RadioBanter - View Single Post - SB-303 heathkit repairs

dxAce[_22_] · July 19th 14, 12:38 PM posted to rec.radio.shortwave

Michael Black wrote:

On Fri, 18 Jul 2014, wrote:

On Friday, July 18, 2014 12:29:27 PM UTC-4, Michael Black wrote:
On Fri, 18 Jul 2014, dave wrote:

On 07/17/2014 04:49 PM, Michael Black wrote:

On Thu, 17 Jul 2014, Scott Smith wrote:

SB-303 heathkit repairs, I bought a heathkit SB-303 radio off ebay,

all it gets are various tones when I tune the dial, any idea on

repairs, thanks in advance, email .

Does it have the crystals? If that's the ham band one (rather than the

one for shortwave), the crystals are the same frequency as used in the

full SB line of ham band equipment. Buying crystals these days has

become quite expensive, so if someone needed the crystals for whatever

reasons, they may have stripped a receiver, rather than buy the crystals

new, or find a set of crystals on the used market.

It's a receiver that tunes a 500KHz segement (I think around 3MHz) with

a crystal controlled converter ahead of it, a crystal needed for each band.

Michael

Anybody roll their own quartz crystals? You need an oven. Big bucks for

energy.

I gather the radio magazines did show how to make your own crystals, back

in the thirties.

I'm sure they started with a slab of quartz, and cut it down and started

grinding.

Michael

Very , very difficult. Even after it is close enough(!)in resonant
frequency- there are a few MORE extremely critical parameters involved
... This is why true "Crystal Filters" were so expensive,even when they
were mass produced ...

First, in the thirties, crystal holders were big, making it so easy.
Second, the need was for stable frequency, ao they just had to get it
within the ham band.

But, after WWII there were a lot of military surplus crystals on the
market. Crystlas are generally ground to order, but the military needed
so much they just churned out crystals on specific frequencies. That was
a bounty, lots of cheap crystals, which lasted decades. And they were so
spread out that usually you could find one that was close enough. If not,
you opened up the case, which back then was held together with a screw,
and actually ground the crystal a bit, to bring it up in frequency. Had
to be careful that you did it evenly or else the crystal might not
oscillate anymore. And if you wet too far, you could lower it back a tad
with some solder or pencil lead. Lots of people did that to get a
crystal where it was needed, starting with one as close as possible (and
you never could move them by much).

I remember having to do that back in the 60's when I was a crystal controlled
novice. Seems like I had some FT-243 crystals thaI either put some pencil lead on or
had some very fine grit and ground them down on some glass.

It always worked. The one thing back then was if one was calling CQ, you'd have to
tune around some to find someone answering because they had a crystal on another
frequency.

Lots of fun for sure.