Howdy Folk's,
Well I recapped a w4-am over the last couple of days and I am having a
problem with the power supply.The amp had been butchered.A Traid
"television" tranny had been cobbeled on to the chassis.So I bolted it down
and checked the voltages and it was pretty close to the old specs..After
insalling all new caps and redoing the power cord to three prong I carfully
checked all my work.It seems right.I went to check the voltages at the first
cap with a 5AR4 instead of the stock5V4G.It is a direct
replacement,right?Well when I fired it up with a fluke digital meter set to
DC on pin 8 of the 5AR4 it started to show some volts after a few seconds
and then topped out at about 75 voltsAfter a few more seconds the rectifier
started to glow so I shut it off.
I have checked all my work over and over.The only changes I made was to use
a 47 uf 450volt as the first cap instead of the two series wired 20 uf 350's
with 100k bypass resistors.I don't see how that would be a problem.The HT
center tap is to the chassis as are the caps.I put the caps on terminal
strips.It's just a power supply!
Here is a link to the schematic.....
http://www.freeinfosociety.com/elect...athkitw4m.html
Anyone got a hint? Not enough load? The 5ar4 tests strong.And I tried two of
them.
Thanks,
WesJ...........

"Wes Jacson"
Well when I fired it up with a fluke digital meter set to DC on pin 8 of
the 5AR4 it started to show some volts after a few seconds and then topped
out at about 75 voltsAfter a few more seconds the rectifier started to
glow so I shut it off.



** Sounds like an electro is wired in reverse polarity.




............ Phil

Thanks Phill, I looked at them over and over.They are wired right.Could it
be a defective cap?
Maybe I will try lifting them one at a time and see if I can isolate
it.Any other ideas?
WesJ.....

"Phil Allison" wrote in message
...

"Wes Jacson"
Well when I fired it up with a fluke digital meter set to DC on pin 8 of
the 5AR4 it started to show some volts after a few seconds and then
topped out at about 75 voltsAfter a few more seconds the rectifier
started to glow so I shut it off.



** Sounds like an electro is wired in reverse polarity.




........... Phil

"Wes Jacson" wrote

Thanks Phill, I looked at them over and over.They are wired
right.Could it be a defective cap?
Maybe I will try lifting them one at a time and see if I can
isolate it.Any other ideas?

The low voltage and glowing rectifier suggest you are drawing *lots*
of current and it must be going somewhere. Are you sure they are
100k resistors?

Assuming the PS is not connected to the amp, the caps and resistors
are the only possible culprits.

cheers, Ian

If you lift the +leg on each cap, you can ohm-meter the power supply caps to
ground. My guess is you've got a short.

"Wes Jacson" wrote in message
news
Thanks Phill, I looked at them over and over.They are wired right.Could it
be a defective cap?
Maybe I will try lifting them one at a time and see if I can isolate
it.Any other ideas?
WesJ.....

"Phil Allison" wrote in message
...

"Wes Jacson"
Well when I fired it up with a fluke digital meter set t o DC on pin 8
of the 5AR4 it started to show some volts after a few seconds and then
topped out at about 75 voltsAfter a few more seconds the rectifier
started to glow so I shut it off.



** Sounds like an electro is wired in reverse polarity.




........... Phil

Well I lifted the caps and I lifted the choke.Starting from the start.I put
everything back after testing with my Teleohmite They where all fine.And the
votages seemed fine as I went. Well I put every thing back.And, it works
now.I think.I must have had a short somewhere I missed,I guess.I hate not
knowing.I tried it with tubes in place.The voltage at the first cap tops out
at 480 ish.With a 5v4G. A little high for the 450 volt caps I used.Now I am
perplexed.The tranny says 775 across the HT.I figure that at around 385 each
side.The primary says 117.I am getting 123 volts at the wall.The original
schematic shows 360 or 380 per side on the HT..It is kinda hard to read.Well
maybe that is just what ya get with those parts.Anyay I guess If I want to
use this tranny I better drop the voltage a bit.That brings up another
question.How big a resistor would I need.I have a bunch of old ceramic wire
wound.Seems ohms law plays in here somewhere.Lets see naugh into naught
equles naught carry the naught...........Anyone care to give me a ball park?
Thanks and Cheers
WesJ............
"tubesforall" wrote in message
...
If you lift the +leg on each cap, you can ohm-meter the power supply caps
to ground. My guess is you've got a short.

