Gentlemen, I am pulling my hair out of whats left of it, I am working on an emerson box type radio I think it may be a model 30 lw based on the tube line up, someone over the years have gotten into it. I have one wire hanging from pin 6 on the 25z5 I can't figure out where this wire went based on this schematic, not sure this schematic is for this radio, this sch also shows the typical res pilot light in the filament circuit, their is nothing like it in this radio unless of course someone removed it, The tube line up is 25z5, 43, 77, 78, 78 any help would be great, George

George: A 25Z5 is a rectifier with 6E basing. Pins 1 and 6 are for the 25-V heater.

Here's the schematic that you suspect it is: http://www.nostalgiaair.org/PagesByModel/571/M0004571.pdf

Based on that schematic, this is an AC/DC set with all the tubes' heaters in series across the 120-V line. But, the heater voltages don't add up to 120V, so there is a 2-segment dropping resistor (135 and 25 ohms) in the heater ckt.

Look at the filament ckt shown on the diagram. One of the 25Z5 heater pins goes the the resistor and the other daisy-chains to the 43 tube. Make sure that you have that resistor and that it isn't burned out. Don't worry about the pilot lamp, or lack thereof, yet - it's not needed for the radio to work.

:Gentlemen, I am pulling my hair out of whats left of it, I am working on an emerson box type radio I think it may be a model 30 lw based on the tube line up, someone over the years have gotten into it. I have one wire hanging from pin 6 on the 25z5 I can't figure out where this wire went based on this schematic, not sure this schematic is for this radio, this sch also shows the typical res pilot light in the filament circuit, their is nothing like it in this radio unless of course someone removed it, The tube line up is 25z5, 43, 77, 78, 78 any help would be great, George

Well, it looks like I was started on poking up a reply also, but by post time I was too late, as the thoughts were exactly concurrent with Sir Doug’s. So I will just supplement what didn’t get mentioned.
How’s about having the set un-powered and run an ohms check from the power switch side AC line and take sequential readings thru the series tubes up to the 25Z5 and confirm that there is total series continuity thru the whole filamental string . If so that will only leave the final connection to the other side of the AC line being completed thru the two series/ or/ tapped power resistor that the 25Z5 needs to connect into. With a total AC power drop in the order of ~71 VAC needing to be made, that should be quite a massive unit in the order of a 20-25 watt wire wound power resistor unit for that amount of dissipation required. With its incorporation of a tap, it might be one of the popular series that was wrapped in a metal sheathing…ext insulated…. and that case was in turn riveted to the chassis for the additional heatsinking factor provided.
No chance that the power resistor unit is now missing, with a prior “troubleshooter” having completely pulled it in a quest for finding a like replacement…and abandoned the job, leaving you with the resultant conundrum now in your hands ???..... all being resplendently complete with a “floating wire” on pin 1.
Well, here we are, standing by for further feed back ……

73’s de Edd

Edd, as big as that dropping resistor must be, it might be one of those jobbies that's enclosed in a screen/mesh (for air cooling) and mounted vertically on top of the chassis.

It seems that this radio is a fairly early try at designing an AC/DC superhet, before a somewhat more suitable line-up of tubes was available.

Well, using 25Z5 and 43 tubes sounds believable. The ideal string of tubes would add up to 120 volts on its own. I do agree on that. Most AC-DC sets prior to 1939 used the above tubes along with some 6.3 volt tubes, though, as well as a filament dropping resistor. This was quite normal and acceptable (not uncommon and strange). 25Z5 and 43 have 25 volt filaments...designed specifically for the AC/DC radio. At .3 amperes, making these have 50 volt filaments would make for one hot tube. I guess at the time noone thought about making .15 ampere tubes. When they finally did design .15 ampere tubes, things all worked out perfectly. 12 volts at .15 amperes still puts out the same amount of wattage in heat necessary to heat a typical cathode found inside a similar .3 ampere 6.3 volt tube. A 50 volt .15 ampere filament provides a wattage in heat similar to a 6V6 or #42.

T.

OK, Thomas - I didn't recall that the 43 had a 25-V heater. This makes the dropping resistor's requirements a little more reasonable.

Still, if my math is right, the set's 160-ohm dropping resistor will consume about 15W. I'd want at least two 10-W resistors in series or parallel. My general preference is use a resistor rated twice the normal, continuous power disipation; on that basis, use three 10-W resistors.

:Well, using 25Z5 and 43 tubes sounds believable. The ideal string of tubes would add up to 120 volts on its own. I do agree on that. Most AC-DC sets prior to 1939 used the above tubes along with some 6.3 volt tubes, though, as well as a filament dropping resistor. This was quite normal and acceptable (not uncommon and strange). 25Z5 and 43 have 25 volt filaments...designed specifically for the AC/DC radio. At .3 amperes, making these have 50 volt filaments would make for one hot tube. I guess at the time noone thought about making .15 ampere tubes. When they finally did design .15 ampere tubes, things all worked out perfectly. 12 volts at .15 amperes still puts out the same amount of wattage in heat necessary to heat a typical cathode found inside a similar .3 ampere 6.3 volt tube. A 50 volt .15 ampere filament provides a wattage in heat similar to a 6V6 or #42.
:
:T.

Yeah, I found that out somewhat recently, too. Pretty cool, though.

T.

:Yeah, I found that out somewhat recently, too. Pretty cool, though.
:
:T. Thanks guys for all the info, I put in 3 10w resistors from pin 1, added new caps and resistors got her going loud and clear then she fades out in 2 to 3 min., also put in a new 25z5 the original one was running about 40% I don't know if it could be the choke.

Hi Geroge

What happens to B+ voltage when your radio fades out? Do you notice voltage going down on pin #3 of your 43 tube?

Pin #4 is grid #1 on a 43. It must remain 15 to 20 volts negative in relation to pin #5. If not overall radio voltage will be reduced, distortion heard and volume will go down.

Norm

::Yeah, I found that out somewhat recently, too. Pretty cool, though.
::
::T. Thanks guys for all the info, I put in 3 10w resistors from pin 1, added new caps and resistors got her going loud and clear then she fades out in 2 to 3 min., also put in a new 25z5 the original one was running about 40% I don't know if it could be the choke.