Hi R.A.T.s, I was looking at some data sheets on the 4CX250
tetrode and just toying with the idea of an ultralinear P-P amp based on a
pair. The output transformer would need an extra primary for the G2
connection so as to not exceed it's maximum voltage rating. Then there's
the cooling to consider on top of that, maybe a clamp on heatsink with it
all inside a large B+ proof cage.

These type of tubes could be run underrated and still have a
large amount of class A output. B+ would have to be three or four multiple
windings with their separate rectifiers and capacitors.

Mark Harriss

"Mark Harriss" wrote in message
...
Hi R.A.T.s, I was looking at some data sheets on the 4CX250
tetrode and just toying with the idea of an ultralinear P-P amp based
on a pair. The output transformer would need an extra primary for the G2
connection so as to not exceed it's maximum voltage rating. Then there's
the cooling to consider on top of that, maybe a clamp on heatsink with it
all inside a large B+ proof cage.

Made for forced air. If you want conduction cooled, there are specific
types, such as the 8873 (indirectly heated triode).
I wouldn't bother with UL, but you are going to need a custom OPT anyway
so suit yourself.
Fan is easy enough. Grab some vented sockets and chimneys off ebay and
shove a blower in the chassis (no open chassis testing, it needs to be
pressurized!). Cheap source for a blower which is surely excess is a
dead microwave oven. Which you could use for the scrap iron as well.
Two of those in parallel (after knocking out the magnetic shunts) ought
to work well for the PS...

These type of tubes could be run underrated and still have a
large amount of class A output. B+ would have to be three or four
multiple
windings with their separate rectifiers and capacitors.

Bah. If you're gonna use beefy tubes, milk it for all it's worth and get
1kW class B, with around 30dB NFB to make it bearable.

Tim

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

Mark Harriss wrote in news:TfMKb.81258
:



Hi R.A.T.s, I was looking at some data sheets on the 4CX250
tetrode and just toying with the idea of an ultralinear P-P amp based on
a
pair. The output transformer would need an extra primary for the G2
connection so as to not exceed it's maximum voltage rating. Then
there's
the cooling to consider on top of that, maybe a clamp on heatsink with
it
all inside a large B+ proof cage.

These type of tubes could be run underrated and still have a
large amount of class A output. B+ would have to be three or four
multiple
windings with their separate rectifiers and capacitors.

Mark Harriss

Everytime someone mentions tubes of the 250+ watt range, I instantly think
about the lethal amounts of B+ required, then the heat, and the noisy
blower.

r


--
Nothing beats the bandwidth of a station wagon filled with DLT tapes.

Mark Harriss wrote:

Hi R.A.T.s, I was looking at some data sheets on the 4CX250
tetrode and just toying with the idea of an ultralinear P-P amp based on a
pair. The output transformer would need an extra primary for the G2
connection so as to not exceed it's maximum voltage rating. Then there's
the cooling to consider on top of that, maybe a clamp on heatsink with it
all inside a large B+ proof cage.

These type of tubes could be run underrated and still have a
large amount of class A output. B+ would have to be three or four multiple
windings with their separate rectifiers and capacitors.

Mark Harriss

There is a reference to 4CX250 at
http://www.mike-willis.com/g0mjw/4cx250.html
and discussions for RF usage at
http://lists.contesting.com/archives.../msg00035.html
To get any power the circuit has to be class B
with a huge voltage swing, and low current swing,
and then to get a decent amount of class A, you'd need to dissipate
lots of heat, and that means a strong airflow, which means noise in the lounge,

which is just not on, so you will have to build a large heatsink to
couple tightly to the anode structure for presumably a limited amount of
passive cooling, and insulate all rather well.

If you look at ARRl handbooks on PS, they use seriesed diodes, series caps,
but only one tranny.

One could use microwave trannies, perhaps ok for 2kV and 700 VA,
with a choke input filter, to get about +1,800V.

RL values are a high number of ohms, so the OPT
needs to be lots of Lp, so a large tranny is needed,
with a lot of interleaving, but well insulated P&S windings,
maybe have the OPT potted in an oil bath, with sealed terminals.

