This is the "FAILURE" power supply I built. IT HAD A VERY BAD HUM PROBLEM. I did not get the hum
under control so I abandonded this circuit and went to a more common configuration of an NPN pass
transistor configuration. ---->> Actually I learned and enjoyed even these failures!!!
I may try to figure out what really went wrong..in the near future. MY SUSPICION is that the PNP pass
transistors are oscillating!! I will build a single pnp pass transistor circuit from the ARRL handbook. And try
the circuit again. When I do. I will write the results here. I present this for information only.
ALSO PRESENTED: a power supply of my own design..simple and worked OK but not good enough
regulation for my FT 757 rig. (The dial lamps would go dim and the ALC circuit kicked in causing distortion
with my design. It did work with my FT301 rig.
under control so I abandonded this circuit and went to a more common configuration of an NPN pass
transistor configuration. ---->> Actually I learned and enjoyed even these failures!!!
I may try to figure out what really went wrong..in the near future. MY SUSPICION is that the PNP pass
transistors are oscillating!! I will build a single pnp pass transistor circuit from the ARRL handbook. And try
the circuit again. When I do. I will write the results here. I present this for information only.
ALSO PRESENTED: a power supply of my own design..simple and worked OK but not good enough
regulation for my FT 757 rig. (The dial lamps would go dim and the ALC circuit kicked in causing distortion
with my design. It did work with my FT301 rig.
The test bench gets kinda messy and cluttered when I embark upon projects.
The black colored solder sucking ventilation fan is shown in the picture (right).
You can see the discoloration of the charcoal filter. Good! It is doing its job of
filtering. I also have a HEPA filter (much larger) not shown in the picture. It also
filters the air when I am working and when I solder.
The black colored solder sucking ventilation fan is shown in the picture (right).
You can see the discoloration of the charcoal filter. Good! It is doing its job of
filtering. I also have a HEPA filter (much larger) not shown in the picture. It also
filters the air when I am working and when I solder.
The blue colored VARIAC transformer was used when testing this supply as was the
very large rheostat resistance and several large tapped wirewound resistors.
Normally I find bench work quite satisfying..but this 4 PNP pass transistor circuit
with its HUM problem was starting to get on my nerves! I had built several versions
of the single PNP pass transistor circuit from the ARRL Handbook in the late 70s
early 80s editions and it was a favourite circuit of mine. I quit on it this time..but I will
try it again maybe this winter and see what gives??? I ""suspect"" the PNP
transistors themselves may be not quite right!??
very large rheostat resistance and several large tapped wirewound resistors.
Normally I find bench work quite satisfying..but this 4 PNP pass transistor circuit
with its HUM problem was starting to get on my nerves! I had built several versions
of the single PNP pass transistor circuit from the ARRL Handbook in the late 70s
early 80s editions and it was a favourite circuit of mine. I quit on it this time..but I will
try it again maybe this winter and see what gives??? I ""suspect"" the PNP
transistors themselves may be not quite right!??
Below: I scanned a page from the 1981 ARRL Handbook. The fold in the middle
doesnt look so good. I will have to fix this later. But you get the idea of the circuit.
It is a single pass transistor (Q1) -- which can be a common 2N2955 PNP transistor
or a TIP 36C ect. I have built this circuit a number of times and have used it to
power qrp rigs and 2 meter rigs. Never any problems with HUM. This
time..HOWEVER.. with the 4 PASS transistors (PNP TIP 36Cs) I had HUM and lots of
it. I suspect the pass transistors are not proper..but I will have to confirm this later.
I still have all the circuits wired up and can work at them again later. I am most
curious to see if I can get a 4 PNP transistor circuit working. I may find some old
Motorola pnp transistors that I know are good quality. The TIP 36Cs with the hum
problem were bought at a discount price from China.
doesnt look so good. I will have to fix this later. But you get the idea of the circuit.
It is a single pass transistor (Q1) -- which can be a common 2N2955 PNP transistor
or a TIP 36C ect. I have built this circuit a number of times and have used it to
power qrp rigs and 2 meter rigs. Never any problems with HUM. This
time..HOWEVER.. with the 4 PASS transistors (PNP TIP 36Cs) I had HUM and lots of
it. I suspect the pass transistors are not proper..but I will have to confirm this later.
