Sender Resistance Testing
I sent a copy of my testing results to Jacques Fortin the other day and he provided me with some very useful feedback.
First, he pointed out I had missed a couple of resistors in the V1J and V5D circuits I was looking at (R29B and R47C). I am on the hunt for them now and will report back on what I find.
The second issue he brought to my attention was regarding the results for R12A and R31D. Both of these resistors were quite different from one another but both tested 8 Ohms. I thought that was odd at the time…end of story. However, Jacques brought to my attention something I had missed in the Circuit Diagrams.
These two resistors are both serving as Feedback Voltage Dividers: R12A on the Primary of Transformer T2A and R31D on the Tertiary of Transformer T3A. As such, they are wired in parallel in these two circuits, so it is not possible to get an isolated Ohms reading from them just by putting your VTVM probes either side of the resistor body. In doing so, the meter reading is biased by the transformer. You need to disconnect one end of the resistor from the circuit involved to get a pure reading of the resistor. Both of these resistors are a bear to get at, so I have decided I will simply replace both resistors outright. Do tricky work once and be done.
The other really nice bit of information from Jacques, was that he took the time to document the best current resistor equivalents that I could use to replace each of these older components. This was something unexpected, but invaluable for me. I simply do not do enough regular electronics work to be comfortable substituting modern resistors for older ones. Bumping up the wattage rating to get a resistor of correct Ohms is one thing and I have done that just fine in the past with 1/4-watt resistors. Modern ones look way too small in a piece of vintage electronics and the leads are always far too short to cover the distance between Panel Tags in a 52-Set in any event. But I am just not comfortable going to higher Ohms ratings for any given circuit. I worry too much I am going to buggar things somewhere down circuit.
Other than that, so far so good.
David
|