[ARC5] REAL regen receivers RAL/RAK.

[Kenneth G. Gordon]

On 8 Jun 2010 at 1:29, Roy Morgan wrote:

> 
> On Jun 7, 2010, at 11:59 PM, Kenneth G. Gordon wrote:
> >
> > I do. I have several now, one in operation, the others on  
> > "standby"....it is a really superb receiver.
> 
> Ken,
> 
>   Have I sent you my notes file on these?

I don't think so, Roy.

>  It includes the  
> modifications suggested by a fellow in Mass who's puzzled over them 
> for quite some time.

Ah! I remember him. It turned out that MOST of his problems with HIS 
RAL were internal component failures. After all, he had gotten a very 
badly abused RAL. It had been lying on its side in an open field for 
some time and was severely deterioriated.

> These changes result in a smoothly operating receiver, the way it
> should have been in 1936. Richard Brunner, AA1P   18 Juli 2003

Yes. That is who I remember.

Well, all I can say is that MY original RAL, which was essentially NIB 
when I got it, never had ANY of the problems that he ran into.

> 
> Detector:
> 1.  Change C112, 510 µµfd grid capacitor to approx. 100 µµfd.
> 2.  Change C120, C121,  51µµfd decoupling capacitors to 600-1000 µµfd.
> These changes change signals from raspy to pure dc, and keep rf out of
>  the audio amplifier.

I NEVER had "raspy" signals. It always sounded PDC, and was pure 
music to my ears, and I AM a musician.

> 
> Audio Amplifier:
> 1.  Disconnect C124, .001 µfd and C133, .01 µfd plate to ground bypass
> capacitors. 2.  Add shielding to all low-level audio leads to the
> extent  possible.  Most come out of the low-    pass filter.  Strip
> braid from old RG-58  coax.  Lift one end of the audio leads and slip
> braid over them.  Ground one end  only of the braid. 3.  Add a tube
> shield to the 41 audio output tube. The 5 or 6 feet of unshielded
> wiring caused a supersonic oscillation (33 volts at the 'phones) and
> the developers added C124 and C133 to limit frequency response enough
> to kill the oscillation.

Again, I never experienced such. I used 600 ohm Navy phones with 
mine too.

>  This is why Broad  and Sharp aren't much
> different.

Well, they most certainly were/are in MY RALs!

>  There is enough capacitance from the 41  plate to adjacent
> wiring for oscillation. (17 volts on the 'phones) 4.  Add approx 4.4
> Meg resistor from one side of the output  transformer (the side that
> doesn't oscillate) to the 6D6 grid.  Inverse feedback reduces ambient
> noise and improves linearity. 5.  Add capacitance to the 6D6 and 41
> cathode bypasses. 6.  Pull back the dc power switch and tape/insulate
> it.  Install an OC  phone jack shunted with a 1 Meg resistor.  Connect
> jack with a .01 µfd  capacitor to the 41 plate.  This gives hi-Z
> output.  The resistor is to  eliminate a big click and charging
> current when the 'phones are plugged in.
> 
> Addendum:
> Change R121, 1 Megohm 41 grid resistor to 470 k Ohms.
> RCA receiving tube manual recommendation.

Well, as I remember a follow-up e-mail from Richard, he undid most of 
those mods following his discovery of what was the original problem, 
and fixing it. I'll see if I have his e-mails somewhere here. If I find them, 
I'll post them to you.

Nonetheless, I am very grateful for your sending them to me. They will 
take some careful thinking on my part. I don't believe in modifying 
original gear. The old engineers had valid reasons for most of what 
they did. Someone on the lists used to have a "tag line" that read, "It 
may be OLD technology, but it is GOOD old technology." with which I 
heartily concur. :-)

On the other hand, we HAVE learned some valuable things since then, 
too.

Ken W7EKB