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 Post subject: Re: Bad rectifier.......Silicon?
PostPosted: Dec Sat 09, 2017 1:01 am 
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[quote="bobwilson1977"]I worked on a Saba 300 last year, also with motorized tuning. The motor was simply seized up on mind and a bit of oil got it back up and running. In order for the automatic tuning feature to work EVERYTHING in that area of the circuit has to be perfect as its a sort of carefully "tuned" system. Replace all of the caps with exactly the same values. Whatever tubes associated with it must also test very good.

So should the tuning dial turn freely when not powered up? Right now when you manually turn the dial, you can hear the motor turn with it as if it's locked on........

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 Post subject: Re: Bad rectifier.......Silicon?
PostPosted: Dec Sat 09, 2017 10:17 pm 
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Whats the best way to replace this dual ended 0.022uf cap?


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 Post subject: Re: Bad rectifier.......Silicon?
PostPosted: Dec Sat 09, 2017 11:29 pm 
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Chop it out tidy up use two individual ones & keep them close to the chassis. One end looks like its going to chassis (ground) so there is the option (can't see the space available) to put & ground one elsewhere, but where it cant have anything induct into it.

The old one is "Outside Foil", the modern ones are not, so some do suffer induction problems, even when put where the old one was.

Marc


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 Post subject: Re: Bad rectifier.......Silicon?
PostPosted: Dec Sat 09, 2017 11:46 pm 
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addyboy wrote:
Whats the best way to replace this dual ended 0.022uf cap?

That looks like a feed-through cap, not a common part. Wires were attached to both capacitor foils at both ends of the cap body. You can confirm that with an ohmmeter.

So you connected the source end at the source, and the other end at the destination.
That guaranteed that current would flow through the cap (and get bypassed) rather than around it.

Any normal two-lead cap would work by connecting the input and output circuit ends together.

-- OR --

It might be a simple dual-section capacitor. Those were similarly uncommon parts.
This is just two independent caps in a single body. Use two separate caps as replacements.

- Leigh

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 Post subject: Re: Bad rectifier.......Silicon?
PostPosted: Dec Sun 10, 2017 12:10 am 
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Post a section of the schematic where this capacitor is located, it may be either of the two scenarios described above.

Dave


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 Post subject: Re: Bad rectifier.......Silicon?
PostPosted: Dec Sun 10, 2017 1:01 am 
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[quote="easyrider8"]Post a section of the schematic where this capacitor is located, it may be either of the two scenarios described above.


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SABA sch (1).jpg
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 Post subject: Re: Bad rectifier.......Silicon?
PostPosted: Dec Sun 10, 2017 1:06 am 
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And where is it located on the schematic?

Dave


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 Post subject: Re: Bad rectifier.......Silicon?
PostPosted: Dec Sun 10, 2017 1:11 am 
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thats a pretty bad scan.......let me post a better one

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 Post subject: Re: Bad rectifier.......Silicon?
PostPosted: Dec Sun 10, 2017 6:57 am 
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The fuzzy schematic shows two shielded 22nF caps, perhaps C48 and C68. These go from the volume control arms to the next audio grids.

You can try regular replacement caps without the shield, and see if you have a hum problem.

If needed, shields can be made from thin brass or even tin can material. You might find some hobby shop brass tubing that will fit over the caps. Aluminum foil will work, but then you have to connect the ground wires somehow.

The capacitor leads might also benefit from shielding.

Ted


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 Post subject: Re: Bad rectifier.......Silicon?
PostPosted: Dec Sun 10, 2017 11:07 am 
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Many radios use a shielded capacitor and/or shielded leads at the volume control wiper, as here.

That is by definition the lowest audio amplitude anywhere in the set.
Consequently, it's the node most susceptible to induced noise/hum.

- Leigh

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 Post subject: Re: Bad rectifier.......Silicon?
PostPosted: Dec Sun 10, 2017 3:22 pm 
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I make shielded capacitors simply by putting the cap inside a length of shrink-fit, and then a piece of braid. More shrink-fit on the outside if necessary.

