Hi all,

I recently bought a pair of Cary CAD 300B SE Signature amps. A friend of
mine (who builds his own amps) advised me to substitute the standard 5U4GB
rectifiers for Mullard CV378s. According to various sources on the web they
are not a drop-in replacement as they are not identical.

As a non-engineer I just wanted a second opinion. Will this substitution
likely cause any problems ? What is the worst that could happen ? Could I
fry my amps (or the Western Electric 300Bs) ?

Cheers

Mick Jennings

In message , RhythMick
writes
Hi all,

I recently bought a pair of Cary CAD 300B SE Signature amps. A friend of
mine (who builds his own amps) advised me to substitute the standard 5U4GB
rectifiers for Mullard CV378s. According to various sources on the web they
are not a drop-in replacement as they are not identical.

As a non-engineer I just wanted a second opinion. Will this substitution
likely cause any problems ? What is the worst that could happen ? Could I
fry my amps (or the Western Electric 300Bs) ?

Cheers

Mick Jennings



I believe the CV378 is a military-spec GZ37. You may need to check the
capacitor value on the output of the rectifier, and also if the heater
current is OK.
--
Chris Morriss

Chris Morriss said:

I recently bought a pair of Cary CAD 300B SE Signature amps. A friend of
mine (who builds his own amps) advised me to substitute the standard 5U4GB
rectifiers for Mullard CV378s. According to various sources on the web they
are not a drop-in replacement as they are not identical.

As a non-engineer I just wanted a second opinion. Will this substitution
likely cause any problems ? What is the worst that could happen ? Could I
fry my amps (or the Western Electric 300Bs) ?

I believe the CV378 is a military-spec GZ37. You may need to check the
capacitor value on the output of the rectifier, and also if the heater
current is OK.

Oh dear. In the Cary 300B SET, there's 1100 uF directly at the cathode
of the GZ37.
I modified many rectifier-eating Carys to 50 uF, choke+ resistor and
then the other 1100.
Using Duncan Munroe's program PSUD, you'll see that even this
arrangement overloads the tube's cathode when charging. Sigh.
Maybe you should stick to 5U4G, they're cheaper than GZ37s :-)

Come to think of it, there's an optional "Power Bank" available for
the Cary, containing multiple electrolytics.
Makes everything worse by a factor 10..............

--
Sander deWaal
Vacuum Audio Consultancy

"François Yves Le Gal" wrote:

On Sat, 17 Jul 2004 17:53:42 +0100, "RhythMick"
wrote:

I recently bought a pair of Cary CAD 300B SE Signature amps.

Oh well.

A friend of
mine (who builds his own amps) advised me to substitute the standard 5U4GB
rectifiers for Mullard CV378s.

The 300BSE Sig is either fitted with CV-378, 5R4 or 5U4-6B (sic) depending
on where you look in the CAD documentation and "Operating Manual".
:-)

As a non-engineer I just wanted a second opinion.

The amp has way too much capacitance loading it's rectifier valve.

"The power supply is a full wave center tap configuration running a CV-378
(heavy duty 5AR4) vacuum tube rectifier. The rectified 430 VDC
is fed to a pi-L filter network. The filter capacitors consist of two (2)
1200 MFD and one (1) 100 MFD computer grade electrolytics for a total of
over 230 Joules of energy storage. Each electrolytic capacitor is by-passed
with a low impedance .22 polystyrene capacitor."
http://www.caryaudio.com/pdfs/CAD-300SESignature.pdf

A valve should not see more than 50 µF for the first C stage in such an
arrangement.

Will this substitution likely cause any problems ?

AFAICT the problems are built-in.

But what exactly is under discussion here?

Where is the schematic?

It is said above there is one 100 uF filter cap, then two 1,200 uF caps,
so what are we to assume?

Does the rectifier tube feed the 100 uF, then the 1,200 uF via R or L????

If there was a 100 uF cap charged straight off the rectifier tube, the
peak charge currents could be easily limited by simply fitting a suitable
value R in series with each rectifier anode.

50 uF is the recommended maximum C value for a tube rectifier.

