united-1: Chevrolet; 364441

I bought this same model radio on ebay with the intention to hopefully get it working, and then to install it in my original 1934 chevrolet standard, which has been in my family since 1960.

My radio appears to be in good condition with no apparent missing or broken parts, but like the one pictured on the website, my radio is missing the external speaker.

I see from the radio schematic on the website that the 6V power and the speaker connect to the external 6-pin male plug on the side of the radio.

Can a modern day radio speaker somehow be used instead of the original type speaker?

I've not yet put any power to the radio.  I'll first need to get a 12V/6V converter because the car was converted to 12V years ago.

 

Thanks for any insight anyone can share about how to test this radio and hopefully get it working.

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Yes a "modern" speaker of correct impedance will work on most radios, except if it uses a Field coil (this  won't) or a reed type (this won't). The two most likely options are 3 Ohms or 8 Ohms.

There are capacitors that need checked before any power is applied. In any case it would be restored on a 6V bench power supply or a fused  6V battery on the work bench.

The 6V to HT PSU needs to be refurbished with a dummy load. I haven't downloaded the circuit, but it looks like a vibrator pack. The value and voltage ratings of the capacitors in it are critical to avoid damage to the vibrator. At least one probably needs replaced.

I recently restored this Kolster Brandes GR13T, It's actually based on a 6V car radio design! So the Power supply and capacitor issues are nearly identical. If you are interested I can upload my notes on it.

So you need to obtain

• Bench 6V power supply about 5A (with adjustable current limit) or 6V battery  with fuse
• Resistors for a couple of dummy HT load for PSU.
• Speaker
• Tester for capacitor leakage
• DMM.

Steps:

• Disconnect PSU HT line from radio
• Check PSU capacitors
• Add Dummy load
• Power the PSU from 6V. There are few tricks to "wake" a sleeping vibrator pack.
• Check critical capacitors in Radio part (Plate to Grid capacitor on audio output is most critical)
• Power up with Radio instead of dummy load. Don't power up without a speaker. Use 3ft of wire as an aerial.

Please upload 933 pixel wide up to 1400 pixel high photos of your model!

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Thanks so much for the information.  I'll upload some photos this weekend so you can see what I have to work with.  I'm fairly techno savvy but am a novice on this stuff, so I'll ask for more help with explaining things, if you don't mind.

I'll get a 6V supply or a sufficient capacity 6V battery and fuse to power the radio.  I have a DMM.  What wattage and ohm resistors should I get for the dummy loads?  Please clarify what HT and PSU mean.

Does PSU by chance mean Power Supply Unit?  Is the PSU supposed to be a separate unit from the radio?  I can see from the schematic for this radio that the incoming power comes in via the box that also holds the external speaker; the external box connects to the radio with a 6-pin plug.  That external box is what I don't have, so if that is also the PSU then I don't have the PSU.

Also, what do I need to test the capacitors for leakage?  Is it something I can get at a place like Radio Shack, or will I need to go to a more hard core electronics shop?

Thanks again.

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I downloaded the circuit schematic so as to give detail advice rather than generic.

 

Speaker

The external box has also the output transformer for push pull. It's possible to cheaply use a dual 120V winding (120  & 120 intended for Europe or USA) 12VA to 20VA transformer with 6V or 9V or 12V secondary (3/4 Ohms, 8 Ohms or 16 Ohms speaker).  The original speaker did use a field coil, which I'd not noticed on a 6V or 12V radio before. It uses a coil in series with the rest of the radio instead of a magnet. You can use a regular speaker and transformer and  use a 0.5A filter choke to feed from battery.

The tube heaters add up to 2.5A @ 6.3V, but don't feed via the choke (formerly field coil of speaker), one connection is chassis/metal work.

I'd be generally suspicious of the schematic accuracy on this one.

PSU: Power supply unit.

It is in the Radio part, though often was in the speaker cabinet  on a tube car radio. The schematic is missing a connection at the "vibrator" pack of the PSU (a transformer, filter and 84 tube full wave rectifier), though there are a pair of  X in circles.

HT: High Tension, or "B+" supply. On tube radios it is anything between 45V (US Pocket sets) to 350V (UK Mains sets).

A Vibrator pack is a mechanical Switch Mode PSU. The simplest is a coil and a change over contact like a relay. When powered the coil pulls the metal reed changing the contacts. This removes the power on the coil and the reed springs back. This has a natural resonance based on mechanical construction and voltage, between 20 Hz and 400Hz. About 80 to 100Hz is common. If the contacts are across a center tapped 6V to 180V  (30:1 ratio) transformer you have AC and thus 180 0 180 approx on the transformer. This can be converted to DC either by a Metal Rectifier, Tube Rectifier, or even using a Vibrator pack with auxilary contacts. The transformer, vibrator contacts and vibrator coil are visible to the left of the type 84 tube.

An input filter on the 6V supply is 2 x 0.5uF capacitors and a choke. This partly stops interference from the car getting in, but more important it stops radiation fron the PSU reed switching getting out and spoiling radio reception. The type 84 tube cathodes connect to a capacitor, choke and 8uF capacitor as an output filter. This feeds HT / B+ line of Radio (anything from 80V to 200V, it doesn't say on schematic) and the center of the loudspeaker push pull transformer primary, middle smaller pin of plug. As the Vibrator pack isn't synchronous (uses 84 tube as rectifier) the PSU/Radio may work on positive or negative "earth" battery, but only on 6V (5.5V to 6.8V actually) unless the PSU transformer, vibrator replaced and heater wiring changed, which I wouldn't do.

 

Testing capacitors

There are two schools of thought. Test them or replace all of type 1 & 2. There are three categories:

1. Electrolytic capacitors. These are larger, 1uF upwards and polarity conscious.
2. Paper capacitors. These are typically 1nF (=1000pF, 0,001uF) to 2uF
3. Other kinds (Mica, Ceramic, Plastic Film)

See Replacing Old Capacitors (Emilio Ciardiello, Italy).

 

Electrolytic.

These naturally have 1uA to 100uA leakage, so can't be tested with a leakage tester. They also can be "reformed" if not used for many years and start to work. I use a 30V (or working voltage of capacitor if lower) Bench PSU with current limiting at about 10mA. One end of capacitor must be disconnected from radio. A DMM (meter) is used on mA (or autoranging) in series to monitor leakage. Most capacitors reform in 10 minutes (current drops from 10mA to under 100uA), but some can take more than 24 hrs. If the capacitor is still over 0.5mA (500uA) after 24hrs it's scrap. The other issue is they can dry out. Put meter across capacitor on 100V DC range and connect +30V (or working voltage if lower). If voltage drops at once to near zero when PSU disconnected the capacitor is scrap (after reforming), if it takes a second or so then the capacitor might be OK.

Never connect a capacitor to a capacitance bridge or Capacitor range on DMM or electronic capacitor meter without discharging first.

 

Paper

These are often between an Anode (Plate) of one valve (tube) and grid of a second one. Any tiny leakage is often too much and will destroy parts. You need a 180V to 300V supply limited to under 100uA to test. Some old testers have leakage mode and neon or magic eye. But you can make a tester out of a less than $8 "single use" camera (with built in flash), a 220nF ot 1uF 400V plastic film capacitor 2 x 1M resistors, a neon and a 100nF 100V Ceramic or plastic film/foil capacitor. These are often faulty and can't be "regenerated"/"reformed

The schematic suggests there is a metal box with seven capacitors (condensers) in it. These are likely all suspect.

Other kinds (Mica, Ceramic, Plastic Film)

These rarely give trouble unless mechanically damaged.

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