"Wes Jacson" wrote in message
news
Thanks Phill, I looked at them over and over.They are wired right.Could
it be a defective cap?
Maybe I will try lifting them one at a time and see if I can isolate
it.Any other ideas?
WesJ.....

"Phil Allison" wrote in message
...

"Wes Jacson"
Well when I fired it up with a fluke digital meter set t o DC on pin 8
of the 5AR4 it started to show some volts after a few seconds and then
topped out at about 75 voltsAfter a few more seconds the rectifier
started to glow so I shut it off.



** Sounds like an electro is wired in reverse polarity.




........... Phil

"Wes Jacson" wrote in message
...
Well I lifted the caps and I lifted the choke.Starting from the start.I
put everything back after testing with my Teleohmite They where all
fine.And the votages seemed fine as I went. Well I put every thing
back.And, it works now.I think.I must have had a short somewhere I
missed,I guess.I hate not knowing.I tried it with tubes in place.The
voltage at the first cap tops out at 480 ish.With a 5v4G. A little high
for the 450 volt caps I used.Now I am perplexed.The tranny says 775 across
the HT.I figure that at around 385 each side.The primary says 117.I am
getting 123 volts at the wall.The original schematic shows 360 or 380 per
side on the HT..It is kinda hard to read.Well maybe that is just what ya
get with those parts.Anyay I guess If I want to use this tranny I better
drop the voltage a bit.That brings up another question.How big a resistor
would I need.I have a bunch of old ceramic wire wound.Seems ohms law plays
in here somewhere.Lets see naugh into naught equles naught carry the
naught...........Anyone care to give me a ball park?
Thanks and Cheers
WesJ............
"tubesforall" wrote in message

You better move up to 600V cap ASAP!!. You want to have a least 20% buffer
room--more is better. Go back to the original design--two back to back 20uf
caps. You should only have about 10uf or less in the first leg of the pi
filter. The choke is sized for the ripple current. Put your extra
capacitance on the downstream side. Since you are adding a dropping
resistor, put your second 47uf on the downstream side of the resistor. Also
bypass this cap. More important is the 47uf filter cap for the small
signal tubes--you could double that as well, and add a 470nf bypass cap.

The HT is probably drawing around 100mils plus or minus. Lift the
downstream leg of the choke and insert a 100 ohm 5 watt resistor in serires.
Measure the voltage across that resistor. That will give you the quiesent
current draw for the amp (I). The draw is more when playing load music.

You want to drop from 385 down to about 360, or a 25V drop. V=IR or
R=25/I. If I = 100 mill then would would want to use a resistor = 250ohms.
Power=Watts=I*I*R=V*V/R=2.5 watts in this example. Use a minimum of a 10
watt resistor. Cermanics should be fine.

The major gain you will get is better PS filtering and reduced ripple. The
5% overspec line voltage is not really a problem, unless you change to PS
filter caps to a below spec value. You may lose some bass response by
adding the dropping network. Use a Japanaese to US line matching
transformer to drop the line voltage without affecting the amp--it will be a
little below spec instead of above. Or find a surplus power line matching
tranny with multiple taps and build your own.

Did you replace the interstage caps?

