I am working on a small vintage Zenith Ultrasonic Cleaner. It has a separate tank that is about a pint size and is great for cleaning small parts, as it takes very little cleaner. My problem is, I cannot get it to work at all. It has 3 tubes. One is a power amp 6CD6, one is an audio amp 6SN7 and the other has no numbers and remains a mystery. I thought it was probably an Oscillator tube of some kind and the little bit of remaining number appears to end in a 4, but I can not be sure, as it is so faint. The mystery tube is the one on the right in the picture below. I have no schematic for this machine and have been unable to locate one. When I turn it on, all tubes light and the meter reads from 150 - 200 milliamps, which changes with the tuning knob. I have no reading at the bottom of the transducer, but I do not know what I should read there. I know the connections are good on the transducer and the transducer housing, but I have no idea how to test the acutual transducer. I realize it the transducer is bad, I might as well scrap the unit for parts and be done with it, but I was still hoping I could get it going. I have tested both tubes I can verify and they are good. My next step was to try to test the third tube, if I can ever determine what it is. Any help on the tube identification, or a direction to test the machine would be appreciated. Thanks in advance for any help.

Looks like a 5R4 from here with the brown base.

A 5R4GYB in particular which has a bit higher PIV rating over earlier versions.

Now the question remains....was the original a ubiquitous 5U4 of some variety or was the HV sufficiently high to start with one of the 5R4 family?

As long as its good Id leave it alone.

Carl

definitely a duo diode rectifier as part of the power supply

it's like a 5U4 or similar full-wave rectifier.

Take care with that thing-- the voltages are high. Also you have that oil-filled rectangular capacitor which has a good probability of being full of PCB oil.

Thanks guys. I will try testing the tube first as a 5R4. If I can determine if the tube is good, I will move forward from there. Anybody know a way to test a transducer in one of these things, or is that not really feasible?

You could measure its capacitance. If it's zero that's not good.

I presume there should be a few hundred volts AC across the transducer when it's running. If there's nothing, I'd suspect the oscillator or amplifier isn't working.

What's that sitting in front of the 5R4? An HV transformer?

-Sam T.

Coil does look bit like a TV EHT transformer. Posibly used as the oscillator coil. Nearly have to trace out circuit, to fully understand the plot.

If its open that would kill it. It has what looks like a Micamold cap. I find them quite unreliable.

Marc

I believe that running it with empty tank might destroy the transducer.
When its working, you will know if the transducer is on. And I also didn't say
to dip your finger in.

There used to be a very effective solvent to fill that with.

Nailed it, Steve... that's what I came here to mention.

NEVER run a ultrasonic cleaner while empty.

also...

DO NOT HABITUALLY IMMERSE ANY BODY PART IN AN OPERATING ULTRASONIC CLEANER.

The mystery tube tested good as a 5R4, so I am sure that was the right information. Thanks for the help.

As an answer to a couple of responses, I have posted another picture that shows the HV transformer in this unit. It is not open and appears to work ok, although I have no specs on it. I have about 375vdc on the feeder side of the transformer, but the output is too high to read on the 600vdc scale on my digital meter. That is the highest scale on the meter. This transformer is definetely not original to the unit. In fact, if you look at the picture closely, you can see the outline where the original part was located in the same area as this transformer.

Marcc, the caps you mentioned are actually Sangamo mica caps, rather than Micomold. I have tested them and they test good.

The ones I wonder about are the 2 little caps that can be seen under the 6SN7 tube. The only marking or writing on them is both say - 47HV. I am thinking that might be 47mmf high voltage(?). One test at 40mmf and the other at 60mmf.

Still working to find the problem and see if I can get it going. So far all components testing good enough to at least work in some capacity.

Not the normal sort of gear we get into, but not in many areas that different to bits of radio & TV. The little caps might be SM's or Ceramic. The only real way to test them is to unsolder one end & HV test. There is also that large cap on the chassis top near the EHT Transformer. I have not had many problems with them. Some of that wiring leaves a bit to be desired: Typical of rubber. Bad wire with EHT, can flash over.

EHT is not the easiest thing to measure and requires a probe that can measure spark plug, TV voltages or a capacitive meter. I do not prefer the method of seeing how big a spark it will throw.. What is that meter measuring.

It would be nice if you could trace out a rudimentary circuit. but if there is EHT and it's a fairly simple looking circuit I a suspicious the the thing may actually be working up to and including the EHT. Sometimes those EHT transformers screemed. The only other way I see is is to place a CRO probe / frequency counter, in a safe place for it, where it can see / read any oscillation.

Did you check the continuity of the panel meter yet? Is the tank got water in while you test?

you might get a 1 to 100 ratio probe or try high voltage probe to chech high voltage , I have one high voltage probe I used to use on TV 's Picture tube high voltage lead , think it goes to 40 k volts

Thanks for the suggestion of the probe. I will see what I can find. I am close to scrapping this one for parts. I don't have a lot of money in it, I just hate to throw things away if I can get them going and I really enjoy trying. Of course, the other thing about this little cleaner is it is so handy to use, as the tank is so small and just right for a few small parts.

Steve, in answer to your questions, yes to both. I do have liquid in the tank when testing and the meter does have continuity and does read 150ma - 200ma when unit is on.