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Author Topic: Looking for Shop/person to do BC-348R restoration  (Read 5615 times)
AC5UP
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« Reply #15 on: October 16, 2012, 11:37:46 AM »

An older AM/CW radio without a product detector can be used for SSB reception but the quality is far less than what you'd expect today... The AVC response curve is less than optimum and the IF bandpass is too wide. This means adjacent channel QRM that wouldn't bother an FT-950 can pump the AVC and make for difficult copy. The drill was to set AVC off, RF gain down, audio volume up, then ride the RF gain for best intelligibility. For a two person rag chew with good signals on a slow day this is reasonable, but with QSB or a crowded band it's not much fun.
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N4NYY
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« Reply #16 on: October 16, 2012, 01:40:18 PM »

That is pretty much what I was asking. What do you typically use this type of rig for? AMBC and SW broadcast?
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KD0REQ
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« Reply #17 on: October 17, 2012, 12:30:27 PM »

as I remember, fighting wars.

you can whistle up a BFO with a FET and a couple of ceramic filters of the right IF frequency.  pad one down and one up with capacitors for USB/LSB, and run a wire from the source into the chassis near the detector circuitry.

it won't be up to Heathkit standards, but you can make out the voices if you are careful adjusting things.
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W8JI
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« Reply #18 on: October 19, 2012, 05:46:47 PM »

That is pretty much what I was asking. What do you typically use this type of rig for? AMBC and SW broadcast?

The BC-348 was AM and CW, but it works OK on SSb too. Mine just has a messed up non-working BFO. I traced it to the oscillator coil, and I put it aside.

By definition, a product detector is just a mixer. A diode detector is a product detector, once injected with BFO signal. We all know a diode makes a good mixer when injected at the correct level. 

A human would be very hard pressed to hear any difference between a complex product detector with a double balanced mixer scheme and a simple single-diode mixer.

The real reason old radios suck for audio quality is they almost always have inadequate BFO injection levels, and they usually have poor AGC while the BFO is on and also for varying levels like SSB and CW.

My SX101 and NC303 have severe audio distortion on CW and SSB when the AGC is used but, like most old rigs, sound pretty good in manual AGC mode.

73 Tom

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G3RZP
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« Reply #19 on: October 20, 2012, 06:59:42 AM »

A problem with the 348 on SSB is the combined AF and RF gain control: with a diode and the usual lack of BFO injection (it makes weak CW sound better), best results means pushing up the AF gain and winding back the RF gain. A bit difficult when they are combined.
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KA5N
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« Reply #20 on: October 20, 2012, 07:38:59 AM »

The BC-348 were common in the 1950's and worked well enough on AM and CW and
since they were surplus were inexpensive.   While they are nifty looking and nostalgia filled,
they are not receivers I would choose for daily usage. 

Allen KA5N
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G3RZP
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« Reply #21 on: October 21, 2012, 03:40:24 AM »

They weren't so cheap here. Early 1950's, they were about 3 weeks pay for the average guy. An HRO was only slightly more. I suppose there were far more HROs and AR88s than BC348s.

Even a BC453 was a quarter of a weeks pay....
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AC2EU
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« Reply #22 on: October 23, 2012, 08:43:13 PM »

Hello,

I have repaired many older ham rigs from various manufacturers. I have also repaired the antique military types as well.
As long as the rare parts are there, they are usually salvageable.

http://www.mcveyelectronics.com/Ham-Radio/

Jim
AC2EU
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