New to forum with Brunswick Panatrope 42DC

[rebrands]

Hi All,
I'm new here. I'm looking for anybody who has knowledge regarding a Brunswick Panatrope with Radio model 42DC. This is a DC powered unit, and this one is considerably different from the Riders schematic: Different tube lineup - 24As instead of 32s and a 27 instead of the 30. Yes, I'm sure what model it is, thinking it may be an early release.

My biggest issue is with a bad interstage transformer that has split secondaries - hard do find, and the schematic/physical wiring don't indicate where the middle secondary wires are connected. Just what looks like a "-18" and a "-22 ½", I'm guessing bias voltages. The wires exit the chassis to a connector with no matching plug on the chassis or cabinet.

I have attached the schematic from Riders and a blowup of the area of concern.

So, my main interest is where to locate a replacement (not likely) or substitute for the transformer, and how to connect the two center secondary leads.

I know it's a big order. I'm working with folks on the Antique Radio Forum also.
Thanks in advance.
reb

[howardpgh]

Some of my thoughts on your Panatrope/radio
The 24A tube is the 5 pin AC version of the 4 pin 32.
The 27 tube is the 5 pin AC version of the 4 pin 30.
It's possible that these tubes were substituted in the design as they might be more rugged than their DC counterparts.
I fixed a audio transformer one time by zapping it.
I did this by charging up a large electrolytic capacitor to 90 volts and the connecting the leads to the open winding of the transformer, the resulting arc welded the open coil and then it showed continuity.
Maybe the -18 and -22 have something to do with grid bias where the grids have to be negative voltage in relation the filaments. Positive goes to +C at the midpoint of the last two 71 filaments on the right in the schematic.
What type of plug/connector is coming out of the chassis? Three pin? Some of the old radio batteries had the mating plug on them.

[ChuckA]

Hi All,
I'm new here. I'm looking for anybody who has knowledge regarding a Brunswick Panatrope with Radio model 42DC. This is a DC powered unit, and this one is considerably different from the Riders schematic: Different tube lineup - 24As instead of 32s and a 27 instead of the 30. Yes, I'm sure what model it is, thinking it may be an early release.

My biggest issue is with a bad interstage transformer that has split secondaries - hard do find, and the schematic/physical wiring don't indicate where the middle secondary wires are connected. Just what looks like a "-18" and a "-22 ½", I'm guessing bias voltages. The wires exit the chassis to a connector with no matching plug on the chassis or cabinet.

So, my main interest is where to locate a replacement (not likely) or substitute for the transformer, and how to connect the two center secondary leads.

reb

A number of manufacturers produced a DC version of their equipment for those areas that were still operating on the old Edison system. These used battery designed tubes.

For the interstage transformer use a standard 3:1 center tapped unit from Hammomd or Stancor. The center tap goes to the negative terminal bias battery (C-) the positive terminal goes to the C+ terminal. The schematic indicates this, you also have a -3v bias that needs to be connected for the first audio tube.

Not sure why Brunswick designed this with different bias voltages on the output tubes, but I would doubt it will make any difference using the same voltage on both pairs of 71A tubes. A standard bias voltage is -22 1/2V which should work OK for this set.

Chuck

[Phototone]

OK, so one assumes this is for use on 110v DC voltage supplied by the power utility. Not uncommon in the Northeast in the 1920's. However it (to my reading of the schematic) doesn't show the voltage dividers and circuits used to produce the lower voltages and negative grid bias voltages. "IF" this is for use on Household DC voltage, then there has to be another chassis with the resistors and inductors needed to provide the various voltages to the points on the schematic as shown.

As as side note, I really really don't like those early schematics, like this one, that don't draw a circle around each tube.

[Uncle Vanya]

Hi All,
I'm new here. I'm looking for anybody who has knowledge regarding a Brunswick Panatrope with Radio model 42DC. This is a DC powered unit, and this one is considerably different from the Riders schematic: Different tube lineup - 24As instead of 32s and a 27 instead of the 30. Yes, I'm sure what model it is, thinking it may be an early release.

