[ARC5] [Milsurplus] BC-230 / SCR-183 "Cheap Tube" Project Report.

[Brian Carling]

Hi David,

Very interesting update on your BC-230.

How did you conclude that hc25 crystals will overheat in a 6AQ5 oscillator? I know people who have done that successfully with a clean signal. Many of them in fact over the past 15 years. At one time we hosted a web site for a group in W1 land selling a kit with a 5 watt CW rig and they used our hc25 crystals with great success and sold a large number of the kits.

Did you try them and experience drift or what?

Best regards - Bry Carling



> On Aug 30, 2014, at 8:11 PM, "David Stinson" <arc5 at ix.netcom.com> wrote:
> 
> The project to revive BC-230 / BC-430 transmitters
> with affordable tubes and to crystal-control them without
> hacking them up has gone well.  Where some information conflicts with earlier posts,
> this one supersedes.
> http://home.netcom.com/~arc5/SCR-183/BC230s.jpg
> From left to right:
> 10109 KC Xtal CW (need meter and cover)
> 7040 KC Xtal CW
> 3890 AM MOPA.
> 
> 5763 tubes:  I finally got these to work.  The fix was so obvious and simple I should have seen it at once.
> A "gimmick" cap adding 2-3 pFd across the Neutralizing
> cap and they tame as easily as the 6AQ5s. 
> The only reason to change the bias resistors is if one wants to use the rig on AM phone with the cheaper tubes.
> If only doing CW, keep the original 20K resistor bias set-up.
> You don't need the MOD tubes if doing CW, but I did
> install them in the two sets I use for CW to keep the filament
> strings original.  The plates and grids are not connected.
> 
> Speaking of neutralizing: One neutralizing setting works for one coil set, but may not work for another, especially if you've
> had to rewind an open Neutralizing coil.  A scope or a good RF probe on a meter is invaluable in neutralizing.
> 
> Xtal Control:
> If you have a C-184 Xtal-Control coil set, it can be
> "fudged" down to 75 meters without much trouble
> but, if you have the 80-75 coil set and a proper power supply, the rig is plenty stable "as-is."
> Putting the rig on 40-meters Xtal control requires
> an FT-243 or bigger-blank crystal, a resistor, an RFC choke and either a 6.2-7.7 MC coil set or a "fudged" 5-6.2 MC set.  Little HC-25s will overheat.
> Nice, solid chirp-free note on 7040 KC.
> 
> Here are the three "finished" sets.
> If anyone wants details on how each was done, just write.
> Output measured with a calibrated scope,
> formula P =  ((Vp-t-p / 2.828)^2) / R 
> 75 Meters AM
> BC-AH-230  Aircraft Radio Corp. Ser.#62
> Order 11482-NY-36  Date 11-25-35
> 3890 KC. Original tubes (VT-25A, not the fake 801s).
> 3200-4000 KC coil set, MO tuning 2075.
> 100 pFd antenna series cap.  ANT coil tap 8 turns from bottom.  4 Watts out.
> 
> 40 Meters CW
> BC-AL-230 Graybar Ser.# 44 (Thanks, Hue!)
> Order 19070-NY-39 Date 6-20-39
> 7040 KC.  6AQ5 tubes.
> 6.2-7.7 coil set, FT-243 Xtal, Osc. shunt-fed.
> MO tuning 1537.  100 pFd antenna series cap.
> ANT tap 5 up from bottom.  7 Watts out.
> 
> 30 Meters CW
> BC-AL-230 Graybar Ser.#836
> Order 19070-NY-39 Date 6-20-39
> 5763 tubes. 10109 KC Xtal via C-184 coil set 5055 xtal doubled in final, PA/ANT coil rewound from a broken 4-5 MC PA/ANT coil, wound over the original coupling winding, 12 turns, PA tap at 9 turns from the bottom,  ANT tap 6 turns from bottom.
> 50 pFd antenna series cap.  5 Watts out.
> This one isn't really "finished."  It still chirps a little.
> Don't have another crystal to test so going to try a programmable osc in place of it.
> 
> 73 DE Dave AB5S
> 
> ______________________________________________________________
> Milsurplus mailing list
> Home: http://mailman.qth.net/mailman/listinfo/milsurplus
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Milsurplus at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html