[bfrohwein]

Howdy!

I'd picked up a 624 to use as a parts set about 6 months ago. I just don't have the heart to destroy it. So I've started testing out things. all the coils are good and it's mostly original (sans a very old paper cap and electrolytic replacement under the chassis. tubes are good.

So I've know popped the vibrator unit open..

How would I go about testing the vibrator? What if I need to replace it? it's a 6 pin and I assume, from previous posts about vibrators it's "synchronous"? I've been perusing oldradios.com. Gary has a bunch of vibrators but I'm not sure which I might have to get and again, how to test them or "repair" them. was wondering, on a "just in case basis" if this might work... "PHILCO 38-9910 6 PIN, 6V, SYNC, 1 1/2"dia" I need some parts that gary has for another project and I need to hit the 20 dollar mark before it's, "worth his while" to fulfill my order.

the part number on the Vibrator is: 41-2015

any advice would be greatly appreciated!

Thanks a bunch!

Bret


photos, schematic, etc:

[Image: http://i1303.photobucket.com/albums/ag14...8bd1e2.jpg]

[Image: http://i1303.photobucket.com/albums/ag14...b3520d.jpg]

[Image: http://i1303.photobucket.com/albums/ag14...970c4a.jpg]

[Image: http://i1303.photobucket.com/albums/ag14...666f62.jpg]

[Image: http://i1303.photobucket.com/albums/ag14...6cb393.jpg]

[Image: http://i1303.photobucket.com/albums/ag14...666f62.jpg]

[Image: http://i1303.photobucket.com/albums/ag14...46626e.jpg]

[Image: http://i1303.photobucket.com/albums/ag14...b6a591.jpg]

[morzh]

I never looked at the vibrator schematic before. I thought it was simply the mechanical DC-AC converter and then it'd be rectified.
No! It is actually both DC-AC AND synchronous rectifier!!! Wow! Ingenious. They rectify by synchronizing the output and the input switches (using the same mechanical actuator) so they need no diodes. And because of that - no voltage / power loss.

[Mondial]

Chances are the vibrator will not be working if the radio has been sitting for many years. What usually happens is that an oxide coating builds up on the contacts which prevents operation. By carefully opening up the bottom where it is crimped to the phenolic pin wafer, you can gain access and remove the mechanism. Then clean the contacts with a thin flat file or folded 220 grit wet or dry sandpaper. This will usually restore proper operation unless the contacts are completely worn out, in which case you will need to find a replacement.

Even a NOS unused vibrator will need contact cleaning as even these are at least 60 years old and the contacts will almost certainly oxidize.

Make sure to replace the buffer capacitor across the secondary of the power transformer with the exact capacitance value high voltage capacitor. This cap acts as a snubber across the transformer and creates a tuned resonant circuit which minimizes arcing and wear at the vibrator contacts.

[morzh]

I wonder if there is any chemical way of removing the oxidation. Files an sandpaper ruin contacts and are never recommended in servicing.

I spent first 3 years of my career servicing NC systems which had lots of large relays that needed cleaning from time to time.
Sandpaper and files were not even a part of the toolkit.

[Mondial]

Normally, abrasive methods are not recommended on the precious metal contacts used on relays, but the vibrator contacts are made of tungsten alloy which is extremely durable and resistant to wear.

The only way to clean tungsten contacts is by aggressive abrasive action. The tungsten oxide is so hard that it takes a lot of effort to remove it, even with a diamond file.

Vibrator contacts are similar in composition to the mechanical contact points used in automotive ignitions of the 1970s and earlier. It was standard procedure to clean and dress these contacts with a small file, specifically called a "point file".

It is recommended that a non residue solvent cleaner be used after the abrasive cleaning to remove any remaining particles and filings from between the contacts. A thin piece of card paper saturated with solvent and rubbed between the contacts works well in this regard.

[bfrohwein]

Thanks for the tips guys. I guess I'd best get myself a 6 volt power source and start recapping. which kind of solvent should I use? is denatured alcohol fine? or maybe CRC contact cleaner? Not to be defensive.. but as a rule, I always start with the component values stated on a schematic or an updated schematic and go from there when needed. I've seen the problems with not sticking to values in critical areas demonstrated @ our little radio clubs workshops and training sessions.

[morzh]

Well, you don't have to stick to exact values especially considering that some of the values are no longer in existence or just so unpopular a cap may be $40 apiece where the popular value is $1 apiece. Just be reasonable about it. If you need 5,000pF - use 4,700pF and most likely you'll be fine.

