Hello, folks.

I couple of weeks back, I posted here about an old BC-348Q I had started
work on. So far, I have:

a) replaced the tubes (found one open filament and some weak tubes)
b) rewired the filaments (including errors introduced by a past owner)
c) recapped the set
d) found several bad resistors, leading me to re-resistor the set
e) repaired the BFO
f) replaced mouse-eaten wires
g) dismanted the "dead" filter crystal, soaked/cleaned it in alcohol,
and reassembled it
h) replaced intermittent BFO and Filter switches
g) aligned the set, as per the service manual. (alignment was way
off...apparently somebody went around "adjusting" slugs and caps
helter-skelter.)

Nifty set, and it seems to work fairly well now, from one end of its
span to the other. I do have a few observations and questions I wonder
if you'd comment on.

1) I notice some apparent variation in sensitivity from band to band. Is
this normal, or am I looking at the possibility of leaky caps inside of
the RF compartments? (If the latter, I may just let this be for now. I
don't relish the idea of trying to get those rf boxes out of the set!)

2) Tracking is a little bit off as far as dial calibration, despite
repeated attempts at alignment. I wouldn't expect digital frequency
display accuracy, but is this typical of this set?

3) The crystal filter works, but the insertion loss is significant. Am I
still looking at a crystal that is not quite up to snuff? Should I try
having a new crystal ground and install that instead? Or, is this
normal? ---Side note: Why is the crystal element so darned thick? I have
32khz realtime clock crystals in the junkbox that are slivers compared
to this 915khz filter crystal....and that filter crystal has got to be
an 1/8 thick!)

4) I have been running the set from bench supplies, and would now like
to build a power supply module to fit where the dynamotor used to go. I
have been running the set with 150 volts on the B+. Somewhere I read
that I should not exceed 200 volts. What is the appropriate plate supply
for this radio?

Thanks for the help.

Pete
AC7ZL

email is
hpf (atsign) gainbroadband (dot) com

Pete,

Sounds like all of your efforts are paying off! Lots of work,
but it had to be done.

The original DM-28 dynamotor put out +220 VDC for the plates.
Sounds to me like it's OK to exceed 200 VDC. Running the set
about 70 Volts low on plate voltage could account for the low
sensitivity.

I have an all-original BC-348-R that I picked up at a recent
hamfest. It's complete and in nice shape, but it's missing
the dynamotor. I need to locate one because once I have the
set restored and working, it's going aboard our Museum's B-17
Flying Fortress (which means it has to run on 28 VDC). Any
leads will be appreciated. I'm also in need of a BC-348-R
manual. Apparently the "R" model is different from all of
the previous models, although I don't have a clue how.

73,
Dean K5DH

In article ,
says...

Hello, folks.

I couple of weeks back, I posted here about an old BC-348Q I had started
work on. So far, I have:

a) replaced the tubes (found one open filament and some weak tubes)
b) rewired the filaments (including errors introduced by a past owner)
c) recapped the set
d) found several bad resistors, leading me to re-resistor the set
e) repaired the BFO
f) replaced mouse-eaten wires
g) dismanted the "dead" filter crystal, soaked/cleaned it in alcohol,
and reassembled it
h) replaced intermittent BFO and Filter switches
g) aligned the set, as per the service manual. (alignment was way
off...apparently somebody went around "adjusting" slugs and caps
helter-skelter.)

Nifty set, and it seems to work fairly well now, from one end of its
span to the other. I do have a few observations and questions I wonder
if you'd comment on.

1) I notice some apparent variation in sensitivity from band to band. Is
this normal, or am I looking at the possibility of leaky caps inside of
the RF compartments? (If the latter, I may just let this be for now. I
don't relish the idea of trying to get those rf boxes out of the set!)

2) Tracking is a little bit off as far as dial calibration, despite
repeated attempts at alignment. I wouldn't expect digital frequency
display accuracy, but is this typical of this set?

3) The crystal filter works, but the insertion loss is significant. Am I
still looking at a crystal that is not quite up to snuff? Should I try
having a new crystal ground and install that instead? Or, is this
normal? ---Side note: Why is the crystal element so darned thick? I have
32khz realtime clock crystals in the junkbox that are slivers compared
to this 915khz filter crystal....and that filter crystal has got to be
an 1/8 thick!)

4) I have been running the set from bench supplies, and would now like
to build a power supply module to fit where the dynamotor used to go. I
have been running the set with 150 volts on the B+. Somewhere I read
that I should not exceed 200 volts. What is the appropriate plate supply
for this radio?

Thanks for the help.

Pete
AC7ZL

email is
hpf (atsign) gainbroadband (dot) com

Hi Dean,

http://www.kg7bz.net/Manuals/BC-348/...R2-3BC-112.pdf

Covers the K, L and R versions.

73,
August Johnson KG7BZ

"-=H=-" wrote in message
et...
Pete,

I have an all-original BC-348-R that I picked up at a recent
hamfest. It's complete and in nice shape, but it's missing
the dynamotor. I need to locate one because once I have the
set restored and working, it's going aboard our Museum's B-17
Flying Fortress (which means it has to run on 28 VDC). Any
leads will be appreciated. I'm also in need of a BC-348-R
manual. Apparently the "R" model is different from all of
the previous models, although I don't have a clue how.