My biggest issue is with a bad interstage transformer that has split secondaries - hard do find, and the schematic/physical wiring don't indicate where the middle secondary wires are connected. Just what looks like a "-18" and a "-22 ½", I'm guessing bias voltages. The wires exit the chassis to a connector with no matching plug on the chassis or cabinet.

So, my main interest is where to locate a replacement (not likely) or substitute for the transformer, and how to connect the two center secondary leads.

reb

A number of manufacturers produced a DC version of their equipment for those areas that were still operating on the old Edison system. These used battery designed tubes.

For the interstage transformer use a standard 3:1 center tapped unit from Hammomd or Stancor. The center tap goes to the negative terminal bias battery (C-) the positive terminal goes to the C+ terminal. The schematic indicates this, you also have a -3v bias that needs to be connected for the first audio tube.

Not sure why Brunswick designed this with different bias voltages on the output tubes, but I would doubt it will make any difference using the same voltage on both pairs of 71A tubes. A standard bias voltage is -22 1/2V which should work OK for this set.

Chuck

A transformer with a split secondary is pretty much a necessity, for otherwise the tubes on one side of the push-pull arrangement will be biased very differently from those in the other side. Split secondary transformers were made by Stancor and others, generally for Class B work. A center tapped transformer will mean that the circuit will be unbalanced rather badly.

110V DC sets were also sold in some quantities for farm use. Large farm lighting plants, (3000 watts or more) were always 110V rather than the commonly remembered 32V. Of course these big lighting plants would be owned by only the most prosperous. They were relatively common, though, at summer homes of the wealthy. I pulled one such set, a Radiola 32 DC, out of a Central Michigan farm house! The owners ran a really large commercial egg operation, hence the big lighting plant, and the funds to afford a $1000 radio in 1927.

[ChuckA]

A transformer with a split secondary is pretty much a necessity, for otherwise the tubes on one side of the push-pull arrangement will be biased very differently from those in the other side. Split secondary transformers were made by Stancor and others, generally for Class B work. A center tapped transformer will mean that the circuit will be unbalanced rather badly.

110V DC sets were also sold in some quantities for farm use. Large farm lighting plants, (3000 watts or more) were always 110V rather than the commonly remembered 32V. Of course these big lighting plants would be owned by only the most prosperous. They were relatively common, though, at summer homes of the wealthy. I pulled one such set, a Radiola 32 DC, out of a Central Michigan farm house! The owners ran a really large commercial egg operation, hence the big lighting plant, and the funds to afford a $1000 radio in 1927.

Bob,

I agree with you in theory, but in the practical world I have replaced these split secondary transformers with a CT unit and they worked fine.


Chuck

[Uncle Vanya]

A transformer with a split secondary is pretty much a necessity, for otherwise the tubes on one side of the push-pull arrangement will be biased very differently from those in the other side. Split secondary transformers were made by Stancor and others, generally for Class B work. A center tapped transformer will mean that the circuit will be unbalanced rather badly.

110V DC sets were also sold in some quantities for farm use. Large farm lighting plants, (3000 watts or more) were always 110V rather than the commonly remembered 32V. Of course these big lighting plants would be owned by only the most prosperous. They were relatively common, though, at summer homes of the wealthy. I pulled one such set, a Radiola 32 DC, out of a Central Michigan farm house! The owners ran a really large commercial egg operation, hence the big lighting plant, and the funds to afford a $1000 radio in 1927.

Bob,

I agree with you in theory, but in the practical world I have replaced these split secondary transformers with a CT unit and they worked fine.


Chuck

Well, I did the same on a DC Mills Do-Re-Mi years ago, and the itching would distort pretty badly at high volume levels. Of course, this machine was using six 48's in parallel push-pull, and ther was an awful lot more DC current flowing through the output transformer, leading, I think, to saturation. The substitution of a Stancor A-4774 "Universal Interstage Transformer" for the center-tapped unit solved the problem nicely. Oddly enough, the 4774 is no more expensive than their old center-tapped unit, if one can find the thing today. I still have a few 4774 transformers put back for just this purpose.

