| Author |
Message |
EC
Guest
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 Posted:
Wed Jan 19, 2005 8:34 am Post subject:
25L6 for hi-fi? |
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I know I should resist... but there's a old tube console
at the local junk shop going cheap. Stereo PP 25L6GT for
power 12AX7 driver and pre-amp sections. There's only
a power transformer on the outside of the chassis. I
imagine the OT's are underneath and pretty small (can't
think a OTL setup would be used in a console).
Looking at the curves at;
http://frank.pocnet.net/sheets/127/2/25L6GT.pdf
they seem pretty linear triode-connected.
Is there anything about the higher heater V and lower
plate V that would make this combination "non-hi-fi"?
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Tim Williams
Guest
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| Posted:
Wed Jan 19, 2005 8:34 am Post subject:
Re: 25L6 for hi-fi? |
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"EC" <EC@nospam.com> wrote in message
news:Xns95E2F3F81D8FCECnospamcom@216.196.97.142...
| Quote: | Is there anything about the higher heater V and lower
plate V that would make this combination "non-hi-fi"?
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Nope. Just wire the heaters with a higher voltage transformer or line
operated as originally intended (check Fred N's site for use of such
methods). nnL6 is a high filament voltage 6W6 (and not 6L6, for some
reason).
Tim
--
"I've got more trophies than Wayne Gretsky and the Pope combined!"
- Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms |
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Chris Hornbeck
Guest
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| Posted:
Wed Jan 19, 2005 8:34 am Post subject:
Re: 25L6 for hi-fi? |
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On Tue, 18 Jan 2005 22:57:24 -0600, EC <EC@nospam.com> wrote:
| Quote: | Is there anything about the higher heater V and lower
plate V that would make this combination "non-hi-fi"?
|
Do (or will possibly) any children, pets, or any other
loved ones have any access to any part of this thing?
Hot chassis' are potentially dangerous. Your call.
It's worse than driving drunk because you can do something
about it *now*.
Chris Hornbeck
"someone might think it's more valuable in the future than he did
in the pasture." -Mike Rivers |
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EC
Guest
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| Posted:
Wed Jan 19, 2005 8:34 am Post subject:
Re: 25L6 for hi-fi? |
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Chris Hornbeck <chrishornbeckremovethis@att.net> wrote in
news:9esru0dg33ma5rh6h5vb5qvp2a0dj4d32u@4ax.com:
| Quote: | On Tue, 18 Jan 2005 22:57:24 -0600, EC <EC@nospam.com> wrote:
Is there anything about the higher heater V and lower
plate V that would make this combination "non-hi-fi"?
Do (or will possibly) any children, pets, or any other
loved ones have any access to any part of this thing?
Hot chassis' are potentially dangerous. Your call.
It's worse than driving drunk because you can do something
about it *now*.
Chris Hornbeck
"someone might think it's more valuable in the future than he did
in the pasture." -Mike Rivers
|
It's 60's era, so not electrically 'hot chassis'... You mean
the 25V heaters make for spankin' hot tubes right? That's
a good point! These tubes seem to have been dead common in
radio's. A bit of a bonus, there's loads around for cheap. |
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Chris Hornbeck
Guest
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| Posted:
Wed Jan 19, 2005 8:34 am Post subject:
Re: 25L6 for hi-fi? |
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On Wed, 19 Jan 2005 00:02:51 -0600, EC <EC@nospam.com> wrote:
| Quote: | It's 60's era, so not electrically 'hot chassis'...
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Well.... you've tested this to your satisfaction? All I'd
urge is to measure twice, cut once. Tubes designed for
low plate voltages and series'd filaments imply...?
Your call. Be safe.
Chris Hornbeck |
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John Stewart
Guest
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| Posted:
Wed Jan 19, 2005 4:54 pm Post subject:
Re: 25L6 for hi-fi? |
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EC wrote:
| Quote: | I know I should resist... but there's a old tube console
at the local junk shop going cheap. Stereo PP 25L6GT for
power 12AX7 driver and pre-amp sections. There's only
a power transformer on the outside of the chassis. I
imagine the OT's are underneath and pretty small (can't
think a OTL setup would be used in a console).
Looking at the curves at;
http://frank.pocnet.net/sheets/127/2/25L6GT.pdf
they seem pretty linear triode-connected.
