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 Post subject: E-cap wiring Silvertone 1906
PostPosted: Mar Sun 04, 2018 7:10 pm 
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Posts: 717
Location: Elko, MN.55020
Have been looking at a Silvertone model 1906 and have a question about the wiring of the 2 e-caps C-9 and C-20.
From what I can read on the schematic, C-9 positive is wired to pin K on the 84 tube, and C-20 positive is wired to the same pin.
Negative on the C-9 is wired to the speaker socket and neg. on the C-20 to chassis ground?
When I fire it up, tubes light, but no audio.
Checked voltage on the 84 tube and I have nothing on the K pin where the e-caps are wired to.
Have over 300V on both (P) pins.
What did I do wrong?
Radio did not play before I replaced the 2 E-caps so I don't know if I wired it wrong or what.
Thanks for any help.
murf


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 Post subject: Re: E-cap wiring Silvertone 1906
PostPosted: Mar Sun 04, 2018 7:27 pm 
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Location: Livermore, CA
murf

Cathode on a rectifier should have DC voltage. If plates have AC, filament lit and nothing at the cathode the 84 tube is bad. Sometimes you can see the internal cathode wire broken with a small ball of metal at the ends. This was caused by excessive current.

Be sure nothing is shorted at the cathode or another 84 tube will burn out.

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 Post subject: Re: E-cap wiring Silvertone 1906
PostPosted: Mar Sun 04, 2018 7:39 pm 
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Joined: Jan Wed 11, 2012 4:21 pm
Posts: 717
Location: Elko, MN.55020
Wow,
Fast reply.
Want to verify that they are wired correctly before I try another tube.
I did test it before I started and tested OK.
I will test it again.
Thanks Norm.
Murf


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 Post subject: Re: E-cap wiring Silvertone 1906
PostPosted: Mar Sun 04, 2018 7:57 pm 
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Schematic link??
Phil

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 Post subject: Re: E-cap wiring Silvertone 1906
PostPosted: Mar Sun 04, 2018 9:32 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Livermore, CA
http://www.nostalgiaair.org/pagesbymode ... 016804.pdf

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 Post subject: Re: E-cap wiring Silvertone 1906
PostPosted: Mar Mon 05, 2018 1:21 am 
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Joined: Jan Wed 11, 2012 4:21 pm
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Location: Elko, MN.55020
Looked at the tube tonight and I am not sure I am seeing what Norm is talking about.
Tube tests good, center filament is lit, but not sure what I am looking for as far as the burned off wire.
Sorry for the confusion on my part.
murf


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 Post subject: Re: E-cap wiring Silvertone 1906
PostPosted: Mar Mon 05, 2018 2:53 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 37069
Location: Livermore, CA
If you have 300 AC on each plate you should have high voltage DC at the cathode. Be sure the 84 filament lights when it's in the radio. Is your 1300 speaker field open?

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 Post subject: Re: E-cap wiring Silvertone 1906
PostPosted: Mar Mon 05, 2018 3:02 am 
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Your 8mfd 350v filter cap should go between the 84 filament and the HV center tap.

You MUST have DC voltage across that capacitor unless there's an open or broken wire.

The second filter cap, 8mfd 250v, is on the other side of the speaker field coil.
You might not have DC voltage there if the field is open or wiring is open.

- Leigh

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 Post subject: Re: E-cap wiring Silvertone 1906
PostPosted: Mar Mon 05, 2018 4:15 am 
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Joined: Jan Wed 11, 2012 4:21 pm
Posts: 717
Location: Elko, MN.55020
Thanks for all the help guys.
Will check DC voltage tomorrow.
All tubes light when powered up.
Did the quick battery test on the speaker and did get the wanted scratching noise.
How can I check the field? The C20 positive is connected to the same pin on the 84 tube as the C9.
Is this right? C20 neg is attached to chassis.
Sorry I am not up on the technical lingo, but its just a fun hobby for me.
Will let you guys know what I find tomorrow.
Thanks a million,
Murf


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 Post subject: Re: E-cap wiring Silvertone 1906
PostPosted: Mar Mon 05, 2018 9:26 am 
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murf wrote:
The C20 positive is connected to the same pin on the 84 tube as the C9.
Is this right? C20 neg is attached to chassis.
Hi Murf,

That's correct for both leads of C20.

- Leigh

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 Post subject: Re: E-cap wiring Silvertone 1906
PostPosted: Mar Tue 06, 2018 3:06 am 
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Joined: Jan Wed 11, 2012 4:21 pm
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Location: Elko, MN.55020
Well, update for today.
Checked voltage on the C9 e-cap and it reads about 250v. Have same reading on the 2 hot pins on the 84 tube.
Funny thing is that I noticed before I started anything that the paint was bubbling off the 400 ohm 1watt resistor R12 as if it had been hot.
Tonight after having it powered up for a few minutes, that resistor started smoking. Paint burning off.
I did notice that I could hear a humm coming from the speaker.
I think that is a good sign.
Still not sure about that 84 tube. Does test good.
Any ideas


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 Post subject: Re: E-cap wiring Silvertone 1906
PostPosted: Mar Tue 06, 2018 4:12 am 
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Location: Livermore, CA
You are past a problem with the 84 tube. Tube is supplying voltage.