Ok! Thanks Tubesforall,Just what I needed.I will go back to the old filters
with resistors.I will use the same values as stock in the first filter.The
stock downstream filters were all 20uf's I installed 33's. So I put a
dropping resistor downstream from the choke? I think I remember reading
about the relationship of filters chokes resistors ect.and how they affect
voltages and such but I am just a wanna be tech.I wish I would have taken
those electronics classes in high school.Grammer too! Anyway I am in your
debt.I live in a rural enviroment and there is not anyone around who can
help.So the net is it.This amp seems to be a good one for my talents.Such as
they are.I did an Eico hf-20 and it turned out real well.Gotta play those
78's.
Thanks again to all who reply.I need all the help I can get.
WesJ.........

"tubesforall" wrote in message
...


"Wes Jacson" wrote in message
...
Well I lifted the caps and I lifted the choke.Starting from the start.I
put everything back after testing with my Teleohmite They where all
fine.And the votages seemed fine as I went. Well I put every thing
back.And, it works now.I think.I must have had a short somewhere I
missed,I guess.I hate not knowing.I tried it with tubes in place.The
voltage at the first cap tops out at 480 ish.With a 5v4G. A little high
for the 450 volt caps I used.Now I am perplexed.The tranny says 775
across the HT.I figure that at around 385 each side.The primary says
117.I am getting 123 volts at the wall.The original schematic shows 360
or 380 per side on the HT..It is kinda hard to read.Well maybe that is
just what ya get with those parts.Anyay I guess If I want to use this
tranny I better drop the voltage a bit.That brings up another
question.How big a resistor would I need.I have a bunch of old ceramic
wire wound.Seems ohms law plays in here somewhere.Lets see naugh into
naught equles naught carry the naught...........Anyone care to give me a
ball park?
Thanks and Cheers
WesJ............
"tubesforall" wrote in message

You better move up to 600V cap ASAP!!. You want to have a least 20%
buffer room--more is better. Go back to the original design--two back to
back 20uf caps. You should only have about 10uf or less in the first leg
of the pi filter. The choke is sized for the ripple current. Put your
extra capacitance on the downstream side. Since you are adding a dropping
resistor, put your second 47uf on the downstream side of the resistor.
Also bypass this cap. More important is the 47uf filter cap for the
small signal tubes--you could double that as well, and add a 470nf bypass
cap.

The HT is probably drawing around 100mils plus or minus. Lift the
downstream leg of the choke and insert a 100 ohm 5 watt resistor in
serires. Measure the voltage across that resistor. That will give you the
quiesent current draw for the amp (I). The draw is more when playing load
music.

You want to drop from 385 down to about 360, or a 25V drop. V=IR or
R=25/I. If I = 100 mill then would would want to use a resistor =
250ohms. Power=Watts=I*I*R=V*V/R=2.5 watts in this example. Use a minimum
of a 10 watt resistor. Cermanics should be fine.

The major gain you will get is better PS filtering and reduced ripple.
The 5% overspec line voltage is not really a problem, unless you change to
PS filter caps to a below spec value. You may lose some bass response by
adding the dropping network. Use a Japanaese to US line matching
transformer to drop the line voltage without affecting the amp--it will be
a little below spec instead of above. Or find a surplus power line
matching tranny with multiple taps and build your own.

Did you replace the interstage caps?

"Wes Jacson" wrote
...I think I remember reading about the relationship of filters
chokes resistors ect.and how they affect voltages and such...

Have you got the free power supply design software from

http://www.duncanamps.com/?

If you use it to simulate your PS, drawing whatever current your amp
takes, you can see how the value and position of a dropping resistor
effects the ripple and maximum voltages seen by all the parts, and
the final HT voltages.

Then you can get the power rating and value of the resistor right,
and check that you are not exceeding the voltage and ripple rating
of the caps.

