[Milsurplus] RAK AND RAL

[Richard]

RBL instability:  Ah - I didn't notice that, and stand corrected, Anyway 
it's an easy fix.

RAK/RAL supply voltage input circuitry:  Yes, but in my RAL I removed it 
to put an AF volume control in the hole.  Both RAK and RAL have 
capacitors connected plate to ground in the AF stages to roll off audio 
response above 1300 cycles.  This is needed in the RAK, but not in the 
RAL, so I removed them, which greatly increased AF gain, and  had a 
vicious supersonic oscillation with 33 volts across the phones.  This 
was due to about five feet of unshielded low level AF wiring; I lifted 
one end of each wire and put on shielding from RG-58 coax, which reduced 
it to 17 volts, which was due to the 41 output tube "looking" at nearby 
low level wiring. Added a shield to the 41 and now it's great for SSB 
and not bad for AM.  SSB actually sounds better than on any modern 
receiver I've used.

Richard, AA1P

On 07/22/2016 01:04 PM, Kenneth G. Gordon wrote:
> On 22 Jul 2016 at 5:30, Richard wrote:
>
>> The RBL is an excellent receiver, as good as the RAK,
> Well, having used both over an extended period, I have to disagree with you, Richard. The
> RBL has many advantages over the RAK, but stability is NOT one of those.
>
> The RAK (and the RAL) have a voltage-regulated detector stage, while the RBL has no
> voltage regulation anywhere.
>
> When using the RBL to monitor the Navy VLF stations back in the 1970s, it became very
> apparent that even slight line-voltage changes caused very obvious frequency changes with
> the RBL, while the RAK never moved.
>
> The stability of the RAK/RAL is outstanding.
>
> In fact, some time ago, I designed a special circuit to enable voltage regulation of the
> detector stage of the RBL which would, in my opinion, make a significant improvement in that
> receiver's stability. So far, other projects have precluded my installing this in my almost-new
> RBL here, though.
>
>> The RAK/RAL power supply has a design defect in that some voltage
>> dropping resistors are nestled underneath a fiber board with no air
>> circulation, and are always shot.  Also they put too much current
>> through the 884 regulator as it's only regulating a half-mill load.
>> It's easy to make a power supply - I've gone both ways, and it may
>> have been less work to make a new one.
> Agreed. In fact, my RAL and RAK operate from a far smaller and lighter power supply (not
> designed by me, BTW) which maintains the RAK/RAL's good stability, yet draws far less
> power and puts out far less heat, while weighing only a few pounds.
>
> BTW, the supply voltage input circuitry of the RAK/RAL is pretty interesting. It is designed so
> that one can operate the receiver from a 6 volt battery for filaments and a 90 V "B" battery,
> the internal connections providing the necsssary voltage to the detector stage while
> automatically bypassing any need for regulated detector B+. Very neat.
>
> Ken W7EKB
> ______________________________________________________________
>