have to stay well below ½ Va-max, or
below 330V, as, relative to B+, both positive and negative plate
voltage swing is, ideally, the same value.

No; the max. rating already takes this into account. Thus, this tube can
handle up to 1320V plate without arcing over. (Even the humble 6V6 is rated
for some 1.5 or 2kV peak in vertical amplifier service.)

However, other reasons and design considerations do make this (300~350V) a
good starting point in general.

Comparing Sylvania published average penthode characteristics
to the penthode characteristics on the audiomatica site bring
about some doubts about the "average-character" of the the latter.
Sylvania average: Ia = 100mA at Va = 300Vand Vg1 = -12V.
Single sample: Ia = 100mA at Va = 300V and Vg1 = - 5.5V(!).
Sylvania average transconductance 23mA/V.
Audiomatica single sample around 16mA/V.

That's awfully low...

On the other hand please note that average characteristics are
at Vg2 = 300V and the single sample is taken at Vg2 = 200V.

That explains it!

Vg2 magnitude has significant impact on the characteristics, but,
in my opinion, cannot explain the a.m. differences to full extend.

WTF?

..Looks like a nice tube, although precise biasing would indeed be a problem
due to the Gm, as it apparently was originally. Heavy on screen current
though, a 1:20 ratio between idle and peak levels (into a high load
resistance)!

Tim

Hmm? So UL would be very much like Triode? If used in Pentode mode
would stabilizing the Vg2 do any good? Besides: because of economical
reasons I will certainly use silicon rectifiers and not a tube.
I just want to use what I have at hand.

Kind regards, Eike

"Eike Lantzsch, ZP6CGE" wrote in message
...
Hmm? So UL would be very much like Triode?

As much as pentode mode is like an average UL setup.

If used in Pentode mode
would stabilizing the Vg2 do any good?

A *lot* of good!

Besides: because of economical
reasons I will certainly use silicon rectifiers and not a tube.
I just want to use what I have at hand.

I know the feeling

If you have some dead computer power supplies, the high voltage transistors
(GASP!!) might be very useful indeed for screen or even plate regulators,
should you feel so inclined.

Tim

--
"That's for the courts to decide." - Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

"Eike Lantzsch, ZP6CGE" schreef in bericht
...

[snip]

Hartelijk bedankt Jan.
This was a really helpful post. I wasn't aware of the differences
between the Sylvania recommendations and the curves on the
automatica site. My 8417 are labeled RCA; the label is etched into the
bulb, so I think they are genuine. Did Sylvania make 8417 for RCA?

I really don't know if Syvania was producing for RCA or not.

FYI, I came across the information that the 6GB8 is VERY similar
to the 8417. There's a lot of info on the web about it. Unfortunately
most, but not all, in Japanese.
If you are really desperate for the translation of a particalar sentence
of either kanji or hiragana, drop me a line.

The valves look new and unused but I cannot be sure.
I thought of purchasing transformers from "Ask Jan First" site. He has
some offer of EI84 transformers but now I see that I will not be able
to get the right Ra with those.

Do you mean the ATRA0288 he has on offer?
DC current capability is rather low at 60mA.
Ra would be OK for UL mode, but there is no UL tap!
So, triode mode or penthode mode are left using that Xfrmr.

ATRA0288 would almost make the penthode match here :
http://www.tubebuilder.com/images/sc...d/6gb8_se1.gif

....and the triode match, except for Ik, here :
http://www01.netweb.ne.jp/~gen/ampli.../amppage1.html
The FW-20S is, probably, a Tango. I'm not sure to what primary
impedance it is wired, but I guess it's 5K, as the info in the schematic
is not consistent to the info I found here :
http://purer.myrice.com/trans/tango.htm

Wuestens Xfrmr's are not expensive I saw.
So, maybe worth an experiment.


So it seems to me that I need to use
two of my many transformers, take the windings off and make my own
SE OPTs. That will be a leasure time problem - I have very little of
such thing ;-)
Funny is that although it is impossible to get good tubes or even a
good transformer here in Paraguay it is quite easy to get the material
to make your own OPT.

Rolling your own certainly is more fun. After rolling that is...


So it is exactly the other way around than in
Europe. We *DO* live here heads down :-))

For that, from my perspective, you'll have to relocate to New Zealand.


And no, I'm not a Berliner, I'm a Hamburger - Muahahahahaha! So we are
back to Curry Ketchup en frieten.

Being a Hamburger is fine. But be sure not to become a hamburger and
find yourself squeezed between halbe Brötchen und Tomatenkleber.


My wife and me imigrated into Paraguay 12 years ago to do voluntary
work. About 20 years ago I learned Flemish in Gent
and still read it
fairly well but I lack practice and so "words don't come easy". Now
I'm better at Spanish and English.

