What kills a valve rectifier?

[N_Cook]

Amp used for the first time, in 2 years of regular mains use, with a
generator. Works fine with no problems. Coincidence ?, next gig back to
usual mains supply, at power up, blows the mains fuse. The GZ34 is failed
both sides, 0 percent output . Inspecting the fuse it has failed at an end ,
not the central (T) section and otherwise complete wire shows no sag or
discolouration. So possibly mechanical failure of fuse. If fast make/break
intermittant action of the fuse wire at an end , would that knock out an RR
valve? What in general happens in the failure of RRs ? I've only ever seen
75 percent , same as new, or 0 percent "goodness" at prescribed current
settings of the Avo valve tester.

 

[Arfa Daily]

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:irg1t5$bvd$1@dont-email.me...

Amp used for the first time, in 2 years of regular mains use, with a
generator. Works fine with no problems. Coincidence ?, next gig back to
usual mains supply, at power up, blows the mains fuse. The GZ34 is failed
both sides, 0 percent output . Inspecting the fuse it has failed at an end
,
not the central (T) section and otherwise complete wire shows no sag or
discolouration. So possibly mechanical failure of fuse. If fast make/break
intermittant action of the fuse wire at an end , would that knock out an
RR
valve? What in general happens in the failure of RRs ? I've only ever seen
75 percent , same as new, or 0 percent "goodness" at prescribed current
settings of the Avo valve tester.

I've had a number of GZ34s fail short circuit, or suffer from serious
flashover, and knock out fuses over the years, but I've always put this down
to saggy filaments or whatever, where the valves are mounted horizontally,
or upside down.

Arfa

 

[Phil Allison]

"Nutcase Kook "

Amp used for the first time, in 2 years of regular mains use, with a
generator. Works fine with no problems. Coincidence ?

** Spooky................

next gig back to
usual mains supply, at power up, blows the mains fuse.

** Noooooo...........

The GZ34 is failed
both sides, 0 percent output . Inspecting the fuse it has failed at an end
,
not the central (T) section and otherwise complete wire shows no sag or
discolouration. So possibly mechanical failure of fuse.

** Chemical fuses are notorious for that.

If fast make/break
intermittant action of the fuse wire at an end , would that knock out an
RR
valve?

** Rolls Royce do not make valves.

What in general happens in the failure of RRs ?

** They " fail to proceed " ..................

I've only ever seen
75 percent , same as new, or 0 percent "goodness" at prescribed current
settings of the Avo valve tester.

** Well, you ain't seen nuthin' - pal.


...... Phil

 

[N_Cook]

Arfa Daily <arfa.daily@ntlworld.com> wrote in message
news:mhMCp.7026$Ky.3031@newsfe24.ams2...

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:irg1t5$bvd$1@dont-email.me...
Amp used for the first time, in 2 years of regular mains use, with a
generator. Works fine with no problems. Coincidence ?, next gig back to
usual mains supply, at power up, blows the mains fuse. The GZ34 is
failed
both sides, 0 percent output . Inspecting the fuse it has failed at an
end
,
not the central (T) section and otherwise complete wire shows no sag or
discolouration. So possibly mechanical failure of fuse. If fast
make/break
intermittant action of the fuse wire at an end , would that knock out an
RR
valve? What in general happens in the failure of RRs ? I've only ever
seen
75 percent , same as new, or 0 percent "goodness" at prescribed current
settings of the Avo valve tester.



I've had a number of GZ34s fail short circuit, or suffer from serious
flashover, and knock out fuses over the years, but I've always put this
down
to saggy filaments or whatever, where the valves are mounted horizontally,
or upside down.

Arfa

What is the state of the fuse with a flashover? vapourised and blackened
fuse barrel presumably.

 

[Arfa Daily]

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:irgc22$ai2$1@dont-email.me...

Arfa Daily <arfa.daily@ntlworld.com> wrote in message
news:mhMCp.7026$Ky.3031@newsfe24.ams2...


