National SW-54 Thoughts

[jr_tech]

Likely the parts in the network are very similar to the discreet parts that the network replaced... I suspect that the Sams charts would be close.

A more basic question... as the set warms up, do you hear anything from the speaker? a slight hum would be normal also slight static as the volume control is turned up and down.

jr

[Dubis7]

Yes to the slight hum and maybe a little static, and it clicks when I switch bands, but that's about it.

[jr_tech]

So it would seem that the speaker and audio stages are at least alive... Have you tried a fairly long antenna wire, perhaps 20 feet or so, to perhaps get some signal through the converter and if stages?

jr

[Dubis7]

Okay, sorry for the delay. I work in healthcare research so things have been crazy.

Anyway, I grabbed voltage and resistance measurements. Here's the breakdown:

V1:
1: 24.5K | -9.3 VDC
2: 2.1 Ohms | 0 VAC
3: 14 Ohms | 13 VAC
4: 26 Ohms | 25 VAC
5: 16.9K | 107 VDC
6: 16.9K | 107 VDC
7: 3.7M | 0 VAC

V2:
1: 3.1M | 0 VAC
2: 1 Ohm | 0 VAC
3: 26 Ohms | 25.7 VAC
4: 37.5 Ohms| 39 VAC
5: 16.9K | 107 VDC
6: 16.9K | 107 VDC
7: 182 Ohms | 252 VDC

V3:
1: 13.7M | -.6 VDC
2: 2 Ohms | 0VAC
3: 14.5 Ohms | 13 VAC
4: 1.7 Ohms | 0 VAC
5: .657M | -2.3 VDC
6: .657M | -2.3 VDC
7: 242K | 69 VDC

V4:
1: 300 Ohms | 9.5 VDC
2: 447K | .02 VAC
3: 85 Ohms | 90 VAC
4: 37 Ohms | 40 VAC
5: 447K | 0 VAC
6: 16K | 115 VDC
7: 15K | 123 VDC

V5:
1: 16.24K | 115 VDC
2: 112.8 Ohms | 121 VAC
3: 110.3 Ohms | 117 VAC
4: NC | 0 VAC
5: 110.3 Ohms | 117 VAC
6: 15.2K | 127 VDC
7: 84.8 Ohms | 90 VAC
8: 15.2K | 127 VDC


I'm noticing a few wonky resistance measurements around the 50C5, and pins 5 and 6 on both V1 and V2. Any idea where I should be looking next?

[Dubis7]

Originally Posted by jr_tech

So it would seem that the speaker and audio stages are at least alive... Have you tried a fairly long antenna wire, perhaps 20 feet or so, to perhaps get some signal through the converter and if stages?

jr

When I first powered it on after my recap, it was pulling in a station (I have an in-home transmitter) that gradually faded away within the first few minutes of it being turned on. Whatever burned out happened within that time frame. I'm looking to get it back to that point.

[jr_tech]

Couple of observations:

There seems to be a note missing in the Sams... the ohm table shows a tag for V1 and V2 pins 5&6, V3 pin 7, V4 pins 6&7. I suspect that these resistances should be measured to the 35Z5 cathode (pin8) and not to ground. With this assumption, your “wonky” restance readings look reasonable.

252 volts on V2 pin 7 can’t be correct or the 100 ohm cathode resistor would be smoking. I would double check the voltage and resistance values at that pin, and around that tube. Perhaps the problem is related to the area around V2.

jr

[Dubis7]

Okay, I rechecked Pin 7 on V2. I wrote it down wrong.

Today it was hovering around 230 mVDC. I forgot to write down the M when I was taking notes. The resistance is measuring the same, though.

[Dubis7]

In looking at the schematic, that one may be a little too low if anything. Could that difference cause my audio to disappear?