73,
Dean K5DH

Hi August,

Wow! Thanks for making the manual available! I downloaded
a copy to my computer just now. I'll burn it to a CD later.

Thanks and 73!
Dean K5DH


In article , says...

Hi Dean,

http://www.kg7bz.net/Manuals/BC-348/...R2-3BC-112.pdf

Covers the K, L and R versions.

73,
August Johnson KG7BZ

"-=H=-" wrote in message
news:fOmdnSc1PqmVcDzZnZ2dnUVZ_vKdnZ2d@centurytel. net...
Pete,

I have an all-original BC-348-R that I picked up at a recent
hamfest. It's complete and in nice shape, but it's missing
the dynamotor. I need to locate one because once I have the
set restored and working, it's going aboard our Museum's B-17
Flying Fortress (which means it has to run on 28 VDC). Any
leads will be appreciated. I'm also in need of a BC-348-R
manual. Apparently the "R" model is different from all of
the previous models, although I don't have a clue how.

73,
Dean K5DH

1) I notice some apparent variation in sensitivity from band to band. Is
this normal, or am I looking at the possibility of leaky caps inside of
the RF compartments? (If the latter, I may just let this be for now. I
don't relish the idea of trying to get those rf boxes out of the set!)

2) Tracking is a little bit off as far as dial calibration, despite
repeated attempts at alignment. I wouldn't expect digital frequency
display accuracy, but is this typical of this set?
==============================
Pete:

Some variation in sensitivity from band-to-band is to be expected, but
some of it may be a alignment/tracking problem. All the BC-348
versions I have worked on have a dial calibration error in excess of
the specs. The RF and Oscillator coils have trimmers to adjust the
high-frequency end of the bands, but only the LF band has a
low-frequency adjustable padder. The padder capacitors for the
high-frequency bands are fixed micas. The coil forms and perhaps the
micas have aged over the last 60+ years and caused the low-end
calibration to be off. There are a lot of small mica capacitors inside
the "coil cans" and many of them are non-standard values. It is
probably not a good idea to mess with them. I "fudged" the coils on my
BC-348-R and got the low-end calibration on spec, but it is a slow,
painful process. But, once done, the alignment has stayed put for the
last 5 years or so. It is one of my favorite receivers.

The size of a crystal is a function of frequency and the mode of
vibration. The BC-348 crystal is a thickness mode crystal is much
larger than a tuning-fork type crystal used at 32kHz. There is some
loss in the crystal filter, but not much. Sometimes the extra
selectivity reduces the sidebands to the point that the sensitivity
seems to be reduced, but the carrier remains strong. I assume you
aligned the IF at the actual Xtal frequency.

Running your BC-348 on something around 200 - 220 VDC should be OK. I
wouldn't go above 220. There would be no advantage to that. Putting
the power supply inside the cabinet of the receiver will raise the
temperature a good bit and raising the B+ above 220 will raise the temp
even more. I always recommend an external power supply. Put it in the
speaker cabinet. Your BC-348 will be a lot happier that way and more
stable too.

Best Regards, Ed

Pete, I'll add my 2-cents worth. Info on the B+ spec posted is, of
course, correct. Remember, though, that B- floats and is NOT at ground
potential. B- has its own connection. One thought, and its helped
several sets I've owned, is to bypass the "gain leveling" pot attached
to the end of the tuning capacitor. The idea was to vary the gain from
one end of the band to the other. I've found it to be more of a problem
than an answer.

de K3HVG

Dean,

... but it's missing
the dynamotor. I need to locate one because once I have the
set restored and working, it's going aboard our Museum's B-17
Flying Fortress (which means it has to run on 28 VDC). Any
leads will be appreciated.

have a look at the following URL, they advertise DM21s at a reasonable
price:

http://www.armyradio.com/arsc/customer/home.php?cat=86

Regards,
Thierry Stora

http://www.chapelon.net

oups, apologies for the mistake, everyone knows that the DM21 runs on
12-14 volts ...

Sorry!

On Wed, 28 Jun 2006 22:38:39 +0200,
wrote:

Dean,

... but it's missing
the dynamotor. I need to locate one because once I have the
set restored and working, it's going aboard our Museum's B-17
Flying Fortress (which means it has to run on 28 VDC). Any
leads will be appreciated.

have a look at the following URL, they advertise DM21s at a reasonable
price:

http://www.armyradio.com/arsc/customer/home.php?cat=86

Regards,
Thierry Stora

http://www.chapelon.net
Thierry Stora

http://www.chapelon.net

Useful thread... thanks all.
I have a working, original, unmodified BC-348-R complete with original
dynamotor that I run off a home-brew 28 VDC supply.
It needs some refurbushing and a tune-up after all these years... as
soon as I can get a "round tuit", a most necessary servicing device,
you will agree! g
Cheers,
Roger

In article . com,
says...


soon as I can get a "round tuit", a most necessary servicing device,
you will agree! g
Cheers,
Roger


I got rid of my Round Tuit a few years ago ... too many projects
were getting done and no time to goof off left!

It was one that State Farm used to pass out to customers...
John k9uwa