[Radioroslyn]

> My biggest concern now is...will that 32 volt vibrator still work. 

Just for grins we may be able to skip the chopper for power supply testing. If we connect 32vAC or so to the primary of the power transformer it should make HV. The unknown is the frequency that the vibrator vibrates at. The AC mains are 60cy and so is are 28v transformer but the vibrator probably isn't and so the HV transformer isn't either. Most of the ones I've seen over the years where around 100-120cy. What this means is that the HV transformer won't work as efficiently at a low frequency (it has less iron in the transformer so it not so resonant at 60cy)

During WWII there was a fair amount of gear that used 115ac to power it. The catch was that it was at 400cy.They used special 400cy ac generators to power them. If you wanted to operate any of this 400cy gear it required a new power transformer. At 60cy all the 400cy transformer would do is make heat. Not too handy. But I digress.

The other issue is that the higher the frequency the less mfd you need to filter the HV output. So if you use a 60cy transformer to power the 120cy transformer there may be some excess hum as the filter cap are smaller.


As David mentions Cleaning up the contacts in the vibrator is not a bad idea. Some vibrators the contacts are coated with a harder metal tungsten I think. Smooth is better rough so if you use sandpaper make it fine grit maybe 400 and finish up with 600 or 1000G. Don't think there are any caps inside the vibrator, there in a metal box next to it. Also take note of C-15. The value is critical as it tunes the secondary of the PT and if it shorts it takes the PT with it. Both voltage rating and capacitance.
GL

[NostalgiaRadioTime]

Very useful information, Terry. I may go that route... it's always good to have a plan B! I have totally recapped the chassis and the vibrator power supply. I may let my dad take a look at the vibrator. He has a 1956 Plymouth that has a Motorola radio and it uses a vibrator. He's been rather successful at taking vibrators apart and bringing some dead one's back to life (he's done it for other owners of the same model car). I still may post an ad here just to see if anyone has a source that may have a 32 volt vibrator. It can't hurt to have a spare on hand.

[David]

   

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Good Morning will try and add two ways of building a replacement vibrator. The first one I have posted before the second is for powering a light at 50-60 Hz. You would use the transformer in the radio I do not understand how they work!!!

[NostalgiaRadioTime]

Thanks, David! All good alternatives that may very well be used.

[Arran]

 There is another alternative if you don't want to deal with the vibrator, you can bypass the vibrator supply, leaving it intact of course, build a normal mains operated power supply to generate the same high voltage that the vibrator supply produced, and feed it into the B+ circuitry of the radio. Then you will only have to deal with powering the tube heaters which are likely in a series parallel arrangement, junk computer printers and stereo amps may offer a source of a 32 (or close enough) volt transformer for this. 
Regards
Arran

[NostalgiaRadioTime]

Thank you Arran. May go that route if the vibrator can't be salvaged. Still waiting on the signal transformer. Was supposed to be delivered by the end of the day yesterday but once again UPS dropped the ball.

[NostalgiaRadioTime]

Once again, I'm reminded of why I am not a fan of UPS. For the second day in a row, my signal transformer failed to be delivered. It had a 'destination scan' at 8 am Thursday morning. It was supposed to have been delivered by the end of the day yesterday. That was amended to today's date, which I'm sure will be amended to Monday's date...if they can still find the parcel. Basically, it's been sitting at the UPS customer center 30 miles away for the past 2 days waiting to be loaded on the truck to be delivered. To add insult to injury, the UPS truck was in the neighborhood yesterday too! In my experience, Fed Ex is far more reliable. They usually beat their estimated arrival time by at least a day. Sorry for the rant...just a bit disappointed. I was looking forward to spending some time this weekend working on this power supply. Now it will probably have to wait until next weekend.

[NostalgiaRadioTime]

Unbelievable. My signal transformer was shipped from Mesa, AZ to Wisconsin on August 5th. Today, the status was updated to "Exception" instead of out for delivery. It says "We're attempting to verify the package location. / Lost package investigation" Wonderful. So the wait continues unless I can find another. Most I find are only 50VA, which may be too low. This one is 175VA.

[NostalgiaRadioTime]

Question for Terry...

