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 Post subject: silvertone 4465 radio
PostPosted: Dec Sun 10, 2017 11:35 pm 
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Location: A0E 1K0 NL Canada
I have a silvertone 4465 radio with chassis 101 410 that I have recapped and now have the radio working but power transformer is over heating . Just wondering what would cause this . Thanks from a0e 1k0 nl Canada.


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 Post subject: Re: silvertone 4465 radio
PostPosted: Dec Sun 10, 2017 11:48 pm 
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How hot is your transformer getting? After an hour of use, it may be getting uncomfortably warm to touch, and that's OK. If it's getting hotter than that, or heating up more quickly, then there is a problem.

One way to check whether the problem is the transformer itself or the load being placed on it by the radio is to pull out the rectifier tube (5Y3). If you turn on the radio with the 5Y3 pulled, the transformer should stay very cool. If it still gets hot, there is one further check (pull all the remaining tubes). If it still gets hot after that, then the transformer is most likely bad (or possibly a short in the transformer wiring under the chassis).

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 Post subject: Re: silvertone 4465 radio
PostPosted: Dec Sun 10, 2017 11:50 pm 
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6N6G tube may be drawing too much current? Measure voltages as shown in Rider. If they are low this tube may be drawing too much current.

Hope you replaced electrolytic filter caps, C27 and C28? These caps need to be rated 450 volts or more. Voltage shown as 360 will be higher during warmup.

http://www.nostalgiaair.org/pagesbymode ... 017053.pdf

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 Post subject: Re: silvertone 4465 radio
PostPosted: Dec Sun 10, 2017 11:51 pm 
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The transformer will start to melt the wax in it after ten minutes. I will do the tube test tomorrow . Thanks.


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 Post subject: Re: silvertone 4465 radio
PostPosted: Dec Sun 10, 2017 11:54 pm 
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Yes Norm I have the filter caps done .I used a 33mfd for the 25mfd and a 22mfd for the 18mfd 450dcv . But I do not have the riders schematic , but I now see what you have posted.. All I used for schematic is what was on inside cabinet.


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 Post subject: Re: silvertone 4465 radio
PostPosted: Dec Mon 11, 2017 3:29 am 
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are both legs of the HV within 5 volts of each other ?

if not, that may indicate a transformer that is on its way south.

steve

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 Post subject: Re: silvertone 4465 radio
PostPosted: Dec Mon 11, 2017 10:22 am 
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Do you mean that when the voltage readings are done on each hv winding that the difference is more than 5 volts apart.


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 Post subject: Re: silvertone 4465 radio
PostPosted: Dec Mon 11, 2017 10:59 pm 
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Pulled tube 5y3 and it still got warm .Also checked voltage on tube 6n6
pin p next to h has 258 dcv
pin p next to g has a voltage that is constantly changing from 278 to 312 dcv


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 Post subject: Re: silvertone 4465 radio
PostPosted: Dec Mon 11, 2017 11:49 pm 
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On the schematic posted, it has a voltage chart: refer to it. I see areas where things can go wrong. That is a back biased set. If the back bias 2 by 18 Ohm is shorted out the set will overload. Overloading fries transformers. The voltage across those resistors will give its current draw.

In my book the filter caps especially the first one should be 600V and C33 may have failed (punched through). C33 on that schematic says 16uF increasing that to 33uF is too close to the limit for a 5Y3. Increasing C33 value will also cause it to generate a higher voltage & the set will draw excessive current and again the transformer risks peril and stress. I will not use under 500V caps with a 5Y3 / #80.

The other thing is a bad heater doing a make & break. With a big swing I would suspect the OP tube. Other caps & resistors can also do that. Caps can get to a certain voltage, discharge & then repeat the act. Similarly I have seen a 500V get to 470 & then start conducting at a hyperbolic rate: New does no mean good.

I as said, I am obliged to insulation test the primary side (regulations). So that means if I do not like the look of a transformer I will lift wires so that I can insulation test between all windings and ground and winding to winding. I think you need to put the Electrolytics back closer to spec. & perhaps totally unload the transformer (pull the 5Y3 & all tubes & dial lamps) and see what temp it gets too. Perhaps even leave an analogue meter hooked to the HV Secondary. If you connect Plate to Plate of the 5Y3 socket (pins 4 & 6) the voltmeter has to be able to withstand 1KV AC, or more.

Marc


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 Post subject: Re: silvertone 4465 radio
PostPosted: Dec Tue 12, 2017 12:16 am 
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What you said is not clear, but if the transformer is overheating without the rectifier tube, there is no need for further testing with that tube installed. Doesn't matter what your DC voltages might be.

