Hi, Military Vacuumlanders,
I'm more a denizen of RAR+P and RAT but I could use some help with a
BC-348-R "boatanchor". I acquired this eons ago but am only now
getting around to refurbushing it. It's totally original with the
dynamotor and it actually works but I'm not sure how well (I can get
some stations on a short wire antenna but there's lots of harsh hum on
the "long wave" band). BTW, I brewed up a 28 VDC bench supply from
which to run it. A long time ago I downloaded a few manuals in a
hurry but did not do a thorough check on the version - so I've got
documentation for versions J, N and Q, but not R. It seems that there
are several different schematics and tube line-ups for BC-348's. My
schematic is for a BC-348Q and it's not at all the same as for the "R"
- different tubes for a start !

By my forensics, the BC-348R has the following tube line-up:
Military tube Civilian equiv.
Function
VT-86 6K7 1st RF
VT 86 6K7 2nd RF
VT-91 6J7 Mixer
VT-65 6C5 Local Osc
VT-86 6K7 1st IF
VT-70 6F7 2nd IF & BFO osc
VT-93 6B8 3rd IF & Detector
VT-152 6K6 Audio O/P

(I hope this "table" holds together!)

Can anyone point me towards a schematic for the "R"?
All replies gratefully received
Thanks & cheers,
Roger

"Reclaim, repair, refurbish, rebuild, reuse, recycle"
Above address is a spam trap...
Any replies to: analogdino "at" rogers "dot" com

Try: http://bama.edebris.com/manuals/military-kg7bz/bc348/

The BAMA alternate site (above) indicates a manual including the "R"
version.

de K3HVG

Engineer wrote:

Can anyone point me towards a schematic for the "R"?
All replies gratefully received
Thanks & cheers,
Roger

On Jul 2, 5:53 am, K3HVG wrote:
Try:http://bama.edebris.com/manuals/military-kg7bz/bc348/

The BAMA alternate site (above) indicates a manual including the "R"
version.

de K3HVG



Engineer wrote:
Can anyone point me towards a schematic for the "R"?
All replies gratefully received
Thanks & cheers,
Roger- Hide quoted text -

- Show quoted text -

Many thank, K3HVG, but I have this one, viz:
"Maintenance manual for BC-348-J, N, Q. rev. 21 June 1948."
....but it is for models J, N and Q only.
The "R" has a different tube line-up (see my OP).
Cheers,
Roger

Engineer wrote:


Many thank, K3HVG, but I have this one, viz:
"Maintenance manual for BC-348-J, N, Q. rev. 21 June 1948."
...but it is for models J, N and Q only.
The "R" has a different tube line-up (see my OP).
Cheers,
Roger

As K3HVG *correctly* noted - the BAMA site has the schematic for the R
(as well as the others). For most purposes - any schematic that
includes the 991 tube (which isn't in your list) will be usable for the R.

--
Sherry

On 7/2/07 9:21 AM, in article ,
"Randy or Sherry Guttery" wrote:

Engineer wrote:


Many thank, K3HVG, but I have this one, viz:
"Maintenance manual for BC-348-J, N, Q. rev. 21 June 1948."
...but it is for models J, N and Q only.
The "R" has a different tube line-up (see my OP).
Cheers,
Roger

As K3HVG *correctly* noted - the BAMA site has the schematic for the R
(as well as the others). For most purposes - any schematic that
includes the 991 tube (which isn't in your list) will be usable for the R.

The AN which is said to include the R model, does not show a 991 tube.

Don

OK, Roger... I checked with the site again and your receiver, the "R"
model is listed as one of two manuals included. Please have a closer
look, under TO 12R2-3BC-112.pdf
The manual cover sheet and contents clearly state the "R" model.

Jeep/K3HVG

Just to make doubly certain, I re-loaded the above ref manual on BAMA
and compared it with my original AN-16-40BC224-2 dated 20 JULY 1945.
The ref des for the regulator is 125. In the BAMA manual, its located
on the last schematic sheet part and in the parts list as 2V991.

Jeep/K3HVG

K3HVG wrote:
OK, Roger... I checked with the site again and your receiver, the "R"
model is listed as one of two manuals included. Please have a closer
look, under TO 12R2-3BC-112.pdf
The manual cover sheet and contents clearly state the "R" model.