Hartelijk gegroet, Eike

Groeten,
Jan.

"JKoning" wrote in message
.nl...
"Choky" schreef in bericht
...
boyz,zasto ne pricate srpski-da vas ceo svet razume?
)

Yu backwards?
I guess I know what you mean

.tein redna nee koo tad oed oz , tdeihcseg U tad tliw tein ijg taW
Dutch backwards.


Rgds, :-)
Jan.
hehe-it is not backwards..
I guess that all foreign languages sound backwards......'till specific
moment.......


--
--
--
.................................................. ........................
Choky
Prodanovic Aleksandar
YU

"don't use force, "don't use force,
use a larger hammer" use a larger tube
- Choky and IST"
- ZM
.................................................. ...........................

JKoning wrote:

"Eike Lantzsch, ZP6CGE" schreef in bericht
...

[snip]

FYI, I came across the information that the 6GB8 is VERY similar
to the 8417. There's a lot of info on the web about it. Unfortunately
most, but not all, in Japanese.
If you are really desperate for the translation of a particalar sentence
of either kanji or hiragana, drop me a line.

drop-------------------------------------------------------------drop
just joking. No, it's OK I was able to derive the info, which I need
without asking for translation. If I will need it in the future I can
always ask some of the japanese people who drop by here once in a
while and who either speak spanish or english :-)

[snip]

Do you mean the ATRA0288 he has on offer?
DC current capability is rather low at 60mA.
Ra would be OK for UL mode, but there is no UL tap!
So, triode mode or penthode mode are left using that Xfrmr.

ATRA0288 would almost make the penthode match here :
http://www.tubebuilder.com/images/sc...d/6gb8_se1.gif

Yes, thank you so much, indeed. That is a very interesting circuit.
I do not really understand the use of R9. I imagine that it provides
some feedback to V1. R6 seems to be superfluous but then one has to make
sure that g1 of V2 is connected to ground during startup. I guess that's
why R6 is there.
Now the power supply is *really* interesting (see Tim's comment about
MOSFETS of dumped PC-supplies).
Yes, I thought about the ATRA0288. But sending it to Paraguay via Miami
will make it a lot more expensive and I might buy a Hammond instead or
wind my own. By the time the stuff is here I might be done too.

...and the triode match, except for Ik, here :
http://www01.netweb.ne.jp/~gen/ampli.../amppage1.html
The FW-20S is, probably, a Tango. I'm not sure to what primary
impedance it is wired, but I guess it's 5K, as the info in the schematic
is not consistent to the info I found here :
http://purer.myrice.com/trans/tango.htm

Wuestens Xfrmr's are not expensive I saw.
So, maybe worth an experiment.

[snip]

Groeten,
Jan.


Thank you for your time and insight.
Kind regards, Eike

JKoning wrote:

"Eike Lantzsch, ZP6CGE" schreef in bericht
...

[snip]

drop-------------------------------------------------------------drop

Licorice????

[snip]

ATRA0288 would almost make the penthode match here :
http://www.tubebuilder.com/images/sc...d/6gb8_se1.gif

Yes, thank you so much, indeed. That is a very interesting circuit.
I do not really understand the use of R9. I imagine that it provides
some feedback to V1.

The node R5/R9/R10 has a portion of V2's anode voltage superimposed
on the supply voltage for V1, and as such on V1's Ia.
But I don't understand this feedback in conjunction with the "NF" feedback.


R6 seems to be superfluous but then one has to make
sure that g1 of V2 is connected to ground during startup. I guess that's
why R6 is there.

Agreed.


Now the power supply is *really* interesting (see Tim's comment about
MOSFETS of dumped PC-supplies).

As stated before, Vg2 magnitude has significant impact on characteristics.
So, stabilizing Vg2 also "stabilizes" transconductance.
The higher Vg2, the higher the transconductance.
But be careful not to choose Vg2 to high as one runs the risk of excessive
Ig2 and Pg2 when the plate swings low.
Also see Tim's comment about this in conjunction with the 8417 grid spec's.

[snip]

Groeten,
Jan

JKoning wrote:

JKoning wrote:

"Eike Lantzsch, ZP6CGE" schreef in bericht
...

[snip]

The node R5/R9/R10 has a portion of V2's anode voltage superimposed
on the supply voltage for V1, and as such on V1's Ia.
But I don't understand this feedback in conjunction with the "NF" feedback.

