Uh, "trans-genred? Yeah, this 10-tube Phantom got turned into a Maverick. A genre-change operation.
It arrived here with a quirky setup, four big 30-Watt rated tubes driving six smaller 20-Watt rated tubes. Just looked backwards. It had clobbered only two of the six small ones. I posted pics of this linear a few weeks ago, and got a suggestion from Linearone (I think) to swap the large tubes into the final stage and the small ones into the driver. Would make it more like a Maverick than a Phantom. The owner of the thing thought this sounded a lot better than buying a set of final tubes. Thanks Linearone, wish I had thought of it first.
Of course it needed more than that. The driver tubes needed fixed bias. The tube-type keying circuit had to go, which means the relay had to be changed from a 110-Volt DC coil to a 12-Volt. The heater wiring had to be changed, since the four large 31LZ6 tubes are wired to take the 120-Volt AC line directly the the four heaters wired in series. Now that the four big tubes are the finals and not the drivers, the two heater pins on each of eight tube sockets get rewired. The monster ham-band coils needed to go, a safety choke was needed on the final Load control. The fixed bias needed blocking diodes so the bias filter caps can be made bigger. If you turn down the radio's carrier with the old bias filter caps you'll see AC ripple on your amplified carrier. Long story short it needed the 47-year update treatment as well as the tube swaperoo.
Gotta figure it wasn't built long after the date on the three transformers. Says second week of 1977.
First the heater circuits get rewired. The two red wires lead to the 120-Volt circuit that also runs the fan. The outboard four final sockets get their heaters wired in series. The blue disc capacitor on each tube socket is a safety-approved capacitor for line-voltage service.
At least one disc cap is needed on each tube's heater. It can become a source of unwanted feedback without them. And yes, I have seen a linear oscillate because those parts were left out.
The original band selector was already taken loose, and the driver coil was cut down for 11 meters only. It was about three times this long from the factory.
The final coil had an odd setup, with one end grounded.
Maybe that works okay, but I stick to what I know.
Probably should have cut it down more, but soldering across three turns was the sweet spot.
Of course all the electrolytic caps are original. They just have to go. The one 1 meg 2 Watt carbon-comp resistor in the pic is a lame bleeder that does nothing. You can't bleed down DC current from capacitors in series. It takes a separate capacitor across each cap. This is how D&A amplifiers got the reputation for severe shocks with the power cord unplugged. No effective bleeder resistors.
I adopted the policy of replacing the original bridge-rectifier diodes. Yes, they're rated at 2.5 Amps, but the new filters will put a bigger surge current through them. Better safe than sorry.
Apparently I failed to snap a pic of the new 1N5408 rectifiers, but you get the idea.
Here are the three 220uf at 500 Volt caps that we use to replace the eight 100uf 350-Volt parts that came out of it. Takes two in series for the high-side B+, and one for the low side. Each cap has a 220K 2 Watt bleeder on it. Takes a minute or two, but it will bleed the filters down and keep them that way.
I didn't snap a pic of the "before" final grid-bias circuit. It had a small 100uf filter cap that won't filter the AC hum from the bias voltage all that well. If this cap is made large enough for good ripple filtering, it will also charge up from the "grid leak" voltage when the tubes' grids act like a rectifier producing a negative DC voltage way higher than the 8 Volts this circuit feeds to them. But there's a simple fix for this either/or dilemma.
There was one empty lug on this tie strip. The green wire leading off to the top of the pic is feeding 6.3 Volts AC to the small rectifier diode. It now charges the 1000f 25 Volt cap with good filtering and very little "hum" ripple. The green wire disappearing below the bottom of the pic leads to the final tubes' grids, by way of a RF choke. The four 2 Watt resistors in series-parallel add up to 1000 ohms at 8 Watts total. This is the return circuit to ground for the grids of the final tubes. The fat diode is in between the filter cap and the wire to the tubes. It will block the high negative DC grid-leak voltage from reaching the filter cap.
Why go to this trouble? Without this added diode the 1000uf cap will charge up to well over negative 25 Volts. More than enough to shut the final tubes down (they call this cutoff bias) until the filter cap bleeds back down the steady negative 8 Volts it's there to provide. Does nasty things to the audio. The second "blocking" diode prevents the higher negative voltage from reaching the filter.
The driver tank coil originally had one end grounded. This provided a DC ground for the final tubes' cathode connections on pin 2. The red RF choke does that now.
