The Stovebolt Site Forums The Shop Area The Electrical Bay The Radio Bench Radio Restoration Help-- No sounds

Hello,

I am in the process of trying to bring a radio back to life in a 1949 truck but I can not get it to produce any sound. The radio is a Delco 986067. I bought the radio on line and have no idea of its history. All of the components inside appeared to be original with the exception of the vibrator which says "replacement vibrator" on it. Below is the steps I have taken.

1) Read the tech tip pages and searched for information
2) Replaced all of the capacitors and resistors (including the 0.006 micro farad 1600 Volt buffer capacitor)
3) Removed the original damaged speaker
4) Installed a modern speaker with two wires to hook up. (There were three wires going into the original speaker. One appeared to go to the output transformer, one to ground, and one to 6V power. The new speaker had 3 ohms resistance across the two wires. When installing the new speaker I hooked one wire to the wire coming from the output transformer and the other wire to the ground wire.
5) Removed the Vibrator
6)Powered the input lead with 6 volts and grounded the chassis using a trickle charger.
7)All of the tubes felt warm like they were heating up
8)Removed power
9)Installed the Vibrator
10) Powered the radio again

When I repowered the radio, I think I heard a very brief sound from the speaker (not positive). I could hear the vibrator humming for about 5 seconds or so. The heaters got warm. Then the vibrator quit humming. I do not hear anything at all from the speakers. The vibrator doesnt appear to be making any sounds. I rechecked the buffer capacitor and get 0.006 micro farad capacitance.

Any tips on where the problem is? Did I burn up the vibrator somehow? Was it just old so it only worked for a very short time or could I have damaged it some other way? Did I install the speaker correctly (Step 4)?

Any recommended sources for vibrators? Is there any specifications that I need to look for when buying one besides the number of prongs and the voltage it is for?

Any input is appreciated. Thanks

1866yellowboy,
congratulations on your new radio. I will try and help you along with the process of debugging your radio.

We can carry on a conversation on this forum, through PMs or email. I will leave the choice up to you.

If you have not yet done so, I would suggest that you measure the DC voltage on the pin marked "K" (cathode) of the 0Z4. It should be 250 volts. If it is much less, pull the tube and measure the Ac voltage across the two pins marked "P'. That reading should be greater than 275V.

Let me know the results.

Good luck,
Fred

Thanks Fred, I appreciate any help you can give me. If you don't have a preference I will leave the conversation here. I found a lot of useful tips along the way by searching the forums and maybe this will help someone else in the future. If you prefer we take it to PM's that is fine with me too.

I checked the voltage where you indicated and had 0 volts in both cases. I have 6 volts DC coming from the back of the switch and into the transformer.

I am assuming this is bad news and my transformer is shot. Is that correct?
I was going to try and open it up but I thought I read somewhere it was filled with rubber inside.

Thanks,
Adam

At the moment, i am thinking that you have a vibrator problem. I need to know if your vibrator is the old mechanical type or a solid state type. If it is solid state, it will say on the can whether it is for negative or positive ground.

Fred,

The vibrator appears old. It does not say positive or negative ground on the can. The can says:

Vokar quality brands
Replacement Vibrator
Universal NP42V 6-Volt
Vokar Vibrators- preferred by leading manufacturers of auto-radios
Super silent
higher output
sure starts

I would guess it is a mechanical type.

Shouldn't the transformer still have a voltage output on the P posts of the OZ4 tube

No, you will get nothing out of the transformer until the vibrator is running. So, lets test the vibrator.

You will want to use your trickle charger for this.

Remove the vibrator and hold it with pins up. Now put the larger pins toward you. Connect the negative to the large pin on your left and the positive to the small pin below it on your left. The vibrator should now buzz. If it buzzes, take a jumper and connect it to the other small pin. Touching the small pin on the left while it is buzzing with the jumper should draw a small spark or at least affect the frequency of the buzzing. If either of these tests fail, we can take it apart and probably get it working.

Fred,

When I connect the positive and negative clamps to the pins that you stated there is no constant buzz. There is a very very brief vibration right when I touch the contact and then again right when I remove the contact but it is not continuous.

I went ahead and opened the can and as you probably already know it is in fact a mechanical type.
It is pretty neat looking.


EDIT:
After taking it apart and manually moving the lever back and forth a few times it seems to pass both of the tests that you mentioned. It vibrates when power is applied as you described and when I jump the two small pins the frequency becomes very slow.

Everything looked clean and undamaged/unburnt inside so I went ahead and put it back together and tried it in the chassis again. I put in all of the tubes and the vibrator and then powered it. I could hear the vibrator buzzing pretty loudly. There was no sound output from the speaker.Side question: Did I hook the speakers up correctly?

I then measured the K post of the OZ4 tube and the DC voltage was about 8 volts DC. I measured the P post to P post voltage and it was 570 Volts AC (with the vibrator and the OZ4 Tube installed). When I removed the OZ4 tube and repowered the radio the vibrator would not work and the P-P post voltage was about 0 volts AC. Should the vibrator work with the OZ4 tube removed? It does not seem to in my radio.

Fred's gonna get ya goin here but I'll just throw this in here.
The mechanical vibrators in regular use were only good for
about a year back when they were new. While it is possible to
clean and fine tune them they are not very reliable. SS
replacements are the only way to go in my opinion.
http://www.radiodaze.com/category/19.aspx
Put it in and you won't have to worry bout it as long as you
have the radio.
Denny G

So, as Denny has stated, in the end you will want to have a solid state vibtator. However, when I rebuild a radio, I always use a mechanical unit for initial tests. If you initially happen to have a short that affects the vibrator, the solid state one will fail instantly whereas the mechanical one won't.