Somehow, I think if one wanted high power from bottles, 1/2 a dozen 845,
13E1, GM70, 211, etc, would perhaps be easier.

And a simpler way for 4CX250 to arrange the OPT without a separate screen
winding
is to consider the acoustical CFB method, with 10% to 20%
CFB, so G2 can be kept at a fixed +V lower than Ea.

I could not find any actual data curves on the 4CX250.
The drive requirements are not tiny...

Patrick Turner.

Hi RATs!

I have a pair of Svetlana 4CX250 awaiting deployment

Please lead the charge!

I think the new quiet muffin fans for 'puter PS may be useful, and temperature
probes to keep your system honest would not be a bad idea.

Some math, not my greatest prowess, would let you know the minimum number of
fans per tube.

Seems monoblock output stage would provide maximum cooling.

I was thinking stereo SE, but a P-P sub amp 8^0

Happy Ears!
Al


Alan J. Marcy
Phoenix, AZ

PWC/mystic/Earhead

I like the 813 (directly heated tetrode) for such an amp. No forced cooling
req'd. Availabilty may be an issue.
Mark S.

"Mark Harriss" wrote in message
...


Hi R.A.T.s, I was looking at some data sheets on the 4CX250
tetrode and just toying with the idea of an ultralinear P-P amp based on a
pair. The output transformer would need an extra primary for the G2
connection so as to not exceed it's maximum voltage rating. Then there's
the cooling to consider on top of that, maybe a clamp on heatsink with it
all inside a large B+ proof cage.

These type of tubes could be run underrated and still have a
large amount of class A output. B+ would have to be three or four
multiple
windings with their separate rectifiers and capacitors.

Mark Harriss

Rich Andrews wrote:

Mark Harriss wrote in news:TfMKb.81258
:



Hi R.A.T.s, I was looking at some data sheets on the 4CX250
tetrode and just toying with the idea of an ultralinear P-P amp based on
a
pair. The output transformer would need an extra primary for the G2
connection so as to not exceed it's maximum voltage rating. Then
there's
the cooling to consider on top of that, maybe a clamp on heatsink with
it
all inside a large B+ proof cage.

These type of tubes could be run underrated and still have a
large amount of class A output. B+ would have to be three or four
multiple
windings with their separate rectifiers and capacitors.

Mark Harriss

Everytime someone mentions tubes of the 250+ watt range, I instantly think
about the lethal amounts of B+ required, then the heat, and the noisy
blower.

r




You're not wrong about the B+ 1000 volts minimum!!!

Eimac made tubes in this power range which could be cooled with water and
convection. Normally we would think of water cooling in 5kW and up range
tubes. QST had an article describing a class-C amp called the "Stanley
Steamer" -- sometime in the 1960's.

Jack

"Rich Andrews" wrote in message
.44...
Mark Harriss wrote in news:TfMKb.81258
:



Hi R.A.T.s, I was looking at some data sheets on the 4CX250
tetrode and just toying with the idea of an ultralinear P-P amp based on
a
pair. The output transformer would need an extra primary for the G2
connection so as to not exceed it's maximum voltage rating. Then
there's
the cooling to consider on top of that, maybe a clamp on heatsink with
it
all inside a large B+ proof cage.

These type of tubes could be run underrated and still have a
large amount of class A output. B+ would have to be three or four
multiple
windings with their separate rectifiers and capacitors.

Mark Harriss

Everytime someone mentions tubes of the 250+ watt range, I instantly think
about the lethal amounts of B+ required, then the heat, and the noisy
blower.

r


--
Nothing beats the bandwidth of a station wagon filled with DLT tapes.

Tim "The Toolman....UGH UGH!!" Williams wrote:

Made for forced air. If you want conduction cooled, there are specific
types, such as the 8873 (indirectly heated triode).
I wouldn't bother with UL, but you are going to need a custom OPT anyway
so suit yourself.
Fan is easy enough. Grab some vented sockets and chimneys off ebay and
shove a blower in the chassis (no open chassis testing, it needs to be
pressurized!). Cheap source for a blower which is surely excess is a
dead microwave oven. Which you could use for the scrap iron as well.
Two of those in parallel (after knocking out the magnetic shunts) ought
to work well for the PS...