Speaking of that cap in question, it will have some tolerance and you probably do not necessarily need 1% either but make sure you chose stable dielectric type over the temperature range, not Z5U or something. Better yet look at the cap that's there. If it is a paper type you will be fine with 5% film.

[Mondial]

Looking at the schematic, the cap in question C46 appears to be a common value .01 uF. It is important that it be replaced with a high voltage film cap of at least 1600 V rating, as it is directly across the full high voltage secondary winding and is subject to the additional switching transient spikes. Check and see what ratings are printed on the original cap.

I would hold off on replacing the small metal can cap located between the transformer and filter choke, at least until you get the radio working. This appears to be the RFI suppression cap 45 and/or 47. It is specially constructed to act as a low impedance bypass to ground for the hash noise created by the switching of the vibrator contacts. This sealed oil filled cap should be pretty reliable with only 6 volts across it and it may be difficult to find a suitable replacement.

As far as a solvent for final cleaning of the contacts, CRC contact cleaner should be fine as long as it is the type that does not contain any oily residue or silicone protectant. I have also used 91% isopropyl alcohol with good results.

[bfrohwein]

Boy I wish this schematic had voltages on it. I have straight contact cleaner but I can use the 99% alcohol (here in texas our isopropyl alcohol is 99% instead of 90-92 like most other states). so these two caps would act like an EMI supression (Y type) cap? Could I get away with just a 1600 Volt cap? hmmm .5 and 1.0 are going to be expensive. I guess I can test these metal ones on my Eico 950B. I don't get to take that out and play with it too often. it's going to be a lot of fun trying to get at the paper caps that are under the plate where the vibrator, power transformer and the dual 8 mf can sit out, re-stuffed and put back. plus it's a real jungle under that chassis.

I'm working on a little power supply for this anyhow. I have prepared myself for needing to get a 6 volt gel cell due to noise, if I can get this to work. Although, a 3 amp transformer, a rectifier, a regulator and a couple of low voltage filter caps don't cost much. I need the electronic project practice anyhow. I'm committed to this now as I just picked up a replacement output transformer for the speaker. I'm a little worried about the permanent magnet. it doesn't seem to be very strong.

[Arran]

There was one guy on the alternative forum, Curt Reed, who used to refurbish vibrators by connecting them to AC mains with a 40 watt lightbulb in series with it. He has since passed away but his posts are likely archived.
In terms of the hash capacitor is it possible to use a ceramic? Ceramic caps are easier and cheaper to find in 1 KV+ sizes?
Regards
Arran

[BrendaAnnD]

Ceramics are not a good idea for that hash filter. They tend to perforate due to the spikes.

As far as a power supply, at least for temporary test use, I've had super results using an old AT power supply on the 5V buss to run old 6V radios. Great regulation, almost no noise at all.

[bfrohwein]

I'll try the "orange drops" I guess.. I ended up building a power supply as a "fun side project" as I've somehow ended up working on 4 radios at once. I'll look for those posts. I've seen a few other posts about light bulbs searching google, no instructions, just anecdotes. maybe everyone's talking about the same person.

others have suggested searching Ebay.. I'd rather spend the money to convert it to A/C!

[bfrohwein]

It's been a while since I've posted.. the restoration is coming along. I ended up using self-healing, pulse suppression caps in the PS filter. as a fun side project, I built myself a nice little 6 volt filtered supply. the power supply is up and running well. I'm worried about what will happen should I need a new vibrator as I can't seem to locate the equivalent one that is in there. I've picked up a couple of philco universal replacements, but they don't seem to have the same pin out as the one in there.

I'm almost done recapping the chassis but I came across 1 that I need help in determining if I'm interpreting this correctly.

cap 20 & 21 is a dual .05 non-electrolytic. here's the blow up of the schematic.

[Image: http://i1303.photobucket.com/albums/ag14...a1c385.jpg]

on the original, there was a metal tap clamped in the middle which the 100 ohm cap going to the filament of the 1A4 tube. the left side when to ground. the right side goes to the I.F., Transformer.

[Image: http://i1303.photobucket.com/albums/ag14...a63db4.jpg]

and this is how I interpret replacing it

[Image: http://i1303.photobucket.com/albums/ag14...bb2b-1.jpg]

[BrendaAnnD]

You interpret correctly.

[bfrohwein]

Thanks BrendaAnn! whadya know.. I'm lernin' ;-)