Is there anything about the higher heater V and lower
plate V that would make this combination "non-hi-fi"?
|
I built several amplifiers, some with phono preamps & tone circuits
using output sections consisting of PP 25L6, 35L6 or 50L6 in the 50's &
early 60's for hifi. All used the Hammond 125D OPT. The 125E was not
then available. All outputs were connected as beam pentodes. Heaters
were all run straight off the line while the B+ came from surplus
transformers I found at a good price. All had some NFB. If you are
interested I still have the circuits on file.
Triode connexion of an existing unit could be a problem since max
voltage on the screens is only 135 volts whereas the plates can run up
to 200 volts.
All the folks that got one were very happy & used them for many years.
Cheers, John Stewart |
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Ruud Broens
Guest
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| Posted:
Wed Jan 19, 2005 5:01 pm Post subject:
Re: 25L6 for hi-fi? |
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"EC" <EC@nospam.com> wrote in message
news:Xns95E2F3F81D8FCECnospamcom@216.196.97.142...
: I know I should resist... but there's a old tube console
: at the local junk shop going cheap. Stereo PP 25L6GT for
: power 12AX7 driver and pre-amp sections. There's only
: a power transformer on the outside of the chassis. I
: imagine the OT's are underneath and pretty small (can't
: think a OTL setup would be used in a console).
:
: Looking at the curves at;
: http://frank.pocnet.net/sheets/127/2/25L6GT.pdf
: they seem pretty linear triode-connected.
:
: Is there anything about the higher heater V and lower
: plate V that would make this combination "non-hi-fi"?
It's an interesting tube to use triode-connected, for sure.
The large heater energy translates to a low dynamic Ra, around 1K,
and none-too-flat penthode curves - as a rule of thumb, giving fine
trioded performance. Set at a 160V, 40 mA in a PP stage, you can
expect quite low distortion - but also rather low output power :-)
(It is of course relatively simple to use paralleled tubes for more power)
The console's OT's may be useful, in which case a 'junk price'
quickly justifies buying it :-)
cheers,
Rudy |
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John Stewart
Guest
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| Posted:
Wed Jan 19, 2005 5:14 pm Post subject:
Re: 25L6 for hi-fi? |
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John Stewart wrote:
| Quote: | EC wrote:
I know I should resist... but there's a old tube console
at the local junk shop going cheap. Stereo PP 25L6GT for
power 12AX7 driver and pre-amp sections. There's only
a power transformer on the outside of the chassis. I
imagine the OT's are underneath and pretty small (can't
think a OTL setup would be used in a console).
Looking at the curves at;
http://frank.pocnet.net/sheets/127/2/25L6GT.pdf
they seem pretty linear triode-connected.
Is there anything about the higher heater V and lower
plate V that would make this combination "non-hi-fi"?
I built several amplifiers, some with phono preamps & tone circuits
using output sections consisting of PP 25L6, 35L6 or 50L6 in the 50's &
early 60's for hifi. All used the Hammond 125D OPT. The 125E was not
then available. All outputs were connected as beam pentodes. Heaters
were all run straight off the line while the B+ came from surplus
transformers I found at a good price. All had some NFB. If you are
interested I still have the circuits on file.
Triode connexion of an existing unit could be a problem since max
voltage on the screens is only 135 volts whereas the plates can run up
to 200 volts.
All the folks that got one were very happy & used them for many years.
Cheers, John Stewart
|
The 6W6GT is the same as the 25L6 family. Check those specs since the
curves for the triode connexion are shown. But for use at increased plate
voltage the plate dissipation rating is reduced.
Cheers, JLS |
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Ruud Broens
Guest
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| Posted:
Wed Jan 19, 2005 5:27 pm Post subject:
Re: 25L6 for hi-fi? |
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"Ruud Broens" <broensr@wanadoo.nl> wrote in message
news:41ee4b81$0$682$cd19a363@news.wanadoo.nl...
:
: "EC" <EC@nospam.com> wrote in message
: news:Xns95E2F3F81D8FCECnospamcom@216.196.97.142...
: : I know I should resist... but there's a old tube console
: : at the local junk shop going cheap. Stereo PP 25L6GT for
: : power 12AX7 driver and pre-amp sections. There's only
: : a power transformer on the outside of the chassis. I
: : imagine the OT's are underneath and pretty small (can't
: : think a OTL setup would be used in a console).
: :
: : Looking at the curves at;
: : http://frank.pocnet.net/sheets/127/2/25L6GT.pdf
: : they seem pretty linear triode-connected.
: :
: : Is there anything about the higher heater V and lower
: : plate V that would make this combination "non-hi-fi"?
:
: It's an interesting tube to use triode-connected, for sure.
