[Engineer[_2_]]

Hi, Vacuumlanders,
I'm trying to find a use for some 6080's (double power triodes) that
I've acquired over the years. One of them is the series regulator of
a home-brew regulated p/s but that still leaves several orphans!
I'm thinking of building a small P-P stereo amplifier pair using two
of them, or even a very small SE stereo pair using just one tube.
Drawing a few load lines on the plate current vs. plate voltage curves
suggests that a SE 3,000 ohm load, with 135 VDC B+, 40 mA plate
current and -60 VDC bias might work but it seems to give only about
1.5 watts max. by my estimate. Also, this tube needs a large drive
voltage. I've a couple of small OPT's from a stereo console that are
2,500 to 8 ohms (for a 50C5) that might be candidates for this. I've
not looked at a P-P configuration yet.
Any experience with the 6080 as an audio amp in this NG? Also, can
anyone point me to some decent 6080 schematics for either P-P or SE
designs?
Thanks for all replies.
Cheers,
Roger

[Andre Jute[_2_]]

On Oct 6, 12:08*am, Engineer wrote:
Hi, Vacuumlanders,
I'm trying to find a use for some 6080's (double power triodes) that
I've acquired over the years. *One of them is the series regulator of
a home-brew regulated p/s but that still leaves several orphans!
I'm thinking of building a small P-P stereo amplifier pair using two
of them, or even a very small SE stereo pair using just one tube.
Drawing a few load lines on the plate current vs. plate voltage curves
suggests that a SE 3,000 ohm load, with 135 VDC B+, 40 mA plate
current and -60 VDC bias might work but it seems to give only about
1.5 watts max. by my estimate. *Also, this tube needs a large drive
voltage. I've a couple of small OPT's from a stereo console that are
2,500 to 8 ohms (for a 50C5) that might be candidates for this. I've
not looked at a P-P configuration yet.
Any experience with the 6080 as an audio amp in this NG? Also, can
anyone point me to some decent 6080 schematics for either P-P or SE
designs?
Thanks for all replies.
Cheers,
Roger

The 6080 is perhaps more commonly seen in OTL designs. Aren van
Waarde's is a particularly elegant OTL implementation for dynamic
headphones with a discussion of drive requirements and output:
http://headwize.com/projects/showfil...aarde1_prj.htm

Andre Jute
Visit Jute on Amps at
http://www.audio-talk.co.uk/fiultra/
"wonderfully well written and reasoned information for the tube audio
constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site containing vital gems of
wisdom"
Stuart Perry Hi-Fi News & Record Review

[Engineer[_2_]]

On Oct 5, 8:17*pm, Andre Jute wrote:
On Oct 6, 12:08*am, Engineer wrote:



Hi, Vacuumlanders,
I'm trying to find a use for some 6080's (double power triodes) that
I've acquired over the years. *One of them is the series regulator of
a home-brew regulated p/s but that still leaves several orphans!
I'm thinking of building a small P-P stereo amplifier pair using two
of them, or even a very small SE stereo pair using just one tube.
Drawing a few load lines on the plate current vs. plate voltage curves
suggests that a SE 3,000 ohm load, with 135 VDC B+, 40 mA plate
current and -60 VDC bias might work but it seems to give only about
1.5 watts max. by my estimate. *Also, this tube needs a large drive
voltage. I've a couple of small OPT's from a stereo console that are
2,500 to 8 ohms (for a 50C5) that might be candidates for this. I've
not looked at a P-P configuration yet.
Any experience with the 6080 as an audio amp in this NG? Also, can
anyone point me to some decent 6080 schematics for either P-P or SE
designs?
Thanks for all replies.
Cheers,
Roger

The 6080 is perhaps more commonly seen in OTL designs. Aren van
Waarde's is a particularly elegant OTL implementation for dynamic
headphones with a discussion of drive requirements and output:
*http://headwize.com/projects/showfil...aarde1_prj.htm

(snip)

Thanks, Andre. I may actually build that headphone amplifier as I
would rather like to have one to drive my HD570's. However, my query
was not for headphone or speaker OTL amplifiers (we know power amps
can be built with stacks of 6080's in parallel - I have just a few,
not stacks!) Rather, I'm looking for a more conventional circuit (P-P
or SE) with a "findable" OPT. I was a bit put off by the low power
output estimate I made for the SE design but, of course, I could have
the wrong circuit, voltage, etc.
Cheers,
Roger