"N_Cook" <diverse@tcp.co.uk> wrote in message
news:irg1t5$bvd$1@dont-email.me...
Amp used for the first time, in 2 years of regular mains use, with a
generator. Works fine with no problems. Coincidence ?, next gig back to
usual mains supply, at power up, blows the mains fuse. The GZ34 is
failed
both sides, 0 percent output . Inspecting the fuse it has failed at an
end
,
not the central (T) section and otherwise complete wire shows no sag or
discolouration. So possibly mechanical failure of fuse. If fast
make/break
intermittant action of the fuse wire at an end , would that knock out
an
RR
valve? What in general happens in the failure of RRs ? I've only ever
seen
75 percent , same as new, or 0 percent "goodness" at prescribed current
settings of the Avo valve tester.



I've had a number of GZ34s fail short circuit, or suffer from serious
flashover, and knock out fuses over the years, but I've always put this
down
to saggy filaments or whatever, where the valves are mounted
horizontally,
or upside down.

Arfa



What is the state of the fuse with a flashover? vapourised and blackened
fuse barrel presumably.

Yes, vapourised

Arfa

 

[Meat Plow]

On Tue, 24 May 2011 11:42:05 +0100, N_Cook wrote:

Amp used for the first time, in 2 years of regular mains use, with a
generator. Works fine with no problems. Coincidence ?, next gig back to
usual mains supply, at power up, blows the mains fuse. The GZ34 is
failed both sides, 0 percent output . Inspecting the fuse it has failed
at an end , not the central (T) section and otherwise complete wire
shows no sag or discolouration. So possibly mechanical failure of fuse.
If fast make/break intermittant action of the fuse wire at an end ,
would that knock out an RR valve? What in general happens in the failure
of RRs ? I've only ever seen 75 percent , same as new, or 0 percent
"goodness" at prescribed current settings of the Avo valve tester.

If I pop a new valve back in, take some measurements and all seem
respectable, I don't try to dive further in and create scenarios in my
head as to the failure mode. UNLESS it comes back a few hours of usage
later with the same failure. However, after it is placed in a cabinet
I stress test all amps into a non-reactive 300 wrms 8 ohm resistor, one
of two I have mounted on a large heat sink from a CNC power supply. I use
a 400 hz tone and monitor the output adjusting the output until I see
just a taste of crossover distortion. I leave it this way until I can
smell and feel the amplifier/ output transformer, choke, mains
transformer etc get more hot than under normal use. Then it's tested
with a guitar and cabinet if it's just a head. I'm a musician so I have
those things laying around. I usually use my 4x12 Peavey cabinet for
amps that aren't combos. And a Fender 4x10 for Bass. I know what the
instruments should sound like though both cabinets with good amps.



--
Live Fast Die Young, Leave A Pretty Corpse

 

[Meat Plow]

On Tue, 24 May 2011 12:04:48 +0100, Arfa Daily wrote:

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:irg1t5$bvd$1@dont-email.me...
Amp used for the first time, in 2 years of regular mains use, with a
generator. Works fine with no problems. Coincidence ?, next gig back to
usual mains supply, at power up, blows the mains fuse. The GZ34 is
failed both sides, 0 percent output . Inspecting the fuse it has failed
at an end ,
not the central (T) section and otherwise complete wire shows no sag or
discolouration. So possibly mechanical failure of fuse. If fast
make/break intermittant action of the fuse wire at an end , would that
knock out an RR
valve? What in general happens in the failure of RRs ? I've only ever
seen 75 percent , same as new, or 0 percent "goodness" at prescribed
current settings of the Avo valve tester.



I've had a number of GZ34s fail short circuit, or suffer from serious
flashover, and knock out fuses over the years, but I've always put this
down to saggy filaments or whatever, where the valves are mounted
horizontally, or upside down.

Arfa

What do you think about subbing the 5AR4 with a 5U4?



--
Live Fast Die Young, Leave A Pretty Corpse

 

[Arfa Daily]

"Meat Plow" <mhywattt@yahoo.com> wrote in message
newsan.2011.05.24.21.25.01@emutt.macspoofer.lmao...

