[Mondial]

Yes I agree. There seem to be a lot of non-stock modifications, regardless of what the radio started life as. I would be afraid to plug it in until you traced out all the AC wiring and confirmed the chassis is isolated and not in any way connected to the AC line conductors.

The power supply looks a bit suspect. There seems to be a type 81 half wave rectifier installed which does not look original, especially after you mentioned the cabinet had to routed out to make it fit. More likely a radio like that would have used a full wave type 80 rectifier. There also appears to have a ballast tube next to the rectifier which does not make much sense in a transformer powered AC radio.

Other than that, the original radio seems to be a usual late 1920's AC set with type 26 RF amps, a 27 detector and push pull 71A outputs.

[GarySP]

I would check the tubes as well. Especially that globe in the corner of the chassis behind the transformer. Looks awful milky to me. Take care and BE HEALTHY! Gary

[Rob Quay]

Agreed. It was quite a revelation that the voltages are messed up. Apparently the radio got plugged into my variac the same way every time. The ammeter showed less than.5 amps at 110 v. so I initially wasn’t overly concerned. Not having a schematic as a road map doesn’t help. We’ll see what happens. Thanks for the input. - Rob Q.

[Chas]

Especially that globe in the corner of the chassis behind the transformer. Looks awful milky to me.

I think, that tube is a ballast. Possibly in series with the power line input. If so careful, that may be the only example. The radio with line regulating ballast often has a 85 volt input so cannot go direct to line...

I wonder, there were few cities that had D.C. That might explain what is going on. I have never come across a DC only radio here in S.E.MA...

IMHO the circuit does seem to be straight forward. But with the power cord issue drawing the circuit will often give the clue when the circuit is referenced to known workable examples.

I have no idea who made the radio but probably from '29-'31...

Chas

[Rob Quay]

Yes Chas, the first tube next to the 81 is an Amperite 6-20 ballast. It would be interesting if it’s a DC radio. 
When I first looked at it I was surprised that none of the transformers were open. Is there something out there that’s the DC equivalent of a variac? I’m not quite ready to give up on the beast. I’ve pinched my fingers too many times in moving this cinder block around the work bench. Thanks. - Rob Q.

[GarySP]

Wow! That's my first view of a glass ballast tube. My only encounters have been metall-cased octal ballasts. Take care and BE HEALTHY! Gary

[Rob Quay]

I guess my next question is- “If this radio is DC, what tube would be used instead of a rectifier tube?” Unless I’m told differently I’d like to bring the set up slowly on DC and measure voltages. Also, an IN4004 has been mentioned as a ballast substitute. Is that appropriate here? Thanks. - Rob Q.

[Mondial]

Before you do anything else, you need to check the wiring and see how the AC line cord is connected. If it connects to a power transformer, then the set can now only be powered on AC.

Also, see if the tube filaments are wired in series or parallel. If it is configured as a DC set, then filaments would be in series. If they are in parallel and connect to the power transformer then it is only AC.

The other question is how is the 81 rectifier tube connected. Does the plate connect to a power transformer or directly to the AC line. What does the ballast tube connect to? You need to trace out the relevant wiring and draw up a rough schematic before you proceed any further.

In any case, using a 1N4004 diode would not be relevant. It is sometimes used in AC/DC sets with series strings of 0.3 Amp filament tubes, which is definitely not the case here.

[radiorich]

Hello Rob,
Nice job so far !

Sincerely Richard

[Rob Quay]

The quest continues. The ballast tube is on one side of the AC line in and the on/off switch is on the other. Tube filaments are in parallel and the plate of the 83 tube is connected to the transformer. When I first got the radio only the ballast and one other tube were in the cabinet. Is it possible that an 80 tube is meant to be used instead of an 83? Setting up the tube lineup was a matter of some conjecture. 
I wish I could find something more about this kit radio. The chassis was cast to have the five Federal Telephone condensers drop into place and be bolted in. Likewise the sockets are marked for connection by someone with limited radio experience. Poring over old magazines from the 20s has shown some of the components but for the most part it’s still a mystery. Thanks for the input! - Rob Q.

[admin]

As we are now getting into the restoration of a radio, this thread has been moved to the appropriate forum.

[Mondial]

I really doubt there should be an 81 tube installed because it is a half wave rectifier and it was usually used in pairs. Most likely there should be an 80 used instead. 

How many terminals are connected on the rectifier socket? For an 81 there should be only three terminals connected with wires from the transformer, with one vacant. If the socket was wired for an 80 all four terminals will be used.

Are you using an 81 or 83 rectifier? It looks like an 81 in the photo. The 83 never would have been originally installed as it first was manufactured in 1933.

[Rob Quay]

It’s an 81 rectifier tube. All four socket terminals are connected. So there should be an 80 rectifier tube then? 
I am at best a fair radio repair guy, not a technician, so this is a bit above my comfort level. Is there anything to be gained by pulling the tubes and checking transformer voltages? Thanks for your input. - Rob Q.

[Chas]

I would suggest doing resistance checks of the power cord up to the switch and transformer input. If all seem well no shorts or opens. Look to see how the ballast tube is wired to the power cord as well it should be in series that is if it is correct.

If the 81 is incorrect, that ballast may well be too and were put there as "hole fillers"

Then, power the radio with the ballast in and the rectifier tube the 80 removed there will be no B+ but the tubes should light, there should b no noises or other heating of the power transformer, the ballast should be warm but not HOT. That test should take some 30 minutes to do. If all is well that confirms the power transformer is good..

Now do resistance checks of the B+ locate the filter pack and what needs to be done to replace the filter condensers. You must also determine if there is a speaker with a field coil that is missing. The field coil is often part of the B+ filter network. There may be a tube socket associated with the speaker and it will be for just the speaker. Often it is a special configuration socket so a tube cannot be plugged in. The radio may use a magnetic speaker, so some tracing and note taking can determine that.

There are other "gotchas", if an RF coil is open it will have to be re-wound, checking them should be relatively simple, most often they are not more than 20 or so ohms. There are also AF transformers, these can go open too. resistance checks of them should be done with an analog meter looking for no more than 8K often they can read 250 ohms on a primary but no less. More than 10K will likely mean an open winding.

Steep learning curve on this radio, made all the worse as there is no schematic as yet...

GL

Chas

[Rob Quay]

Thanks Chas. I’ll get busy sorting things out. Is there any merit to looking at some schematics with a similar tube lineup? My thought is that someone putting together a radio kit would begin with a proven design. 
The ballast tube seems to make sense in the circuit as the socket is only wired for two pins. If it turns out that there’s no other radio like this one that’s survived (and this one almost didn’t) I really don’t want to mess it up beyond repair. - Rob Q.