[Andre Jute[_2_]]

On Oct 6, 4:01*am, Engineer wrote:
On Oct 5, 8:17*pm, Andre Jute wrote:





On Oct 6, 12:08*am, Engineer wrote:

Hi, Vacuumlanders,
I'm trying to find a use for some 6080's (double power triodes) that
I've acquired over the years. *One of them is the series regulator of
a home-brew regulated p/s but that still leaves several orphans!
I'm thinking of building a small P-P stereo amplifier pair using two
of them, or even a very small SE stereo pair using just one tube.
Drawing a few load lines on the plate current vs. plate voltage curves
suggests that a SE 3,000 ohm load, with 135 VDC B+, 40 mA plate
current and -60 VDC bias might work but it seems to give only about
1.5 watts max. by my estimate. *Also, this tube needs a large drive
voltage. I've a couple of small OPT's from a stereo console that are
2,500 to 8 ohms (for a 50C5) that might be candidates for this. I've
not looked at a P-P configuration yet.
Any experience with the 6080 as an audio amp in this NG? Also, can
anyone point me to some decent 6080 schematics for either P-P or SE
designs?
Thanks for all replies.
Cheers,
Roger

The 6080 is perhaps more commonly seen in OTL designs. Aren van
Waarde's is a particularly elegant OTL implementation for dynamic
headphones with a discussion of drive requirements and output:
*http://headwize.com/projects/showfil...aarde1_prj.htm

(snip)

Thanks, Andre. *I may actually build that headphone amplifier as I
would rather like to have one to drive my HD570's. *However, my query
was not for headphone or speaker OTL amplifiers (we know power amps
can be built with stacks of 6080's in parallel - I have just a few,
not stacks!) *Rather, I'm looking for a more conventional circuit (P-P
or SE) with a "findable" OPT. *I was a bit put off by the low power
output estimate I made for the SE design but, of course, I could have
the wrong circuit, voltage, etc.
Cheers,
Roger

The Dutchmen de Haan and Heuvelman schemed a 10W PP amp with 6080 that
is well reputed for its exceptionally low distortion, though they do
use 8dB of feedback, not unreasonable in the circumstances (duck
now!). Note that they have an adjustor for the inequality often found
between 6080 halves (P3 on their schematic). Try he
http://www.wimdehaan.nl/various/tube...s7g/index.html
(Mmm, I see Flipper has already found it. Lucky, that boy.) You can
download the schematic from the *text highlight* (the PDF logo slug is
dead) down the page a bit.

As always, I like high-current drivers because they absolutely kill
Miller. Among the high-mu tubes, my fave 417A is probably a bit pricey
these days -- I haven't looked in a long time since I was lucky to get
a super-selected batch from the same guy who decided to keep the 6080
for himself -- but the 7044 is probably still cheap even if its
workalike the 5687 may be rarer and more valuable.

Andre Jute
Not everything in materials is dreamt of in Timoshenko

[Engineer[_2_]]

On Oct 6, 11:10*am, Andre Jute wrote:
On Oct 6, 4:01*am, Engineer wrote:



On Oct 5, 8:17*pm, Andre Jute wrote:

On Oct 6, 12:08*am, Engineer wrote:

(snip)

Thanks for all replies. I now have enough info to build a decent P-P
6080 amplifier and a headphone amp. However, any advice on a SE
stereo amplifier for speakers? I may just build a notional 2 x 1.5
watter to try it out. I'd prefer the driver tubes to be from the 12A
[i]7 family as I have many of them, but no E88CC's. I realize that
the 6080 needs a large drive voltage.
Cheers,
Roger

[Bret L]

[i]
Thanks for all replies. *I now have enough info to build a decent P-P
6080 amplifier and a headphone amp. *However, any advice on a SE
stereo amplifier for speakers? *I may just build a notional 2 x 1.5
watter to try it out. *I'd prefer the driver tubes to be from the 12A
7 family as I have many of them, but no E88CC's. *I realize that
the 6080 needs a large drive voltage.
Cheers,
Roger

The high drive voltage is the flaw in the flue. You either need a
transformer to drive it with and give up on putting NFB around it or
a driver stage with a higher voltage than the output tube's own B+.
This actually takes a little moxie to avoid motorboating or a brute
force solution with multiple separate PT's or at least secondaries.


