[Milsurplus] BC-9 Loop Test: Scratching My Head

[Hubert Miller]

People want to make it a regenerative receiver. It was never intended for AM reception. If you want to label it, it's called an 'autodyne detector'.  The bias pot sets the level of oscillation  and plate current.
If you had 2 of the SCR-77-A, the set with no dropping resistor, there is no receive-transmit offset. With 2 of these operating, just tune them 1 kHz apart
and you're in business. Much more difficult with Dave's set !! If not impossible !
I agree that some low-mu triode such as #30 might be a reasonable alternative. With socket adapter of some sort.

Dentron had a novice ham radio transceiver, the "Station One", which never reached actual production, but also had no provision for CW RIT. Depended
on the other station offset. The AN/ARC-2 is another one with no CW offset.

The redrawn BC-9 schematic needs to show B- going to the +4 battery.

Again, i would just for fun, increase the value of the plate section of the feedback ratio capacitor. But i actually think there is NO complete resolution to the problem except to revert to
the SCR-77-A  circuit.
-Hue

From: Michael Bittner [mailto:mmab at cox.net]
Sent: Saturday, February 11, 2017 5:47 PM
To: Hubert Miller <Kargo_cult at msn.com>; milsurplus at mailman.qth.net
Cc: David Stinson <arc5 at ix.netcom.com>
Subject: Re: [Milsurplus] BC-9 Loop Test: Scratching My Head.

My first 1-tube radio, at Cub Scout age, was the Electrokit #1 that had a continuously running Colpitts oscillating detector with no regeneration control.  The ease with which it could be tuned to zero-beat on strong BCB stations indicates that said stations must have been pulling the oscillator.  Tuning weak BCB to zero-beat was extremely difficult, but it worked. I have posted the Electrokit schematic along with my revised schematic of the BC-9-A at: https://photos.google.com/album/AF1QipMcbDYu2T5UqFGM1i9hArx3PweTpaeVSUhSPlPK

In order to receive CW on the BC-9, its Colpitts oscillating detector must be offset from the received frequency by an audio amount, but I don't see any control for doing this.

All of the triode grids have a slight negative bias due to the battery connections.  Increasing the R4 rheostat increases the negative bias on the RF triode.  Is this a regeneration control?

I still don't get how the controls work for transmit and receive.

Someone suggested a replica using 01A or type 30 triodes.  I was thinking of using 955 or 958A acorn triodes for a miniature version with cool factor.

Thanks, Dave for posting my schematic.  I think I've figure out how to use Google Photos now.

Mike, W6MAB


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