"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)

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


"Carter-k8vt" wrote in message
t...
Unrevealed Source wrote:
Looking for help on this one. Am I reading the schematic correctly -
265V across the 5U4 filament, and 268V across the plate?

You are interpreting it incorrectly.

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).

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.

I also notice that the tap to the pilot lamps is not labeled,
although I know from the parts list that they are 6.3V.

Yes, this feeds 6.3 volts AC to the pilot lights and the filaments of the
other tubes.

Assuming that this radio is intended for use at (nominally) 115 VAC, you
will need a transformer with a 110-120 v primary, and the following three
secondaries: 500 volts center tapped (250-0-250), 6.3v and 5 v.

I'm looking to replace the fried transformer, but I'm a bit in over my
head with regard to what to replace it with or whether to have it
rewound.

Jeff

This is a fairly typical receiver transformer. Check the web site of
Antique Electronics Supply and Hammond Transformers. Look for one with
these approximate electrical characteristics and physical characteristics
that most closely match the existing one. Rewinding will probably cost
more than a new one.

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.

Needless to say, check the radio for other faults so as not to toast the
replacement transformer.

Merry Christmas and good luck!

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/

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/