[ARC5] BC-221 frequency meter

[Richard Knoppow]

----- Original Message ----- 
From: "KG4KGL" <kg4kgl at gmail.com>
To: <arc5 at mailman.qth.net>
Sent: Wednesday, January 01, 2014 4:11 PM
Subject: [ARC5] BC-221 frequency meter


> Alright before I start, you have to promise not to laugh 
> at me.
>
> I bought this freq. meter and when I powered it up with my 
> Heath PS-4, I read the wrong scale on the meter and 
> applied ~300v B+. Oops. So I saw a little smoke and 
> thought I fried one of the old fixed caps, so I recapped 
> it.
>
> Now it worked at that high voltage and it works after the 
> recap, but I get nothing out of it when I put it in the 
> Crystal position. Am I right in assuming I have fried the 
> crystal? Everything else works fine.
>
> Does anyone have a spare xtal they would be willing to 
> sell?
>
> Tnx,
>
> Robert
> KG4KGL

     The crystal is probably OK, there is no way for the 
voltage to get to it.  Smoke is more likely to have come 
from a resistor or choke than a capacitor.  There are three 
resistors and a choke in the B+ circuit.  The choke is in 
the plate circuit of the crystal oscillator, check to see if 
its open. There is a handbook on BAMA. There are a lot of 
small variations from one version of the BC-221 to another 
but they are fundamentally the same. Check the tube pins for 
voltage. If the choke is open there will be no voltage on 
the plate of the triode section of this tube.  There is a 
chart showing voltages and commercial type numbers for the 
military VT designations in the book.  The 135V B+ is for 
when the set is operated from batteries, when it is used 
with the AC power supply the B+ is closer to 250V so I think 
is more likely that some weak part burned than that your 
mistake did it.
    When the function knob is in "Crystal Check" you should 
be able to hear a beat in the headphones when tuning across 
one of the crystal check points indicated on the calibration 
charts.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com