The part of the schematic that I didn't post does indeed show 117 volts as
the expected input.

So one final question, and then I think I've got it. I've gone online and
found a few sources for what should be a compatible transformer. 270-0-270,
plus 5V and a 6.3V. I also looked up the current draw of a 5U4 and found
that I need at least 3A across the filmanent, so I'll be sure to buy one
that is appropriate. But about that 270V - do I need to take into account
any kind of voltage drop across the plate? Obviously the schematic is
showing resulting voltages, not transformer output voltages as I originally
though. So is 270 the right spec? The 5U4 has about a 50V drop across the
plate.

Jeff



"Carter-k8vt" wrote in message
. net...
Unrevealed Source wrote:
"Carter-k8vt" wrote in message
t...

The 268 volts you are seeing on each plate is 268 volts -AC- to ground;
to put it another way, you are looking at a transformer with a 268-0-268
volt secondary (or a transformer with a 536 volt *center-tapped*
secondary).

I've got that part - thanks for confirming.

Let me toss you a minor curve ball: If you were repairing this radio in
its era, you would indeed be looking for a replacement transformer with
approximately a 270-0-270 high voltage secondary winding; this is
because it was designed for 110 volts AC coming out of the socket on
your wall. Today, that voltage is 115 to 120 volts or even a bit higher
and using -today's- line voltage with a 270-0-270 winding would give you
a bit more than the 265 volts DC B+ that you are looking for. So, what I
am saying is that you could (should?) look for a transformer with a
220-0-220 or 250-0-250 high voltage winding; i.e. less (than 270-0-270)
is better.

The 265 volts you refer to is +265 volts -DC-, measured from the
filament (cathode) to ground. The voltage -across- the 5U4 filament
is 5 volts AC, the filament voltage of a 5U4.

So I need to apply 5V AC across the filament (pins 2 and 8). That's
consistent with what my understanding would have been.

Yes. That is why your replacement transformer needs a 5 volt secondary
winding (with enough current for a 5U4 filament).

And the 265V is generated by the tube, correct?

Yes, the tube changes (or 'rectifies') the 268 volts AC to 265 volts DC.

This would be a pulsed DC, would it not, coming directly off the tube?

Yes.

In circuit, it is constant DC due to the filter capacitors?

Yes (and also due to a filter choke if one is present (rest of the
schematic is cut off).

Do I understand this correctly?

Yes.

By the very nature of your question, it indicates that you are a
beginner -- which is OK; we were all beginners at one time. Just be
careful; these voltages, if not fatal, can at least be harmful.

Yes, relative to almost all of you, I am indeed a relative beginner. And
this is my first experience with a transformer/rectifier-based radio, so
I apologize if my questions are somewhat stupid.

Jeff

Nope, not stupid. Again, we were ALL beginners at one time. Asking
questions is how you learn...

Again, I do not have the schematic so I cannot read what you are
quoting.

http://www.nostalgiaair.org/Resources/451/T0000451.htm

Look here. There are several to choose from. Perhaps there is a run or
version number to be had. Start with the first H104.

http://www.nostalgiaair.org/PagesByM...3/M0024073.pdf This page
identifies the different suffixed chassis. A tube change.



Paul P.

And perhaps some of these links may be helpful.
http://www.ppinyot.com/HomePage.htm

I put this together to help out other hobbiest. Nothing for sale on this
web site.

Paul
www.ppinyot.com

Mark Oppat wrote:
Carter wrote:
The 268 volts you are seeing on each plate is 268 volts -AC- to ground; to
put it another way, you are looking at a transformer with a 268-0-268
volt secondary (or a transformer with a 536 volt *center-tapped*
secondary).

Carter,
lets get in the habit of saying "to CHASSIS" rather than "to GROUND". I
mentioned this before in this group... its really the correct term to be
using, especially since sometimes we are working on "hot chassis" sets too.

Good response, otherwise!

Mark Oppat

Mark, you are absolutely correct! As I stand at the Gateway to
Geezerdom, old (bad) habits die hard. ;-) To CHASSIS is indeed the
proper way to state it...

HNY,
Carter K8VT

In article ,
"Mark Oppat" wrote:

Carter wrote:
The 268 volts you are seeing on each plate is 268 volts -AC- to ground; to
put it another way, you are looking at a transformer with a 268-0-268
volt secondary (or a transformer with a 536 volt *center-tapped*
secondary).

Carter,
lets get in the habit of saying "to CHASSIS" rather than "to GROUND". I
mentioned this before in this group... its really the correct term to be
using,

"CHASSIS" sounds good for AC sets like the one being discussed here.

especially since sometimes we are working on "hot chassis" sets too.

How many "hot chassis" sets actually have a hot chassis? "GROUND" seems
more correct for "AC/DC" sets where the power line neutral is not
connected to the chassis, in the case of "AC/DC" sets "NEUTRAL" would
seem to be most accurate, except for those sets using full wave voltage
doublers, which calls for yet another word.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

"Unrevealed Source" wrote in message
...
The part of the schematic that I didn't post does indeed show 117 volts as
the expected input.

So one final question, and then I think I've got it. I've gone online and
found a few sources for what should be a compatible transformer.
270-0-270, plus 5V and a 6.3V. I also looked up the current draw of a 5U4
and found that I need at least 3A across the filmanent, so I'll be sure to
buy one that is appropriate. But about that 270V - do I need to take into
account any kind of voltage drop across the plate? Obviously the
schematic is showing resulting voltages, not transformer output voltages
as I originally though. So is 270 the right spec? The 5U4 has about a
50V drop across the plate.