Gary Schneider has at least one listed in the inventory on his audio transformer page, about halfway down. New in box for $22.00. It may be seen here: http://www.oldradioparts.com/2a23cfl.txt
His stock number for the part is 1267-940

[Uncle Vanya]

OK, so one assumes this is for use on 110v DC voltage supplied by the power utility. Not uncommon in the Northeast in the 1920's. However it (to my reading of the schematic) doesn't show the voltage dividers and circuits used to produce the lower voltages and negative grid bias voltages. "IF" this is for use on Household DC voltage, then there has to be another chassis with the resistors and inductors needed to provide the various voltages to the points on the schematic as shown.

As as side note, I really really don't like those early schematics, like this one, that don't draw a circle around each tube.

Nope. The filament (or heater) resistances are part of the bias circuit in this set. The effective bias on the output tubes varies depending upon where they are in the filament string, hence the different supplementary grid bias voltages for the different sides of the balanced circuit.

[rebrands]

Thanks for the replies. I apologize for not coming back sooner, I neglected to check for notification of replies and thought nobody was replying. My bad.

I've been busy doing more in depth tracing of the filament circuit. It has been complicated by bad connections, failed switches and open hookup wire. I think I'll be able to shed some light on the voltage dividing after I post my tracing results.

[rebrands]

I'e been busy entertaining three granddaughters, ages 7, 5, and 2 today. For some reason they take priority over radios, so I'm doing this after their bedtime. Their parents get them back Sat. Exhausting and exhilarating.

I fixed a audio transformer one time by zapping it.
I did this by charging up a large electrolytic capacitor to 90 volts and the connecting the leads to the open winding of the transformer, the resulting arc welded the open coil and then it showed continuity.

I never thought of zapping a transformer to revive it. I've nothing to lose. I'll let you know the outcome. I'm not too hopeful as it looks to have been overheated previously - bubbly tar.

Positive goes to +C at the midpoint of the last two 71 filaments on the right in the schematic

I've not yet located any connection corresponding to the C+ label on the schematic.

What type of plug/connector is coming out of the chassis? Three pin? Some of the old radio batteries had the mating plug on them

The wire pair/connector is in the attached photo, but a battery connection may be a possibility.

For the interstage transformer use a standard 3:1 center tapped unit from Hammomd or Stancor. The center tap goes to the negative terminal bias battery (C-) the positive terminal goes to the C+ terminal. The schematic indicates this, you also have a -3v bias that needs to be connected for the first audio tube.

Most interstage transformers list their ratio as 1:2 or 1:3, rather than 2:1, 3:1. I assume that is the primary to secondary ratio. If so I would need to reverse a 1:2 to arrive at a 2:1 winding ratio. Maybe two transformers in series or parallel to arrive at the winding arrangement I need?

I am mystified why the two pairs of output tubes would be biased differently. They look balanced to me, but maybe the way the filaments are powered as mentioned?

doesn't show the voltage dividers and circuits used to produce the lower voltages and negative grid bias voltages. "IF" this is for use on Household DC voltage, then there has to be another chassis with the resistors and inductors needed to provide the various voltages to the points on the schematic as shown.

The three volt bias is adjusted with an external pot.

I've attached a couple scans of a schematic I have drawn up. It isn't complete, still have more wire tracing to do in the area of V4 and V5. I think the filament circuit diagram should shed some light on the voltage dropping required. The 65 ohm center tapped resistor in parallel with the field coil is a monster, mounted on the bottom of the cabinet with a patch of ASBESTOS insulating it from the cabinet, and a wire mesh to keep from touching it. Yeah, I hate the style of the original schematic and don't grasp the "dual grids" around the plates.