These type of tubes could be run underrated and still have a
large amount of class A output. B+ would have to be three or four
multiple
windings with their separate rectifiers and capacitors.

Bah. If you're gonna use beefy tubes, milk it for all it's worth and get
1kW class B, with around 30dB NFB to make it bearable.

Tim

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


I have a quad of some serious GOSS C core iron, but I'll have to check
how thick the tape is if I want to use it for output work.

For the B+ I have a 3KVA X-ray tranny I could rewind which would
be big enough for a stereo pair.

I thought about blowers etc, but the idea of having to clean filters and
making temperature and airflow safeties to stop overheating doesn't
appeal to me: I have a friend who's interested in casting copper
alloy or aluminium alloy heatsinks and machining a snug clamp
fit on the outside of the valve. I could maybe top them with a plastic
pancake blower to keep them managable in size.

Mark Harriss wrote:

Hi R.A.T.s, I was looking at some data sheets on the 4CX250
tetrode and just toying with the idea of an ultralinear P-P amp based on a
pair. The output transformer would need an extra primary for the G2
connection so as to not exceed it's maximum voltage rating. Then there's
the cooling to consider on top of that, maybe a clamp on heatsink with it
all inside a large B+ proof cage.

These type of tubes could be run underrated and still have a
large amount of class A output. B+ would have to be three or four multiple
windings with their separate rectifiers and capacitors.

Mark Harriss

A lot of the 4CX and 3CX series will die just from the heater power if
not forced air cooled. There is a conduction cooled version of the 4CX250
- an 8000 series number, I forget which, but these are rare. Blower noise
is definitely your enemy here and I think you would be better off with 813s,
plus you get those lovely bright thoriated tungsten filaments. Ned's site
has a circuit for an 813 based amp somewhere.

DIY conduction cooling may not work as the cathode and grid seals may exceed
their rated temperatures without the air flow. Your conduction block will not
be in very good thermal contact with anything but the anode. You will also have
a large chunk of hot metal at full B+. A little difficult to mount, perhaps?

If you can install the amp remote from the listening area, then go for a good
snail blower, otherwise convection cooled valves will be much simpler.

best

Andy Cowley

On Wed, 07 Jan 2004 14:36:48 +0000, the highly esteemed Andy Cowley
enlightened us with these pearls of wisdom:

Mark Harriss wrote:

Hi R.A.T.s, I was looking at some data sheets on the 4CX250
tetrode and just toying with the idea of an ultralinear P-P amp based on
a pair. The output transformer would need an extra primary for the G2
connection so as to not exceed it's maximum voltage rating. Then
there's the cooling to consider on top of that, maybe a clamp on
heatsink with it all inside a large B+ proof cage.

These type of tubes could be run underrated and still have a
large amount of class A output. B+ would have to be three or four
multiple windings with their separate rectifiers and capacitors.

Mark Harriss

A lot of the 4CX and 3CX series will die just from the heater power if not
forced air cooled. There is a conduction cooled version of the 4CX250 - an
8000 series number, I forget which, but these are rare.

Actually, they aren't rare at all. The tube in question is the 8560AS.
Here is the data sheet:
http://www.svetlana.com/graphics/pro...pdf/8560AS.pdf



--
Greg

--The software said it requires Win2000 or better, so I installed Linux.

"Andy Cowley" wrote in message
...
Mark Harriss wrote:

Hi R.A.T.s, I was looking at some data sheets on the 4CX250
tetrode and just toying with the idea of an ultralinear P-P amp based on
a
pair. The output transformer would need an extra primary for the G2
connection so as to not exceed it's maximum voltage rating. Then
there's
the cooling to consider on top of that, maybe a clamp on heatsink with
it
all inside a large B+ proof cage.

These type of tubes could be run underrated and still have a
large amount of class A output. B+ would have to be three or four
multiple
windings with their separate rectifiers and capacitors.

Mark Harriss

A lot of the 4CX and 3CX series will die just from the heater power if
not forced air cooled. There is a conduction cooled version of the 4CX250
- an 8000 series number, I forget which, but these are rare. Blower noise
is definitely your enemy here and I think you would be better off with
813s,
plus you get those lovely bright thoriated tungsten filaments. Ned's site
has a circuit for an 813 based amp somewhere.