[snip]
Groeten,
Jan


I think I got the idea of R5/R9/R10. This is positive feedback, which
allows much greater voltage swing for the driver stage. This seems to
be unstable theoretically but I remember that this trick is used in
my 1958 PPP (circlotron) 2 x EL34 amplifier to allow the use of just
one ECC83 as a driver. Surprisingly this setup works very stable and
linear. It gets a voltage swing out of the ECC83 of about 108Veff by
backfeeding from the anodes of the EL34 to the anodes of the ECC83.
And still overall negative feedback is used on the same amplifier as
if one thing does not have to do with the other.
It seems that the same trick is used on this 6GB8 amplifier.
But is such a high swing necessary to drive the 6GB8? This is what
still puzzles me.

Kind regards, Eike

"Tim Williams" wrote in message
...
"Eike Lantzsch, ZP6CGE" wrote in message
...
Hmm? So UL would be very much like Triode?

As much as pentode mode is like an average UL setup.

If used in Pentode mode
would stabilizing the Vg2 do any good?

A *lot* of good!

Besides: because of economical
reasons I will certainly use silicon rectifiers and not a tube.
I just want to use what I have at hand.

I know the feeling

If you have some dead computer power supplies, the high voltage
transistors
(GASP!!) might be very useful indeed for screen or even plate regulators,
should you feel so inclined.

Tim

8417's in UL are a hand full, ask anyone whose ever spent time with a Dynaco
Mk. VI. Screen regulated pentode is best from my experience. Another option
is an OPT that has a separate screen winding so you can run the screen at a
lower potential than the plate.
Mark

"Eike Lantzsch, ZP6CGE" schreef in bericht
...

JKoning wrote:

[snip]

The node R5/R9/R10 has a portion of V2's anode voltage superimposed
on the supply voltage for V1, and as such on V1's Ia.
But I don't understand this feedback in conjunction with the "NF"
feedback.

[snip]

Groeten,
Jan


I think I got the idea of R5/R9/R10. This is positive feedback,
which allows much greater voltage swing for the driver stage.

I'm confused now. In my opinion it's negative feedback.
Think of a positive going signal on the grid of V1(lower),
resulting in NEGATIVE going signal on top of R4.
This again results in positive going signal on plate of V2,
of which the node R5/R9/R10 carries a portion, as does
the node R5/plateV1(upper), as does the node cathode
V1(upper)/R4 carry a POSITIVE portion.
So the result is working AGAINST the origin.
Do I miss, or mess up, something here?

In case I did'nt mess up, I still don't understand this kind
of NFB "on top of" an SRPP stage, especially not in
conjunction with the "normal" feedback.
In case I messed up, I don't understand the reason for
PFB as V2 requires only low drive voltage (see below).

This seems to
be unstable theoretically but I remember that this trick is used in
my 1958 PPP (circlotron) 2 x EL34 amplifier to allow the use of just
one ECC83 as a driver. Surprisingly this setup works very stable and
linear. It gets a voltage swing out of the ECC83 of about 108Veff by
backfeeding from the anodes of the EL34 to the anodes of the ECC83.
And still overall negative feedback is used on the same amplifier as
if one thing does not have to do with the other.
It seems that the same trick is used on this 6GB8 amplifier.
But is such a high swing necessary to drive the 6GB8?

I don't think so. Assuming stated idle voltages are correct,
for V2 there's only a 4V g1 to cathode difference.
Vg1 = -4V is not an odd figure at all if you do a rough
extrapolation, for plate curves @ Vg2 = 350V, 300V and
250V, down towards plate curves @ Vg2 approx. 150V.
At that Vg2 an idle of 66mA @ g1 = -4V makes sense.
Vg2 value in the 6GB8 schematic is 138V, but who cares.

Anyway, maximum possible swing for V2's g1 is only
8Vpp max., or ~2.8Vrms, which seems like a low figure.
If, as above, transconductance is roughly extrapolated
from given curves, towards curves @ Vg2 ~ 150V then
transconductance should be around the 15mA/V mark.
And again, Vg1 = -4V makes sense as ± 4V g1 swing
results in around S x Vg = ± 60mA plate current swing.

BTW, assuming fig's are not too far off, Ia = 120mApp
results in Va = 600Vpp, results in Po around 9Watts.

So, a high swing necessary to drive the 6GB8?
As said, I don't think so.

6GB8 data & curves for various Vg2 and S in links :
page 1: http://www.triodeel.com/6gb8.gif
page 2 : http://www.triodeel.com/6gb8a.gif
page 3 : http://www.triodeel.com/6gb8b.gif
page 4 : http://www.triodeel.com/6gb8b.gif

Conveniently, a set of 6GB8 curves are drawn @ Vg2 = 300V.
As such they can be compared to Sylvania 8417 curves directly.
It seems to me that 6GB8 is VERY comparable to 8417 indeed.

So, a high swing necessary to drive the 8417?
I don't think so.

This is what still puzzles me.

Still?


Kind regards, Eike

Groeten,
Jan.