Thank you everyone for your help on this project. I’m starting to feel very dumb about now .. I didn’t think that I’d put so much time into this project and not get satisfactory results by now :-(
So, here’s what I’ve done to date:
- Added six (6) 0.005uFD caps .. one to each filament connection.
- Added 0.004 to the feed end of the plate choke to keep RF above deck.
- Removed plates from the neutralizing capacitor. (I did this before reading N2EY’s message .. )
Here are some photo's .. (Please let me know if I'm doing this correctly ..)
Here’s the choke bypass .. Hope I did this right. I only had 0.002’s so I paralleled them.http://www.bignick.net/ssb/choke_bypass.jpg
I don’t know if this was in my last photo’s, but I used braided leads to the Neutralization cap.http://www.bignick.net/ssb/braid_to_neut.jpg
Here’s the 6DQ5 w/added filament cap. There already are bypass caps on pins 3 and 6 as indicated in the schematic. Are these leads too long?
Voltages as follows:
Pin-1 Grid (-107VDC) key up, (-81VDC) Key down.
Pin-8 Screen 148VDC
Pin-3 Cathode 0.0VDC Key up; 0.288 VDC, key down; (across a 27 Ohm Cathode resistor = ~11 mA)
Here's something that I didn't know - Plate Voltage - Key up 1,066VDC, Key down; 966VDC.
Could that be causing too much gain? I'm using a Hammond 278X transformer; 800V CT 200MADC.http://www.bignick.net/ssb/6DQ5.jpg
Here’s the 6CL6 w/added filament cap. The plate voltage is ~355VDC which seems high. Cathode is about 5.56VDC. Grid to ground is 0.012VDC so I suppose the grid is negative relative to the cathode? I didn’t see any parasitics. The tube manual says that pin-7 goes to cathode but ARRL has it indicated as connected to ground? It already has a 0.01uFD bypassing its screen.
Pin-8 (screen) is 245VDC.http://www.bignick.net/ssb/6CL6.jpg
Here’s the 6BA7 w/filament cap. It already has a 0.001uFD cap bypassing its screen.http://www.bignick.net/ssb/6BA7.jpg
Here’s the 6AU6 w/filament cap. 0.001uFD bypasses pin-6.http://www.bignick.net/ssb/6AU6.jpg
Here’s the 6CG7 w/filament bypass cap. Not much to bypass ‘cause it’s a triode.http://www.bignick.net/ssb/6CG7.jpg
Here’s the driver cap between 6CL6 and 6DQ5. It’s rated at 630VDC. I’ll need to find a larger voltage replacement.http://www.bignick.net/ssb/driver_cap.jpg
Here’s an under the chaassis view.http://www.bignick.net/ssb/under.jpg
Filament voltage measures 6.7 VAC with 110VAC line voltage. Is that too high? If so, how could I correct it?
Do you suppose that I should re-dress those fat RF leads?
The driver tube runs very hot, but the plate is not red.
Some of the tubes have redundant pins. Should these be connected?
Note: Instability happens with the 80 meter coils but not the 20 meter coils. I’m not sure if this is a clue. Also, last night I had connected my Rigol DSA815-TG to the output section with the transmitter powered down. I injected the tracking generator at pin-6 of the 6CL6 and the input to the analyzer to the coax output.
I could easily see that I could peak and move the peak resonance for 80m. But, there is a second strong peak at 1.5MHz as well as the desired 3.5MHz peak.
I don’t know what is causing the 1.5MHz peak or if it’s an issue or not.
Bottom line – unfortunately, no discernible change. Looking at the output with the +700VDC, 27 Ohm and 5.1K resistors disconnected, the output is minimum when the Neutralization capacitor plates are full open. I have yet to try and additional 10 p in series. I’m not certain that I could get the neutralization leads any shorter or more direct that they are. I’ve replace the old “White-Wire” with a heavy gage single conductor.
I’m out of time for now but will pick up on this again soon.
Thanks again! I’m stuck!