[rolleiflex]

Good Afternoon

Looking forward to learning more from this forum! I'm in the process of working on a 38-3 with a fellow ham and have it mostly working but have had some strange things happen when it comes to receiving signals.

There were three bad tubes that we found using a tube tester and we were able to get some signals once those were replaced. In the setup where the radio is able to receive AM, the Red terminal is attached to the copper pipes and there is nothing connected to the ground lug. If the ground lug is attached to the copper pipes and a random wire is attached to the red terminal, nothing comes through.

In this setup are the pipes of the house operating as the antenna? Is this a safe way to operate the radio? If not what changes need to be made? It's entirely possible that we have a bad ground on the pipes (house built in 1884).

Thanks in advance!

[rolleiflex]

Basically just wondering how the radio could work with the red terminal attached to ground and with nothing attached to the ground terminal.

[Radioroslyn]

Hi and welcome,

I suppose it could be dirty contacts on the band switch or rf leakage between the coil. The main concern is to check for open windings (lightning hit).

https://philcoradio.com/library/download...l.%202.pdf

de N3GTE

[rolleiflex]

Terry,

Thanks! Is it safe to keep operating the radio in this way or should I try and problem solve this first?

When it comes to open windings is that in the transformer or other part of the circuit? I pretty thoroughly cleaned the contacts with contact cleaner but can also double check that as well.

n0mon

[rolleiflex]

Whoops, got the part number wrong. It's actually a 38-3. not sure if that changes anything

   

[Radioroslyn]

Yeah circuit looks a little different...

https://philcoradio.com/library/download...%20277.pdf

[rolleiflex]

I noticed on the schematic a pilot light is called out--where exactly is that? Is it one of the three flood lamps?

[rolleiflex]

Also, whenever the radio is plugged in there's 60 odd ac volts going between both the ground and red terminals to the copper pipes. Is this normal? Am I essentially sinking some of the ac line voltage to ground?

[MrFixr55]

Are you measuring between the antenna or ground terminal and the water pipe with a no wire from the radio connected to the pipe? is the "black" terminal jumpered to ground? Most radios of this vintage require an external antenna. There will be a tuned transformer with a relatively low primary resistance. For this radio, the listed resistance is 0.7 Ohm for 2 of the coils, 0.1 Ohm for one of them. You may see slightly higher and not be worried. If an open reading, check the band switch.

A couple of thoughts:

In the schematic, between the power plug and the power transformer primary winding, you will find 2 caps. one between each leg and the chassis. the ground lug goes to the chassis also. Since caps pass AC, there could be 60V between the floating chassis and electrical ground. Please replace these caps with safety caps. If one of these caps short, the chassis could become electrically hot.

Check between the power line and the pipes with a DVM with a 10KOhm resistor across the leads. If you don't get 120V between the Hot terminal of the power plug and the pipes, the pipes are floating. Although the house is 140some odd years old, someone may have replaced a main line with PEX or PVC. You may want to further investigate water pipe grounding, as the water main service pipe is a common binding point.

A house that old likely used threaded iron or steel pipe. If someone used an excessive amount of pipe dope and failed to tighten the pipes sufficiently to displace enough dope to have a metal to metal contact. This is not an issue with a plumbing system consisting of soldered copper tubing.

[rolleiflex]

Thanks!

Yes, I was measuring those values with no wire connected to the pipes. Black and Ground were not jumpered--should I do that right away?

By saftey caps do you mean modern electrolytics? Or is there something else I should use? Is this the same idea as the so called "death cap" from old guitar tube amplifiers?

In the meantime will I be able to operate the radio in the current configuration or is there the potential to damage components with the radio in its current state? I have not done any component replacement besides the light bulbs.

[Chas]

In the meantime will I be able to operate the radio in the current configuration or is there the potential to damage components with the radio in its current state? I have not done any component replacement besides the light bulbs.

No, as it stands the radio, though may work, is not in a robust condition to use.

The primary issue is with the power supply electrolytic capacitors, those large round metal cans or paper covered sleeves with "+" & "-" lead markings (mostly).

Find them and identify from the schematic v.s. the radio. Note how the OEM installation is made. An error when installing replacements can cause severe damage. Replacement may not fit in same location, some technicians prefer to install replacements inside the old, others, disconnect the old completely and install under the chassis, still others leave the old in place on top of chassis and replacement under.

Further restoration will include replacing all other paper type caps that may be in Bakelite housings. The best method is to removed the "innards" and install new caps inside housing, thus preserving the wiring patterns. It is not a good idea to re-route any wiring but do replace wires with rotted insulation in the same path.

There are many other "gotchas". Wherein you have a working radio that means certain irreplaceable (very difficult) components are good, others are weak.

There is one principle when restoring a radio that is helpful. Replace two components at a time and then test. If a failure occurs then it was one or the other component (installation) that has failed. Beware of solder blobs and wire snips too.
"shotgunning" the radio, meaning replacing all caps and some if not all resistors all at once, no in between testing, is very risky if the radio is not familiar to the technician.

Do NOT tinker in the RF/OSC circuits unless proven defective. The mica type caps in general do not fail, do not twist them to verify, disturbing the wiring in that area can make the radio fail by altering wire positions.

GL

Chas

[GarySP]

The 'safety caps' referred to are inside a bakelite case (part 69) and are connected one to each incoming AC leg and connected together to chassis ground. They should be replaced with Y caps. These are small disc caps specially designed to fail Open. In your case they are .015 mfd, and should be rated for double the line voltage. Here is some interesting reading on the subject; https://www.vicorpower.com/resource-libr...capacitors
Tutorials are available in this phorum on rebuilding bakelite enclosures. Really simple to do. Hope this helps out.
Take care and BE HEALTHY! Gary

[rolleiflex]

Awesome, thanks for the input everyone--it seems like I'm going to have to dive into this radio and take my time with it.