[Hallicrafters] questions on s-38 and s-38c

[Troglodite at aol.com]

In a message dated 1/10/03 9:53:59 AM Central Standard Time, 
paulrinehart at sprintmail.com writes:

> 1. my s38 has had the bfo transformer taken from it, this is t-6 which i'm 
> sure some of you are familiar. if any of you has a spare, i would like to 
get 
> my hands on it.
>  if one can not be found, i was wondering if one can be jerry rigged? from 
> the schematic, this looks to be a 455khz slug tuned transformer which 
> hallicrafters attached a shaft and knob to. would it work to get a 455khz 
> transformer from say AES, and rig a shaft to it and try to fit it into the 
> chassis and hole?

The problem with using a 455kHz transformer would be that there is no tap on 
the winding, as is required for the BFO circuit used in the S-38. On the 
other hand, a BC oscillator coil from the same source might work, if you put 
the right amount of capacitance across it.

>  2. the service instructions say that the voltage readings shoul be taken 
> with a VTVM. is there a problem with just using a regular volt meter? i 
used 
> a digital meter and it seemed to work just fine, except for my shaking 
hands 
> for fear of being fried or zapped.

A "modern" multi-meter, digital or otherwise is usually 20,000 ohms per volt 
or better. In the past, they were more like 1000 ohms per volt, which would 
seriously affect the readings. Digital meters are fine for everything except 
alignment, where you are just looking for a simple peak or dip.
  
>  3. how close to the published voltages must the readings be, rather how 
far 
> off can they be before one suspects a problem?

Unless the chart specifies the line voltage at which the readings were taken, 
they will probably all be off somewhat anyway, as this parameter has changed 
over the years. Normally, a tolerance of 20% is within reason. The voltage 
readings were met to be a rough guide to spot major problems, not to be taken 
as absolute gospel.

Bear in mind the S-38 chassis is directly connected to one side of the line, 
so be very careful when making measurements, or use an isolation transformer.
  
Doug Moore KB9TMY