Jeep/K3HVG

On Jul 2, 3:52 pm, K3HVG wrote:
Just to make doubly certain, I re-loaded the above ref manual on BAMA
and compared it with my original AN-16-40BC224-2 dated 20 JULY 1945.
The ref des for the regulator is 125. In the BAMA manual, its located
on the last schematic sheet part and in the parts list as 2V991.

Jeep/K3HVG



K3HVG wrote:
OK, Roger... I checked with the site again and your receiver, the "R"
model is listed as one of two manuals included. Please have a closer
look, under TO 12R2-3BC-112.pdf
The manual cover sheet and contents clearly state the "R" model.

Jeep/K3HVG- Hide quoted text -

- Show quoted text -

Many thanks... and to other posters and emailers, too.
I have retrieved the "R" schematic! Now the harder work starts...
My plan is to keep it as original as possible but find a way to take
the dynamotor "off line" (to preserve it in the radio for "all
time"... and to cut the mechanical noise), then run the B+ from an
external regulated tube supply and the heaters from an external 4 x
6.3 = 25.2 VDC supply - I can adapt of my 28 VDC dynamotor supply,
but now only 0.7 A total. I'll go the other side of resistor "76-A"
that appears to drop 28 - 25.2 = 2.8 volts for the series/parallel
heater group (resistor "76-B" accommodating the higher (0.4 A) 6K6GT
heater current.) On second thoughts, the 25 volts could now be AC,
even easier (perhaps using a recycled s/s receiver power transformer)
- the 28 VDC supply staying untouched for "dynamotor days"!
Very best,
Cheers,
Roger

"Reclaim, repair, refurbish, rebuild, reuse, recycle"
Above address is a spam trap...
Any replies to: analogdino "at" rogers "dot" com

Like your idea of leaving it 'as original as possible'. While having
it work for today using mains electric power. Good for you.
Just a thought the original system worked off 28 volt aircraft
batteries. And of course the aircraft 28 v engine generators.
Batteries have a low impedance and might have done much to 'shunt'
brush noise of the various dynamotors? Could you try adding more shunt
filter to your 28 volt supply just to see if it could reduce the hash;
presumably coming back from the input brushes of the dynamotor? Or if
from brushes on the output side check hash filter caps there?
Finally could you unplug the dynamotor and have a cable from external
PS plug into that socket? No other changes whatsoever! Retain
dynamotor (perhaps attached to PS?) for future re-installation.
Good luck with your project.

Terry, see below in your text after ************

On Jul 7, 2:53 pm, terryS wrote:
Like your idea of leaving it 'as original as possible'. While having
it work for today using mains electric power. Good for you.

************** Thanks. We are only temporary custodians of "our
stuff".

Just a thought the original system worked off 28 volt aircraft
batteries. And of course the aircraft 28 v engine generators.
Batteries have a low impedance and might have done much to 'shunt'
brush noise of the various dynamotors?

************ True, but my 28 VDC supply is also very low impedance.

Could you try adding more shunt
filter to your 28 volt supply just to see if it could reduce the hash;
presumably coming back from the input brushes of the dynamotor?

************ I don't think that is happening
Or if
from brushes on the output side check hash filter caps there?

*********** Ditto.

Finally could you unplug the dynamotor and have a cable from external
PS plug into that socket? No other changes whatsoever! Retain
dynamotor (perhaps attached to PS?) for future re-installation.

*********** No, I can't risk the physical separation - the executors
of my estate won't go looking for the dynamotor! Neither do I want to
rewire the rear P/S socket - keep it original. My solution was to
installed a new 4 screw terminal plate (2 new small chassis holes...
sorry, can't help that!) with a captive power cord to the external
supplies. The dynamotor wires were just lifted carefully from the
original 5 terminal block to the new 4 terminal one (two are shorted
together in the original - see schematic. As we all now know for the
BC348, the external B- is NOT to chassis due to the odd biasing of the
6K6 o/p stage (it's about 14 VDC negative to chassis), so keep
external B- isolated!

Good luck with your project.

************* Thanks, keep 'em playing, cheers, Roger.

"Reclaim, repair, refurbish, rebuild, reuse, recycle"
Above address is a spam trap... any direct replies to: analogdino "at"
rogers "dot" com