On Tue, 24 May 2011 12:04:48 +0100, Arfa Daily wrote:

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:irg1t5$bvd$1@dont-email.me...
Amp used for the first time, in 2 years of regular mains use, with a
generator. Works fine with no problems. Coincidence ?, next gig back to
usual mains supply, at power up, blows the mains fuse. The GZ34 is
failed both sides, 0 percent output . Inspecting the fuse it has failed
at an end ,
not the central (T) section and otherwise complete wire shows no sag or
discolouration. So possibly mechanical failure of fuse. If fast
make/break intermittant action of the fuse wire at an end , would that
knock out an RR
valve? What in general happens in the failure of RRs ? I've only ever
seen 75 percent , same as new, or 0 percent "goodness" at prescribed
current settings of the Avo valve tester.



I've had a number of GZ34s fail short circuit, or suffer from serious
flashover, and knock out fuses over the years, but I've always put this
down to saggy filaments or whatever, where the valves are mounted
horizontally, or upside down.

Arfa

What do you think about subbing the 5AR4 with a 5U4?

Never tried it, but looking at the specs, they look rather different from
one another, see -

http://www.r-type.org/exhib/aaa0997.htm

and

http://www.r-type.org/exhib/aaa0504.htm

The 5U4 appears to be able to handle more current, but at a lower max plate
voltage. Also, the heater requires substantially more current. Might be an
issue for the transformer supplying it ?

Arfa

 

[Phil Allison]

"Arfa Daily"

What do you think about subbing the 5AR4 with a 5U4?


Never tried it, but looking at the specs, they look rather different from
one another, see -

http://www.r-type.org/exhib/aaa0997.htm

http://www.r-type.org/exhib/aaa0504.htm

** Useless info.

The big difference between the 5AR4 and the 5U4 is in amount of voltage drop
across each diode when conducting.

The 5AR4 is uses an indirectly heated cathode, close coupled to each plate
and the voltage drop is very low, about 35 volts at 700mA peak.

The 5U4 uses a directly heated cathode with lotsa space between the plates
and the cathodes - so there is a much bigger drop in voltage, more like
100 volts at peak current.

So, if you drop a 5U4 in place of a 5AR4 - expect to lose 60 to 70 volts DC
straight off the B+.

Also, the 5AR4 is rated to work reliably with a large filter cap on the
cathodes ( 60 uF) compared to the 5U4 ( 40uF).

So the proposed sub is bad news all around.


...... Phil

 

[Phil Allison]

"spamtrap1888"


Considering that the vacuum tube rectifier was the first tube to be
eliminated (in receiving sets at least), why not replace it with a
semiconductor diode circuit? What effect would it have on the
amplifier's sound?

**See:

http://www.guitaramplifierblueprinting.com/rectifiers.html


** Hard to find a single, technically correct statement in the whole blurb.

But that is what these loonies believe.


..... Phil

 

[spamtrap1888]

On May 24, 6:38 pm, "Phil Allison" <phi...@tpg.com.au> wrote:

"Arfa Daily"



What do you think about subbing the 5AR4 with a 5U4?

Never tried it, but looking at the specs, they look rather different from
one another, see -

http://www.r-type.org/exhib/aaa0997.htm

http://www.r-type.org/exhib/aaa0504.htm

** Useless info.

The big difference between the 5AR4 and the 5U4 is in amount of voltage drop
across each diode when conducting.

The 5AR4 is uses an indirectly heated cathode, close coupled to each plate
and the voltage drop is very low, about 35 volts at 700mA peak.

The 5U4 uses a directly heated cathode with lotsa space between the plates
and the cathodes -  so there is a much bigger drop in voltage,  more like
100 volts at peak current.

So, if you drop a 5U4 in place of a 5AR4 - expect to lose 60 to 70 volts DC
straight off the B+.

Also, the 5AR4 is rated to work reliably with a large filter cap on the
cathodes ( 60 uF) compared to the 5U4 ( 40uF).

So the proposed sub is bad news all around.

Considering that the vacuum tube rectifier was the first tube to be
eliminated (in receiving sets at least), why not replace it with a
semiconductor diode circuit? What effect would it have on the
amplifier's sound?

