[Hammarlund] BC-779 Question

[Roger D Johnson]

Carole White-Connor wrote:
> I'm working on a BC-779B. The radio plays well and has decent sensitivity.
> The audio is not as good as it should be and it's noisier than it should
> be. I sense some distortion and the AVC seems sluggish. (I'm comparing it
> to the civilian SP-210 that I have).  I've already replaced the paper caps
> and about a half-dozen out-of-spec resistors. All voltages are pretty close
> to spec.
> 
> I'm looking at C-13, which is a 91 mmf grip-coupling cap. The part list
> specifies that it is a silver mica. It looks like a standard paper cap.
> 
> Here are my questions:
> 
> 1. Is this type of silver mica of this vintage prone to failure? It looks
> crappy but that may just be the moisture-proofing compound sprayed rather
> liberally on the underside of this set.
> 
> 2. The closest replacement I have is 82 mmf. Is that good enough?
> 
> 3. Are the .05 mfd bathtub caps along the side of the set prone to failure?
> 
> 4. The manual specifies 6F6s for the audio section. The prior owner had
> 6K6s there. Is this good, bad or indifferent?
> 
> As always, thanks for your help!
> 
> 
> Joe Connor

Why are you suspicious of C-13? According to my schematic it's the
coupling cap from the oscillator to the mixer. Silver micas are
generally pretty reliable.

The 6F6s are pentodes connected as a triodes in this set. The 6K6 is a
beam power tube. I've never seen beam power tubes connected as triodes
so I would definitely replace them with the proper tubes.

73, Roger


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