[ARC5] TM ident for BC-946, please

[Kenneth G. Gordon]

On 28 Apr 2014 at 7:04, Leslie Smith wrote:

>   Good-morning list readers,
>   I have a well-hacked BC-946 I'm seeking to restore to working
>   condition.
>   Can any-one advise the series that the BC-946 belongs to, and/or the
>   TM manual for this series?

I think Jeep provided what information you need for that part of this effort. 
The BC-946 also has the variable selectivity IFs in the same way that the 
BC-453 does: pull up on the rods to increase the selectivity.

The Navy styled both the R-23(*)/ARC-5 and the R-24/ARC-5 as "Navigation 
Receivers", except for tuned circuit values, they are otherwise identical, 
circuit wise.
 
>   This set has seen a good deal of work by some-one with side-cutters.
>   Everything under and over the dyno plate is missing.

Oh, great! But that is a typical mod which was meant to turn it into a "hi fi" 
AM "tuner".

>   The detector is now a 6H6 and the 12A6 has been replaced by a triode.
>   Does any-one remember a "mod" where this was done?

The early Surplus Conversion Manual, or the Command Sets manual had 
detailed instructions in that direction.

The purpose of using the 6H6 was to provide both detection and AGC, which 
the BC-946 lacked in its original condition. The reason for the triode was 
because that was normally followed by at least a single-tube audio amp, 
usually a 6V6, but sometimes a 6L6. The triode was the audio preamp.

>   (Also, the output transformer is missing.

Yes. That mod mentioned above required removal of the audio output 
transformer and the BFO transformer too. As I remember it, you found a 
source for the missing BFO transformer.

>   I'll try a 240 .. 12v
>   filament transformer as a replacement and advise the result.

That may work quite well. However, an audio output transformer from a 
so-called AA-5 tube-type table radio would work at least as well, if not better. 
Also, a Radio Shack line-transformer works perfectly. 

In addition, one of us may have a spare original one around here. I don't at 
the moment, since so many of my "pre-hacked" receivers here are missing 
those. However, I can't restore ALL of them either, so I eventually may have 
an extra one.

>  Will the
>   D.C. in the plate circuit saturate the transformer core?

Most likely, no.

>   The filaments in the set are wired in parallel.

Another typical mod from the period, also detailed in several of the 
modification articles in those manuals I mentioned above. BTW, I believe I 
have ALL of those manuals in PDF form on my website.

>   Has anyone seen an original BC-946 with the filaments wired for 12
>   volts?

Never. The only original "ARC-5" receiver I have ever even heard about that 
was wired for 12 V is the R-148/ARC-5, an R-23(*)/ARC-5 factory wired for 
12V input and with a 12 V dynamotor.

>   As an additional point difference all the "tubes" are 6 volts types,
>   so - as I got it - the set is meant to operate from a 6v filament
>   supply.

Yes. Again, that was common "back in the day" and was also mentioned in 
more than one article in the manuals I mentioned above.

BTW, I keep copies of those "manuals" in order to "reverse-engineer" the 
"pre-hacked" receivers I am trying to restore.

>  I suppose that somewhere in the past some-one had a 6 volt
>   filament transformer and decided to use that.

Well, back in the day, 6.3 VAC filament transformers were FAR more 
common than either 12.6 or (heaven forbid) 25.2 VAC filament transformers. 
It was only with the advent of COMMON transistor construction articles that 
12.6 and 25.2 VAC filament transformers became common.

>   Most of the circuit in front of the detector seems intact, apart from
>   the fact that two of the four tag-strips are missing.

I have extras of those. Let me know which you need and I'll dig them out and 
send them.

>   Anyway, this set is so far from original it can only be restored to
>   functional.

Yes. I have several in that condition. Very sad...

>   The top deck and rear panel of the dyno area are cut away, so I'll
>   need to fabricate two Al plates to cover the damage. 

I have at least one BC band receiver in that condition, except that mine is so 
far gone otherwise that it is useful only for (a few) parts.

>   With careful work the set will work and look cosmetically
>   acceptable.

Yes. Well, that is a good thing, Les.

vy 73,

Ken W7EKB