: The large heater energy translates to a low dynamic Ra, around 1K,
: and none-too-flat penthode curves - as a rule of thumb, giving fine
: trioded performance. Set at a 160V, 40 mA in a PP stage, you can
: expect quite low distortion - but also rather low output power :-)
: (It is of course relatively simple to use paralleled tubes for more power)
: The console's OT's may be useful, in which case a 'junk price'
: quickly justifies buying it :-)
: cheers,
: Rudy
:
Filament supply: I'd use a 24V 50VA transformer & rect.- you can use it
to supply ccs filament power, 1 regulator per tube still doesn't cost much,
and you can also get a negative bias voltage from this. Use it with a
little circuit and the B+ switched by a relay and it starts to look like an
elegant design :)
Rudy |
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John Byrns
Guest
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| Posted:
Thu Jan 20, 2005 2:05 am Post subject:
Re: 25L6 for hi-fi? |
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In article <41EE4F15.2E888AF9@sympatico.ca>, jh.stewart@sympatico.ca wrote:
| Quote: | John Stewart wrote:
Triode connexion of an existing unit could be a problem since max
voltage on the screens is only 135 volts whereas the plates can run up
to 200 volts.
|
I can't find the 135 volt screen rating you mention, all my tube books
give a "design center" rating of 125 volts for the 25L6 screen. The
"design center" ratings for the very similar 6W6 are 300 volts max. on the
plate and 150 volts max. on the screen. Triode connected the rating for
the 6W6 is given as 225 volts max. on the plate. This is substantially
higher than the voltage the 6W6 screen is rated for in the pentode
connection, so I would assume that the 25L6 is also not limited by the
screen voltage rating when operated as a triode, maybe it can run in
triode mode at nearly the full 200 volt rating of the plate. Since the
6W6 and 25L6 are virtually the same tube, and I have seen tubes with 12
volt heaters dual labeled as 12W6GT/12L6GT, I wonder why the max. voltage
ratings are different?
| Quote: | All the folks that got one were very happy & used them for many years.
|
I'm sure they were happy, the 25L6GT is a very nice tube, and seems to run
forever too.
Regards,
John Byrns
Surf my web pages at, http://users.rcn.com/jbyrns/ |
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robert casey
Guest
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| Posted:
Thu Jan 20, 2005 3:11 am Post subject:
Re: 25L6 for hi-fi? |
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Heaters
| Quote: | were all run straight off the line while the B+ came from surplus
transformers I found at a good price.
|
I would avoid doing that, as the heater-cathode insulation
rating is rather low. As the powerline sees lots of
transient spikes, parts seeing powerline and the
isolated load should have insulation rating of 1.4KV DC.
I'd use a 25V transformer to heat the tubes. |
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John Stewart
Guest
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| Posted:
Thu Jan 20, 2005 6:29 am Post subject:
Re: 25L6 for hi-fi? |
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John Byrns wrote:
| Quote: | In article <41EE4F15.2E888AF9@sympatico.ca>, jh.stewart@sympatico.ca wrote:
John Stewart wrote:
Triode connexion of an existing unit could be a problem since max
voltage on the screens is only 135 volts whereas the plates can run up
to 200 volts.
I can't find the 135 volt screen rating you mention, all my tube books
give a "design center" rating of 125 volts for the 25L6 screen.
|
John, you are correct. I just pulled the 135 volt number out of space as I
typed. Same for the 35L6. I just had a look. Anyway, that should not stop
anyone from building an amp with those tubes if they are motivated to do so.
| Quote: | The "design center" ratings for the very similar 6W6 are 300 volts max. on
the
plate and 150 volts max. on the screen. Triode connected the rating for
the 6W6 is given as 225 volts max. on the plate. This is substantially
higher than the voltage the 6W6 screen is rated for in the pentode
connection, so I would assume that the 25L6 is also not limited by the
screen voltage rating when operated as a triode, maybe it can run in
triode mode at nearly the full 200 volt rating of the plate. Since the
6W6 and 25L6 are virtually the same tube, and I have seen tubes with 12
volt heaters dual labeled as 12W6GT/12L6GT, I wonder why the max. voltage
ratings are different?
|
I think some of the triode specs could be pushed a bit for audio applications.
The Pd rating given is for TV use where the tube runs into larger current &
voltage spikes than in a normal audio app. Just have a look at tubes like the
6W6 or 6K6 & see that the audio specs are written for pentode operation while
the TV specs are given for triode operation. I think you can safely jack up the
Pd by 30 to 40% for audio when running triode. Just need to keep a lid on the
supply volts.