With a DC draw of 160 mA for 2 x 300B + driver stages,
ripple v with 50 uF = 7vrms at 100 Hz, so if XC = 32 ohms, the ripple current
is
220mA rms, and the peak current somewhat higher because the % of the cycle
for charging is shorter than the discharge cycle at thre cap.

If about 50 ohms was placed before the 100 uF cap, the charge currents would be
limited
to probably less than those with 50 uF, and the rectifier won't go north so
soon.

The addition of 10 ohms and a measurement of the peak voltage across the 10
ohms would establish exactly what
is going on.

The amount of series R should not be excessive, lest the value of the B+ be
lowered too much.
But just enough R should be used to limit excessive charge current.
The extra series R won't make any difference to the measured rms ripple
voltage,
or ripple current at the capacitor,
but the charge cycles of the waveform at the cap will be longer.

The extra series R may also reduce noise in the power tranny caused by the high
peak charge currents
switching on and jerking the windings with a magnetic switching pulse.

Patrick Turner.

Patrick Turner said:

Does the rectifier tube feed the 100 uF, then the 1,200 uF via R or L????

Nope. There's 1100 or 1200 uF right at the cathode of the GZ.
Horrors!

With a DC draw of 160 mA for 2 x 300B + driver stages,
ripple v with 50 uF = 7vrms at 100 Hz, so if XC = 32 ohms, the ripple current
is
220mA rms, and the peak current somewhat higher because the % of the cycle
for charging is shorter than the discharge cycle at thre cap.

The 300B SE is a monoblock, so there's only one 300B.

Are you familiar with PSUD, the power supply design program by Duncan
Munro?
You can download it for free at www.duncanamps.co.uk
This is a neat and helpful tool in designing power supplies.

--
Sander deWaal
"SOA of a KT88? Sufficient."

In message , Sander deWaal
writes
Patrick Turner said:

Does the rectifier tube feed the 100 uF, then the 1,200 uF via R or L????

Nope. There's 1100 or 1200 uF right at the cathode of the GZ.
Horrors!

With a DC draw of 160 mA for 2 x 300B + driver stages,
ripple v with 50 uF = 7vrms at 100 Hz, so if XC = 32 ohms, the ripple current
is
220mA rms, and the peak current somewhat higher because the % of the cycle
for charging is shorter than the discharge cycle at thre cap.

The 300B SE is a monoblock, so there's only one 300B.

Are you familiar with PSUD, the power supply design program by Duncan
Munro?
You can download it for free at www.duncanamps.co.uk
This is a neat and helpful tool in designing power supplies.


1200uF directly at the cathode? He must sell a lot of replacement GZ34s
then (or whatever the rectifier is).
--
Chris Morriss

Sander deWaal said:

You can download it for free at www.duncanamps.co.uk

Ahum....that should read:

www.duncanamps.com


--
Sander deWaal
"SOA of a KT88? Sufficient."

Sander deWaal wrote:

Patrick Turner said:

Does the rectifier tube feed the 100 uF, then the 1,200 uF via R or L????

Nope. There's 1100 or 1200 uF right at the cathode of the GZ.
Horrors!

With a DC draw of 160 mA for 2 x 300B + driver stages,
ripple v with 50 uF = 7vrms at 100 Hz, so if XC = 32 ohms, the ripple current
is
220mA rms, and the peak current somewhat higher because the % of the cycle
for charging is shorter than the discharge cycle at thre cap.

The 300B SE is a monoblock, so there's only one 300B.

Are you familiar with PSUD, the power supply design program by Duncan
Munro?
You can download it for free at www.duncanamps.co.uk
This is a neat and helpful tool in designing power supplies.

I always work from first principles.

Having 1,100 uF fed by a tube rectifier would be wrong.
But placing a series R somwhat higher than the 50 ohms I suggested could be tried.

Better would be to retire the tube rectifier, and install SS diodes feeding
100uF, then have a small choke of maybe 2H to feed the 1,100 uF.
The B+ could then be trimmed with series R in front of the diodes and 100 uF,
since the B+ would be too high when the tube rectifier equivalant series R was
taken from the circuit.