I did some major digging around in the basement and actually found a transformer that measures 120V / 24V from an old furnace. It's only a 40 or 50VAC, so I was a bit skeptical but wanted to at least see if it would light the rectifier tubes. Not wanting to damage the correct value components, I connected things together per your drawing. I only had one 10000 mfd / 100V capacitor, so I went with a 100 mfd / 200V cap just to try it. Well not only did the vibrator instantly come to life, the two rectifier tubes did as well. So, holding my breath, I inserted the other tubes and they too all lit. I even got a faint station or two, albeit with a lot of interference and motor boating on one end of the dial (I did have the antenna lead clipped on to my antenna wire downstairs). The radio and vibrator power supply have been totally recapped, so I don't believe the interference is caused from that.

So my question is, how did you determine the value of the electrolytic cap on the new power supply? I thought 10000 mfd may have been overkill, but perhaps the higher value is needed to quiet down the buzz and interference?

[Radioroslyn]

What sort of dc voltage are you getting to the set? I'm try to figure if your transformer is large enough. We two possibilities for buzz. Does it sound like 60cy hum or is it a raspy sound a buzzer or a old skool electric shaver?

If it sounds like 60cy hum then we need to look at the filter in the outboard 32vdc supply. If it is a raspy sounding it's the coming from the vibrator. If the dc input voltage is low this may cause the motorboating issue. Also a good gnd  and a long ant may help. With out it may be prone to pickup is own  arcing from the vibrator contacts.

100mf is dinky go with 10K

[NostalgiaRadioTime]

I didn't do a whole lot of testing tonight...was just happy to get something out of it. But it's definitely more like an old electric shaver. It may be that the contacts need to be cleaned on the vibrator...I didn't take the shell off of it yet. There is a ground wire and an antenna wire, and I didn't do anything with the ground wire, but thinking back, it's not going direct to chassis ground. ie, I don't get continuity from the end of the wire to the chassis itself. It looks like it may a floating ground. I also didn't have the tube shields on yet, as I wanted to make sure the tubes were lighting first.

My preliminary readings...both with no load...are from the 24 V transformer I get 27 VAC out. With an 8 amp bridge retificer & 100 mfd cap I had 37 VDC.

[Radioroslyn]

I didn't do a whole lot of testing tonight...was just happy to get something out of it. But it's definitely more like an old electric shaver. It may be that the contacts need to be cleaned on the vibrator...I didn't take the shell off of it yet. There is a ground wire and an antenna wire, and I didn't do anything with the ground wire, but thinking back, it's not going direct to chassis ground. ie, I don't get continuity from the end of the wire to the chassis itself.  It looks like it may a floating ground. I also didn't have the tube shields on yet, as I wanted to make sure the tubes were lighting first.

My preliminary readings...both with no load...are from the 24 V transformer I get 27 VAC out. With an 8 amp bridge retificer & 100 mfd cap I had 37 VDC.

Need to know what the voltage is under load. No load doesn't tell any thing.

[David]

With only 100mfd you are feeding AC ripple plus DC in to the vibrator. The vibrator which should only be feeding DC square wave into the step up transformer. The output of the transformer should only be high voltage DC square wave. Your output contains some part of the AC ripple! David

[NostalgiaRadioTime]

Sorry for the delay. I ran out of time last night and then work today. So here's where I'm at tonight:

I replaced the 100 mfd cap with the 10K mfd cap and it made considerable difference. The dial lights aren't flickering anymore and I was able to pick up the local AM station, 1470 AM, loud and clear! Here are the readings I was getting WITH a load (set is ON):  24 VAC out from the transformer, and through the bridge rectifier / capacitor I got 28.3 VDC, which after the set was playing for a while dropped to 27.3 VDC.

The main issue I'm having now is below 1000 on the dial, I get nothing but a buzz. Not the same buzz like last night, this is more a steady monotone buzz, like the kind you'd get from a fluorescent light. Turning down the volume seems to decrease it a bit, but I'm only able to get the one local station. I should be able to get 620 AM WISN out of Milwaukee loud and clear on that end of the dial. The buzzing starts to lessen by 900 on the dial and is gone by 1000, but below 900 it's just buzz. The good news is no more motor boating, just buzz now.

Any ideas on what could be causing that? Terry?

[Radioroslyn]

Try plugging in a variac to the p/s and crank it up a bit to see if the lower end reception gets better with more juice. Just monitor the 32v side to be sure it's around 30-32vdc. If the hv is too low the local osc may be dyeing at the lower frequencies.