If you care to try and revive your old one, this is how to proceed: Undo the crimp at the bottom of the can and slide the can off the base. You can make a series of little cuts around the base and then just peel the crimp back. Now you will see a moving armature with a set of points on either side. The trick here is to try and clean between the points with paper first, then maybe sandpaper or a fine file. You don't want to bend them and mess up the alignment if possible. You can then try the test again with the cover off.

Good suggestion Fred. The SS vibrators do set you back about
forty bucks with the shipping.
Here are a few pictures of the way I've restored the mechanical
vibrators in the past:
http://www.pbase.com/dennygraham/vibrator
The tube tester is a Sylvania 225 and the vibrator adaptor is a
Sencore VB-2. Besides cleaning the contacts, they both have to have
the correct air gap and the correct spark gap and both have to
be in balance.
Denny Graham
Sandwich, IL

Thanks for the suggestions Denny and Fred. I will go ahead and get a ss vibrator ordered. Does the information below indicate a bad oz4 tube? If so I will order both.

After taking the vibrator apart and manually moving the lever back and forth a few times it seems to pass both of the tests that you mentioned. It vibrates when power is applied as you described and when I jump the two small pins the frequency becomes very slow.

Everything looked clean and undamaged/unburnt inside so I went ahead and put it back together and tried it in the chassis again. I put in all of the tubes and the vibrator and then powered it. I could hear the vibrator buzzing pretty loudly. There was no sound output from the speaker.Side question: Did I hook the speakers up correctly?

I then measured the K post of the OZ4 tube and the DC voltage was about 8 volts DC. I measured the P post to P post voltage and it was 570 Volts AC (with the vibrator and the OZ4 Tube installed). When I removed the OZ4 tube and repowered the radio the vibrator would not work and the P-P post voltage was about 0 volts AC. Should the vibrator work with the OZ4 tube removed? It does not seem to in my radio.

1866,
I forgot to comment on your speaker wiring. Yes, one speaker connection should go to the audio output transformer. The other connection is to ground. The third wire on your old speaker supplied 12 volts to the electro-magnet on the speaker. They were called electro-dynamic speakers.

The vibrator not operating without the tube is a bit of a puzzle. Normally it would operate with no tube.

For the lack of DC voltage, either the 0Z4 is bad or there is some kind of short in the high voltage circuit. If the old capacitors in the can were not changed and the old terminals completely disconnected, they could be shorting out the B+ (high voltage supply). Also, if new electrolytics were installed backwards, they would cause a short too.

I went through the wiring and all of the electrolytic capacitors are installed with the negative end grounded to the chassis. Also, all of the connections were removed from the old can of electrolytic capacitors.

When I powered the radio I looked on the teminal size of the OZ4 tube and I can see blue light inside the can.

I am thinking that the best course of action is to just buy an OZ4 tube and throw it in if I can find one online.

Thanks for all of the help

I buy my tubes, all NOS from here. Antique Elactronics Supply I think an NOS 0Z4 costs $3.40. They have your vibrator there too, negative ground, 6 volt, P-V1015N. I think they cost 29.95.

I must comment on the appearance of the 0Z4. I am rebuilding a radio at the moment, for my 38 Chev Master. It came with an 0Z4 that is quite different than I have seen before. The base starts off in metal and then there is a round almost spherical bulb on top which houses the rest of the tube. The glass is quite dark and it shows a blue flashing glow inside. It is also defective. I am guessing that this is the earliest physical version of this tube that was made.

I'd like to see a picture of that tube Fred.
Here are a couple of pictures of how I treat an OZ4:
http://www.pbase.com/dennygraham/image/131744003/large
Denny G

Denny,
I had another looks at the tube and I guess in my initial assessment of my Chev Master radio, I saw the glass version for the first time. I put it aside and didn't look at it again until this morning. The base is actually black plastic, not metal and the tube is quite small. For the first time viewing it is an odd looking tube.

I would be interested to know how you are configuring the resistors in your remake of the 0Z4.

Fred

The dropping resistors are just in series with each of the
diodes and tied to pins 3 and 5.
The diodes are tied together at the common pin 8 and the shell
to pin 1:
http://www.pbase.com/dennygraham/image/131744006
looks original when the shell is slipped back on and will last
100 years. But, if it don't, it only costs you a couple of
pennies to replace the guts.
dg

Denny,
they look like 220 ohm resistors, maybe 1 watt? I guess they help emulate the tube characteristics and limit the current through the diodes.

That looks right Fred. It's been several years since I did those
and I'm not really much of a electronics tech. Got the info
from the Antique Radio Forum some years ago and have used them
without problem. I get into these things, make it thru then put
it out of my memory. I've got it all documented somewhere but
with the move it will be years before I get it all sorted out
where I can find anything.
All I can tell you for sure is they work just fine in these
radios. You might ask about them on the ARF in the TUBE forum
and maybe the member that gave me the info can give you the
specs.
DG

Thanks Fred and Denny for all the help on getting this radio going.

I got the OZ4 tube (ordered from the site Fred mentioned above and got the tubes within 3 days of placing the order) and plugged it in. Voltage output on the K post of the OZ4 tube went from 8 V DC on the old one to 250 V DC on the new one.

Powered it up and it plays like new.

Thanks again

I have to say that a good news story like this really makes my day! Congratulations.