There's nothing special about rewiring pin 4 and 5 of each driver-tube socket. The driver sockets had been wired with four 31-Volt heaters in series, so the 6.3-Volt power for the small driver tubes has to be restored. The two fat red wires bring 12.6 Volts from the transformers. The left two driver sockets are wired in series, to split the voltage and put 6.3 Volts on each tube. The two right-hand sockets are in series. The "midpoint" wire that runs from one tube socket to the next gets grounded. This gets us 6.3 Volts to feed a bias rectifier.
Also visible in this pic are pin 2 and pin 6 of each driver socket. They were soldered to ground and got (gently) unsoldered from the saddle ring of the socket. Those two pins are jumped together inside the tube. A cheap chinesium .01uf disc cap goes from either pin 2 or 6 to ground on each driver socket and a wire ties the control-grid pins of each driver socket together.
Now that all four driver tubes have the control grid taken loose from ground and all four tied together the parts get removed from the keying-tube socket. They're just in the way and we need the single-lug tie strip for the next step. Be nice to the axial RF choke connected to the keying tube socket. We'll need it later on.
A rectifier diode has the cathode (banded) end on pin 5 of the lower tube socket where the fat red wire is feeding 6.3 VAC. The other end of the diode goes to the tie strip and to the negative end of another 1000uf 25 Volt filter cap. A 1k 5 Watt resistor goes from pin 6 of the upper socket to ground. Last missing link is another rectifier diode from the negative 8 Volts on the tie strip lug to pin 6 of the upper driver tube socket, This delivers the negative 8 Volts bias to the control grid of each tube while isolating the filter cap from any higher negative DC voltage generated on the grid pins of the driver tubes. This will prevent the driver tubes from running hot when the radio's carrier is turned down. Grounding the driver grids the way the factory did it would cause that.
The sharp-eyed reader will observe that the antenna relay has been removed. A relay with a 12-Volt DC coil will take the place of the 1977 relay with the 110-Volt DC coil. First we need a source of low-voltage DC to power the new relay. The Phantom wasn't built with one. Has to be mounted somewhere. Rather than drill a mount hole for this tie strip, an empty hole where a toggle switch used to be gets fat washers to mount it with a #6 screw.
A half-wave voltage doubler circuit takes two diodes and two filter caps. Most low-voltage keying circuits feed the hot side of the 12 Volts into the standby switch, and then on to the relay. The Phantom has one side of the standby switch grounded. It was meant to cut the keying tube's ground connection for standby. I didn't feel like running a new wire all the way to the standby switch, so we'll just connect the ground side of our voltage doubler through the standby switch. The blue wire on the left is bringing 6.3 Volts AC.
Here is the rest of the half-wave voltage doubler. The red wire barely visible at the top leads to the hot side of the relay coil. Note that the ground lug at the center of this tie strip has nothing soldered to it.
Open-frame 3-pole relays with a 12 Volt DC coil have gotten hard to track down. This relay is still sold by Mouser and others. There's no room for the plastic cap so it has to go.
The flexible lead from the common pole on the two outer circuits is unsoldered from its lug. A commutating diode goes across the two coil lugs and two wires leading to the keying circuit are easier to install before it's mounted.
These used to be made with a threaded hole in the solenoid's core. Made mounting one of these easier. But VHB to the rescue. If you're not familiar with this stuff, it has an aggressive adhesive bond that strengthens with heat. Doesn't dry out and fall off like the stuff from the drug store office-supply aisle.
There is barely room for this relay, but it fits.
The two free black pigtail leads are not very visible here, but one goes to the center pin of each coax socket. This keeps the unshielded wire path your barefoot signal passes through as short as possible. Keeps down the SWR the Phantom will add to the antenna by being in line while turned off. The fat coax is the output from the topside Load control. The small red RF choke is the one we kept after dismantling the old keying circuit on the tiny tube socket. It's called a "safety" choke. Yeah, you need it. I'll skip why. Too much more ground to cover.
I had to drill a hole in the back panel to mount the keying circuit. Into every life a little rain must fall. It mounts by the keying transistor's metal tab. The black wire from the relay coil isn't clearly visible here, but it goes to the "out" pad on the keying-circuit board.
The front-panel "SSB" switch has to have one of its two wires soldered to ground. The other one goes to the pad marked "SSB" on the keying circuit.
Last detail is to turn on the high-voltage relay when the antenna relay closes. The green wire on the center circuit of the relay goes to the hot side of the HV relay's coil. And this makes 20 images so this will have to continue in a second post. Pretty sure 20 images per post is the limit I ran into last time this came up.