Too much current is being drawn. This in turn would cause the 400 ohm resistior to burn. Positive on electrolytic caps go toward left in schematic. If reversed it would act similar to a short. Caps are best rated at 450 volts.

Be sure C19, .003mf has been replaced. Also C18, .02 mf. Either of these shorted/leaky will cause too much current to be drawn.

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 Post subject: Re: E-cap wiring Silvertone 1906
PostPosted: Mar Tue 06, 2018 6:18 am 
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Joined: Jan Wed 11, 2012 4:21 pm
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Location: Elko, MN.55020
Norm,
Did replace both of those caps. They looked like they had got pretty warm before.
Definitely getting too much power thru that resistor.
Replaced that 400 ohm 1 watt with a 40 k 1 watt resistor and now I have no hum thru the speaker.
Noticed the wiring from the transformer top side that runs thru a grommet to the underside is loosing all its insulation.
Don't see anything shorting yet.
Can I remove the side cover from the tranny and splice in some new wires?
Looking more and more like a donor chassis.
murf


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 Post subject: Re: E-cap wiring Silvertone 1906
PostPosted: Mar Tue 06, 2018 6:26 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 37069
Location: Livermore, CA
murf

40K would drop too much voltage. To prevent burning while testing resistance should remain the same but wattage increased. That's still not the best way to troubleshoot.

Be sure electrolytic caps aren't reversed.. In this radio you can remove all tubes except the 84 and see if you have voltages without burning the resistor.

Unless obvious shorted I wouldn't remove the transformer cover.

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 Post subject: Re: E-cap wiring Silvertone 1906
PostPosted: Mar Tue 06, 2018 10:31 pm 
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Joined: Jan Tue 16, 2007 7:02 am
Posts: 2663
Location: Lexington, KY USA
You can use spagetti tubing over the transformer wires to avoid extra solder joints. Heat shrinkable is fine. You can get colors to more or less match original wire colors. Probably still need to take the cover off the transformer to get the tubing slipped over the full wire length.

Measure the DC voltage across the resistor that is getting hot.

If the resistor is getting hot, best not to power the set for very long at a time until this is fixed. Excessive current can harm more than the resistor.

If you have a variac, this could be used to reduce the fault current while you troubleshoot.

Ted


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 Post subject: Re: E-cap wiring Silvertone 1906
PostPosted: Mar Wed 07, 2018 12:18 am 
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Joined: Jan Wed 11, 2012 4:21 pm
Posts: 717
Location: Elko, MN.55020
Used shrink tube on the tranny wires and it brought the ac voltage on C9 up to 350v.
Still no audio though.
What can I use to to replace the 400 ohm 1 watt resistor?
I thought the 40k 1 watt would work? Silvertones are too problematic for a rookie like me.
Stick to Zenith, RCA, and just about anything .This one has me pulling my hair out.


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 Post subject: Re: E-cap wiring Silvertone 1906
PostPosted: Mar Wed 07, 2018 12:27 am 
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Posts: 33580
Location: Maryland 20709, USA
murf wrote:
What can I use to to replace the 400 ohm 1 watt resistor?
I thought the 40k 1 watt would work?

The 40K resistor is 100 times too large.

Use a 400-ohm 1 watt resistor.

Mouser has four different ones in stock from $1.58 to $2.74 each.
I see no particular advantage to one over another.
https://www.mouser.com/Passive-Componen ... z3Z1z0x89a

- Leigh

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http://www.AtwaterKent.info
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 Post subject: Re: E-cap wiring Silvertone 1906
PostPosted: Mar Wed 07, 2018 2:36 am 
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Joined: Jan Wed 11, 2012 4:21 pm
Posts: 717
Location: Elko, MN.55020
Understood Leigh,
Looked at the conversion table and it is .4 k. OOPS.
Just have to figure out why the 400 ohm resister was getting hot to the point of burning the paint off.
Apparently the transformer wires were overheating too.
Insulation was practically melted off the wires
Maybe I will install the old 400 ohm resistor. It still checks within specs.
murf


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 Post subject: Re: E-cap wiring Silvertone 1906
PostPosted: Mar Wed 07, 2018 4:15 am 
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Location: Maryland 20709, USA
Hi Murf,

The 400 ohm resistor (R12) is between the speaker field coil and ground (via 22 ohm R13).

I cannot figure out any mis-wiring or excessive current that would cause R12 to overheat.

One gross wiring error would be if the speaker field was connected in series with the B+ line rather than being in the HV center tap line to ground.

This radio uses filtering in the negative supply lead rather than the positive lead.

- Leigh

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http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


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 Post subject: Re: E-cap wiring Silvertone 1906
PostPosted: Mar Thu 08, 2018 3:04 am 
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Joined: Jan Wed 11, 2012 4:21 pm
Posts: 717
Location: Elko, MN.55020
Put the old 400 ohm resistor back in and now have the hum back, though faint.
Gonna try to sleeve the power tranny wires to eliminate any possible shorts.Will have to get back to you guys.
Thanks for all the advice.
murf


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