inductive kick killer

[w4bfs]

a lot of vintage radio modifying activity on the forum lately has reminded us of the need to look at solid state rectifiers replacing vacuum tubes as a means to increase supply efficiency, heat reduction, output voltage, etc.  a total system review should be performed by measurement to see what has changed and those systems that are affected.

example: an EFJ ranger has been solid stated and recapped.  

     sounds simple.   hmmm lets see .... HV 5r4 ... looks like B+ went up about 100V
                                                          LV 6AX5...looks like that C+ went up about 100V too- smells like something hot                                                             bias 6AL5 .... looks like that went up 40V
                                                          fil AC .... up to 7V AC on the 6.3 fil supply

      the point here is this .... this simple change is now driving a power supply redesign including but not limited to:
1. adding step start or some other start current limiting - ignoring this places function (on-off) switch at jeopardy
2. inductive kick or back emf damage to all those diodes facing inductor input supplies.  a few small value capacitors or transsorbs placed in the right positions can help this.
3. wire up the 5r4 5V fil winding to buck the primary to lower that 6.3V (and other windings) back  to closer spec



 
                                                          
 

[n8fvj]

a lot of vintage radio modifying activity on the forum lately has reminded us of the need to look at solid state rectifiers replacing vacuum tubes as a means to increase supply efficiency, heat reduction, output voltage, etc.  a total system review should be performed by measurement to see what has changed and those systems that are affected.

example: an EFJ ranger has been solid stated and recapped.  

     sounds simple.   hmmm lets see .... HV 5r4 ... looks like B+ went up about 100V
                                                          LV 6AX5...looks like that C+ went up about 100V too- smells like something            ishot
                                                          bias 6AL5 .... looks like that went up 40V

 
                                                          
 

With Johnson Ranger 115 volt transformer on 120 volts, SS 5R4 is about 70 volts rise. 6AX5 being cathode based tube rise is 25 volts rise and 6AL5 is also cathode based, but bias due to divider resistor is about 2 volts higher. I can live with bias and LV solid-state, but do not like 5R4 extra 70 volts and that supplies modulator tubes. SS 5R4 over volts the modulator 1614 tube plates and would require 6550 tubes rated at 600 volts to be safe.

[w4bfs]

a lot of vintage radio modifying activity on the forum lately has reminded us of the need to look at solid state rectifiers replacing vacuum tubes as a means to increase supply efficiency, heat reduction, output voltage, etc.  a total system review should be performed by measurement to see what has changed and those systems that are affected.

example: an EFJ ranger has been solid stated and recapped.  

     sounds simple.   hmmm lets see .... HV 5r4 ... looks like B+ went up about 100V
                                                          LV 6AX5...looks like that C+ went up about 100V too- smells like something            ishot
                                                          bias 6AL5 .... looks like that went up 40V

 
With Johnson Ranger 115 volt transformer on 120 volts, SS 5R4 is about 70 volts rise. 6AX5 being cathode based tube rise is 25 volts rise and 6AL5 is also cathode based, but bias due to divider resistor is about 2 volts higher. I can live with bias and LV solid-state, but do not like 5R4 extra 70 volts and that supplies modulator tubes. SS 5R4 over volts the modulator 1614 tube plates and would require 6550 tubes rated at 600 volts to be safe.

the often unrecognized problem is the increase in C+ from 275V nominal to 375V.  In an unmodified ranger this increases the 4W dissipation on the drive control to 6.635W .  It has been a while since I encountered this and my line voltage in those days was higher.  if modifications are not wanted to be made then I would consider using a Variac to lower the line V.

[w4bfs]

oh yes 6550 tube is a hi buck goodie.  you could use a sovtek 5881 which loves 600V on plate in the modulator

[n8fvj]

the often unrecognized problem is the increase in C+ from 275V nominal to 375V.  In an unmodified ranger this increases the 4W dissipation on the drive control to 6.635W .  It has been a while since I encountered this and my line voltage in those days was higher.  if modifications are not wanted to be made then I would consider using a Variac to lower the line V

The C+ as you state (low voltage) is rectified by a 6AX5 cathode type rectifier. Tube voltage drop is about 20 volts. Supplies 370 volts no load and 340 volt underload (keyed). Using a solid-state 6AX5 rectifier would add about 19 volts higher.

(edited)

[K8DI]

oh yes 6550 tube is a hi buck goodie.  you could use a sovtek 5881 which loves 600V on plate in the modulator

Another higher plate voltage option is 6CA7/EL34.  Costs much less than a 6550, is fine at 600v, but does require a minor mod (its cathode and suppressor/G3 are not internally tied together like they are in the 1614/6L6/6550 tubes so you have to connect pins 1 and 8 together at the socket).

Ed

[W2JBL]

   Step start for a Ranger? Really? People new to boatanchors with little or know experience read this kind of BS and end up scared of their rigs. Bought a fairly decent Ranger a year ago, and among other mods, I solid stated the power supply, just like the one I had some 40 years ago I used as a (continous duty) pirate radio transmitter. No smoke, no issues at all. Gennie original 1614's in the modulator too. More Power out and runs cooler. Line voltage is 125. No Variacs, step start, or full radio condoms here. The truth is that this technology is far more robust and reliable over a wide variety of conditions than most people who did not grow up with it realize.  And by the way- The "C" voltage is for BIAS, not LV B+. It's in the ARRL handbook (pre solid state).