DIY conduction cooling may not work as the cathode and grid seals may
exceed
their rated temperatures without the air flow. Your conduction block will
not
be in very good thermal contact with anything but the anode. You will also
have
a large chunk of hot metal at full B+. A little difficult to mount,
perhaps?

Ground anodes and loads the cathodes !!!!!!
Not the simpler approach indeed but with interstage trannies ......?
When I used a PP of such toobs for a 2 meters RF amp (B class),
correspondents
clearly heard the blower !!!


If you can install the amp remote from the listening area, then go for a
good
snail blower, otherwise convection cooled valves will be much simpler.

best

Andy Cowley

In article , Mark Harriss
wrote:

Hi R.A.T.s, I was looking at some data sheets on the 4CX250
tetrode and just toying with the idea of an ultralinear P-P amp based on a
pair. The output transformer would need an extra primary for the G2
connection so as to not exceed it's maximum voltage rating. Then there's
the cooling to consider on top of that, maybe a clamp on heatsink with it
all inside a large B+ proof cage.

These type of tubes could be run underrated and still have a
large amount of class A output. B+ would have to be three or four multiple
windings with their separate rectifiers and capacitors.


Hi Mark,

I the days when the vinyl stereo disk was young, Fairchild built a stereo
cutter head amplifier using a pair of 4CX250Bs in each channel. There is
an article on this stereo amplifier in the "Journal of the Audio
Engineering Society", Volume 7, Number 4, October 1959. The article
doesn't state the design power output, but it does say the amplifier runs
class A. The anode voltage is 1,200 volts, and each tube is said to be
dissipating 150 Watts. That would seem to put the class A power output at
something less than 150 Watts, but they quote numbers for difference tone
distortion at distortion 100 Watts and 200 Watts, which they claim are
"very low", and they have a graph of the 60 Hz and 7 kHz 4:1 IM distortion
that doesn't hit the wall until 500 Watts, clearly well into class AB
territory. The stereo amplifier was built on a shallow rack mount
chassis, and the four 4CX250Bs were cooled by a "small centrifugal blower"
which must be sandwiched inside the chassis somewhere, as none of the
cooling system is visible in the photo, except the tops of the 4cX250B
anodes under a protective cage. The front end and driver tubes are all of
the 9 pin miniature variety.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

there was an article a while ago about a guy who built a PP amp with
ceramics and he mounted cpu fans under the tube socket
ran the cermamic tubes way under spec and got decent results but if I
remember right it wasnt that much bigger than a PP 6550 amp
maybe on the svetlana website?
I will look and see

Doug


"Mark Harriss" wrote in message
...
Tim "The Toolman....UGH UGH!!" Williams wrote:

Made for forced air. If you want conduction cooled, there are specific
types, such as the 8873 (indirectly heated triode).
I wouldn't bother with UL, but you are going to need a custom OPT
anyway
so suit yourself.
Fan is easy enough. Grab some vented sockets and chimneys off ebay and
shove a blower in the chassis (no open chassis testing, it needs to be
pressurized!). Cheap source for a blower which is surely excess is a
dead microwave oven. Which you could use for the scrap iron as well.
Two of those in parallel (after knocking out the magnetic shunts) ought
to work well for the PS...

These type of tubes could be run underrated and still have a
large amount of class A output. B+ would have to be three or four
multiple
windings with their separate rectifiers and capacitors.

Bah. If you're gonna use beefy tubes, milk it for all it's worth and
get
1kW class B, with around 30dB NFB to make it bearable.

Tim

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


I have a quad of some serious GOSS C core iron, but I'll have to check
how thick the tape is if I want to use it for output work.

For the B+ I have a 3KVA X-ray tranny I could rewind which would
be big enough for a stereo pair.