You can also experiment with changing the load slightly to see the
effect on voltage.

cheers, Ian

Thank You Ian, That is a slick little program,I think. I must admit it will
take some pondering to get it to work.I am without any technical training so
alot of the numbers are beyond me.If I try to edit say the cap in the
example displayed it wants a resistance figure.Not sure what it wants to
know.If I change the transformer voltage it wants to know source
resistance.Again not sure what to say. And the results are hard for a dunce
like me to cypher out.Not that the program is not very cool it just shows me
yet again how much I don't know.My hat is off to all the folks who paid
attenion in school and share what they have learned with fools like me.Wish
I could find a group of electronics junkies in northwest washington state.I
have met some of the old time radio crowd and they are helpful and
friendly.Any way I have some homework to do if I want to make this amp work
as well as it should.
Thanks Again,
WesJ........

Yes, put the resistor downstream from the choke.

from the tranny HT output it would look like this:

HT--Choke--Resistor--
! ! !
10uf 40uf 40uf
! ! !
-------Ground-----------






"Wes Jacson" wrote in message
...
Ok! Thanks Tubesforall,Just what I needed.I will go back to the old
filters with resistors.I will use the same values as stock in the first
filter.The stock downstream filters were all 20uf's I installed 33's. So I
put a dropping resistor downstream from the choke? I think I remember
reading about the relationship of filters chokes resistors ect.and how
they affect voltages and such but I am just a wanna be tech.I wish I
would have taken those electronics classes in high school.Grammer too!
Anyway I am in your debt.I live in a rural enviroment and there is not
anyone around who can help.So the net is it.This amp seems to be a good
one for my talents.Such as they are.I did an Eico hf-20 and it turned out
real well.Gotta play those 78's.
Thanks again to all who reply.I need all the help I can get.
WesJ.........

"tubesforall" wrote in message
...


"Wes Jacson" wrote in message
...
Well I lifted the caps and I lifted the choke.Starting from the start.I
put everything back after testing with my Teleohmite They where all
fine.And the votages seemed fine as I went. Well I put every thing
back.And, it works now.I think.I must have had a short somewhere I
missed,I guess.I hate not knowing.I tried it with tubes in place.The
voltage at the first cap tops out at 480 ish.With a 5v4G. A little high
for the 450 volt caps I used.Now I am perplexed.The tranny says 775
across the HT.I figure that at around 385 each side.The primary says
117.I am getting 123 volts at the wall.The original schematic shows 360
or 380 per side on the HT..It is kinda hard to read.Well maybe that is
just what ya get with those parts.Anyay I guess If I want to use this
tranny I better drop the voltage a bit.That brings up another
question.How big a resistor would I need.I have a bunch of old ceramic
wire wound.Seems ohms law plays in here somewhere.Lets see naugh into
naught equles naught carry the naught...........Anyone care to give me a
ball park?
Thanks and Cheers
WesJ............
"tubesforall" wrote in message

You better move up to 600V cap ASAP!!. You want to have a least 20%
buffer room--more is better. Go back to the original design--two back to
back 20uf caps. You should only have about 10uf or less in the first leg
of the pi filter. The choke is sized for the ripple current. Put your
extra capacitance on the downstream side. Since you are adding a
dropping resistor, put your second 47uf on the downstream side of the
resistor. Also bypass this cap. More important is the 47uf filter cap
for the small signal tubes--you could double that as well, and add a
470nf bypass cap.

The HT is probably drawing around 100mils plus or minus. Lift the
downstream leg of the choke and insert a 100 ohm 5 watt resistor in
serires. Measure the voltage across that resistor. That will give you
the quiesent current draw for the amp (I). The draw is more when playing
load music.

You want to drop from 385 down to about 360, or a 25V drop. V=IR or
R=25/I. If I = 100 mill then would would want to use a resistor =
250ohms. Power=Watts=I*I*R=V*V/R=2.5 watts in this example. Use a
minimum of a 10 watt resistor. Cermanics should be fine.

The major gain you will get is better PS filtering and reduced ripple.
The 5% overspec line voltage is not really a problem, unless you change
to PS filter caps to a below spec value. You may lose some bass response
by adding the dropping network. Use a Japanaese to US line matching
transformer to drop the line voltage without affecting the amp--it will
be a little below spec instead of above. Or find a surplus power line
matching tranny with multiple taps and build your own.

