Local score!

[stusnyder]

Just picked up a 1929 Grebe model super - synchrophase sk-4 plus the guy threw in a shopping bag full of nos tubes in the boxes yet!
Set is complete, cabinet needs a good cleaning.

[bandersen]

Very nice Both chassis and the speaker look to be in great condition. Is that cylinder on the bottom right a capacitor or maybe a ballast ?

[stusnyder]

actually it's a voltage regulator. I found only 1 paper cap in it, a .02 uf, replaced it. Replaced the power cord. No volume, have to check the tubes next. There's not much to these things. Cabinet I think going to have to strip...theres what appears to be yellowish - green paint overspray on it.

[Reece]

That's a wonderful radio. The chassis look very nice and I love the look of all of those silver cylinders. I'm guessing a couple of ST 45's on the lower chassis? Nice big speaker. I'll be very interested in your progress.

[stusnyder]

yea 2 45's tested bad in that section. Had 2 silvertone 45's in the boxes which is some of the tubes that came with it. They were dated by the label 1934. Tested those and were very good. Popped those in and got audio. hooked up the outside longwire and picked up a number of stations
The paint of the chassis is exellent, just needs to be gone over with a wet towel to get the dust off.

[stusnyder]

I was playing this last night, unplugged it for a few min, plugged it back in....no audio. Checked all the tubes, all light and test good. Very small amount of hum from speaker. So looking at it tonight, found what appears to be ecaps in it. Big black box ful of tar. Problem is the drawing in my riders book show no value or polarity Why are these old diagrams so vague???
Anyhow how do I figure out polarity and value?? Nothing on box, some writing on the bottom(see pic)

[bandersen]

Those big tar block caps don't have polarity. They're really just paper and foil caps potted in tar. I have a similar one in my WR8 Radiola chassis. The filter caps were around 1-2 uF.
I used Cornel Dubilier non polarized poly caps for the replacements.

[stusnyder]

yea but what kind of voltage? This thing is huge about 4" x 4" x 6"

[bandersen]

I went overkill and used 850 volt caps like this: http://www.mouser.com/ProductDetail/...aesrioxw%3d%3d

Expensive, but they'll outlast me

[stusnyder]

well I did something stupid right before it quit. For a antenna ground, I used a wire connected to the ground rod outside....the one hooked to the panel box. After that I got no audio. I put a meter across the chassis and the wire and got 60 volts...now I have no idea where to start looking....nothing obvious...any pointers? Everything lighting up but no audio...just a slight hum out of the speaker.

[Reece]

Not unusual to get some voltage between grounds, but look at the schematic and check continuity of coils in the antenna input region. Touch the grid of the first audio tube before anything: should get hum from the speaker so that your other troubleshooting progress can be heard.

[stusnyder]

I checked all the coils I could find, all checked ok. If I put a meter across the grid of the audio tubes ( the small dia pins) I get noise thru the speaker. Voltage across the large dia pins is 2.3 volts. I'm assuming thats filament voltage. These are type 44 tubes. Also across the line ballast I'm getting a output of 83 volts. So 120v on one side of the ballast, 83v coming out. Does that seem low?

[Reece]

Use one probe of your meter and leave the other disconnected. This way the probe wire becomes an antenna. Touch the probe to pin 3 (the one by itself) on the 27 tube. Should get scratching and hum, maybe a weak station (not tunable). Then proceed to the 24 tube just in front of the 27 and touch the top cap: should get noise and maybe a weak station. Keep working towards the antenna on the top caps of the 24's. If you lose noise/signal, trouble is in that stage.

If the trouble is in the very first antenna coils etc., remove your outside antenna wire and touch it to the top cap of the first 24 at the left on the schematic, then the second, etc. This will also isolate a stage.

The schematic calls for 2.5 volts at the filament windings of the transformer, so if you're getting 2.3 at the filaments of the output tubes that's reasonable and the ballast is OK. All of these tubes take whopping (for a tube) amps to light and could use a cleaning of the pins and the tube socket contacts, but first you need to get it going again.

[stusnyder]

did'nt get nothing past the first coil at the 27 tube. There was a mica across the 27, replaced it. Still nothing. right in that area are 2 tar cans, 2 sections each. replaced 1 can, now got pulsating humming. Changed the other can, got loud normal operation Funny how they can go just like that... There are a few others left in there, just going to change all of them. Thanks for your help. The cabinet is next in line.

[stusnyder]

Started on the cabinet. Some moron spray painted the cabinet a pukey green color You can see the tell tale spray can lines. I stripped the top. This is what I found under the paint.