You have to use cathode bias. Traditionally this is done on this tube
with a wirewound pot, either end connected to a cathode and the center
tap tp ground. Fixed bias is specifically disrecommended in all the
tube manuals.

The _Audio Anthologies_ of CG McProud fame are in their early volumes
full of such amps, all no feedback and transformer coupled. Most use a
6N7 (not 6SN7) driver.

Building an amp to use a tube on hand is false economy, There is a
practical reason why no one builds them and I learned this through
practical experience. You wind up with a halfway decent 10 watt amp
that costs more to build than a good 50 watt amp.

[Engineer[_2_]]

On Oct 7, 2:19*pm, Bret L wrote:[i]
Thanks for all replies. *I now have enough info to build a decent P-P
6080 amplifier and a headphone amp. *However, any advice on a SE
stereo amplifier for speakers? *I may just build a notional 2 x 1.5
watter to try it out. *I'd prefer the driver tubes to be from the 12A
7 family as I have many of them, but no E88CC's. *I realize that
the 6080 needs a large drive voltage.
Cheers,
Roger

*The high drive voltage is the flaw in the flue. You either need a
transformer to drive it with and give up on putting NFB around it *or
a driver stage with a higher voltage than the output tube's own B+.
This actually takes a little moxie to avoid motorboating or a brute
force solution with multiple separate PT's or at least secondaries.

*You have to use cathode bias. Traditionally this is done on this tube
with a wirewound pot, either end connected to a cathode and the center
tap tp ground. Fixed bias is specifically disrecommended in all the
tube manuals.

The _Audio Anthologies_ of CG McProud fame are in their early volumes
full of such amps, all no feedback and transformer coupled. Most use a
6N7 (not 6SN7) driver.

Building an amp to use a tube on hand is false economy, There is a
practical reason why no one builds them and I learned this through
practical experience. You wind up with a halfway decent 10 watt amp
that costs more to build than a good 50 watt amp.

Thanks, Bret. I'd figured on the need for a higher driver B+ (at low
current) than the lower 6080 B+ (at a much higher current) but hadn't
yet figured how best to do it with what I've got in the scrap... er,
surplus parts box.. Re. cost: I expected to breadboard this thing for
next to nothing except for the OPT, but I may even have one that will
do for a prototype! I don't plan to transformer-couple as I don't
have one, so will need to experiment with RC coupling and a large
driver swing (separate driver tubes after phase splitter.)
Does anyone have a design for a small SE stereo unit (for 8 ohm
speakers) with just one 6080? Unfortunately, all my trial load lines
and o/p voltage swings so far show less than 2 watts RMS per channel.
This looks like a lost cause!
Cheers,
Roger

[Ian Iveson]

Roger wrote:

Thanks, Bret. I'd figured on the need for a higher driver
B+ (at low
current) than the lower 6080 B+ (at a much higher current)
but hadn't
yet figured how best to do it with what I've got in the
scrap... er,
surplus parts box.. Re. cost: I expected to breadboard this
thing for
next to nothing except for the OPT, but I may even have one
that will
do for a prototype! I don't plan to transformer-couple as I
don't
have one, so will need to experiment with RC coupling and a
large
driver swing (separate driver tubes after phase splitter.)
Does anyone have a design for a small SE stereo unit (for 8
ohm
speakers) with just one 6080? Unfortunately, all my trial
load lines
and o/p voltage swings so far show less than 2 watts RMS per
channel.
This looks like a lost cause!

**Surely there must be a way of determining the maximum
output power quite easily?

**If you draw the max power dissipation limit on the anode
characteristic curves, is it true that the operating point
for maximum power will be on that line?

**For maximum power, must the points where the loadline
crosses the zero grid volts line and the voltage axis be
equidistant from the operating point?

**If so, then it shouldn't be hard, pivoting a line around a
few points on the dissipation limit, to see which way the
wind blows.

**I suspect that you need to be brave, and use stacks more
current. That might limit the choice of output transformer
to one intended for bigger valves.

