The AM Forum

I just purchased a BC-1004 from Frank, KB3AHE.  Thanks again Frank.  :)
It had what appeared to be a well constructed HB PS that only had one problem with it - a fried 7k power voltage divider resistor between the high end and the first tap.

The next day I drew a wiring diagram and verified the voltage divider power resistor was indeed fried in the lasy 1k.  I was able to find a 1.5k power resistor to wire in place of the the 1k section and was able to get the following voltages stabilized after an hour or two:


rx rear power connector (view from rear):
[ ( 1) ( 2) ( 3) ( 4) ( 5)   ( 6) ( 7) (8 ) ( 9) (10) ]

 1) gnd (n/c)
 2) 117 VAC mains in from PS mains master SW
 3) 117 VAC mains out to PS primaries
 4) -64 VDC (-1, -1, -64 VDC at 30, 60, 90 min)
 5) +405 VDC (+394, +395, +405 VDC at 30, 60, 90 min)

 6) +219 VDC (+166, +175, +219 VDC at 30, 60, 90 min)
 7) +135 VDC (+94, +100, +135 VDC at 30, 60, 90 min)
8 ) gnd
 9) 6.3 VAC
10) gnd


From what I could find on the net it appears that the power supply should be presenting these voltages to the radio:


+380 VDC at  50mA ( 5)
+250 VDC at 100mA ( 6)
+100 VDC at 4.5mA ( 7)
 -50 VDC at  11mA ( 4)
 6.3 VAC at   7A  ( 9)


I guess what I would like to ask is, are the voltages I am getting usable / ok / close enough, or should I be working to get them closer to spec to get the most receiver performance out of this radio?

You need to check the voltages when connected to the receiver.

Ought to be close enough.

Dave,
       Like John said, you must check them with the rest of the radio connected to it. Those resistor values were calculated to drop the voltages under OPERATING load. Without the rest of the radio connected the multimeter doesnt draw enough current to make the voltage dividers work properly. (they will read very high)

                                                            The Slab Bacon

Yes, these voltages are taken from the back of a receiving receiver taken at approx 30, 60, and 90 min running.

Frank, You were right about (what you said in person about) the bias voltage, as far as I can tell, since once the voltage on ( 4) went from -1 to -64 VDC the BFO started working (though it is barely perceptible) and the sensativity control started working (solidly, unlike the BFO).

Increase the coupling from the BFO into the IF, that'll take care of the weak BFO.

Looks like the bleeder resistor is heating up and changing value upwards as it heats.  Check resistor values cold and hot, see which one's changing, and replace it.

I have gotten some nice shocks off the back of the Super-Pro! 400V on a receiver is serious stuff and when you get hit with that it sure wakes you up. I always put a nice piece of electrical tape across the back when I am servicing it now.

There are a lot of stsges and the class A push-pull is a hog. The first bleed tap has a lot of juice going through it so it does not surprise me that it is getting hot. More power! Go BIG on that resistor.

There are a ton of modifications published for this set. But before you go there, check the resistor values of all of the B+ feeds. Some of them can go up as much as 100% and this starves that stages (BFO?). Also, I am assuming that all of the bypass caps were changed out and tubes were checked recently.

73's Mike WU2D

hey Mike ... you got any urls/ addresses for those mods ?   thanks  John

Actually no. They are published in older magzines like CQ and 73 in the late 50's and early 60's.

Souping the SuperPro - CQ Dec 1957 (Pullen Mixer Mod etc..)
If you Can't Move it , Paint it - CQ Dec 1957
Save your SuperPro for SSB CQ September 1958 ( 6BE6 Product Detector mod etc...)
A Super SuperPro - Surplus Conversion Handbook, Tom Kneitel 1964
Update that SuperPro Part 1, Bill Kleronomos Electric Radio
Update that SuperPro Part 2, Bill Kleronomos Electric Radio
Update that SuperPro Part 3, Bill Kleronomos Electric Radio

Mike WU2D

thanks, Mike ... a hunting I will go, a hunting I will go, hi ho the derry-o, a hunting I will go ...73 ..John

Same here, Mike. The last hit I got was from a Super Pro last year when I reached around and grabbed the back of either the ps or receiver to move it, completely forgetting that one of the covers was missing. Caused my arm to move backwards rapidly, dragging my hand across the back of an exposed screw. MAN did that sting! Think I shut everything off, got a beer, and watched TV the rest of the night.

The pre-war SP-200 I have has been modified with all the front end tubes changed to 7 or 9 pin miniatures along with one other stage (Beat Oscillator or AVC?). Even the SP-100 has been modified this way except using metal octals instead (6SN7s), moving all the plate cap connections to under the chassis. Looks like an older version of the same mods, so they've been around for a while.

It would be interesting to do a side-by-side of an original, unmodified version next to a hopped-up model to see what the gains vs drawbacks are. I'm gonna go look up the ER articles Bill wrote to see what he discovered.

Only thing more shocking that the terminals on the back of the receiver are the terminals on the power supply! :o

Simply Shocking!

Here is some info on the power supply from an old manual.

My SP-400 had a miniature 6BE6 product detector and a mini 0A2 voltage regulator for the HFO and BFO stages. It was was fairly common in the 60's to soup up the SuperPro with miniature tubes. People did this by making an adapter plate that held the miniature tube socket (and shield) and they extended the grid connection to get down to the grid through the chassis (because mini tubes had no grid cap). A typical lineup would be a 6DC6 or 6BZ6 first stage, 6BA6 second RF, 12AT7 Pullen Mixer and 12AT7 HFO. 6BE6 product detector and a VR regulator. This was a lot of work! And talk about excess gain!

Mike WU2D

Which reminds me, I just got my first 200VDC hit from my BC-1004.  I even took the time to test every IF adjuster screw too with a DMM to note which are (though I have been assuming all are) and I grazed one anyway and zap.  At least it didn't hurt for more than a split second.

If any one of these voltages could be regulated, which would be best to be regulated?  The -50?

+380 VDC at  50mA
+250 VDC at 100mA
+100 VDC at 4.5mA
 -50 VDC at  11mA
 6.3 VAC at   7A

Whichever one feeds the local oscillator, prolly the +100V.

The -50 is bias, no reason to regulate that.  The +380 is for the B+ on the audio outputs, no reason to regulate that either.  The +250 is the plate supply for the IF and RF amps, doesn't need to be regulated either.