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 Post subject: Re: Bad rectifier.......Silicon?
PostPosted: Dec Sun 10, 2017 4:35 pm 
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Just went and verified the pins and Ted is correct........thanks for all the help and will let you know how I get on.


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 Post subject: Re: Bad rectifier.......Silicon?
PostPosted: Dec Tue 12, 2017 9:38 pm 
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Because the originals are tucked in there tightly and there is ample room for the replacement caps away from their original tight quarters......will there be an issue having longer connections and will this help to use less or no shielding?

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 Post subject: Re: Bad rectifier.......Silicon?
PostPosted: Dec Tue 12, 2017 10:17 pm 
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You want to keep them in the original location, keep the leads short and the capacitor tucked down tight against the chassis.

Dave


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 Post subject: Re: Bad rectifier.......Silicon?
PostPosted: Dec Tue 12, 2017 10:24 pm 
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If your Saba blows the line fuse when the automatic search feature is enabled, but not when it is disabled,
you may have a shorted winding in the motor. The motor has four coils, each wound on a plastic form. If the
motor overheats, the coil can melt through the plastic form and short to the steel core... which is connected to
chassis ground. This presents itself as a dead short from B+ to ground.

This happened to me on a Saba Konstanz 8 and a little troubleshooting + 3 blown fuses positively indicted the motor.
At the time (several years ago) it was hard to find replacement parts for these motors, so I cut out the bad coil, made a new plastic coil form, and wound a new coil on it. Repair worked fine. I've since noticed that used motors and coils regularly turn up on eBay if you search the ebay.de website (ebay deutschland). I'm not 100% certain of this, but I think that the motors (and coil sets) are all the same from the 7 series through the end of tube set production (14/15 series?). The 6 series motors look a bit different but they, too, may be electrically the same.


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 Post subject: Re: Bad rectifier.......Silicon?
PostPosted: Dec Wed 13, 2017 11:06 pm 
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lorenz200w wrote:
If your Saba blows the line fuse when the automatic search feature is enabled, but not when it is disabled,
you may have a shorted winding in the motor. The motor has four coils, each wound on a plastic form. If the
motor overheats, the coil can melt through the plastic form and short to the steel core... which is connected to
chassis ground. This presents itself as a dead short from B+ to ground.


It was blowing the fuse when the automatic feature was enabled and disabled........

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 Post subject: Re: Bad rectifier.......Silicon?
PostPosted: Dec Wed 13, 2017 11:19 pm 
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That being the case; Being a transformer set, I think you need to start at the power plug & see if there is not a short Primary/ Motor side. The transformer can be disconnected as so can the motor. Lets now put the horse back in front of the cart.

Marc


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 Post subject: Re: Bad rectifier.......Silicon?
PostPosted: Dec Thu 21, 2017 11:40 pm 
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So, just finished the re-cap and a couple of issues.
No left channel......right channel is good but low output.....so I need to go back in there and check my work.
But the strange thing is no radio at all......I did have to disconnect the auto-tuning motor because it was still blowing the mains fuse and I wonder if that has a direct link to the radio functionality......will give the schematic a good read tonight.

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 Post subject: Re: Bad rectifier.......Silicon?
PostPosted: Dec Fri 22, 2017 4:55 am 
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I presume that the tuner can be operated manually: If so the dial can be swept to get a station. However, I would sort out the dud amps first, using the nearly good one for voltage references etc. Be aware of what any wave change switch is on. My next step would then be to run an IF alignment for BC to see if the IF is working.

Marc


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 Post subject: Re: Bad rectifier.......Silicon?
PostPosted: Dec Sat 23, 2017 12:24 am 
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Marcc wrote:
I presume that the tuner can be operated manually: If so the dial can be swept to get a station. However, I would sort out the dud amps first, using the nearly good one for voltage references etc. Be aware of what any wave change switch is on. My next step would then be to run an IF alignment for BC to see if the IF is working.
Marc


So found the dead channel culprit, a solder had broken off......maybe when I was putting the chassis back in?
The radio works.......yes, I have no idea why it didn't the first time......manual tuner works fine.
Just low output, should be twice as loud..........

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