The AM Forum

Wondering if anyone else has come up against a split slug in the BFO can on the R-388/51-J??

In my rig the BFO output has been low since I got it, and the last time I looked at it the top slug
is stuck, likely cracked and seized. I wanted to peak it up to get more output so I could hear SSB
without turing the aRefF gain down quite so much... I was considering chucking it entirely and
doing the product detector mod, but I am worried that it won't do as good a job as the present
detector does on AM - I have no problem with the "super modulation" guys at all! Sounds sweet.

...comments on the product detector mod??

Any really good ideas, or better still anyone who HAS ONE (either the whole can or the guts) available??
...input would be appreciated.

(anyone with an extra J-4 style Xtal filter "IF can" let me know too...!) :D

The other issue is that I really don't want to get the thing OUT and then not have a back up
position... although likely that won't happen... anyone see that Murphy guy hanging about?

                        _-_-bear

"The product detector mod" - which one?

A really easy mod uses the existing BFO and using 1/2 the 12AU7 used as the IF output cathode follower.  You need to drop the front panel to use the AM/CW switch to switch the audio from the product detector to the envelope detector.  A couple parts, a few wires, and yer done.

 the one with the 7360 I was thinkin' about... a few more wires... and solder...

               _-_-bear

Not necessary.  Use what's already in the rig.  Works Extra Fine Business OM.  No extra holes and prolly takes an hour, if the knobs come off the front panel easily.

Check any old ARRl handbook for a triode product detector, and just re-wire that cathode follower.  Feed the Beef-Oh into it thru a coupling cap, take the audio off the plate.  can't remember if I fed the Beef-oh into the grid or the cathode, and the IF signal into the grid or vice-versa.  Easy to finger out...

Ok, well then I am back to the defective BFO coil slug problem...

                  _-_-bear

The product detector mod isn't going to do you any good for AM, unless you go all out and add a PLL circuit to lock the BFO in phase onto the AM carrier.

Also, a product detector won't help a bad slug in the BFO.  If you can't find a replacement, try disassembling the coil assembly and glueing the slug back together.

Don, when not in SSB mode, afaik the product detector is switched into simple AM detector mode...

                _-_-

When I got my R-388, previous owner used Orr's article in Ham Radio Mag. to add a product detector. Changed the 6BA6 BFO tube to a 6BE6, moved some wires around, added a component or two. Unfortunately, when I got it, the change wasn't working because he accidentally bridged two pins with a sliver of solder shorting them together. Remove the bridge and now it works great on SSB.

BEAR: What is the collins number on the schematic, I mite have the coil.
Regards,
Gary...WZ1M

Gary,

I will have to look - not at the QTH right now...

you want the number off the CAN or the number off the schematic on the top cover??

                _-_-


Pete, how does it sound on AM - have you compared it to the standard R-388 AM sound??

BEAR: How about both numbers. Email me direct.
xfrmrs@roadrunner.com.
Regards,
Gary

I also did the 6BA6 to 6BE6 mod on my 51J-3 some years ago and it works great.

This basically shows it: http://www.boatanchors.org/R388sn2256pix/R388ProdDet2.JPG

Yeah, I have the original article on that one... Dallas Langford... I think in CQ Mag, not sure...

             Howz it sound on Yay Emm compared to the original detector??

                                  _-_-bear

You use the orignal detector on AM.

I'm not a fan of self-excited 6BE6 product detectors.  You need to carefully balance the IF input with the LO level so as to avoid distortion.  Also strong signals tend to pull the oscillator frequency. 

Using the existing triode in the IF output is much easier and gives a much better result.  If you insist on doing the self-excited product detector, use a 6BY6 instead of a 6BE6 - it's a little better.

Hard to beat a good old triode product detector! The lowly HW-16 has an excellent 12AX7 product detector albeit only for CW!