[MRCA] [MMRCG] GRC-9 Bias Battery

[Tim]

Hi Ray - Yep, I looked into that as well.  The designers were biasing the
3Q4 at the proper voltage to minimize AF distortion.  When properly biased
the 3Q4 is rated at 7% distortion, not biasing it makes that worse.  But as
a practical matter I can't tell the difference at low audio levels after
some experiments and data gathering.  So I bias my sets at - 4.5 V as the
tube and radio's designers intended.  I use 3 series cells taken from a 9
volt battery.  Easy, works, lasts "forever".
For my deeper dive into the GRC-9 RX bias battery effects take a look here,
about midway down the article:
https://www.n6cc.com/angrc-9-radio-set/

Have fun with your GRC-9 !
Tim
N6CC

On Mon, Nov 18, 2024 at 11:56 AM Ray Fantini via groups.io <RAFANTINI=
salisbury.edu at groups.io> wrote:

> Just started doing awork on a bunch of GRC-9 transmitter / receivers.
> Never spent much time on them before but getting an education now. The big
> question for today is the receivers bias battery, lot of stuff on line
> about this from its only there to improve audio response to it is limiting
> current in the audio output tube and absolutely necessary.
>
> It only provides cutoff voltage to the audio output tube, nothing else. I
> have seen where people have built up battery packs and all sort of stuff
> but when I look at it am going to assume it draws almost no current at all
> in normal operation thru grid current. When the radio is turned off no
> current is drawn, unless something like C54 gets leaky So why use big cells
> (AA, AAA) for this and just stuff a lithium 3.6-volt clock backup battery
> in its place?
>
> Would look a lot better than some clump of AA cells and can fit in the
> original holder. The other option is to just use the radio without the
> battery. Cannot hear any difference between the audio with or without the
> bias.
>
> Another thought, if you don’t use the battery should you jumper C54 to
> ground to prevent any positive DC voltage from developing acrost the grid
> of V6, maybe a 1.0 K resistor to keep you from grounding the grid?
>
> So, lets see what the prevailing opinion is on this?
>
>
>
> Ray F/KA3EKH
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