07-07-2016, 02:09 PM
Well, I finished the alignment of all ten bands. There were clear peaks on all bands except for the 19 meter band spread band. I was supposed to start with the trimmer at maximum tightness and then back off to the SECOND peak. I only found one peak, although there was reception on the band.
I was quite disappointed with the performance of the radio. One would think that a radio with a tuned RF amplifier stage and two IF amplifier stages would be quite sensitive. But it did not appear to be that sensitive. My antenna is only a 40 foot length of insulated wire strung across the basement ceiling (and I am in a rural area). Adding a ground connection did not help. I rechecked all the tubes, and all of them were good. I checked the voltages, and all seemed reasonable, but the available documentation does not have the voltages marked. The AVC voltage varied from -2.7 volts (with no antenna) to a maximum of -6.5 volts. That seems low to me, but there are no high power stations nearby. I plan on checking this voltage again with a strong signal from the signal generator. Some of the voltages I measured were:
B+ 233, B- 89
RF amplifier Plate +213, Screen +144, Suppressor -6.65
First Detector Plate +233, Screen +87, Grid -3.37
Oscillator Plate +131, Oscillator Grid -15
First IF amplifier Plate +234, Screen +87, Grid -2.8, Cathode +4.41 (with R301 maximum CW)
Second IF amplifier Plate +233, Screen +87, Control Grid and Suppressor -3.8
First Audio Amplifier Plate 68, Grid -3.45
Audio Outputs (6V6) Plates 223/216, Grids -11, Screens +233
All capacitors were changed/restuffed except for the mica capacitors. All resistors are in tolerance except for the 47K filter resistor inside the third IF transformer R302A (it measured 26% high) and R403 68 ohms (measured 23% high). I did not want to risk tearing into the IF transformer to change R302A. R403 was hidden under the band switch and would have been very dangerous to try and change – lots of hair-thin wires around.
Adjustment of the variable resistor on the back of the chassis (R301) does not seem to change the performance. This resistor varies the cathode bias of the first IF amplifier over a narrow range (4.36 to 8 volts). There is no mention of this resistor or how to adjust it in the available documentation.
If anyone has any troubleshooting suggestions, I would really like to hear them. I plan on checking the AVC voltage with a strong signal from my signal generator. Since the background noise is high, I also plan on shutting down all computers and monitors and listening at night vs. in the middle of the day. There are some mica capacitors in the RF signal chain that I did not check. I suppose I should check or change them.
I was quite disappointed with the performance of the radio. One would think that a radio with a tuned RF amplifier stage and two IF amplifier stages would be quite sensitive. But it did not appear to be that sensitive. My antenna is only a 40 foot length of insulated wire strung across the basement ceiling (and I am in a rural area). Adding a ground connection did not help. I rechecked all the tubes, and all of them were good. I checked the voltages, and all seemed reasonable, but the available documentation does not have the voltages marked. The AVC voltage varied from -2.7 volts (with no antenna) to a maximum of -6.5 volts. That seems low to me, but there are no high power stations nearby. I plan on checking this voltage again with a strong signal from the signal generator. Some of the voltages I measured were:
B+ 233, B- 89
RF amplifier Plate +213, Screen +144, Suppressor -6.65
First Detector Plate +233, Screen +87, Grid -3.37
Oscillator Plate +131, Oscillator Grid -15
First IF amplifier Plate +234, Screen +87, Grid -2.8, Cathode +4.41 (with R301 maximum CW)
Second IF amplifier Plate +233, Screen +87, Control Grid and Suppressor -3.8
First Audio Amplifier Plate 68, Grid -3.45
Audio Outputs (6V6) Plates 223/216, Grids -11, Screens +233
All capacitors were changed/restuffed except for the mica capacitors. All resistors are in tolerance except for the 47K filter resistor inside the third IF transformer R302A (it measured 26% high) and R403 68 ohms (measured 23% high). I did not want to risk tearing into the IF transformer to change R302A. R403 was hidden under the band switch and would have been very dangerous to try and change – lots of hair-thin wires around.
Adjustment of the variable resistor on the back of the chassis (R301) does not seem to change the performance. This resistor varies the cathode bias of the first IF amplifier over a narrow range (4.36 to 8 volts). There is no mention of this resistor or how to adjust it in the available documentation.
If anyone has any troubleshooting suggestions, I would really like to hear them. I plan on checking the AVC voltage with a strong signal from my signal generator. Since the background noise is high, I also plan on shutting down all computers and monitors and listening at night vs. in the middle of the day. There are some mica capacitors in the RF signal chain that I did not check. I suppose I should check or change them.