Did you replace the interstage caps?

Note: you can double the capacitance after the resistor and add a 470nf
bypass capacitor.

"tubesforall" wrote in message
...
Yes, put the resistor downstream from the choke.

from the tranny HT output it would look like this:

HT--Choke--Resistor--
! ! !
10uf 40uf 40uf
! ! !
-------Ground-----------






"Wes Jacson" wrote in message
...
Ok! Thanks Tubesforall,Just what I needed.I will go back to the old
filters with resistors.I will use the same values as stock in the first
filter.The stock downstream filters were all 20uf's I installed 33's. So
I put a dropping resistor downstream from the choke? I think I remember
reading about the relationship of filters chokes resistors ect.and how
they affect voltages and such but I am just a wanna be tech.I wish I
would have taken those electronics classes in high school.Grammer too!
Anyway I am in your debt.I live in a rural enviroment and there is not
anyone around who can help.So the net is it.This amp seems to be a good
one for my talents.Such as they are.I did an Eico hf-20 and it turned out
real well.Gotta play those 78's.
Thanks again to all who reply.I need all the help I can get.
WesJ.........

"tubesforall" wrote in message
...


"Wes Jacson" wrote in message
...
Well I lifted the caps and I lifted the choke.Starting from the start.I
put everything back after testing with my Teleohmite They where all
fine.And the votages seemed fine as I went. Well I put every thing
back.And, it works now.I think.I must have had a short somewhere I
missed,I guess.I hate not knowing.I tried it with tubes in place.The
voltage at the first cap tops out at 480 ish.With a 5v4G. A little high
for the 450 volt caps I used.Now I am perplexed.The tranny says 775
across the HT.I figure that at around 385 each side.The primary says
117.I am getting 123 volts at the wall.The original schematic shows 360
or 380 per side on the HT..It is kinda hard to read.Well maybe that is
just what ya get with those parts.Anyay I guess If I want to use this
tranny I better drop the voltage a bit.That brings up another
question.How big a resistor would I need.I have a bunch of old ceramic
wire wound.Seems ohms law plays in here somewhere.Lets see naugh into
naught equles naught carry the naught...........Anyone care to give me
a ball park?
Thanks and Cheers
WesJ............
"tubesforall" wrote in message

You better move up to 600V cap ASAP!!. You want to have a least 20%
buffer room--more is better. Go back to the original design--two back
to back 20uf caps. You should only have about 10uf or less in the first
leg of the pi filter. The choke is sized for the ripple current. Put
your extra capacitance on the downstream side. Since you are adding a
dropping resistor, put your second 47uf on the downstream side of the
resistor. Also bypass this cap. More important is the 47uf filter cap
for the small signal tubes--you could double that as well, and add a
470nf bypass cap.

The HT is probably drawing around 100mils plus or minus. Lift the
downstream leg of the choke and insert a 100 ohm 5 watt resistor in
serires. Measure the voltage across that resistor. That will give you
the quiesent current draw for the amp (I). The draw is more when
playing load music.

You want to drop from 385 down to about 360, or a 25V drop. V=IR or
R=25/I. If I = 100 mill then would would want to use a resistor =
250ohms. Power=Watts=I*I*R=V*V/R=2.5 watts in this example. Use a
minimum of a 10 watt resistor. Cermanics should be fine.

The major gain you will get is better PS filtering and reduced ripple.
The 5% overspec line voltage is not really a problem, unless you change
to PS filter caps to a below spec value. You may lose some bass
response by adding the dropping network. Use a Japanaese to US line
matching transformer to drop the line voltage without affecting the
amp--it will be a little below spec instead of above. Or find a surplus
power line matching tranny with multiple taps and build your own.

Did you replace the interstage caps?