Restoring A WARDS AIRLINE RADIO MODEL 93BR-1201 WARDS AIRLINE RADIO MODEL 93BR-1201

[Rick73]

I am in the process of restoring this old radio. I believe that it was manufactured in the late 40's or early 50's. If anyone has some suggestions on where to start, I would appreciate that.

Thanks,
Richard

 

[BradtheRad]

Switching it on quickly sends a shock of high voltage through aged components. Tubes and capacitors are prone to fail at that time.

Do you have a variac? Use it to power up the radio slowly.

How slow is too slow? Certain circuitry can behave strangely if exposed to substandard voltage in the process. It would take an expert to predict if damage might result if you gradually raise voltage too slowly.

A different school of thought could say twenty seconds is reasonable for you to raise the voltage to normal. However long it takes the tubes to warm up.

 

[Rick73]

I don't have any idea of when it was last used. I is my sisters radio and I told her I could give it a shot. Here is a photo I got off of the internet of the chassis.

I suspect that the three electrolytics on the right side will have to be replaced. I have a copy of the schematic, but it does not show any values of the components. I was thinking of pulling the rectifier tube and just see if the transformer still works. The schematic is in a pdf and I'm not sure if one can post a pdf on this site.

I am a ham radio operator, but sadly I had to give it up. My license is still good, K0UXU, but as I can not hear, i sold all my ham gear years ago. It was a rather sad day when that gear went out the door.

 

[D.A.(Tony)Stewart]

Start with a schematic. https://www.radiomuseum.org/r/montgomery_93br1201a.html get a DMM to measure the DC hiV and the ripple AC.

An alternative to Brad's idea is to put a 60W lightbulb in series so the diode tube surge current is reduced charging up the caps which may need repair. If the light stays bright, there is a problem.

 

[Rick73]

Yeah, I thought about the light bulb idea and I may us that when I get ready to power it up. I looked at the wiring under the chassis last night and I see that someone has already done some changes/improvements.

Can anyone suggest a switch contact clearer ? It used to be that you could just drive over to the local Radio Shack and pick some up. But no more. There is a Axe Man store near me, maybe they will have some.

Richard

 

[D.A.(Tony)Stewart]

Electrons can move thru WD-40 with sufficient voltage and clean off contamination where you want insulation. I use it for contacts except film pots.

circa early '70's
I discovered when my distributor shorted out above 0'C then insulated when frozen with the hood up.
When the engine heat thawed the cap, the engine stopped at around -20' C. So I remembered I had WD-40, cleaned the carbon trails off the dist. cap on my '63 MGB during the late-night storm on a silent road, and got home safely. I don't believe the fish tales about it come from fish oil. But bass might like the stink bait.

At least it has less residue than some Isoprop's.

 

[Rick73]

I have some photos of the one I'm working on.
Here is the back view:

Here is the bottom view:

The large yellow capacitor at the top left is a substitute for the metal can one that can be seen in the rear view photo.

 

[BradtheRad]

I guess you intend to vacuum (or blow compressed air) to remove dust. One thing I don't recommend is washing the tubes with water. I did that to a bunch of old tubes and their part numbers washed off.

 

[Rick73]

I guess you intend to vacuum (or blow compressed air) to remove dust. One thing I don't recommend is washing the tubes with water. I did that to a bunch of old tubes and their part numbers washed off.

I did use compressed air to blow off the big chunks of dust. I hope I did use to much force.

I was wondering about how to get the dust off of the tubes. And I think you are correct, I seem to remember washing some tubes in the past and then wondering what happened to the tube number. I would like to clean them us some, but fear that just using a clothe to get off the dust and dirt may also clean off the tube numbers.

I did some capacitor checking today and it appears that most of the waxed caps are bad. Will have to make a shopping list.

Richard

 

[Rick73]

There are two of these "things" in the chassis of this radio.

The ones in the chassis are longer with a part number 10655. Does anyone know what the purpose of this device is ?

Richard

 

[Rick73]

There are two of these "things" in the chassis of this radio.
View attachment 195683

The ones in the chassis are longer with a part number 10655. Does anyone know what the purpose of this device is ?

Richard

I have figured out what this is. It is a power resistor, typically around 5 to 8 watts. I don't know if there is any relationship between the part number and the resistance of the item.

--- Updated Jan 31, 2025 ---

I have some photos of the one I'm working on.
Here is the back view:
View attachment 195550

Here is the bottom view:
View attachment 195551
The large yellow capacitor at the top left is a substitute for the metal can one that can be seen in the rear view photo.

I have replaced all the wax/paper caps and the electrolytics.
Here are the old wax/paper caps I replaced. The second photo shows the new caps in place.

 

[Rick73]

Help !

This power supply B+ is putting out a lot more voltage than it should be. I measured my AC line voltage and it is 120 V AC, so I don’t see a problem there.

The voltage on terminal 5 of the speaker field coil is listed to be 340V DC measured from ground.

The voltage on terminal 1 of the speaker field coil is listed to be 240V DC, measured from ground.

Here are the voltages that I have measured.

Speaker Field coil Terminal 5 = 466V DC

Speaker Field coil Terminal 1 = 380V DC

These measured voltages are well over 100V more than specked in the schematic.

I have tried putting a 150W light bulb in series with the AC line to reduce the voltage of the B+ and that did lower the B+ to levels that are specified in the schematic, but the filament voltages are about a volt lower than they should be. I don’t think that is acceptable.

Some of the tubes connected to this B+ supply are not rated for this high voltage.

Does anyone have any ideas on how to lower the B+ voltage ?

Perhaps resistors in the lines from the HV transformer that go to 5U4 tube pins 4 and 6. Or maybe some voltage dropping Zener?

I have attached the schematic.

Richard

 

[betwixt]

I doubt those voltages would cause trouble in real life. The 150W light bulb trick is only to allow the capacitors to 're-form' and it should be removed afterwards. Cycle power with the bulb in place for a few times then remove it. The idea is is limits the current that can flow until the capacitors are restored and under worst case conditions of a complete short circuit it cannot sink more than the bulb rating.

I f you measured higher voltages with the bulb still in circuit, what is probably happening is the filaments are not hot enough for the tubes to draw enough current and its that same current that 'drags' the power supply voltages down. At full emission the current draw on the HT line will probably bring it down to expected levels.

Brian.

 

[Rick73]

Well you do have a point, I do not have all the tubes in place. I have 5 of them on order. Four of them are the 6F6's that are the push-pull audio output tubes.

Some of the tubes that I looked up for their maximum applied voltage have a limit of 300, and the supply voltage is greater than that.

Thanks for you input.

Richard