[ARC5] Starting on a RAL clone

[Kenneth G. Gordon]

On 20 Mar 2013 at 12:32, Bill Cromwell wrote:

> I will be using miniature tubes. Think 6BA6 or something like that. I
> have them by the dozens. To help with the decision about which tubes to
> use I'll compare their characteristics to the 6D6 and 41 tubes used in
> the RAL.

Bill: the 6D6 is the same as the 6K7, which is a double-ended 6SK7. The 41 is the same as 
the 6K6. 

You might wish to look closely at the schematic diagram for National's RBL. It appears to me 
to be a somewhat updated (uses later tubes) and simplified version of the RAK.

The two RF amps in the RAL are used, primarily, to prevent detector radiation from reaching 
the antenna, and to isolate the detector from antenna effects...although the RF tuned circuits 
also provide considerable RF selectivity.

The gain of the two RF amps is purposely kept fairly low.

Remember that the detector stage 1) operates at fairly low voltage, and 2) that the most 
critical voltages at the detector are all regulated.

The RBL really should have been designed to include regulated voltages to the detector: it 
drifts noticeably.

Also, all the coils in the RAL (and the RAK) are toroidal, wound with Litz wire. They are very 
high "Q", and unusually low resistance.

I MAY have a junker RAL here out of which I could grab the coils and the tuning mechanism 
for you if you want them. They would certainly be cheaper to ship than an entire receiver.

It will take some time for me to find anything useful though...

Ken W7EKB