Cheers, John Stewart
| Quote: | All the folks that got one were very happy & used them for many years.
I'm sure they were happy, the 25L6GT is a very nice tube, and seems to run
forever too.
Regards,
John Byrns
Surf my web pages at, http://users.rcn.com/jbyrns/ |
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John Stewart
Guest
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| Posted:
Thu Jan 20, 2005 6:38 am Post subject:
Re: 25L6 for hi-fi? |
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robert casey wrote:
| Quote: | Heaters
were all run straight off the line while the B+ came from surplus
transformers I found at a good price.
I would avoid doing that, as the heater-cathode insulation
rating is rather low. As the powerline sees lots of
transient spikes, parts seeing powerline and the
isolated load should have insulation rating of 1.4KV DC.
I'd use a 25V transformer to heat the tubes.
|
The spikes & other glitches on the line are true enough but all those
tubes were designed from the ground up to run straight off the line. I
never had one fail.
Cheers, JLS |
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ptaylor
Guest
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| Posted:
Thu Jan 20, 2005 4:08 pm Post subject:
Re: 25L6 for hi-fi? |
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John Stewart wrote:
| Quote: | robert casey wrote:
Heaters
were all run straight off the line while the B+ came from surplus
transformers I found at a good price.
I would avoid doing that, as the heater-cathode insulation
rating is rather low. As the powerline sees lots of
transient spikes, parts seeing powerline and the
isolated load should have insulation rating of 1.4KV DC.
I'd use a 25V transformer to heat the tubes.
The spikes & other glitches on the line are true enough but all those
tubes were designed from the ground up to run straight off the line. I
never had one fail.
Cheers, JLS
|
I generally don't like the idea of line-op stuff,cause it's kind of
dangerous.(if something is mis-wired,amp,outlet,housewiring)
The speaker outputs are isolated with the OPT's,but the inputs and
chassis aren't.
If the amp gets plugged in the outlet with the plug reversed,it could
end up with 120vac between it,and the chassis of the CD player (or
whatever) below it.(RCA cables have been known to go up in smoke,the
shield gets shorted across the mains!...Tim?..don't feel bad,I did it
once too!) Not a happy feeling if/when you become the current
path,instead of the interconnect cable...
Granted *if* everything is correctly wired,it *should* be okay.
Use a polarized plug,or 3 prong plug,and use a tester to make sure the
outlet(s) in the house are wired correctly.
I'd still advise a power tranny however.
I actually have a quad of NOS 12L6's I've been meaning to build an amp
with.Maybe I'll get around to it someday. ;-) |
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John Stewart
Guest
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| Posted:
Thu Jan 20, 2005 4:52 pm Post subject:
Re: 25L6 for hi-fi? |
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ptaylor wrote:
| Quote: |
I generally don't like the idea of line-op stuff,cause it's kind of
dangerous.(if something is mis-wired,amp,outlet,housewiring)
The speaker outputs are isolated with the OPT's,but the inputs and
chassis aren't.
If the amp gets plugged in the outlet with the plug reversed,it could
end up with 120vac between it,and the chassis of the CD player (or
whatever) below it.(RCA cables have been known to go up in smoke,the
shield gets shorted across the mains!...Tim?..don't feel bad,I did it
once too!) Not a happy feeling if/when you become the current
path,instead of the interconnect cable...
Granted *if* everything is correctly wired,it *should* be okay.
Use a polarized plug,or 3 prong plug,and use a tester to make sure the
outlet(s) in the house are wired correctly.
I'd still advise a power tranny however.
I actually have a quad of NOS 12L6's I've been meaning to build an amp
with.Maybe I'll get around to it someday. ;-)
|
A safe alternative would be the use of an isolation transformer such as the
Hammond
169TS or 169VS. See at http://www.hammondmfg.com/169.htm
The input & driver tubes required for each channel would use up most of the
remaining volts. For the B+ a half wave doubler will get more than enough
volts. That can be got down to a little more than the needed 220 volts
easily with a power FET source follower such as an IRF840 on a suitable
heatsink. Why 220 volts? The extra 20 volts make up for the cathode bias &
the R drop in the OPT primary winding. If the lead-in cap of the half-wave
doubler is properly selected the drop across the FET & resulting dissipation
can be kept to a minimum. With that arrangement there will be no DC in the
isolation transformer secondary. A full-wave doubler is not suitable for
this application where the heaters & B+ are derived from a common winding.
And you can end up with a pretty good stereo amp, provided you select a
suitable OPT. There are many choices available.
Cheers, John Stewart |
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