73
It arrived here with a quirky setup, four big 30-Watt rated tubes driving six smaller 20-Watt rated tubes. Just looked backwards. It had clobbered only two of the six small ones. I posted pics of this linear a few weeks ago, and got a suggestion from Linearone (I think) to swap the large tubes into the final stage and the small ones into the driver. Would make it more like a Maverick than a Phantom. The owner of the thing thought this sounded a lot better than buying a set of final tubes. Thanks Linearone, wish I had thought of it first.
Of course it needed more than that. The driver tubes needed fixed bias. The tube-type keying circuit had to go, which means the relay had to be changed from a 110-Volt DC coil to a 12-Volt. The heater wiring had to be changed, since the four large 31LZ6 tubes are wired to take the 120-Volt AC line directly the the four heaters wired in series. Now that the four big tubes are the finals and not the drivers, the two heater pins on each of eight tube sockets get rewired. The monster ham-band coils needed to go, a safety choke was needed on the final Load control. The fixed bias needed blocking diodes so the bias filter caps can be made bigger. If you turn down the radio's carrier with the old bias filter caps you'll see AC ripple on your amplified carrier. Long story short it needed the 47-year update treatment as well as the tube swaperoo.
Gotta figure it wasn't built long after the date on the three transformers. Says second week of 1977.
First the heater circuits get rewired. The two red wires lead to the 120-Volt circuit that also runs the fan. The outboard four final sockets get their heaters wired in series. The blue disc capacitor on each tube socket is a safety-approved capacitor for line-voltage service.
At least one disc cap is needed on each tube's heater. It can become a source of unwanted feedback without them. And yes, I have seen a linear oscillate because those parts were left out.
The original band selector was already taken loose, and the driver coil was cut down for 11 meters only. It was about three times this long from the factory.
The final coil had an odd setup, with one end grounded.
Maybe that works okay, but I stick to what I know.
Probably should have cut it down more, but soldering across three turns was the sweet spot.
Of course all the electrolytic caps are original. They just have to go. The one 1 meg 2 Watt carbon-comp resistor in the pic is a lame bleeder that does nothing. You can't bleed down DC current from capacitors in series. It takes a separate capacitor across each cap. This is how D&A amplifiers got the reputation for severe shocks with the power cord unplugged. No effective bleeder resistors.
I adopted the policy of replacing the original bridge-rectifier diodes. Yes, they're rated at 2.5 Amps, but the new filters will put a bigger surge current through them. Better safe than sorry.
Apparently I failed to snap a pic of the new 1N5408 rectifiers, but you get the idea.
Here are the three 220uf at 500 Volt caps that we use to replace the eight 100uf 350-Volt parts that came out of it. Takes two in series for the high-side B+, and one for the low side. Each cap has a 220K 2 Watt bleeder on it. Takes a minute or two, but it will bleed the filters down and keep them that way.
I didn't snap a pic of the "before" final grid-bias circuit. It had a small 100uf filter cap that won't filter the AC hum from the bias voltage all that well. If this cap is made large enough for good ripple filtering, it will also charge up from the "grid leak" voltage when the tubes' grids act like a rectifier producing a negative DC voltage way higher than the 8 Volts this circuit feeds to them. But there's a simple fix for this either/or dilemma.
There was one empty lug on this tie strip. The green wire leading off to the top of the pic is feeding 6.3 Volts AC to the small rectifier diode. It now charges the 1000f 25 Volt cap with good filtering and very little "hum" ripple. The green wire disappearing below the bottom of the pic leads to the final tubes' grids, by way of a RF choke. The four 2 Watt resistors in series-parallel add up to 1000 ohms at 8 Watts total. This is the return circuit to ground for the grids of the final tubes. The fat diode is in between the filter cap and the wire to the tubes. It will block the high negative DC grid-leak voltage from reaching the filter cap.
Why go to this trouble? Without this added diode the 1000uf cap will charge up to well over negative 25 Volts. More than enough to shut the final tubes down (they call this cutoff bias) until the filter cap bleeds back down the steady negative 8 Volts it's there to provide. Does nasty things to the audio. The second "blocking" diode prevents the higher negative voltage from reaching the filter.
The driver tank coil originally had one end grounded. This provided a DC ground for the final tubes' cathode connections on pin 2. The red RF choke does that now.
