[Milsurplus] BC-348R Oscillator Issue output Frequency is 0 for part of band 4 : 6 - 9.5 MC

[jphutch60bj]

Thanks for all the input.   I need to replace a lot of resistors, and a 
few paper caps.

The "Real" Mica's are still good!

Time to do some surgery on the RF deck.

JPHutch


On 8/22/2025 1:27 PM, Ray Fantini via Milsurplus wrote:
>
> On the BC-348R that’s the old design with separate oscillator and 
> mixer tubes, they feed the output of the oscillator into the mixer 
> tube on the cathode. That’s a low impedance circuit so no worries 
> there. The Q,N and J all use a more modern pentagrid converter tube 
> that’s both oscillator and mixer and more prone to loading but think 
> the old school R is not that delicate!
>
> But I can always be wrong, my wife will tell you about how often I am 
> wrong. I think observing with a scope will tell you a lot about what’s 
> going on and what happens before the signal disappears.
>
> Ray F/KA3EKH
>
> *From:* milsurplus-bounces at mailman.qth.net 
> <milsurplus-bounces at mailman.qth.net> *On Behalf Of *Mark K3MSB
> *Sent:* Friday, August 22, 2025 1:47 PM
> *To:* hwhall at aol.com <hwhall at compuserve.com>
> *Cc:* milsurplus at mailman.qth.net
> *Subject:* Re: [Milsurplus] BC-348R Oscillator Issue output Frequency 
> is 0 for part of band 4 : 6 - 9.5 MC
>
> You can load down an oscillator real fast by a direct connection with 
> a probe.   I use this when adjusting oscillators....
>
> .... attached to either a scope or frequency counter.    I have a few 
> of them with different loop sizes and number of loops.
>
> 73 Mark K3MSB
>
> On Thu, Aug 21, 2025 at 11:24 PM hwhall--- via Milsurplus 
> <milsurplus at mailman.qth.net> wrote:
>
>     That's an unusual approach to aligning the tuning.  Are you quite
>     sure the freq counter isn't loading down the oscillator output &
>     sometimes just killing it?
>
>     Wayne
>     WB4OGM
>
>     On Thursday, August 21, 2025 at 05:47:35 PM MDT, jphutch60bj
>     <jphutch60bj at gmail.com> wrote:
>
>     Reading the Manual TO-12R2-3BC-112, Revised 15 April 1957,  Page
>     4-3 paragraph 'e'.
>
>     On the four lower frequency tuning bands the
>     oscillator frequency is higher than the desired signal
>     by the intermediate frequency. On the two higher
>     frequency ranges, bands 5 and 6, the oscillator is on
>     the low frequency side of the desired signal. The latter
>     results in a more uniform tuning ratio over these
>     bands and increases the image rejection ratio.
>
>     Before I start doing Brain surgery on BC-348R by pulling the RF
>     Units .....
>
>     I was Checking Oscillator output frequency with a frequency
>     counter, tweaking the outputs from the oscillator on each band.
>
>     Band 4, frequency range of : 6 - 9.5 MC,  reading the manual the
>     Oscillator High Side output should be between 6.915 - 10.415 MC 
>     for band 4?
>
>     My Oscillator goes dead no output,  between DIAL Frequency reading
>     of:  7.2  to 8.8 MC - which equates to an Oscillator output
>     frequency of  "+.915"  should be between  8.115 - 9.715 MC.
>
>     Issue the output Frequency goes to 0 as measured  on Pin 8, VT-91,
>     6J7.
>
>     If the manual is not wrong,  why is the oscillator output dropping
>     to 0, on this one band?
>
>     It aint the tuning cap!-} , as there are no problems with other bands.
>
>
>     Thanks for you thoughts in advance.
>
>     JPHutch
>
>
>
>
>
>
>
>
>
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