[R-390] Tracking down low sensitivity 0 to 8 mhz problem

[Larry H]

Hi Jordan,  Sorry, I misunderstood.  When you measure DC in an active
circuit (such as E402) on the control grid or plate, any vtvm you use will
load or detune the circuit (unless the probe contains an isolation resistor
of appropriate size (1 Meg Ohm - 5 MOhm)), one will need to be added and
used right at the test point.

For the variable IF's, the books are all good for that.  But, since your
problem is below 8 MH, the 2nd var IF and mixer should be good as is.

Regards, Larry

On Sat, Apr 13, 2024 at 9:51 AM Jordan Arndt <Outposter30 at shaw.ca> wrote:

> Hi Larry...
>
> I was actually referring to the 1st and 2nd variable IF alignment, not the
> alignment of the IF deck. I should have added the "variable" to my question.
>
> I may have to break out my 50Meg VTVM to check E402, because my 10 Meg DVM
> and 10 Meg FET VOM kill anything appearing at E-402 when I try to measure
> the voltage at that test point...
>
>
> 73...Jordan VE6ZT
>
> ----- Original Message -----
> *From:* Larry H <larry41gm at gmail.com>
> *To:* Jordan Arndt <Outposter30 at shaw.ca>
> *Cc:* Collins R-390 HF Receiver List <r-390 at mailman.qth.net>
> *Sent:* Saturday, April 13, 2024 9:21 AM
> *Subject:* Re: [R-390] Tracking down low sensitivity 0 to 8 mhz problem
>
> Good questions, Jordan.  I use a vtvm that has 11 Meg Ohms input
> resistance, but 10 M Ohms should be good enough.  For a probe that fits
> snugly into E208 - E211 and E402, I use a piece of solid copper wire #16
> gauge about 4.5 " long that has about 1/2 " of insulation removed on both
> ends.
>
> For the 1st and 2nd IF alignment, I assume you are referring to the IF
> deck.  See my post that follows that is also at the end of the 'IF Deck'
> section in the Pearls.  It is important to not straight tune an IF deck
> that was designed to be stagger tuned, as the gain may be too high to
> correctly adjust the IF gain R519 for correct operation of the AGC and
> carrier level meter.
>
> Regards, Larry
>
>