[ARC5] BC-610 questions

[Kenneth G. Gordon]

On 18 Nov 2012 at 23:13, Richard Knoppow wrote:

> It appears that there were many versions of 
> the BC-610 and evidently they were built into the 1950s.

Yes. At one time, I owned an -E model and an -I model, and there were 
many others.

> I also didn't know 
> that each tuning unit had a VFO on it. How did one adapt a 
> TX to an external VFO, or is that even possible.

Each tuning unit had a XTAL/VFO switch, and a socket for a large crystal: 
one of those early FT-241s as I remember it. All it took to "adapt" one for an 
external VFO was to flip the XTAL/VFO switch to XTAL and plug in an 
adapter that connected the external VFO's output cable to the crystal socket. 
You could use two small banana plugs in fact.

In fact, there were military RTTY adapters that did just that.

>     I rather like the large number of meters on the earlier 
> versions but it appears the later ones used a multi-purpose 
> meter for some of those functions.

Yes. There were only two meters on the -E and the -I models that I used.

>     What I mainly want to ask is if anyone on this list has 
> an active BC-610 of any version on the air?  What sort of 
> opinions do users have of them?  Are they actually 
> practical?

I don't have one on the air at the moment, but I have had them on the air 
back in the 1960s and 1970s. My opinion of those I used was 1) that they 
were AWFULLY big for what they put out in stock condition, 2) they were 
very, very reliable and tougher than nails.

And, yes, they are very practical, but (again) awfully big. 

For AM you must have the external speech amp/control, the BC-614, and 
you really should use the external antenna coupler too. As I remember it, 
that was the BC-939, designed and made by B&W.

I got the two '610s I had from AFMARS. The -E model was VERY well used 
when I got it. There is a plate RF choke under a phenolic board that the plate 
coil sockets are mounted to: that RF choke was burnt up...and there were 
other problems.

I eventually accumulated all the plate coils and tuning units which covered 
the range from something like 1500 KHz through 18 MHz. I even had one 
that someone had modified to cover up to 25 MHz. There were two special 
plate coils and tuning units that covered the low end of the AM BC band. I 
had those and the vacuum capacitors one had to plug-in in parallel with the 
final tank tuning cap.

Since the final amp tube, a 250TH, was missing in mine, I mounted the 
socket for a 304TL in it. I had to do something about the very heavy filament 
current requirements of the 304TL, 5 V at 25 A, but can't remember exactly 
what I did. I think I may have paralleled the original 250TH filament 
transformer with the one that originally fed the 100THs in the modulator. The 
100THs were missing too.

I modified the bias supply by adding a bias-shunt regulator, adjusted the bias 
for "projected Class B cutoff", replaced the 866s with 3B28s, and used the -E 
model as a (not very) linear amp. (304TLs are NOT very good linear amp 
tubes.)

I drove it with my modified SB-100 to about 3 KW input for SSB when doing 
'phone patching for AFMARS in the 500 KHz band just above 20 meters. 
Plate voltage under load was 3 KV and plate current was 1 amp.

I also used it at reduced power of 1KW input for RTTY and CW. I drove it for 
RTTY with, first, a modified Heathkit VF-1 (added a "shift-pot" FSK circuit to 
the VF-1) which then drove a beefed up Heathkit DX-35, which was my first 
transmitter when I was a novice in 1956.

The '610 would take anything we threw at it and would just keep smiling. We 
did this to another BC-610-E for another AFMARS member and a friend of 
mine who lived across town. This was in Missoula, Montana. Both of us ran 
patches into Vietnam and other SEA sites.

The -I model I also got from AFMARS. It was NIB when I got it, but I never 
put it on the air since I had the old -E model working like gangbusters by 
then.

Other things were happening with my life about that time and I finally got rid 
of all of that stuff and moved to Kansas for a bit. Then I got married and 
moved back to the NW. That was over 30 years ago.

Ken W7EKB