I thought about blowers etc, but the idea of having to clean filters and
making temperature and airflow safeties to stop overheating doesn't
appeal to me: I have a friend who's interested in casting copper
alloy or aluminium alloy heatsinks and machining a snug clamp
fit on the outside of the valve. I could maybe top them with a plastic
pancake blower to keep them managable in size.

http://tec-sol.com/3CX300A1_amp_english.htm

guess it was a squirrel cage on the bottom of the chassis

Doug

"doug" wrote in message
news:Wp_Kb.16806$JQ1.5023@pd7tw1no...
there was an article a while ago about a guy who built a PP amp with
ceramics and he mounted cpu fans under the tube socket
ran the cermamic tubes way under spec and got decent results but if I
remember right it wasnt that much bigger than a PP 6550 amp
maybe on the svetlana website?
I will look and see

Doug


"Mark Harriss" wrote in message
...
Tim "The Toolman....UGH UGH!!" Williams wrote:

Made for forced air. If you want conduction cooled, there are
specific
types, such as the 8873 (indirectly heated triode).
I wouldn't bother with UL, but you are going to need a custom OPT
anyway
so suit yourself.
Fan is easy enough. Grab some vented sockets and chimneys off ebay
and
shove a blower in the chassis (no open chassis testing, it needs to be
pressurized!). Cheap source for a blower which is surely excess is a
dead microwave oven. Which you could use for the scrap iron as well.
Two of those in parallel (after knocking out the magnetic shunts)
ought
to work well for the PS...

These type of tubes could be run underrated and still have a
large amount of class A output. B+ would have to be three or four
multiple
windings with their separate rectifiers and capacitors.

Bah. If you're gonna use beefy tubes, milk it for all it's worth and
get
1kW class B, with around 30dB NFB to make it bearable.

Tim

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


I have a quad of some serious GOSS C core iron, but I'll have to check
how thick the tape is if I want to use it for output work.

For the B+ I have a 3KVA X-ray tranny I could rewind which would
be big enough for a stereo pair.

I thought about blowers etc, but the idea of having to clean filters and
making temperature and airflow safeties to stop overheating doesn't
appeal to me: I have a friend who's interested in casting copper
alloy or aluminium alloy heatsinks and machining a snug clamp
fit on the outside of the valve. I could maybe top them with a plastic
pancake blower to keep them managable in size.

TubeGarden wrote:
Hi RATs!

I have a pair of Svetlana 4CX250 awaiting deployment

Please lead the charge!

The specs claim 26ma of grid current, maybe run them SE in A2?


Adam

Andy Cowley wrote:

Mark Harriss wrote:

Hi R.A.T.s, I was looking at some data sheets on the 4CX250
tetrode and just toying with the idea of an ultralinear P-P amp based on
a pair. The output transformer would need an extra primary for the G2
connection so as to not exceed it's maximum voltage rating. Then there's
the cooling to consider on top of that, maybe a clamp on heatsink with it
all inside a large B+ proof cage.

These type of tubes could be run underrated and still have a
large amount of class A output. B+ would have to be three or four
multiple windings with their separate rectifiers and capacitors.

Mark Harriss

A lot of the 4CX and 3CX series will die just from the heater power if
not forced air cooled. There is a conduction cooled version of the 4CX250
- an 8000 series number, I forget which, but these are rare. Blower noise
is definitely your enemy here and I think you would be better off with
813s, plus you get those lovely bright thoriated tungsten filaments. Ned's
site has a circuit for an 813 based amp somewhere.

DIY conduction cooling may not work as the cathode and grid seals may
exceed their rated temperatures without the air flow. Your conduction
block will not be in very good thermal contact with anything but the
anode. You will also have a large chunk of hot metal at full B+. A little
difficult to mount, perhaps?

If you can install the amp remote from the listening area, then go for a
good snail blower, otherwise convection cooled valves will be much
simpler.

best

Andy Cowley


You are absolutely right about the extra non anode cooling
required, the screen dissipates 12 watts or so that would require an
extra heatsink as well. I'm more or less stuck with 4CX250's as thats
what I already have. I guess some blower experiments are in order.

Thanks
Mark

TubeGarden wrote:

Hi RATs!

I have a pair of Svetlana 4CX250 awaiting deployment

Please lead the charge!

I think the new quiet muffin fans for 'puter PS may be useful, and
temperature probes to keep your system honest would not be a bad idea.

Some math, not my greatest prowess, would let you know the minimum number
of fans per tube.

Seems monoblock output stage would provide maximum cooling.