Usually, in such cases, the transformer itself is the problem, but you can check to see if some secondary is overloaded. Try it without the rest of the tubes. A last resort is to try disconnecting (and insulating) the transformer secondaries and see if it still overheats.

It might be good to measure the AC Line current into the transformer. Dim bulb tester might be a good idea. Certainly a line fuse is indicated.

Ted


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 Post subject: Re: silvertone 4465 radio
PostPosted: Dec Tue 12, 2017 1:22 am 
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First Marcc you are looking at the wrong chassis schematic, has I posted in the beginning and also Norm pointed out that the caps are c*27 c-28 and are 25 and 18 mfd has I stated earlier. Also I now have two opinions on removing tubes and checking pt. Also I do not understand the back bias resistor you have mentioned.


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 Post subject: Re: silvertone 4465 radio
PostPosted: Dec Tue 12, 2017 2:19 am 
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Agree with Ted. Test with all tubes removed (will rule out the unlikely problem of a filament short in one of the tubes). Then as a last desperate measure completely disconnect all secondary winding wires from the radio. If it still overheats with just the primary connected, the transformer is the problem.

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 Post subject: Re: silvertone 4465 radio
PostPosted: Dec Tue 12, 2017 2:24 am 
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Will pull all tubes tomorrow evening and try. But what is this bias resistor Marcc was talking about.


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 Post subject: Re: silvertone 4465 radio
PostPosted: Dec Tue 12, 2017 2:29 am 
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With the 5Y3 pulled, the bias resistor is not a factor.

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 Post subject: Re: silvertone 4465 radio
PostPosted: Dec Tue 12, 2017 2:30 am 
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Perfect thanks.


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 Post subject: Re: silvertone 4465 radio
PostPosted: Dec Tue 12, 2017 3:00 am 
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On the circuit Norm posted which I assumed was the right one. The centre tap of the HT is taken to ground / chassis by two eighteen ohm resistors R18, R19. Where the CT is floated like that it is back biased.

As all of the cathode current passes through those resistors, that voltage across them is produced by the current flow. That tells you what current the set is drawing. The bias on the OP tube for one will not be right if
that voltage is not correct

Correct: Pulling the 5Y3 cuts of the secondary AC & you only have open circuit volts. To insulation test to HV winding to ground, the CT has to be lifted. There will be no DC. produced but B+ has to be disconnected to test 5V winding (and I have seen one shorted)


Marc


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 Post subject: Re: silvertone 4465 radio
PostPosted: Dec Tue 12, 2017 4:26 am 
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spsquires wrote:
Do you mean that when the voltage readings are done on each hv winding that the difference is more than 5 volts apart.

with all tubes removed, take a voltage reading from the center tap to leg one of the HV. then, do the other.

both readings should not be further apart than 5 volts of each other.

for example: 375-0-379 or closer--good. 375-0-380 or more, be concerned that the transformer is shot, although the radio can still "work" as the transformer will eventually mess the bed.

i've seen this a few times.

steve

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 Post subject: Re: silvertone 4465 radio
PostPosted: Dec Tue 12, 2017 8:45 am 
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Dutch Rabbit wrote:
spsquires wrote:
Do you mean that when the voltage readings are done on each hv winding that the difference is more than 5 volts apart.

with all tubes removed, take a voltage reading from the center tap to leg one of the HV. then, do the other.

both readings should not be further apart than 5 volts of each other.

for example: 375-0-379 or closer--good. 375-0-380 or more, be concerned that the transformer is shot, although the radio can still "work" as the transformer will eventually mess the bed.

i've seen this a few times.

steve


Steve, this test is not needed if the xfmr is getting warm with the rectifier out. Pulling the other tubes is a rarely needed double check, but worth trying. The only other issue is a possible short in the filament windings, including the pilot bulb sockets. Worth checking that but again, rarely an issue except with bad rubber wire used in some radios mainly 1938-1942 era, and the Atwater Kent radios 1928-1936. A few others suffer that bad wire too after WW2 but rare.
Be sure to start with a room temp xfmr. It should STAY about room temp after 15 mins of running with just the rectifier removed. This is the first test to do with ANY transformer powered radio.

Mark Oppat


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 Post subject: Re: silvertone 4465 radio
PostPosted: Dec Tue 12, 2017 10:05 am 
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The wire on this radio is in a bit rough shape , so do you mean wires from pt or any wire at all.


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 Post subject: Re: silvertone 4465 radio
PostPosted: Dec Tue 12, 2017 11:12 am 
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With all tubes pulled it went to 48 degrees Celsius in 15 minutes.


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