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

[n4buq at knology.net]

On Mon, 25 Sep 2006 19:05:46 EDT, Flowertime01 at wmconnect.com wrote :

> 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.
> 
> 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

Roger,

I'm not looking at the radio right now so can't check things, but I'm 
wondering about something.  With the line meter switch set to +10, the 2UV 
reading translates to 12UV.  Does 12UV correspond to 26dB (400mW)?

I've looked for a way to convert these and haven't found exactly what I'm 
looking for.  A 1000cps signal into 600 ohms at 1mW should show 0UV, but I 
don't know how to translate 12UV into dB.

As I say, with 150uV modulated into the IF deck and -7V at the diode load, 
I get 2UV with the switch set to +10; however, I only see about 15mW on the 
TS585.  Since the line meter and it's associated hardware are all wired in 
the main harness, the problem would most likely not be in the AF deck.  I 
assume I probably have something going on with the resistor network on the 
terminal board where the line out is located but not sure about that.

Any input on this?

Thanks,

Barry