I was thinking stereo SE, but a P-P sub amp 8^0

Happy Ears!
Al


Alan J. Marcy
Phoenix, AZ

PWC/mystic/Earhead

The URL provided by Pat mentions a substantial blower is required
as for the neccessary math needed to calculate cooling: there is none, I
understand you rig a water manometer and connect it to the cabinet to
measure the correct pressure before the tubes.

There may be a bit of mucking around for a passive cooler but I'd
scale it according to transistor amps and suck it and see.

Mark Harriss

Mark S wrote:

I like the 813 (directly heated tetrode) for such an amp. No forced
cooling req'd. Availabilty may be an issue.
Mark S.

Hi Mark, I've eyed the 813 off before in the past but I have
4CX's available readily so I thought I'd investigate using them. I even
bought 6 x 4CX 10000D's for an induction heater project but they sent
lower rated A series which were smashed in the post and were
writeoff's.

Greg Pierce wrote:

Actually, they aren't rare at all. The tube in question is the 8560AS.
Here is the data sheet:
http://www.svetlana.com/graphics/pro...pdf/8560AS.pdf


Thanks Greg, I'll take a look.

Mark Harriss

Adam Stouffer schrieb:

TubeGarden wrote:
Hi RATs!

I have a pair of Svetlana 4CX250 awaiting deployment

Please lead the charge!

The specs claim 26ma of grid current, maybe run them SE in A2?

Adam


those 26mA are class C

specs for AB1 push-pull are as follows:

Ua Ia Ig2 Pout

1000 2x250 2x10 240W

1500 2x250 2x8 430W

2000 2x250 2x5 600W

common data for all anode voltages:

Ig1=0, Ug1 -55, Ia_idle 2x100mA, Ug1g1ss 100V, Ug2 350V

cooling: 0,11m³/minute at 8mm of water


Peter

Mark Harriss schrieb:

I even
bought 6 x 4CX 10000D's for an induction heater project but they sent
lower rated A series which were smashed in the post and were
writeoff's.

4CX10000Ds can be rebuilt


Peter

Patrick Turner wrote:


There is a reference to 4CX250 at
http://www.mike-willis.com/g0mjw/4cx250.html
and discussions for RF usage at
http://lists.contesting.com/archives.../msg00035.html
To get any power the circuit has to be class B
with a huge voltage swing, and low current swing,
and then to get a decent amount of class A, you'd need to dissipate
lots of heat, and that means a strong airflow, which means noise in the
lounge,

which is just not on, so you will have to build a large heatsink to
couple tightly to the anode structure for presumably a limited amount of
passive cooling, and insulate all rather well.

If you look at ARRl handbooks on PS, they use seriesed diodes, series
caps, but only one tranny.

One could use microwave trannies, perhaps ok for 2kV and 700 VA,
with a choke input filter, to get about +1,800V.

RL values are a high number of ohms, so the OPT
needs to be lots of Lp, so a large tranny is needed,
with a lot of interleaving, but well insulated P&S windings,
maybe have the OPT potted in an oil bath, with sealed terminals.

Somehow, I think if one wanted high power from bottles, 1/2 a dozen 845,
13E1, GM70, 211, etc, would perhaps be easier.

And a simpler way for 4CX250 to arrange the OPT without a separate screen
winding
is to consider the acoustical CFB method, with 10% to 20%
CFB, so G2 can be kept at a fixed +V lower than Ea.

I could not find any actual data curves on the 4CX250.
The drive requirements are not tiny...

Patrick Turner.


Hi Pat, I found my PDF datashe
et at: http://www.mif.pg.gda.pl/homepages/frank/sheets41.html
where it's also known as a 7203 (4CX250B). If you look up
the RCA data on the '250B you can see specifications for
use as an audio frequency class AB1 push pull amp.

I'd be looking at say a 4.5K P-P transformer, a 1250V B+,
plate current of 135 mA and an output of 300 watts out
of a possible 590 watts theoretical maximum for a pair.

This would run them at half power. The screen would have
to run at 350 V according to the datasheet, I'm not too
familiar with CFB operation despite all of the discussions
here on RAT, so I'll have to do some reading about it first.