**While I happen to be in a slightly grumpy mood, I should
take the opportunity to point out that "Watts RMS" is a daft
construction. Actually you mean the mean power. "Watts" is
the perfect description, and erroneous qualifications
detract from that clarity.

Ian

[Bret L]

The _Audio Anthologies_ of CG McProud fame are in their early volumes
full of such amps, all no feedback and transformer coupled. Most use a
6N7 (not 6SN7) driver.

Building an amp to use a tube on hand is false economy, There is a
practical reason why no one builds them and I learned this through
practical experience. You wind up with a halfway decent 10 watt amp
that costs more to build than a good 50 watt amp.

Thanks, Bret. *I'd figured on the need for a higher driver B+ (at low
current) than the lower 6080 B+ (at a much higher current) but hadn't
yet figured how best to do it with what I've got in the scrap... er,
surplus parts box.. *Re. cost: I expected to breadboard this thing for
next to nothing except for the OPT, but I may even have one that will
do for a prototype! *I don't plan to transformer-couple as I don't
have one, so will need to experiment with RC coupling and a large
driver swing (separate driver tubes after phase splitter.)
Does anyone have a design for a small SE stereo unit (for 8 ohm
speakers) with just one 6080? *Unfortunately, all my trial load lines
and o/p voltage swings so far show less than 2 watts RMS per channel.
This looks like a lost cause!


I seem to remember optimum impedance for a single 6080 in push pull
was something like 1250 to 1500 ohms.

If you have driver tubes after the phase splitter and you apply
feedback, you may have the kinds of stability problems Williamson
had.

If you can find "High Fidelity Techniques" the good one (Newitt, not
the POS Gernsback Library Langham) there is a worked example in there
of a successful one.

If you want to run open loop, a suitable driver xfmr will be a lot
cheaper and less hassle. I'm guessing there is a socketed octal
packaged part you can get used dirt cheap that will work fine.

[Patrick Turner]

On Oct 7, 3:03*am, Engineer wrote:[i]
On Oct 6, 11:10*am, Andre Jute wrote:

On Oct 6, 4:01*am, Engineer wrote:

On Oct 5, 8:17*pm, Andre Jute wrote:

On Oct 6, 12:08*am, Engineer wrote:

(snip)

Thanks for all replies. *I now have enough info to build a decent P-P
6080 amplifier and a headphone amp. *However, any advice on a SE
stereo amplifier for speakers? *I may just build a notional 2 x 1.5
watter to try it out. *I'd prefer the driver tubes to be from the 12A
7 family as I have many of them, but no E88CC's. *I realize that
the 6080 needs a large drive voltage.
Cheers,
Roger

The 6080/6AS7 has a very low gain, but also has very low Ra so gm is
good enough to get 20W from a 4 pack on PP OTL. The tubes work in near
class B2 condition and yes you need a high grid drive and one able to
overcome grid current.

With the right loading which excludes all OTL designs, the SE or class
A PP amp should be able to get anode efficiency up to 30% which means
that if you have 60W being the anode dissipation of say 4 6080 tubes,
then you should get 18W of audio power.
The OPT used to get this is a special item and I doubt Hammond make
anything to suit.
BUT, for PP you might find that a mains toroidal transformer could be
used, and one with two 120V primaries meant for either 120V or 240V
mains. The secondary might be two 35V windings for a transistor amp.
These could be paralleled and you have a 240V primary with CT : 35V.
This makes for a 6.8:1 turn ratio, with ZR = 47, so an 8 ohm load
becomes 376 ohms anode to anode at the primary. The Circlotron design
suits 6080.

There are many ways to use 6080, but I prefer a 6550.

I prefer a 6C33c if I ever was going to use a large low Ra triode.

Patrick Turner.

[Engineer[_2_]]

On Oct 7, 10:06*pm, "Ian Iveson"
wrote:

(snip)


**While I happen to be in a slightly grumpy mood, I should
take the opportunity to point out that "Watts RMS" is a daft
construction. Actually you mean the mean power. "Watts" is
the perfect description, and erroneous qualifications
detract from that clarity.