I still have all the circuits wired up and can work at them again later. I am most
curious to see if I can get a 4 PNP transistor circuit working. I may find some old
Motorola pnp transistors that I know are good quality. The TIP 36Cs with the hum
problem were bought at a discount price from China.
ABOVE; pictured a schematic of one of the 20 to 25 amp power supply circuit that I had hoped to build. I built a number of different variations of the above circuit.
I always used the same TIP36C pnp pass transistors. I only used 4 of the pass transistors vs. 6 (as in this schematic).
I did many of my own mods and experiments on this circuit..but always HUM on the output. Rather than beat a dead horse..I gave up on the PNP transistors..at least
for now. I then designed an NPN pass transistor supply based on my own ideas of a simple circuit that might work. SEE THE SCHEMATIC BELOW:
I always used the same TIP36C pnp pass transistors. I only used 4 of the pass transistors vs. 6 (as in this schematic).
I did many of my own mods and experiments on this circuit..but always HUM on the output. Rather than beat a dead horse..I gave up on the PNP transistors..at least
for now. I then designed an NPN pass transistor supply based on my own ideas of a simple circuit that might work. SEE THE SCHEMATIC BELOW:
This circuit looked like a
good simple power supply
with NO FRILLS.
I didnt get it going properly.
Doesnt mean it would not
work if you tried it.
I ((think)) it may have been a
fault with the actual
transistors I was using.
The TIP 36C s I was using
might have been mislabelled
or something.
I think they were oscillating
at a low frequency and
causing all the HUM
problems.
good simple power supply
with NO FRILLS.
I didnt get it going properly.
Doesnt mean it would not
work if you tried it.
I ((think)) it may have been a
fault with the actual
transistors I was using.
The TIP 36C s I was using
might have been mislabelled
or something.
I think they were oscillating
at a low frequency and
causing all the HUM
problems.
I actualled corresponded with an Engineer about his above circuit. He was quite an expert when it comes to these types of power supply circuits. Basically
what this fellow told me ..was that my circuit..ABOVE SCHEMATIC..was a type of VOLTAGE CLAMP CIRCUIT. It was not a regulated power supply in the true
sense!!
He is probably right..I am ""CLAMPING"" THE BASES OF the pass transistors at about 13.8 volts but IAM not directly regulating the output of the supply.
Still..the supply works but the regulation is not or was not stiff enough to allow the FT 757GX transceiver to work at 100 watts output. As the current
demand on the above supply went over about 14 amps or so..the "voltage" output of the supply dropped off significantly.
I might try this design later..with a modification. I may CLAMP THE OUTPUT VOLTAGE AT 13.8VOLTS WITH THE VOLTAGE REGULATOR AND AS WELL CLAMP
THE BASE OF THE TRANSISTORS WITH AN ADDITIONAL VOLTAGE REGULATOR OF ABOUT 12.6 VOLTS. THAT SHOULD (PERHAPS) WORK. --THE OVERVOLTAGE
CIRCUITRY (CROWBAR) WOULD NOT BE NECESSARY SINCE THE CLAMPING OF BOTH THE BASE AND COLLECTORS OF THE PASS TRANSISTORS SHOULD
PROVIDE ENOUGH REDUNDANT PROTECTION. -- I may try this circuit with another homebrew supply. When I do..I will write it up here!
In the above circuit..if the VOLTAGE REGULATOR FAILS -- THE PASS TRANSISTORS DO NOT CONDUCT AND THE OUTPUT DROPS TO ZERO..SO IT IS A WELL
PROTECTED CIRCUIT. A CROWBAR IS ACTUALLY REDUNDANT AND if I build this circuit back up and a homebrew power supply, I will not include an Over
Protection Crow Bar circuit on the output.
what this fellow told me ..was that my circuit..ABOVE SCHEMATIC..was a type of VOLTAGE CLAMP CIRCUIT. It was not a regulated power supply in the true
sense!!
He is probably right..I am ""CLAMPING"" THE BASES OF the pass transistors at about 13.8 volts but IAM not directly regulating the output of the supply.
Still..the supply works but the regulation is not or was not stiff enough to allow the FT 757GX transceiver to work at 100 watts output. As the current
demand on the above supply went over about 14 amps or so..the "voltage" output of the supply dropped off significantly.