There's nothing special about rewiring pin 4 and 5 of each driver-tube socket. The driver sockets had been wired with four 31-Volt heaters in series, so the 6.3-Volt power for the small driver tubes has to be restored. The two fat red wires bring 12.6 Volts from the transformers. The left two driver sockets are wired in series, to split the voltage and put 6.3 Volts on each tube. The two right-hand sockets are in series. The "midpoint" wire that runs from one tube socket to the next gets grounded. This gets us 6.3 Volts to feed a bias rectifier.
Also visible in this pic are pin 2 and pin 6 of each driver socket. They were soldered to ground and got (gently) unsoldered from the saddle ring of the socket. Those two pins are jumped together inside the tube. A cheap chinesium .01uf disc cap goes from either pin 2 or 6 to ground on each driver socket and a wire ties the control-grid pins of each driver socket together.
Now that all four driver tubes have the control grid taken loose from ground and all four tied together the parts get removed from the keying-tube socket. They're just in the way and we need the single-lug tie strip for the next step. Be nice to the axial RF choke connected to the keying tube socket. We'll need it later on.
A rectifier diode has the cathode (banded) end on pin 5 of the lower tube socket where the fat red wire is feeding 6.3 VAC. The other end of the diode goes to the tie strip and to the negative end of another 1000uf 25 Volt filter cap. A 1k 5 Watt resistor goes from pin 6 of the upper socket to ground. Last missing link is another rectifier diode from the negative 8 Volts on the tie strip lug to pin 6 of the upper driver tube socket, This delivers the negative 8 Volts bias to the control grid of each tube while isolating the filter cap from any higher negative DC voltage generated on the grid pins of the driver tubes. This will prevent the driver tubes from running hot when the radio's carrier is turned down. Grounding the driver grids the way the factory did it would cause that.
The sharp-eyed reader will observe that the antenna relay has been removed. A relay with a 12-Volt DC coil will take the place of the 1977 relay with the 110-Volt DC coil. First we need a source of low-voltage DC to power the new relay. The Phantom wasn't built with one. Has to be mounted somewhere. Rather than drill a mount hole for this tie strip, an empty hole where a toggle switch used to be gets fat washers to mount it with a #6 screw.
A half-wave voltage doubler circuit takes two diodes and two filter caps. Most low-voltage keying circuits feed the hot side of the 12 Volts into the standby switch, and then on to the relay. The Phantom has one side of the standby switch grounded. It was meant to cut the keying tube's ground connection for standby. I didn't feel like running a new wire all the way to the standby switch, so we'll just connect the ground side of our voltage doubler through the standby switch. The blue wire on the left is bringing 6.3 Volts AC.
Here is the rest of the half-wave voltage doubler. The red wire barely visible at the top leads to the hot side of the relay coil. Note that the ground lug at the center of this tie strip has nothing soldered to it.
Open-frame 3-pole relays with a 12 Volt DC coil have gotten hard to track down. This relay is still sold by Mouser and others. There's no room for the plastic cap so it has to go.
The flexible lead from the common pole on the two outer circuits is unsoldered from its lug. A commutating diode goes across the two coil lugs and two wires leading to the keying circuit are easier to install before it's mounted.
These used to be made with a threaded hole in the solenoid's core. Made mounting one of these easier. But VHB to the rescue. If you're not familiar with this stuff, it has an aggressive adhesive bond that strengthens with heat. Doesn't dry out and fall off like the stuff from the drug store office-supply aisle.
There is barely room for this relay, but it fits.
The two free black pigtail leads are not very visible here, but one goes to the center pin of each coax socket. This keeps the unshielded wire path your barefoot signal passes through as short as possible. Keeps down the SWR the Phantom will add to the antenna by being in line while turned off. The fat coax is the output from the topside Load control. The small red RF choke is the one we kept after dismantling the old keying circuit on the tiny tube socket. It's called a "safety" choke. Yeah, you need it. I'll skip why. Too much more ground to cover.
I had to drill a hole in the back panel to mount the keying circuit. Into every life a little rain must fall. It mounts by the keying transistor's metal tab. The black wire from the relay coil isn't clearly visible here, but it goes to the "out" pad on the keying-circuit board.
The front-panel "SSB" switch has to have one of its two wires soldered to ground. The other one goes to the pad marked "SSB" on the keying circuit.
Last detail is to turn on the high-voltage relay when the antenna relay closes. The green wire on the center circuit of the relay goes to the hot side of the HV relay's coil. And this makes 20 images so this will have to continue in a second post. Pretty sure 20 images per post is the limit I ran into last time this came up.
73
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