[R-390] Still wondering about the 100mV detector test

[Barry]

> Barry,
>
> The real old test from the TM is as follows.
>
> Line gain to max
> Local gain to max
> RF gain to max
> Mode to MGC
> Bandwidth to 2KC
> BFO off
> Line meter to +10
>
>
> Hang a DC voltmeter on the diode load.
> Hand a TS585 on the line output.
> (AC volt meter with DB scale and 600 ohm resistor)
> Inject about 150 micro volts of 455 with 30% modulation into the IF deck.
> Set the gain adjust or the signal generator for - 7volts on the Diode
load.
>

Okay, did this.  I got about 40mW max on the line gain; however, was able to
get +2VU with -7V on the diode load.  If I increase the IF gain to maximum,
I can get -10V on the diode load.

I switched the TS585 to the local gain and there I got over 500mW out
with -7V on the diode load.  Hmmm.  Looks like I have some issues with the
line out somewhere past the output transformer.  Probably resistors/wiring
around the back terminals.  I also have an open between the headphone jack
and the rear terminal board (haven't checked this before so something else
to fix).

Looks like maybe the IF deck is performing to specs?

> Read at least 400 milliwatt or +26 DB on the audio output.
> This should be +2 VU on the line meter scale.
>
> A good receiver will get you 500 milliwatt.
>
> This is a go no go test.
>
> You either got -7 volts and at least  .4 watt out or you have an audio
deck
> problem between the diode load and the point you are measuring (line out
or
> local out on the terminal board).
>
> 150 UV at 455 should get you an easy -10 volts on the diode load or you
have
> an IF deck problem before the diode load. IF deck problems manifist more
as
> not making signal to noise ratio than not having enough gain.
>
> If both line and local fail its the common stuff. If only one audio
channel
> fails its in that channel.
>
> All the other test are just to help narrow problems down.
>
> Any thing you read any where between the original TM and an Email today is
> subject to the same disclaimer. Errors in print do happen.
>
> Do the test and put you anxiety to rest.
>
> Your off looking at these point that change with every tube.
> Pick a point near a tube. Swap at least three tubes into the circuit and
> measure the same point with no change except to swap the tube. Wait for
the tube
> to warm up and settle down. Take a reading. If you get two tubes that give
you
> the same meter reading you are lucky.
>
> Roger AI4NI
>

I'm still concerned about the IF transformers.  It's all I can do to get
T501 and T502 to peak unless I'm really forcing the slug down to it's limit.
I'm still thinking I have some bad mica caps on those that need addressing.

I really do appreciate all this advice.  You are a wealth of knowledge on
these old radios.  I'm somewhat amazed all that is still at your
"fingertips" as I assume it has been some years since you did this fulltime,
right?

Thanks again,

Barry - N4BUQ