Patrick Turner.




--
Sander deWaal
"SOA of a KT88? Sufficient."

Back to the original question: if You just swap the 5U4G with a GZ37 and
leave the 1100 uF cap there, You'll get two results:

- blow a 50$ NOS tube every once in a while instead of a 5$ current
production Russian tube (all coke-bottle 5U4G I saw were indeed Svetlana's
"winged C" rectifiers, CCCP type 5Z3S)
- increase high voltage due to the lower resistance of the GZ37, therefore
changing the operating point of the 300Bs in a non-conservative way

Your amp should just be modified by a qualified technician in order to
present a much lower capacitance at the rectifier cathode (filter input).
Recommended value for 5U4G is 40 uF or less. A suitable cap and a
resistance can be inserted between the tube and the existing filter.

Ciao

Fabio



"RhythMick" ha scritto nel messaggio
...
Hi all,

I recently bought a pair of Cary CAD 300B SE Signature amps. A friend of
mine (who builds his own amps) advised me to substitute the standard 5U4GB
rectifiers for Mullard CV378s. According to various sources on the web
they
are not a drop-in replacement as they are not identical.

As a non-engineer I just wanted a second opinion. Will this substitution
likely cause any problems ? What is the worst that could happen ? Could I
fry my amps (or the Western Electric 300Bs) ?

Cheers

Mick Jennings

Fabio Berutti wrote:

Back to the original question: if You just swap the 5U4G with a GZ37 and
leave the 1100 uF cap there, You'll get two results:

- blow a 50$ NOS tube every once in a while instead of a 5$ current
production Russian tube (all coke-bottle 5U4G I saw were indeed Svetlana's
"winged C" rectifiers, CCCP type 5Z3S)
- increase high voltage due to the lower resistance of the GZ37, therefore
changing the operating point of the 300Bs in a non-conservative way

Your amp should just be modified by a qualified technician in order to
present a much lower capacitance at the rectifier cathode (filter input).
Recommended value for 5U4G is 40 uF or less. A suitable cap and a
resistance can be inserted between the tube and the existing filter.

A cap of 40 uF and a choke of 2H would be far better, because you won't
get the voltage drop across the R, which has to be
around 5 times reactance of the 40 uF, or 200 ohms to prevent the rectifier tube
from
"seeing" the 1,100 uF cap.

Patrick Turner.



Ciao

Fabio

"RhythMick" ha scritto nel messaggio
...
Hi all,

I recently bought a pair of Cary CAD 300B SE Signature amps. A friend of
mine (who builds his own amps) advised me to substitute the standard 5U4GB
rectifiers for Mullard CV378s. According to various sources on the web
they
are not a drop-in replacement as they are not identical.

As a non-engineer I just wanted a second opinion. Will this substitution
likely cause any problems ? What is the worst that could happen ? Could I
fry my amps (or the Western Electric 300Bs) ?

Cheers

Mick Jennings

"Patrick Turner" ha scritto nel messaggio
...


Fabio Berutti wrote:

Back to the original question: if You just swap the 5U4G with a GZ37
and
leave the 1100 uF cap there, You'll get two results:

- blow a 50$ NOS tube every once in a while instead of a 5$ current
production Russian tube (all coke-bottle 5U4G I saw were indeed
Svetlana's
"winged C" rectifiers, CCCP type 5Z3S)
- increase high voltage due to the lower resistance of the GZ37,
therefore
changing the operating point of the 300Bs in a non-conservative way

Your amp should just be modified by a qualified technician in order to
present a much lower capacitance at the rectifier cathode (filter
input).
Recommended value for 5U4G is 40 uF or less. A suitable cap and a
resistance can be inserted between the tube and the existing filter.

A cap of 40 uF and a choke of 2H would be far better, because you won't
get the voltage drop across the R, which has to be
around 5 times reactance of the 40 uF, or 200 ohms to prevent the
rectifier tube
from
"seeing" the 1,100 uF cap.

Patrick Turner.


