20-07-2020, 08:39 AM
Tried it from dusk. It does pick up a few UK MW stations. Very sharp tuning. Still nothing on either SW band or LW.
So I measured the few resistors. Apart from the coil/switch unit it's a very minimalist battery valve superhet
Using the designations on the circuit I edited:
(code@measured)
R1: 27K @ 33K, DK96 g1 LO grid stopper
R -: 150 @ 180, DK96 g1 LO grid stopper
R2: 33K @ 28K, DK96 LO HT via coil to g2 (pseudo triode anode). No decoupler!
R3: none, it's HT filter for DF96 on the Philips G77. The DF96 g2 is often fed from the R2, LO HT dropper/filter. Here g2 and IFT HT go to main HT.
R4: 3M3 @ 3M7, AGC filter feed. The AGC only feeds V2, there is no AGC to the DK96.
R5: 47K @ 76K, IF stop to volume pot. Now replaced. Little if any change.
R6: 1M pot. A new one was fitted due to faulty switch on the old one.
R7: 10M @ 11M3, DAF96 grid leak / bias.
R8: 2M2 @ 3M1, DAF96 screen grid / g2. The leaky "hunts modseal style" 40nF cap was replaced on the first day, that would have killed gain.
R9: 1M @ 967K, DAF96 anode load. C18 maybe should be checked as audio is muffled.
R10: 2M2 @ 3M1, DL96 g1 bias. Soldered between B7G socket and power switch HT- as it is switched. A wire returns to the B7G power socket where the R11 and R12 are fitted.
R11: 330. Was replaced early as it was about 400Ω. Part of DL96 bias via HT-. Mounted between pins 2 & 3 of B7G power socket, but no plug connection.
R12: 100. Was replaced on first day as was about 450Ω. R11 and R10 giving about -3.5V for bias. Mounted between pin 2 of B7G power socket and earth / OV common on the corner of audio transformer surround.
Still no LW, though works at about right frequencies on sig gen with 1 or 2 turns around ferrite rod.
MW reception was poor / quiet.
Buzz when touching signal points on volume control as loud as would be expected on 62V HT.
I've double checked this "minimalist superhet"
No RF / Mixer AGC (DK96)
No grid leak resistor on RF grid, pin 6 DK96. The pin 6 to ground:
OC1: 1.6 to 1.7Ω
OC2: 1.6 to 1.7Ω
MW: 2.4Ω
LW: 10Ω
All buttons out: 2.4Ω.
There are four coils at the four switches. The one at the LW switch looks to have too few turns for LW. It also seems to have alloy slugs. Perhaps this is the SW RF in coil for both SW bands.
The coil at the 2nd switch, OC2 (what I called SW1 earlier, 50m to 40m) looks more like MW or LW. The coil at the MW switch is similar. The coil at the 1st switch, OC1, does look like a SW LO coil. A theory to test. Check signal on g2 of DK96 (even at 10:1 the scope probe on g1/LO tuning cap pulls the frequency down to much. See are there only three LO coils (the LW and MW could share a coil) and if coil at LW switch position, 4th, is actually a SW RF coil. It's not even impossible that there are only two LO coils, one for all of SW and one for LW and MW, as there are five silver mica caps at the switch/coil unit.
The valve sockets seem OK apart from the DAF96, which is slightly intermittent. The checking of LO at g2 DK96 and feeding sig gen via a 10:1 scope probe to RF section of tuning should establish if the switch bank is working and what the four coils do.
So I won't give up just yet as it looks like it's now close to working?
So I measured the few resistors. Apart from the coil/switch unit it's a very minimalist battery valve superhet
Using the designations on the circuit I edited:
(code@measured)
R1: 27K @ 33K, DK96 g1 LO grid stopper
R -: 150 @ 180, DK96 g1 LO grid stopper
R2: 33K @ 28K, DK96 LO HT via coil to g2 (pseudo triode anode). No decoupler!
R3: none, it's HT filter for DF96 on the Philips G77. The DF96 g2 is often fed from the R2, LO HT dropper/filter. Here g2 and IFT HT go to main HT.
R4: 3M3 @ 3M7, AGC filter feed. The AGC only feeds V2, there is no AGC to the DK96.
R5: 47K @ 76K, IF stop to volume pot. Now replaced. Little if any change.
R6: 1M pot. A new one was fitted due to faulty switch on the old one.
R7: 10M @ 11M3, DAF96 grid leak / bias.
R8: 2M2 @ 3M1, DAF96 screen grid / g2. The leaky "hunts modseal style" 40nF cap was replaced on the first day, that would have killed gain.
R9: 1M @ 967K, DAF96 anode load. C18 maybe should be checked as audio is muffled.
R10: 2M2 @ 3M1, DL96 g1 bias. Soldered between B7G socket and power switch HT- as it is switched. A wire returns to the B7G power socket where the R11 and R12 are fitted.
R11: 330. Was replaced early as it was about 400Ω. Part of DL96 bias via HT-. Mounted between pins 2 & 3 of B7G power socket, but no plug connection.
R12: 100. Was replaced on first day as was about 450Ω. R11 and R10 giving about -3.5V for bias. Mounted between pin 2 of B7G power socket and earth / OV common on the corner of audio transformer surround.
Still no LW, though works at about right frequencies on sig gen with 1 or 2 turns around ferrite rod.
MW reception was poor / quiet.
Buzz when touching signal points on volume control as loud as would be expected on 62V HT.
I've double checked this "minimalist superhet"
No RF / Mixer AGC (DK96)
No grid leak resistor on RF grid, pin 6 DK96. The pin 6 to ground:
OC1: 1.6 to 1.7Ω
OC2: 1.6 to 1.7Ω
MW: 2.4Ω
LW: 10Ω
All buttons out: 2.4Ω.
There are four coils at the four switches. The one at the LW switch looks to have too few turns for LW. It also seems to have alloy slugs. Perhaps this is the SW RF in coil for both SW bands.
The coil at the 2nd switch, OC2 (what I called SW1 earlier, 50m to 40m) looks more like MW or LW. The coil at the MW switch is similar. The coil at the 1st switch, OC1, does look like a SW LO coil. A theory to test. Check signal on g2 of DK96 (even at 10:1 the scope probe on g1/LO tuning cap pulls the frequency down to much. See are there only three LO coils (the LW and MW could share a coil) and if coil at LW switch position, 4th, is actually a SW RF coil. It's not even impossible that there are only two LO coils, one for all of SW and one for LW and MW, as there are five silver mica caps at the switch/coil unit.
The valve sockets seem OK apart from the DAF96, which is slightly intermittent. The checking of LO at g2 DK96 and feeding sig gen via a 10:1 scope probe to RF section of tuning should establish if the switch bank is working and what the four coils do.
So I won't give up just yet as it looks like it's now close to working?