I might try this design later..with a modification. I may CLAMP THE OUTPUT VOLTAGE AT 13.8VOLTS WITH THE VOLTAGE REGULATOR AND AS WELL CLAMP
THE BASE OF THE TRANSISTORS WITH AN ADDITIONAL VOLTAGE REGULATOR OF ABOUT 12.6 VOLTS. THAT SHOULD (PERHAPS) WORK. --THE OVERVOLTAGE
CIRCUITRY (CROWBAR) WOULD NOT BE NECESSARY SINCE THE CLAMPING OF BOTH THE BASE AND COLLECTORS OF THE PASS TRANSISTORS SHOULD
PROVIDE ENOUGH REDUNDANT PROTECTION. -- I may try this circuit with another homebrew supply. When I do..I will write it up here!
In the above circuit..if the VOLTAGE REGULATOR FAILS -- THE PASS TRANSISTORS DO NOT CONDUCT AND THE OUTPUT DROPS TO ZERO..SO IT IS A WELL
PROTECTED CIRCUIT. A CROWBAR IS ACTUALLY REDUNDANT AND if I build this circuit back up and a homebrew power supply, I will not include an Over
Protection Crow Bar circuit on the output.
Above: pictured: 4 PNP pass transistors type TIP36C. They are wired in parallel
and can use either an LM7812 or LM317 regulator chip. The circuit is a bit
simpler than the ones that use NPN pass transistors. I wired this all up and it
seemed to function fine..but when used with my 2 mtr FM transceiver I had
reports of real bad hum. I never got this circuit working (yet). I suspect that the
pass transistors might be oscillating or something?? Perhaps they are
amplifying the hum. I blame the transistors..but I cannot really prove it. What I
have to do is use another pass transistor..perhaps an old MOTOROLA
transistor like a 2n2955 (pnp complement of 2n3055). And build up another
circuit and try it to see if it works.
I switched over to NPN pass transistors and had no hum problems at all. I have
(previously) used an LM317 power supply with a single PNP pass transistor
with great sucess. Could the transistors be to blame??? I will have to figure
that out later.
and can use either an LM7812 or LM317 regulator chip. The circuit is a bit
simpler than the ones that use NPN pass transistors. I wired this all up and it
seemed to function fine..but when used with my 2 mtr FM transceiver I had
reports of real bad hum. I never got this circuit working (yet). I suspect that the
pass transistors might be oscillating or something?? Perhaps they are
amplifying the hum. I blame the transistors..but I cannot really prove it. What I
have to do is use another pass transistor..perhaps an old MOTOROLA
transistor like a 2n2955 (pnp complement of 2n3055). And build up another
circuit and try it to see if it works.
I switched over to NPN pass transistors and had no hum problems at all. I have
(previously) used an LM317 power supply with a single PNP pass transistor
with great sucess. Could the transistors be to blame??? I will have to figure
that out later.
This old circuitry pictured above (4 pnp transistors wired in parallel) did not work. I
still dont know why there was so much hum and ripple when I used this circuitry and
these parts. I still have this circuit in my junkbox and will later try it again to see if I
can get it to work. I blamed the transistors for awhile! I thought..maybe they were
oscillating or something. A mystery to be solved at a later date.
When I switched over to a more common old 2n3055 NPN pass transistor design..my
ripple and hum problems disappeared. I went a step furthur and implemented an
RS10 power supply regulator board and power transformer into my revamped
FP757HD supply. It has been working fine with my FT301D for the last 6 months and
now works equally well with my FT757GX.
still dont know why there was so much hum and ripple when I used this circuitry and
these parts. I still have this circuit in my junkbox and will later try it again to see if I
can get it to work. I blamed the transistors for awhile! I thought..maybe they were
oscillating or something. A mystery to be solved at a later date.
When I switched over to a more common old 2n3055 NPN pass transistor design..my
ripple and hum problems disappeared. I went a step furthur and implemented an
RS10 power supply regulator board and power transformer into my revamped
FP757HD supply. It has been working fine with my FT301D for the last 6 months and
now works equally well with my FT757GX.
BELOW A CIRCUIT FROM THE INTERNET. I used only 4 pass transistors and I tried
various regulation schemes but always hum.
various regulation schemes but always hum.
I will be adding more to this page a little later..73 earl ve3ab 14 July 2011.
link to my home page www.hamelectronicsmagazine.com
link to my home page www.hamelectronicsmagazine.com