 

[N_Cook]

spamtrap1888 <spamtrap1888@gmail.com> wrote in message
news:bd8dbf0e-9a3e-4397-a570-7af6541e38cd@d26g2000prn.googlegroups.com...
On May 24, 6:38 pm, "Phil Allison" <phi...@tpg.com.au> wrote:

"Arfa Daily"



What do you think about subbing the 5AR4 with a 5U4?

Never tried it, but looking at the specs, they look rather different
from
one another, see -

http://www.r-type.org/exhib/aaa0997.htm

http://www.r-type.org/exhib/aaa0504.htm

** Useless info.

The big difference between the 5AR4 and the 5U4 is in amount of voltage
drop
across each diode when conducting.

The 5AR4 is uses an indirectly heated cathode, close coupled to each plate
and the voltage drop is very low, about 35 volts at 700mA peak.

The 5U4 uses a directly heated cathode with lotsa space between the plates
and the cathodes - so there is a much bigger drop in voltage, more like
100 volts at peak current.

So, if you drop a 5U4 in place of a 5AR4 - expect to lose 60 to 70 volts
DC
straight off the B+.

Also, the 5AR4 is rated to work reliably with a large filter cap on the
cathodes ( 60 uF) compared to the 5U4 ( 40uF).

So the proposed sub is bad news all around.

Considering that the vacuum tube rectifier was the first tube to be
eliminated (in receiving sets at least), why not replace it with a
semiconductor diode circuit? What effect would it have on the
amplifier's sound?


+++++

I totally agree a couple of 1N4007 and sag Rs would be fine by me but we are
talking musos here and the "valve sound" would magically dissappear. Of
course if I told them nothing about swapping to SS, the valve sound would
not disappear - strange old world isn't it.

 

[Phil Allison]

"Nutcase Kook"

I totally agree a couple of 1N4007 and sag Rs would be fine by me but we
are
talking musos here and the "valve sound" would magically dissappear. Of
course if I told them nothing about swapping to SS, the valve sound would
not disappear - strange old world isn't it.

** Just fit the diodes ( two pairs in series is a good idea ) and add
resistance only if it seems essential to do so.

he dud GZ34 can stay for ornamental value.

Tell the owner you fixed it.

BTW:

I fix lots of octal a valves, for bad soldering on the pins and flash burns
between plate and heater pins - even if it means removing the octal base to
do so.

Well worth it with newish 6550s, KT88s etc.


..... Phil

 

[Ian Field]

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:iriaeb$4jg$1@dont-email.me...

spamtrap1888 <spamtrap1888@gmail.com> wrote in message
news:bd8dbf0e-9a3e-4397-a570-7af6541e38cd@d26g2000prn.googlegroups.com...
On May 24, 6:38 pm, "Phil Allison" <phi...@tpg.com.au> wrote:
"Arfa Daily"



What do you think about subbing the 5AR4 with a 5U4?

Never tried it, but looking at the specs, they look rather different
from
one another, see -

http://www.r-type.org/exhib/aaa0997.htm

http://www.r-type.org/exhib/aaa0504.htm

** Useless info.

The big difference between the 5AR4 and the 5U4 is in amount of voltage
drop
across each diode when conducting.

The 5AR4 is uses an indirectly heated cathode, close coupled to each
plate
and the voltage drop is very low, about 35 volts at 700mA peak.

The 5U4 uses a directly heated cathode with lotsa space between the
plates
and the cathodes - so there is a much bigger drop in voltage, more like
100 volts at peak current.

So, if you drop a 5U4 in place of a 5AR4 - expect to lose 60 to 70 volts
DC
straight off the B+.

Also, the 5AR4 is rated to work reliably with a large filter cap on the
cathodes ( 60 uF) compared to the 5U4 ( 40uF).

So the proposed sub is bad news all around.


Considering that the vacuum tube rectifier was the first tube to be
eliminated (in receiving sets at least), why not replace it with a
semiconductor diode circuit? What effect would it have on the
amplifier's sound?


+++++

I totally agree a couple of 1N4007 and sag Rs would be fine by me but we
are
talking musos here and the "valve sound" would magically dissappear. Of
course if I told them nothing about swapping to SS, the valve sound would
not disappear - strange old world isn't it.