The grounded Anode idea of Yves looks like it
would bear further investigation too and there is a conduction
cooled Svetlana '250 with a solid slug anode that Greg mentions
I would hope the numerous fins on an aircooled model
would conduct enough heat to the outside anode rim to
allow heatsink cooling at half power.


Regards
Mark Harriss

John Byrns wrote:

Hi Mark,

I the days when the vinyl stereo disk was young, Fairchild built a stereo
cutter head amplifier using a pair of 4CX250Bs in each channel. There is
an article on this stereo amplifier in the "Journal of the Audio
Engineering Society", Volume 7, Number 4, October 1959. The article
doesn't state the design power output, but it does say the amplifier runs
class A. The anode voltage is 1,200 volts, and each tube is said to be
dissipating 150 Watts. That would seem to put the class A power output at
something less than 150 Watts, but they quote numbers for difference tone
distortion at distortion 100 Watts and 200 Watts, which they claim are
"very low", and they have a graph of the 60 Hz and 7 kHz 4:1 IM distortion
that doesn't hit the wall until 500 Watts, clearly well into class AB
territory. The stereo amplifier was built on a shallow rack mount
chassis, and the four 4CX250Bs were cooled by a "small centrifugal blower"
which must be sandwiched inside the chassis somewhere, as none of the
cooling system is visible in the photo, except the tops of the 4cX250B
anodes under a protective cage. The front end and driver tubes are all of
the 9 pin miniature variety.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/





Thanks for the information John, If I can find the article, then someone
has already done the hard yards for me. I'd like to see just how they went
about the task and solved the problems along the way.

Regards
Mark Harriss

Hi Doug, that sounds like the 3CX300A 300W push pull amp.

Andy Cowley wrote in
:

Mark Harriss wrote:

Hi R.A.T.s, I was looking at some data sheets on the 4CX250
tetrode and just toying with the idea of an ultralinear P-P amp based
on a pair. The output transformer would need an extra primary for the
G2 connection so as to not exceed it's maximum voltage rating. Then
there's the cooling to consider on top of that, maybe a clamp on
heatsink with it all inside a large B+ proof cage.

These type of tubes could be run underrated and still have a
large amount of class A output. B+ would have to be three or four
multiple windings with their separate rectifiers and capacitors.

Mark Harriss

A lot of the 4CX and 3CX series will die just from the heater power if
not forced air cooled. There is a conduction cooled version of the
4CX250 - an 8000 series number, I forget which, but these are rare.
Blower noise is definitely your enemy here and I think you would be
better off with 813s, plus you get those lovely bright thoriated
tungsten filaments. Ned's site has a circuit for an 813 based amp
somewhere.

DIY conduction cooling may not work as the cathode and grid seals may
exceed their rated temperatures without the air flow. Your conduction
block will not be in very good thermal contact with anything but the
anode. You will also have a large chunk of hot metal at full B+. A
little difficult to mount, perhaps?

If you can install the amp remote from the listening area, then go for a
good snail blower, otherwise convection cooled valves will be much
simpler.

best

Andy Cowley


Speaking of high power tubes, anyone toy with a 572B in audio service?

r


--
Nothing beats the bandwidth of a station wagon filled with DLT tapes.

"Rich Andrews" wrote in message
.44...
Speaking of high power tubes, anyone toy with a 572B in audio service?

Addendum for Rich: at MORE than 20mA

Tim

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

Peter Völpel wrote:

Mark Harriss schrieb:

I even
bought 6 x 4CX 10000D's for an induction heater project but they sent
lower rated A series which were smashed in the post and were
writeoff's.

4CX10000Ds can be rebuilt


Peter


Hi Pete, They were sold to me as "rebuilt" units but turned
out to be old used units with signs of overheating and arcing and
weren't even the type I paid for. The cooling fins on the anodes were
badly dented too so they may have been beyond rebuilding.

I eventually was able to get a refund after some time.

Mark Harriss

Yves Monmagnon wrote:
perhaps?

Ground anodes and loads the cathodes !!!!!!
Not the simpler approach indeed but with interstage trannies ......?
When I used a PP of such toobs for a 2 meters RF amp (B class),
correspondents
clearly heard the blower !!!