Ian

Ian, I agree. You were, indeed, grumpy but quite correct! I was too
lazy to write "continuous" and didn't think of "mean", but wanted to
avoid any notion of transient power. I, too, criticize people for the
same offence.
Cheers,
Roger

[Engineer[_2_]]

On Oct 8, 7:34*pm, flipper wrote:
On Thu, 8 Oct 2009 07:59:41 -0700 (PDT), Engineer



wrote:
On Oct 7, 10:06*pm, "Ian Iveson"
wrote:


(snip)

flipper wrote:

"Watts RMS" is technically incorrect but you can see the 'real world'
problem manufacturers faced trying to sell a, for example, 12 Watt car
radio against the "500 Watt" (PMPO) competition.

PMPO = Pompous Musical Pimp Outrage? [Not my best day for acronyms!]
Cheers,
Roger

[Don Pearce[_3_]]

On Sat, 10 Oct 2009 12:09:54 -0700 (PDT), Engineer
wrote:

On Oct 8, 7:34*pm, flipper wrote:
On Thu, 8 Oct 2009 07:59:41 -0700 (PDT), Engineer



wrote:
On Oct 7, 10:06*pm, "Ian Iveson"
wrote:


(snip)

flipper wrote:

"Watts RMS" is technically incorrect but you can see the 'real world'
problem manufacturers faced trying to sell a, for example, 12 Watt car
radio against the "500 Watt" (PMPO) competition.

PMPO = Pompous Musical Pimp Outrage? [Not my best day for acronyms!]
Cheers,
Roger

How about PreMeditated Preposterous Overstatement?

d

[Engineer[_2_]]

On Oct 8, 5:41*am, Patrick Turner wrote:[i]
On Oct 7, 3:03*am, Engineer wrote:



On Oct 6, 11:10*am, Andre Jute wrote:

On Oct 6, 4:01*am, Engineer wrote:

On Oct 5, 8:17*pm, Andre Jute wrote:

On Oct 6, 12:08*am, Engineer wrote:

(snip)

Thanks for all replies. *I now have enough info to build a decent P-P
6080 amplifier and a headphone amp. *However, any advice on a SE
stereo amplifier for speakers? *I may just build a notional 2 x 1.5
watter to try it out. *I'd prefer the driver tubes to be from the 12A
7 family as I have many of them, but no E88CC's. *I realize that
the 6080 needs a large drive voltage.
Cheers,
Roger

The 6080/6AS7 has a very low gain, but also has very low Ra so gm is
good enough to get 20W from a 4 pack on PP OTL. The tubes work in near
class B2 condition and yes you need a high grid drive and one able to
overcome grid current.

With the right loading which excludes all OTL designs, the SE or class
A PP amp should be able to get anode efficiency up to 30% which means
that if you have 60W being the anode dissipation of say 4 6080 tubes,
then you should get 18W of audio power.
The OPT used to get this is a special item and I doubt Hammond make
anything to suit.
BUT, for PP you might find that a mains toroidal transformer could be
used, and one with two 120V primaries *meant for either 120V or 240V
mains. The secondary might be two 35V windings for a transistor amp.
These could be paralleled and you have a 240V primary with CT : 35V.
This makes for a 6.8:1 turn ratio, with ZR = 47, so an 8 ohm load
becomes 376 ohms anode to anode at the primary. The Circlotron design
suits 6080.

There are many ways to use 6080, but I prefer a 6550.

I prefer a 6C33c if I ever was going to use a large low Ra triode.

Patrick Turner.

Thanks, Patrick. I thought mains power transformers had too low
primary inductance for audio. I actually tried a 6080 P-P a year or
two ago using a 240 VAC CT EI core power transformer. It had no bass
and only a watt or two, IIRC. But likely the wrong ratio (not a 35 v
secondary.) This raises the possibility of using old solid state
receiver PT's - they have 30-0-30, etc, secondaries. But there's
still that primary inductance problem.
Yes, there are far better tubes than the 6080 for audio but I have a
stack of 6080's for my sins so it's in the experimental and spares-
box vein!
BTW, I got some SE results since the OP using a small radio OPT...
When I get the time I'll post as a new topic.
Cheers,
Roger

[Engineer[_2_]]

On Oct 19, 6:30*pm, Engineer wrote:
On Oct 8, 5:41*am, Patrick Turner wrote:

BTW, I got some SE results since the OP using a small radio OPT...
When I get the time I'll post as a new topic.
Cheers,
Roger

I posted it but can't see it yet!
Cheers,
Roger