I'd go for 2x 4007's in series to be on the safe side - not forgetting equal
value x-class capacitors in parallel with each diode to damp & equalise any
spikes.

As well as an added sag resistor, you need to make sure each rectifier path
is protected by a fuse, when silicon rectifiers fail short circuit - they do
it for keeps.

 

[Phil Allison]

"Ian Field"

I'd go for 2x 4007's in series to be on the safe side - not forgetting
equal value x-class capacitors in parallel with each diode to damp &
equalise any spikes.

** Quite unnecessary - any voltage spikes are clamped by the first filter
cap.

Class X caps are more likely to fail than 1N4007 diodes are.

As well as an added sag resistor,

** Not essential - there will be only 30 volts increase in the B+.

you need to make sure each rectifier path is protected by a fuse,

** Absolutely un-necessary.

when silicon rectifiers fail short circuit - they do it for keeps.

** So what?

The AC supply fuse will blow immediately.

You are obviously not very familiar with valve guitar amps.


..... Phil

 

[N_Cook]

Ian Field <gangprobing.alien@ntlworld.com> wrote in message
news:SXaDp.18414$6K4.7746@newsfe14.ams2...

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:iriaeb$4jg$1@dont-email.me...
spamtrap1888 <spamtrap1888@gmail.com> wrote in message

news:bd8dbf0e-9a3e-4397-a570-7af6541e38cd@d26g2000prn.googlegroups.com...
On May 24, 6:38 pm, "Phil Allison" <phi...@tpg.com.au> wrote:
"Arfa Daily"



What do you think about subbing the 5AR4 with a 5U4?

Never tried it, but looking at the specs, they look rather different
from
one another, see -

http://www.r-type.org/exhib/aaa0997.htm

http://www.r-type.org/exhib/aaa0504.htm

** Useless info.

The big difference between the 5AR4 and the 5U4 is in amount of voltage
drop
across each diode when conducting.

The 5AR4 is uses an indirectly heated cathode, close coupled to each
plate
and the voltage drop is very low, about 35 volts at 700mA peak.

The 5U4 uses a directly heated cathode with lotsa space between the
plates
and the cathodes - so there is a much bigger drop in voltage, more like
100 volts at peak current.

So, if you drop a 5U4 in place of a 5AR4 - expect to lose 60 to 70
volts
DC
straight off the B+.

Also, the 5AR4 is rated to work reliably with a large filter cap on the
cathodes ( 60 uF) compared to the 5U4 ( 40uF).

So the proposed sub is bad news all around.


Considering that the vacuum tube rectifier was the first tube to be
eliminated (in receiving sets at least), why not replace it with a
semiconductor diode circuit? What effect would it have on the
amplifier's sound?


+++++

I totally agree a couple of 1N4007 and sag Rs would be fine by me but we
are
talking musos here and the "valve sound" would magically dissappear. Of
course if I told them nothing about swapping to SS, the valve sound
would
not disappear - strange old world isn't it.


I'd go for 2x 4007's in series to be on the safe side - not forgetting
equal
value x-class capacitors in parallel with each diode to damp & equalise
any
spikes.

As well as an added sag resistor, you need to make sure each rectifier
path
is protected by a fuse, when silicon rectifiers fail short circuit - they
do
it for keeps.

As for sag R I tried 50R and 100R and a couple of GZ34 on Avo CT160 tester
set for 120mA per anode.
each GZ34 showed the usual 75 percent "goodness" .
4007s and 100R showed 70 percent
4007s and 50R, 10W showed 75 percent

 

[Phil Allison]

"Arfa Daily"

I've had a number of GZ34s fail short circuit, or suffer from serious
flashover, and knock out fuses over the years, but I've always put this
down to saggy filaments or whatever, where the valves are mounted
horizontally, or upside down.

** GZ34s have an indirectly heated cathode - just like most other valves.

Sooo, the cathode is a solid tube of metal, with a heater wire inside it.

Ergo - it simply cannot sag.

Only directly heated cathode types do that

- like 5Y3s, 5U4s, 5AS4s etc.