So the only obstacle to running an amp with a positive
grounded anodes would be isolation of the inputs and outputs via
interstage and output transformers?.


Regards
Mark

Mark Harriss wrote:

Yves Monmagnon wrote:
perhaps?

Ground anodes and loads the cathodes !!!!!!
Not the simpler approach indeed but with interstage trannies ......?
When I used a PP of such toobs for a 2 meters RF amp (B class),
correspondents
clearly heard the blower !!!



So the only obstacle to running an amp with a positive
grounded anodes would be isolation of the inputs and outputs via
interstage and output transformers?.


Regards
Mark


Just like a microwave oven circuit in some ways!!

"Tim Williams" wrote in news:vvq6jm8cdklgb6
@corp.supernews.com:

"Rich Andrews" wrote in message
.44...
Speaking of high power tubes, anyone toy with a 572B in audio service?

Addendum for Rich: at MORE than 20mA

Tim



Thanks! (:)

The heater alone is quite hungry. I used to mess with these in RF service
and I was always impressed with the size and thickness of the plates, how
much you can over drive them, and how serious they looked even when
powered off. Makes a TV sweep tube look small. Again, fan cooling is
necessary. I must have been crazy to mess with stuff like that. Heck,
monster klystron based TV transmitters are safer than what I was playing
with.

r

--
Nothing beats the bandwidth of a station wagon filled with DLT tapes.

Rich Andrews wrote:

"Tim Williams" wrote in news:vvq6jm8cdklgb6
@corp.supernews.com:

"Rich Andrews" wrote in message
.44...
Speaking of high power tubes, anyone toy with a 572B in audio service?

Addendum for Rich: at MORE than 20mA

Tim


Thanks! (:)

The heater alone is quite hungry. I used to mess with these in RF service
and I was always impressed with the size and thickness of the plates, how
much you can over drive them, and how serious they looked even when
powered off. Makes a TV sweep tube look small. Again, fan cooling is
necessary. I must have been crazy to mess with stuff like that. Heck,
monster klystron based TV transmitters are safer than what I was playing
with.

Could not the whole output power tube module be
enclosed in a tank of oil with a convection heat exchanger?
To my mind, the 4CX tubes are good for the large PO one might want,
rather than using them for SE peanut power.
Is it possible to fit a tight fitting yoke around the top of the tube, and
have
some 12mm copper pipe brazed onto the yoke,
so that rubber hose for water cooling could be pumped quietly to a heat
exchanger,
which need only be quite a few metres of folded copper pipe
on a wall outside the house in summer, and inside the house in winter.

KT88 are definately easier and cheaper.....

Patrick Turner.



r

--
Nothing beats the bandwidth of a station wagon filled with DLT tapes.

"Mark Harriss" wrote in message
...
Yves Monmagnon wrote:
perhaps?

Ground anodes and loads the cathodes !!!!!!
Not the simpler approach indeed but with interstage trannies ......?
When I used a PP of such toobs for a 2 meters RF amp (B class),
correspondents
clearly heard the blower !!!



So the only obstacle to running an amp with a positive
grounded anodes would be isolation of the inputs and outputs via
interstage and output transformers?.

If you persist, I've posted an idea at ABSE (4CX250PP)
But, how large is your living room ;-)

Yves.


Regards
Mark

Mark Harriss wrote:


Hi Mark
I have made a power amp using 4CX250's as triodes.
I run them at 500 volts 80Ma. 5k A--A
I have a computer fan under each tube.
They sound great. Great bass.
Apart from needing the fan 4CX250's are much simpler to use than many
other transmitting tubes. Tried some 4E27's recently using DC on the
heaters. Getting rid of the heat from the 4 bridge rectifiers is some
problem.
Phil.
Hi R.A.T.s, I was looking at some data sheets on the 4CX250
tetrode and just toying with the idea of an ultralinear P-P amp based on a
pair. The output transformer would need an extra primary for the G2
connection so as to not exceed it's maximum voltage rating. Then there's
the cooling to consider on top of that, maybe a clamp on heatsink with it
all inside a large B+ proof cage.

These type of tubes could be run underrated and still have a
large amount of class A output. B+ would have to be three or four multiple
windings with their separate rectifiers and capacitors.

Mark Harriss