[600MRG] How to Convert your BC-453 to 166 kHz.

[Kenneth G. Gordon]

On 23 May 2017 at 13:24, Paul Signorelli wrote:

> If you have not been able to receive my 166.666 kHz beacon because you
> don't have a LF receiver, 
> 
> Here is how you can convert your BC-453 to 166 kHz.
> 
> Just parallel  a 480 pF capacitor across each of the 3 main variable capacitor sections.

I would use some sort of temperature compensating capacitor for the HFO, which is the 
center section of the tuning capacitor.

> You need 3 caps.
> 
> That will place the BC-453 on 166.6 kHz with a dial reading of 480 kHz.
> 
> Of course it is not stable enough for data modes.

But see below.

> The resulting tuning range is about 140 to 175 kHz, Lots of band spread.

Well done, Paul.

> W7EKB, Ken, is probably the only one around who has a BC-453.

I have a number of them here, but all would require refurbishment in order to be put into 
operation. The BC-453 or the later R-23(*)/ARC-5 are commonly available on eBay for 
generally very reasonable prices in various conditions.

One thing that should be mentioned: the stability of these receivers is actually quite good. 
Unusually so for a reciever which is over 70 years old. There were "stabilized" versions of the 
AN/ARC-5 series, which can be discovered by looking for a large yellow letter "S" inside a 
yellow circle stamped on the front panel.

I use my own BC-453 with several pieces of software and a laptop to monitor digital modes 
on LF.

One can enhance the stability of the BC-453 or R-23(*)/ARC-5 easily enough by:

1) Dropping the HV to around 170 VDC from its normal 250 VDC. One MAY wish to move 
the screen voltage feed from the junction of the two big black resistors in the rear of the 
receiver to the HV input to that voltage divider, but often that is not necessary. However, 
doing so if you have done the next step will result in voltage regulated screen voltage too.

2) Voltage regulating the HV. I prefer VR tubes for their color, but modern Zeners actually do 
a somewhat better job. I use 2 ea VR-90s (180 VDC), or two VR-75s (150 VDC), or a VR-90 
and a VR-75 (165 VDC). Maximum current drain at 250 VDC with the audio and RF gain 
wide open is normally about 50 mA. At around 170 VDC, that falls to around 30 mA, and 
since we seldom run the audio gain wide open, mine runs at around 15 mA.

3) Run the filaments on DC and voltage-regulate that DC filament voltage. This requires a 
Zener or two, or some sort of Zener-regulated pass transistor circuit. Easily enough done.

4) Running the entire reciever on batteries: 12.6 VDC battery for filaments if the receiver has 
been converted to all parallel filaments, or 2 ea 12.6 VDC battery if still stock, and a stack of 
a dozen 9 VDC transistor batteries in series for about 184 VDC. The current drain at that rate 
is very low.

Lastly, sensitivity of these receiver is also unusually good. In tests of my refurbished 
receivers, I find MDS of my refurbished receivers after a proper alighment, at 500 kHz to be 
on the order of 0.3 microvolt with the BFO on using all original tubes and about 170 VDC B+. 

Here is a youtube video of one of my receivers:

https://www.youtube.com/watch?v=vlz83QXM66A

Later, 

Ken W7EKB

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