..... Phil

 

[Arfa Daily]

"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:946dsvFe7oU1@mid.individual.net...

"Arfa Daily"


I've had a number of GZ34s fail short circuit, or suffer from serious
flashover, and knock out fuses over the years, but I've always put this
down to saggy filaments or whatever, where the valves are mounted
horizontally, or upside down.


** GZ34s have an indirectly heated cathode - just like most other
valves.

Sooo, the cathode is a solid tube of metal, with a heater wire inside it.

Ergo - it simply cannot sag.

Only directly heated cathode types do that

- like 5Y3s, 5U4s, 5AS4s etc.



.... Phil

Agreed, but I did say "or whatever". I've not taken that much notice of the
actual failure mechanism. I think you can spend too much time in a
commercial world, agonising over exactly what went wrong. I have a roof to
keep over my head, and I don't have time to analyze how every fault
occurred, and why and how every component expired in the way it did,
interesting as that may be.

Suffice to say that in 'modern' amps that use a GZ34, I have seen more than
a few with a vapourised fuse and no obvious short causing it. Often, a
replacement fuse holds up, until you clout the valve with the butt end of a
screwdriver, whereupon a miniature fireworks display is launched inside, and
the fuse goes out again. Sometimes, it's spontaneous, and only needs the
voltage to be present. More often than not, it seems to occur when the
valves are not upright. This would imply that gravity acting on the
structure has something to do with it. But what is touching what or why - I
really don't care. Popped fuse - new fuse - clouted valve - fireworks - new
valve - new fuse - soak test - write bill - phone customer. Job done. Cash
in bank.

Arfa

 

[Phil Allison]

"Arfa Daily"

"Phil Allison" "Arfa Daily"


I've had a number of GZ34s fail short circuit, or suffer from serious
flashover, and knock out fuses over the years, but I've always put this
down to saggy filaments or whatever, where the valves are mounted
horizontally, or upside down.


** GZ34s have an indirectly heated cathode - just like most other
valves.

Sooo, the cathode is a solid tube of metal, with a heater wire inside it.

Ergo - it simply cannot sag.

Only directly heated cathode types do that

- like 5Y3s, 5U4s, 5AS4s etc.


Agreed, but I did say "or whatever".

** Fine - but you also had no idea what was importantly different about a
GZ34 / 5AR4 compared to other rectifiers.

I've not taken that much notice of the actual failure mechanism. I think
you can spend too much time in a commercial world, agonising over exactly
what went wrong.

** Many times, such analysis pays off in the long term.

Cos failure mechanisms that are not dealt with by the service tech are bound
to be repeated.

Suffice to say that in 'modern' amps that use a GZ34, I have seen more
than a few with a vapourised fuse and no obvious short causing it. Often,
a replacement fuse holds up, until you clout the valve with the butt end
of a screwdriver, whereupon a miniature fireworks display is launched
inside, and the fuse goes out again.

** Seen that scenario many times myself - especially with Chink valves.

Sometimes, it's spontaneous, and only needs the voltage to be present.
More often than not, it seems to occur when the valves are not upright.
This would imply that gravity acting on the structure has something to do
with it.

** Valves are generally not upright when servicing is going on - and a great
many amps have the power valves mounted horizontally or inverted in normal
use.

Owners of same can operate the amp any damn way up they like - and do.

Popped fuse - new fuse - clouted valve - fireworks - new valve - new
fuse - soak test - write bill - phone customer. Job done. Cash in bank.

** As posted by me earlier - the best way to fix recurring problems with
crappy GZ34s is called a 1N4007.

Works a treat in Quad Mk2s, long as you get rid of those dreadful oil
filled filter caps.



.... Phil

 

[N_Cook]

So no thoughts on generator use , followed by rectifier failure.

It seems the mains fuse I have here was not necessarily the original one.
Someone looked at the amp and replaced the fuse, probably with this probably
previously mechanically broken one (knocked about in a toolbopx). The
original may not have failed but assumed to have fused and so just rectifier
failure.
Could generator brownout or spikes or something weaken a valve rectifier so
it is ok while warm but gives up the ghost on the next powerup from cold?