As usual You're right.
I was concerned about the place available "under the hood": a 2H/200mA choke
needs some room, say 2"x2", while a 9W wirewound resistor can be hammered in
anywhere.
Indeed, one more CL filter will improve hum ... if feasible, it's better for
sure.

Ciao

Fabio




Ciao

Fabio

"RhythMick" ha scritto nel messaggio
...
Hi all,

I recently bought a pair of Cary CAD 300B SE Signature amps. A friend
of
mine (who builds his own amps) advised me to substitute the standard
5U4GB
rectifiers for Mullard CV378s. According to various sources on the web
they
are not a drop-in replacement as they are not identical.

As a non-engineer I just wanted a second opinion. Will this
substitution
likely cause any problems ? What is the worst that could happen ?
Could I
fry my amps (or the Western Electric 300Bs) ?

Cheers

Mick Jennings

Thanks all,

As a non-electrician I've found much it difficult to follow much of the
discussion.

However, the consensus seems to be that there is a big questionmark over the
longevity of the rectifier valve given the high capacitance placed at the
cathode.

To give an update, I've put the CV378s in place - with a massive improvement
in sound. Huge.

I'll consult my engineer friend (and Dennis Had) about the capacitance.
Anyone know why he put them there ? Must be a reason ?

Cheers


"RhythMick" wrote in message
...
Hi all,

I recently bought a pair of Cary CAD 300B SE Signature amps. A friend of
mine (who builds his own amps) advised me to substitute the standard 5U4GB
rectifiers for Mullard CV378s. According to various sources on the web
they
are not a drop-in replacement as they are not identical.

As a non-engineer I just wanted a second opinion. Will this substitution
likely cause any problems ? What is the worst that could happen ? Could I
fry my amps (or the Western Electric 300Bs) ?

Cheers

Mick Jennings

"RhythMick" said:

To give an update, I've put the CV378s in place - with a massive improvement
in sound. Huge.

Not for long, though.
Cary assures that only their recommended CV378 will withstand this
absurd abuse of the rectifier. I'm so blunt as to not believe them.

BTW did you know that there are at least 3 different drive
arrangements for the same Cary 300B SE amp (that I know of)?
One with 6SJ7 in triode, one with 6SN7 and one with 6SL7.
"Our designs are subject to changes without further notice"

I'll consult my engineer friend (and Dennis Had) about the capacitance.
Anyone know why he put them there ? Must be a reason ?

Cary moves in mysterious ways.
Let your tech friend modify them according to the age-old rules of
tube power supply designing.

Find the program "PSUD" at

www.duncanamps.com and look in the download directory.

This will help him in sensible power supply designing.
While you're at it, tell your friends at Carys to look into that as
well.

--
Sander deWaal
"SOA of a KT88? Sufficient."

I don't understand why you are getting shirty with me. I've reviewed my post
and can't see anything which would reasonably cause you to react that way.

If you don't want newbies asking questions, just let us know.

Mick


"François Yves Le Gal" wrote in message
...
On Fri, 23 Jul 2004 21:56:41 +0100, "RhythMick"
wrote:

However, the consensus seems to be that there is a big questionmark over
the
longevity of the rectifier valve given the high capacitance placed at the
cathode.

Nope, the consensus is that the Cary amps are very poorly designed, just
as
are numerous amps from "boutique" operations.

And there is no question mark : the valve sees *TWENTY* times it's maximum
load, thus shortening considerably it's lifespan and greatly diminishing
the
amp's MTBF.

To give an update, I've put the CV378s in place - with a massive
improvement
in sound. Huge.

Yeah, sure. Whatever.

I'll consult my engineer friend (and Dennis Had) about the capacitance.
Anyone know why he put them there ? Must be a reason ?

Everything has been explained in detail, please refer to earlier posts in
this thread. And If you don't like the answers, don't ask questions.

Also - "Yeah, sure. Whatever" ... what gives ? Surely sound improvements are
the goal for us all ? Or am I missing something ?


"RhythMick" wrote in message
.. .
I don't understand why you are getting shirty with me. I've reviewed my
post
and can't see anything which would reasonably cause you to react that way.

