[EdHolland]

Actually that transfomer is tapped, but probably not center tapped as you would have with push-pull out put tubes. There is a winding that appears to be used as a smoothing choke. If you replace the transformer, alternative arrangements will need to be made for the line of the supply that goes the the RF and detector circuits.

Cheers

Ed

[morzh]

Would you mind showing me the exact place where it says "centertapped"?

[captainclock1988]

Would you mind showing me the exact place where it says "centertapped"?

I didn't say it said that it was center-tapped, I was saying that by the looks of the schematic it looks like its center-tapped. 

But EdHolland answered my question in a much more polite manner.

The output transformer is Tapped but not center-tapped it seems, but the schematic and parts list doesn't specify how the transformer is tapped and what the purpose is of that tap on the output transformer.

[captainclock1988]

Actually that transfomer is tapped, but probably not center tapped as you would have with push-pull out put tubes. There is a winding that appears to be used as a smoothing choke. If you replace the transformer, alternative arrangements will need to be made for the line of the supply that goes the the RF and detector circuits.

Cheers
Ed

Thanks for the information, it seems finding a replacement transformer might be a little tricky for this radio as the specs for it in the Rider's are not given in the parts list, just some resistance readings on the schematic and that's it.

[morzh]

It is not feedback....anywho.

[captainclock1988]

It is not feedback....anywho.

What do you mean by that? 

[EdHolland]

I think what Mike is trying to say is that the extra winding (presumed for power supply choke) is not really part of the audio circuit, because it is decoupled by the large electrolytic. In some audio designs, transformer taps are used to provide feed-back of the audio signal, either to the input of the output tube, or to an earlier stage in the audio chain.

In this case, it is a good thing that your radio doesn't have that design. You will be able to use a substitute transformer that does not feature the extra winding. BUT it will require a slight rearrangement of the power supply. The wire that was connected between the extra tap and the 50 mF electrolytic (C3) could, for example be connected to the main B+ through a suitable series resistor to get the correct voltages shown on the RF tubes. Alternatively, a small choke could be used, but the choice of value would be guesswork.

[captainclock1988]

OK, so I'm replacing the filter caps in this radio. I'm wondering, could I put a 100 MFD cap in place of the 50 MFD caps, or would that be too much? 

I'm asking because that's all I could find in my capacitor stash that came remotely close to the original caps voltage and capacitance values without having to order anything.

[morzh]

Even 50 is wrong. Should not exceed 40uF.

[captainclock1988]

Even 50 is wrong. Should not exceed 40uF.

morzh, 50 MFD is NOT incorrect, that's what's in there right now, its a 3 section can that has 2 sections that are rated at 50 MFD @ 150 WVDC and then a 3rd section that is 20 MFD @ 25 WVDC, the filter cap can that's in there right now is the original unit to the radio, the Riders even calls for a 50/50 MFD @150 WVDC  and 20 MFD @ 25 WVDC.

Unfortunately there's no such thing as a 50 MFD cap anymore since they changed the capacitor rating system back in the 1970s, so the next closest thing is a 47 MFD (which I don't have on hand right now, I would have to order it) or a 68 MFD Cap (which I don't have any of those around either and those would have to be ordered too).

So either way right now the only capacitor I had on hand was the one that could replace the 20 MFD at 25V unit, which I replaced that with a 22 MFD at 63V.

But the good thing is, the place where all of the e-caps need to go are conveniently located near a terminal strip with an unused lug that ties to chassis ground so all I need to do is get some axial lead 47 MFD or 68 MFD @ 160 V e-caps to replace the remaining sections of the old can and solder the negative leads to the unused terminal strip that's tied to chassis ground and then tie the positive leads to their respective terminal leads, and that has eliminated about a foot and a half of wire out of the chassis that was used to connect the old can cap to their respective tie points, and thus cleaning up the chassis more.

Also in regards to the output transformer that I had said was "dead" it actually isn't because when I was probing around in the radio with it turned on with my DMM (the radio was plugged into an isolation transformer) I was able to get it to produce a hum, a loud hum at that, so I'm wondering if there isn't a cold solder joint on one of the output transformer primary leads and where they connect.

[morzh]

I am not gonna argue.
Look in here.

https://frank.pocnet.net/sheets/093/3/35W4.pdf
oR IN HERE
https://www.radiomuseum.org/tubes/tube_35w4.html

[captainclock1988]

I am not gonna argue.
Look in here.

https://frank.pocnet.net/sheets/093/3/35W4.pdf
oR IN HERE
https://www.radiomuseum.org/tubes/tube_35w4.html

[url=https://www.radiomuseum.org/tubes/tube_35w4.html][/url]


Well I'm not going to argue with you either, but take a look at the original Schematic! 

Westinghouse Model 1821 Service Manual.pdf Size: 246.58 KB  Downloads: 90

As you can see on the original Schematic, this radio uses FROM THE FACTORY 2 50 MFD @ 150 WVDC filter caps and 1 20 MFD @ 25 WVDC Capacitor which is precisely what's in the original filter can on the chassis, please don't try and argue with me about my radio when I have the actual service information for it in front of me.

[Greg]

You don't want to replace the two 50uF's with a single 100uF. They and the 1K resistor (plus transformer inductance) make up a PI filter (https://circuitdigest.com/tutorial/pi-fi...esign-tips, https://electronicscoach.com/pi-filter.html).

As far as the values new capacitors you get probably have a 20% tolerance (50uF => 40uF-60uF). I have to think the originals weren't any better...

[captainclock1988]

You don't want to replace the two 50uF's with a single 100uF. They and the 1K resistor (plus transformer inductance) make up a PI filter (https://circuitdigest.com/tutorial/pi-fi...esign-tips, https://electronicscoach.com/pi-filter.html).

As far as the values new capacitors you get probably have a 20% tolerance (50uF => 40uF-60uF). I have to think the originals weren't any better...

No, I wasn't talking about replacing the 2 50 MFDs with a single 100 MFD, I was talking about replacing each 50 MFD with a 100 MFD for each 50 MFD, but I was told that wouldn't be a good idea.

So I'm just going to replace them with  a 47 MFD at 250 WVDC which the Voltage rating is higher than the originals so that there is more surge voltage to work with than the originals. 

Now as for the output transformer (which apparently I had forgotten that I had figured out it was bad until I had revisited this thread the other day) I ended up ordering a Hammond P-T125J Output Transformer, because its primary and Secondary winding specs were much closer to the original output transformer's specs than the one that was suggested here (the P-T125ASE), plus it has the extra tap like the original did.
Here's the link to the transformer in question:

Hammond P-T125J Output Transformer

[David]

CEO to the marketing Department we need to sell more 35W4 tubes. Yes Sir. Production this is the marketing Dept start using 50UF & 50UF no more 30UF & 50UF this is from the top!!!  Not trying to be a wise @&$ but do what  mike suggest.