[Boatanchors] CE-200V progress/problems - Status update

[Paul]

I'm copying the boatanchors group on this in case there may be some interest outside the Central Electronics community. It concerns my attempts at getting a newly acquired CE-200V operational. For those in the BA community not familiar with the CE 100V/200V family they are a broadband transmitter, meaning once initial setup controls are set, just switch bands 80 thru 10 (with 160 as an option) and adjust the VFO to the frequency. That's it. No tuning etc. Common operation today, but leading edge state-of-the-art back in the late 1950's very early 1960's. 
 
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First off, my sincere thanks to the many that have offered suggestions, comments, and provided copies of various documents regarding the 100V/200V family, all were very helpful in making progress on this project.
 
A little long winded here, but it may help someone in the future, so I've relisted the problem as originally found as a refresher, along with the status so far :
 
Problem 1. Scope: the scope trace focus isn't working properly. The smallest point I can get is about 3/8" diameter which expands to about 1/2" diameter by adjusting the focus control. I can't get any finer point. The intensity control does seem to work OK, as the intensity adjusts from dim to a bright glow. The scope does seem to detect the RF as the 3/8"diameter spot does expand vertically as power is increased. 
 
Status: Resolved - Focus voltage should be in the 200vdc range, found mine in the 13vdc range. Problem was a small bit of corrosion had formed between one of the terminals of the focus control pot and the case of the pot, resulting in a 55 ohm resistance on the input side of the pot, dropping a whole bunch of voltage, resulting in a focus voltage swing of 13vdc to 0vdc. I didn't have an exact replacment pot at  hand so I disassembled the original pot, completely cleaned it out removing all corrosion in the process and reassembled. The pot now has the full 500K swing, with voltage varying from 380vdc to 0 vdc. I have perfect focus at 198vdc. Intensity control is working fine. RF vertical display is fine.
 
Problem 2. Power output is low on 80/40 meters. In CW, with the CW carrier and power controls set at max (fully clockwise) all I get on my 50 ohm Waters dummy load/wattmeter is 26 watts on 80 meters and 12 watts on 40 meters. An undistorted carrier is displayed on my external scope (Kenwood SM-220) consistent with those power readings. On the CE-200V input power meter, the reading is 90 watts input on both 80 and 40 meters. Meter reads 0 as expected when not keyed. AM position reads the same as CW.
 
Status: Resolved for 80 meters, improved on 40 meters - This was a multiple step solution, it required resolving problem 4 (poor sideband suppression) first. Once the sideband suppression problem was resolved, I was able to properly set the driver and final bias. Adjusting the driver bias level brought the 80 meter power up quite a bit, I was showing about 150 watts input on the 200V's meter and 80 watts output into my Waters dummyload/wattmeter. I had read a comment in one of the articles I was sent about trying different mixer tubes. I don't have a spare 6EH7 for the first mixer but I have several 6EJ7's for the second mixer. Swapped out the tubes and the first replacement tube I tried actually lowered the input/output wattage. But the second tube brought the power way up to specifications, I now have a full 175 watts input showing on the 200V meter and about 105 watts output on my Waters. This input/output remains constant across the 3.6mc to
 4.0mc range, output does drop just a slight amount, maybe 5 watts or so, when going below 3.6mc. RF display on my external scope still looks clean. As for 40 meters, this also improved somewhat with the driver adjustment and replacement of the 2nd mixer tube, but nowhere near maximum. Then quite by accident when switching between 80 and 40 meters, I failed to adjust the VFO from 3.8 to 7.2mc as I had been doing previously. That meant the VFO was at 6.8mc. Low and behold I had full power on 40 meters! 175 watts input indicated and 100 watts output. Started adjusting the VFO towards the 40 meter band and the power dropped right off. Right now I have full power between 6.5mc and 6.8mc but it drops off quickly when reaching 6.9mc. So I have a broadband alignment problem on 40 meters. I'm hoping/expecting it is in the driver/mixer stages which are adjustable. Problem is I don't have a RF sweep generator, I always borrowed one from work for nearly 38
 years, but since I retired and the business sold out and left town, that resource isn't available to me anymore. Guess I need to look for a sweep generator. Any suggestions or recommendations?
 
Problem 3. There is no power output at all on 20, 15 or 10 meters. With the same power control settings as 80 and 40, there is no power output displayed on either the dummy load wattmeter or external scope. The 200V meter indicates about 50 watts input with no output.
 
Status - Partially resolved - Once I had 80 and 40 working reaonably well, I re-tried 20, 15 and 10. Still nothing but, recalling the corrosion problem with the focus pot, I simply removed and cleaned the crystal sockets/pins. That got all three bands oscillating without doing anything else. I still don't have anywhere near full power on those three bands, they are all showing about 100 watts input and 25 watts output after tweaking the oscillators, but at least they are functioning. Another case of where I need to get a sweep generator so I can perform a good alignment, and also look real careful at all pin/socket junction points for corrosion effects. I think now that all bands are at least somewhat functional I will pull the coil assemblies to clean them and while they are out, add the 160 meter coil sets from Nick Tusa.
 
Problem 4. Poor sideband suppression: I switched to LSB and USB and find I am not able to null out the carrier. On 80 meters, in LSB, I have about 15 watts of output power showing. If I adjust the A null knob fully clockwise and the B null knob fully counterclockwise I can drop the power to about 10 watts, manipulation of the null controls cannot null the carrier more than that.
 
Status: Resolved - Here is where everyone who offered comments hit the nail on the head. All offered the suggestion to replace the caps and diodes in the caps/diode module can sets. I didn't have any 6mf but I made up some sets of paralled 4.7mfd and 1mfd caps until I found four sets that gave me 5.8mfd. Then I replaced the diodes (CK715's) with 1N4148's that I matched so each had a fe of .600. Plugged the cans back in and sideband suppression worked perfectly. After performing this step I read another article that was sent me indicating that the 6mfd wasn't all that critical, you could use anywhere from 4mf to 10 mf, just so the caps were matched. I've also had suggestions about problems in the PS2 area and I will probably look into that, particularly regarding adding the 1mfd/400v coupling cap between the PS2 module and plate of the Audio Phase Inverter. For the moment I'm leaving that alone as it all seems to be working fine now.
 
So what's next?
 
Trying to locate an RF Sweep Generator, but meanwhile, now that 80 meters CW seems to be working fine, tonight I plan to hook up the microphone and see how the audio stages are.
 
If all goes well, then I'll try to get it on 75 meters and see how it does in the real world.
 
73,
Paul W2EC