[ARC5] 10 meter BC-454

[Kenneth G. Gordon]

On 7 Feb 2013 at 0:41, WA5CAB at cs.com wrote:

> L2 is untuned and should be self resonant well above 30 MC.

In this case, L2 is resonant, in circuit, at 24 MHz. I have not checked its 
resonance out of the circuit. I suspect that tube interelectrode or stray 
capacitance is pretty big. From my calculations, it appears that there is 
something like 45 pfd of capacitance somewhere in that circuit.

>  If you
> pad it down to be resonant at say 29 MC and you want the receiver to
> tune 27 to 30, sensitivity will peak at 29 and fall off substantially
> in both directions.

I had wondered about that. I couldn't see how it could possibly be broad 
enough to cover the entire range if there was any fixed capacitance in the 
circuit at all. Obviously, the coil still has too many turns

> Unfortunately, the RAT and RAV manuals do not give the capacitance
> range for the tuning capacitor main sections or the turns in the coils
> for the 46109 (20-27 MC) which would have been a good starting point.

It doesn't matter here, as the tuning capacitor has only one rotor plate left in 
all sections: the slotted one. As far as I can tell right now, its range is 22 pfd 
fully meshed to about 11 pfd fully open, but I am going to test that more 
accurately tomorrow.

Originally, according to the SCR-274N manual I have, that capacitor had 8 
rotor plates and 9 stator plates and had about 147 pfd at full capacity per 
section.
 
> Say again the number of turns in L1,

6 turns - #20. This circuit peaks up just perfectly between 28 and 30 MHz 
with the front panel antenna tune cap. That cap is somewhat more than 1/2 
open at the peak. The peak is very strong and sharp.

> L3

5 turns #18 or #20 - spaced. At this point, with the tuning capacitor as it now 
is, that circuit tunes from 60 to 83 MHz. I think it should tune 28 to 30 MHz. 
According to my measurements and calculations, it is 0.3973 uH.

L2 is 9 turns of the original wire (#36), interwound with L3, widely spaced. 
According to my measurements and calculations, it is 1.051 uH.

L2 is resonant at 24 MHz when mounted in-circuit.

> and L5. 

5 turns - #20. This, with the tuning capacitor as modified, now tunes properly 
from 28 to 30 MHz, with a small bit of overlap on the high end.

> I take it that you
> confirmed that the slugs were still in all of the coil sets.

Yes. They are all there.