That 50V drop is figured into the resulting DC output voltage, once
filtered. (DC filtered voltage = AC voltage (of one half of the transformer
at any peak) x 1.414)

How about COMMON? This would take care of the AC/DC sets with a floating
"ground", any set using the chassis as the power return connection, sets
with back bias, sets with printed circuit boards and no chassis, and battery
portables with nothing like an earth ground connection.
--
Jim Mueller

To get my real email address, replace wrongname with eportiz. Then replace
nospam with sacbeemail.

"John Byrns" wrote in message
...
In article ,
"Mark Oppat" wrote:


snip


Carter,
lets get in the habit of saying "to CHASSIS" rather than "to GROUND".
I
mentioned this before in this group... its really the correct term to be
using,

"CHASSIS" sounds good for AC sets like the one being discussed here.

especially since sometimes we are working on "hot chassis" sets too.

How many "hot chassis" sets actually have a hot chassis? "GROUND" seems
more correct for "AC/DC" sets where the power line neutral is not
connected to the chassis, in the case of "AC/DC" sets "NEUTRAL" would
seem to be most accurate, except for those sets using full wave voltage
doublers, which calls for yet another word.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

""to common B-" is fine if thats what you are tying to on a return side, but
"to chassis" is the correct term in the case we were dealing with here.

I just want to break the habit many servicers have of saying "to GROUND" as
its definitely NOT "GROUND" unless you bond the chassis to ground...and, 90%
of the time its just not... and a goodly portion of the sets being restored
are indeed what can be called "hot chassis" or AC-DC sets... which, unless
converted to have a polarized plug with ground can not be referred to ever
as being grounded.

Mark Oppat

"Jim Mueller" wrote in message
...
How about COMMON? This would take care of the AC/DC sets with a floating
"ground", any set using the chassis as the power return connection, sets
with back bias, sets with printed circuit boards and no chassis, and
battery portables with nothing like an earth ground connection.
--
Jim Mueller

To get my real email address, replace wrongname with eportiz. Then
replace nospam with sacbeemail.

"John Byrns" wrote in message
...
In article ,
"Mark Oppat" wrote:


snip


Carter,
lets get in the habit of saying "to CHASSIS" rather than "to GROUND". I
mentioned this before in this group... its really the correct term to be
using,

"CHASSIS" sounds good for AC sets like the one being discussed here.

especially since sometimes we are working on "hot chassis" sets too.

How many "hot chassis" sets actually have a hot chassis? "GROUND" seems
more correct for "AC/DC" sets where the power line neutral is not
connected to the chassis, in the case of "AC/DC" sets "NEUTRAL" would
seem to be most accurate, except for those sets using full wave voltage
doublers, which calls for yet another word.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

Mark, it is worth noting that some modern high tech IC based equipment
is built on multilayer PC boards, and one of the layers is commonly
referred to as the "ground plane", and even in lesser equipment using
simple two sided boards, there are often large areas of foil referred to
as a "ground plane".

I think your condemnation of the term "ground" is misplaced given its
common usage even in the most modern technologically advanced equipment.
I think the problem is that you are confusing "ground" with "earth" and
they are not always the same thing.


Regards,

john Byrns


In article ,
"Mark Oppat" wrote:

""to common B-" is fine if thats what you are tying to on a return side, but
"to chassis" is the correct term in the case we were dealing with here.

I just want to break the habit many servicers have of saying "to GROUND" as
its definitely NOT "GROUND" unless you bond the chassis to ground...and, 90%
of the time its just not... and a goodly portion of the sets being restored
are indeed what can be called "hot chassis" or AC-DC sets... which, unless
converted to have a polarized plug with ground can not be referred to ever
as being grounded.

Mark Oppat

--
Surf my web pages at, http://fmamradios.com/

John,
I stand my "ground" here. "Ground" IS INDEED "earth", one is the USA term,
one is used in the UK and elsewhere most often. However, in antique
radios we should use the term "CHASSIS" if that is what you are tying onto,
or "B-", also called "Common Negative, or Common neg" when you are tying to
that.

Mark Oppat


"John Byrns" wrote in message
...
Mark, it is worth noting that some modern high tech IC based equipment
is built on multilayer PC boards, and one of the layers is commonly
referred to as the "ground plane", and even in lesser equipment using
simple two sided boards, there are often large areas of foil referred to
as a "ground plane".

I think your condemnation of the term "ground" is misplaced given its
common usage even in the most modern technologically advanced equipment.
I think the problem is that you are confusing "ground" with "earth" and
they are not always the same thing.


Regards,

john Byrns


In article ,
"Mark Oppat" wrote:

""to common B-" is fine if thats what you are tying to on a return side,
but
"to chassis" is the correct term in the case we were dealing with here.

I just want to break the habit many servicers have of saying "to GROUND"
as
its definitely NOT "GROUND" unless you bond the chassis to ground...and,
90%
of the time its just not... and a goodly portion of the sets being
restored
are indeed what can be called "hot chassis" or AC-DC sets... which,
unless
converted to have a polarized plug with ground can not be referred to
ever
as being grounded.

Mark Oppat

--
Surf my web pages at, http://fmamradios.com/