[Milsurplus] BC-669 Problems

[Kenneth G. Gordon]

On 12 Oct 2017 at 19:04, arc5 at ix.netcom.com wrote:

> 
> I second Meir's suggestion.  It appears you've lost it drive  to the final.  Need to determine if the 
> oscillator is running.What kind of Crystal are you using? Power down, open the top and remove 
> the power amplifier tubes until you can be sure that the oscillator is running and delivering power 
> to the grid circuit.

And I "third" Meir's suggestion: no drive to the final. Most probably, your crystal has died. 
The BC-669 pulls a lot of crystal current, most probably too much for any "modern" crystal, 
and even probably too much for an FT-243. 

The transmitter's oscillator is a modified-Pierce oscillator, using a 6L6. 

While the  modified-Pierce circuit is normally quite easy on crystsls, the use of a 
beam-pentode, and especially, a 6L6, completely negates any advantage of either the 
modified-Pierce OR the ECO (electron-coupled oscillator) circuits.

Hallicrafters (especially) and many other makers of the period did this, and I have never 
understood why.

The 837 and the 802, and even the 6F6, which are power pentodes, and NOT "beam tubes" 
were FAR easier on crystals, and made superior oscillators. The Navy figured this out, at 
least.

I'll have to examine the circuit and its parameters a bit more closely, but you MAY 
experience better operation by replacing your 6L6 with a 6F6. Maybe....

Ken W7EKB

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