Dove right in! Help with RCA 21-D-8628

[old_coot88]

Originally Posted by BandDirector

Top 3:

Tan (right 11)
& Yellow Green (7)
=44.6 ohms

Tan 3
&Yellow Green 7
=26.4 ohms

Tan 3
&Tan 11
=18.4 ohms

Lower:

Tan 2
&Black and Yellow 4|
=.1 ohm

Black 1
& Black and Yellow 4
=.6 ohm

Yellow Green 5
&Yellow 6
=.1 ohm

Black 10
&Yellow Black
=.4 ohms


The numbers reflect a left to right order, they have been paired according to continuity and ohms.

So next step is to apply power to the lowest ohm pairs? Then measure output voltage?

Nooooooooooooooo please !! Don't apply mains power to anything yet.

First off, the three tans (on top) would be the center-tapped hv secondary (one side is higher ohms than the other because there's more wire per turn with increased radius of the outer winding layers). And sorry, my guessitimation of ohmic values was quite a ways off.

The .6 ohm pair is probably the primary. That's where you'd apply power. But for starters, only through a variac or a resistive load like an incandescent light bulb.

[old_coot88]

Lacking a variac or a resistive load, what you could safely do is this - apply mains power to half of the hv secondary. The whole xfmr will then be in step-down mode. The voltages coming out of the other windings will be a given percentage of their normal values, probably around 20 - 30% or so. Allowing for the step-down factor, it'd be easy to identify which winding is which.

[Kevin Kuehn]

Originally Posted by old_coot88

First off, the three tans (on top) would be the center-tapped hv secondary (one side is higher ohms than the other because there's more wire per turn with increased radius of the outer winding layers).

Normally I would expect more like 2-3 ohms increase for radius on the center taped HV windings. 8-9 ohms difference would indicate a lot more turns.

[old_coot88]

Originally Posted by Kevin Kuehn

Normally I would expect more like 2-3 ohms increase for radius on the center taped HV windings. 8-9 ohms difference would indicate a lot more turns.

True that. But I still think it's worth putting mains voltage on half of the hv winding, record the other windings' readings, then put mains voltage on the other half, and see if the readings are the same. Also see if voltage out of the unconnected half remains the same both ways.

Real hillbilly troubleshooting

See pictures. I used a RCA Senior VoltOhmyst

Perhaps seeing readings on a VTVM will make the readings easier.

I am about to tackle the RCA UHF tuner and see how to ground up see how something works. I still haven't found a radio to work on. My grandmother has a tube radio intercomm so I may be pulling that out of the wall. Yep. Pulling it out.

[old_coot88]

That's a timeless and venerable piece of gear. Are you zeroing the meter for the ohms measurements?

Originally Posted by old_coot88

That's a timeless and venerable piece of gear. Are you zeroing the meter for the ohms measurements?

I did before I ran the series of tests. I downloaded the manual/schematic Wednesday when it arrived. I followed the process to 'tune' it and I have only two days experience with it. The ac/dc probe came today, from a B/K unit, just a random eBay find. I have just begun this whole process in a random way. I don't really now what tools to assemble, so it is just a scavenger hunt as I make small steps. I don't even know what to call the probe's connection to the chassis, a screw type sort of coax?

I love the whole nature of this ordeal and I am hell-bent. Just need to stay calm.

Tools I have:

CRT tester
RCA Senior vtvm VoltOhmyst
B/K solid state 2-channel oscilliscope
B/K Dynascan 1070 (does not have test pattern)
RCA Bias Supply
HP VHF signal generator

Projects:

1957 RCA KCS116C 21"
Rangeaire AM/FM tube radio from 1964 - learning project radio

I have been told to put the tv chassis components back together, and to find a compatible transformer. A smaller project was advised to first tackle how to restore a tube electronic, hence the Rangeaire.

Problems:
I do not know how to measure resistance in ohms, therefore it will be difficult identifying the resistors I removed from the tv chassis.
I know how to callibrate the vtvm via the RCA manual.
I know how to setup the oscilliscope via the B/K manual.
I do not know how to measure a capacitor using my DMM, even assuming the cap is dead, I cannot pinpoint whether my reading is accurate. Therefore I cannot accurately place the old tv caps unless I can trust what is written on each one. They are clearly marked with volts and +- % for identification.
The tv crt is rated good.
The Rangeaire radio does work, a little low on volume but it does work. I can study and test the caps and resistors, tubes, and voltages to learn AC/DC measurements.

Now what?

Mimi's Rangeaire Intercom AM/FM radio

No wires or components have been removed. This unit works well, except that all intercoms in the bedrooms and door have bwen removed. The master bedroom com no longer works, the door com speaker may still be behind the grill outside, however it has not worked in my memory. This will not be missed, and when restored, will be saved as my own intercom system for later in my own home!.