If you don't want newbies asking questions, just let us know.

Mick


"François Yves Le Gal" wrote in message
...
On Fri, 23 Jul 2004 21:56:41 +0100, "RhythMick"
wrote:

However, the consensus seems to be that there is a big questionmark
over
the
longevity of the rectifier valve given the high capacitance placed at
the
cathode.

Nope, the consensus is that the Cary amps are very poorly designed, just
as
are numerous amps from "boutique" operations.

And there is no question mark : the valve sees *TWENTY* times it's
maximum
load, thus shortening considerably it's lifespan and greatly diminishing
the
amp's MTBF.

To give an update, I've put the CV378s in place - with a massive
improvement
in sound. Huge.

Yeah, sure. Whatever.

I'll consult my engineer friend (and Dennis Had) about the capacitance.
Anyone know why he put them there ? Must be a reason ?

Everything has been explained in detail, please refer to earlier posts
in
this thread. And If you don't like the answers, don't ask questions.

And what the **** is wrong with top posting? Seriously.

Tim (shooting a quick reply, for instance as here)

--
"I've got more trophies than Wayne Gretsky and the Pope combined!"
- Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

"François Yves Le Gal" wrote in message
...
On Mon, 26 Jul 2004 17:24:36 +0100, "RhythMick"
wrote:

If you don't want newbies asking questions, just let us know.

You're not a newbie, you're a moron and a top poster.

"RhythMick" wrote in message
.. .
I don't understand why you are getting shirty with me.

Because we are all engineers, if not with the credentials (aka,
hacker/experimenter) and don't give a damn about snake-oil-filled cables,
for instance. Which reminds me, you should grab up some $600/ft. cable and
replace the stuff running from your fusebox to the outlet.

Tim

--
"I've got more trophies than Wayne Gretsky and the Pope combined!"
- Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

Thanks Tim - where do I buy such wonder-cable ...


"Tim Williams" wrote in message
...
"RhythMick" wrote in message
.. .
I don't understand why you are getting shirty with me.

Because we are all engineers, if not with the credentials (aka,
hacker/experimenter) and don't give a damn about snake-oil-filled cables,
for instance. Which reminds me, you should grab up some $600/ft. cable
and
replace the stuff running from your fusebox to the outlet.

Tim

--
"I've got more trophies than Wayne Gretsky and the Pope combined!"
- Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

Thanks all for the advice. I took a risk with the CV378s and thought the
group would be interested to hear that it improved the sound fantastically.
From one or two responses I'm no longer sure the group is interested ...

I'm grateful for the information passed to me - without which I would not
have been aware of the risk to rectifiers from the Cary design. I do intend
to take this further, will monitor the life of the CV378s (may even report
back if I don't get it thrown back at me), will ask Cary about the design
and may get my friend to look at modifying the design (let's see what he
says when back from holidays). Grateful for the PSU design info at Duncan
Amps.

Cheers all.


"Sander deWaal" wrote in message
...
"RhythMick" said:

To give an update, I've put the CV378s in place - with a massive
improvement
in sound. Huge.

Not for long, though.
Cary assures that only their recommended CV378 will withstand this
absurd abuse of the rectifier. I'm so blunt as to not believe them.

BTW did you know that there are at least 3 different drive
arrangements for the same Cary 300B SE amp (that I know of)?
One with 6SJ7 in triode, one with 6SN7 and one with 6SL7.
"Our designs are subject to changes without further notice"

I'll consult my engineer friend (and Dennis Had) about the capacitance.
Anyone know why he put them there ? Must be a reason ?

Cary moves in mysterious ways.
Let your tech friend modify them according to the age-old rules of
tube power supply designing.

Find the program "PSUD" at

www.duncanamps.com and look in the download directory.

This will help him in sensible power supply designing.
While you're at it, tell your friends at Carys to look into that as
well.

--
Sander deWaal
"SOA of a KT88? Sufficient."

top posting is rude

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

"don't use force, "don't use force,
use a larger hammer" use a larger tube
- Choky and IST"
- ZM
.................................................. ...........................
"Tim Williams" wrote in message
...
And what the **** is wrong with top posting? Seriously.

Tim (shooting a quick reply, for instance as here)

--
"I've got more trophies than Wayne Gretsky and the Pope combined!"
- Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

"François Yves Le Gal" wrote in message
...
On Mon, 26 Jul 2004 17:24:36 +0100, "RhythMick"
wrote:

If you don't want newbies asking questions, just let us know.

You're not a newbie, you're a moron and a top poster.

"François Yves Le Gal" wrote in message
...
Because it messes up the flow of reading.

How? Do you read the thread all in one post? No one (Pat T aside) even
keeps two posts quoted, let alone back to the OP. Duhhh....

No. You read one post at a time and look for unquoted text to read. So
again, WTF is wrong with it? Seriously.

Tim

--
"I've got more trophies than Wayne Gretsky and the Pope combined!"
- Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

"RhythMick" wrote in message
...
Thanks Tim - where do I buy such wonder-cable ...

I'll sell ya some, e-mail me.

Tim

--
"I've got more trophies than Wayne Gretsky and the Pope combined!"
- Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

.... and of course calling people a moron is socially acceptable behaviour
....

"Choky" wrote in message ...
top posting is rude

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

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

.................................................. ...........................
"Tim Williams" wrote in message
...
And what the **** is wrong with top posting? Seriously.

Tim (shooting a quick reply, for instance as here)

--
"I've got more trophies than Wayne Gretsky and the Pope combined!"
- Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

"François Yves Le Gal" wrote in message
...
On Mon, 26 Jul 2004 17:24:36 +0100, "RhythMick"
wrote:

If you don't want newbies asking questions, just let us know.

You're not a newbie, you're a moron and a top poster.

"RhythMick" said:

... and of course calling people a moron is socially acceptable behaviour

You must pardon Yves, he's run into Arny Krooger too often :-)

--
Sander deWaal
"SOA of a KT88? Sufficient."

sometimes is juice more important than envelope

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

"don't use force, "don't use force,
use a larger hammer" use a larger tube
- Choky and IST"
- ZM
.................................................. ...........................
"François Yves Le Gal" wrote in message
...
On Tue, 27 Jul 2004 22:05:15 +0100, "RhythMick"
wrote:

... and of course calling people a moron is socially acceptable behaviour

Yep, but top posting morons don't understand why.

"François Yves Le Gal" wrote in message
...
On Wed, 28 Jul 2004 20:57:06 +0200, "Choky" wrote:

sometimes is juice more important than envelope

Too much Kruskovac, Choky?
:-)



nope
Sljivovica is better than Kruskovac......
in fact, in Summer days-Beer is better ;
but ,Ice cream is best
)--
.................................................. ........................
Choky
Prodanovic Aleksandar
YU

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

"RhythMick" wrote in message
...
Thanks all for the advice. I took a risk with the CV378s and thought the
group would be interested to hear that it improved the sound
fantastically.
From one or two responses I'm no longer sure the group is interested ...

I'm grateful for the information passed to me - without which I would not
have been aware of the risk to rectifiers from the Cary design. I do
intend
to take this further, will monitor the life of the CV378s (may even report
back if I don't get it thrown back at me), will ask Cary about the design
and may get my friend to look at modifying the design (let's see what he
says when back from holidays). Grateful for the PSU design info at Duncan
Amps.

Cheers all.


Alot of people here are doubtful of "improvements" to the sound of amps by
making simple changes to them.
They have reasons to be. First after spending a lot of money on buying our
supposed upgrades we really want it to sound better. Then when the amp
sounds different we convince ourselves that this it better. It is not always
so. Sometimes changing the operating point of the output tube can push up
the distortion figures from the amp. Some people think of this softer sound
as more tube-like. If you enjoy it then that is great. You have justified
your expense. But it is doubtful that you have made it better. A serious amp
would be designed with low distortion and wide bandwidth in mind as well as
the ability to drive diffiicult loads. By changing the operating point of
your output tube through raising the B+ in your amp you have probably made
your amp worse in all 3 instances. But measuring might be interesting.

Doug