JacquesThe same losses in B+ voltage due to choke copper loss also occur in the
R-390A/URR. The sealed chokes I used were both standard, that is not swing
chokes and both were rated for 125mA. They had a comparable size and DC
resistance to the chokes used in the R-390A/URR. This did not seem to make
much difference since the ripple voltage was still quite low and close to what
one expects out of a pass voltage regulator. In other words, the chokes were
nowhere near saturation.
It is interesting to note that after several hours of operation, the feared
higher B+ voltage due to solid state rectifiers was much lower then common
knowledge suggests. A worst case increase of about 14 volts is equivalent to
a 5 volt rise in the line voltage. I had originally published this test data
on the CCA website a week or so ago in a response to a question. Perhaps I
should have done so here where there is more interest?
Test Data:R-390/URR power supply configured as R-390A/URR power supply without
electronic voltage regulation6H series L, 68uF shunt C, 6H series L, 68uF shunt
C then to the load resistanceload R = 900Ω for B+ & 8.3Ω or 6.6Ω for AC heater
windingMeasured ripple volts was 0.075 volts @ 120 cycles under load, worst
case, for all rectifiersTemperature was measured with an IR thermometer.
FR207 silicon diode, Xfmr end temp = 93 ºFFR207 silicon diode, Xfmr start
temp = 75 ºF after 3hrs AC Line V B+ V
B+ mA Heater V Cal Htr A B+ V B+ mA Heater V
Cal Htr A100.00 160.60 177.40 22.70 2.73
152.20 168.80 22.50 2.71105.00 167.90 185.50
23.80 2.87 160.40 178.00 23.70 2.86110.00
176.10 194.70 24.90 3.00 168.70 187.10
24.90 3.00115.00 183.10 202.50 26.00 3.13
176.40 195.10 26.00 3.13120.00 190.90
211.30 27.00 3.25 183.90 204.10 27.10
3.27125.00 198.40 219.50 28.10 3.39 190.60
211.50 28.10 3.39130.00 207.10 229.40 29.40
3.54 197.90 219.50 29.20 3.52Average
Average Average Average Average Average Average Average
Average115.00 183.44 202.90 25.99 3.13
175.73 194.87 25.93 3.12 ± ±
± ± ± ± ±
± ±13.04% 12.90% 13.06% 13.14% 13.14%
12.62% 12.64% 12.62% 12.62%
18 ºF transformer
temperature rise after 3 hours
1st pair 26Z5 rectifier, Xfmr end temp = 105 ºF, 1st pair
26Z5 rectifier, Xfmr start temp = 93.1 ºF after 3.5hrs AC Line V
B+ V B+ mA Heater V Cal Htr I B+ V B+ mA
Heater V Cal Htr I100.00 140.70 155.90 22.60 2.72
141.20 156.50 22.70 2.73105.00 147.50
163.50 23.60 2.84 147.50 163.50 23.60
2.84110.00 155.30 172.30 24.80 2.99
155.90 171.70 24.70 2.98115.00 162.20 179.70
25.80 3.11 162.70 180.30 25.90
3.12120.00 169.80 188.20 27.00 3.25 170.10
188.50 27.00 3.25125.00 177.20 196.30 28.10
3.39 177.60 196.70 28.10 3.39130.00
188.40 205.00 29.20 3.52 184.90 205.10
29.20 3.52Average Average Average Average Average
Average Average Average Average115.00 163.01 180.13
25.87 3.12 162.84 180.33 25.89 3.12
± ± ± ± ±
± ± ± ±13.04% 15.57%
13.81% 12.87% 12.87% 13.55% 13.74% 12.80% 12.80%30
ºF transformer temperature rise after 3.5 hoursΔ B+ with FR-207 is 13.8 volts
higher then 26Z5 @ 120V line
2nd pair 26Z5, 6.6Ω heater voltage
load, after 2nd pair 26Z5, 8.3Ω load, after 2 hours, 98º F Xfmr
additional 2 hours, 107º F XfmrAC Line V B+ V B+ mA Heater V
Cal Htr A B+ V B+ mA Heater V Cal Htr A100.00
142.00 157.00 22.60 2.72 140.60 155.80
22.40 3.39105.00 149.10 165.20 23.60 2.84
149.20 165.20 23.60 3.58110.00 156.80
173.80 24.70 2.98 155.50 172.40 24.60
3.73115.00 164.70 182.40 25.90 3.12
163.50 181.20 25.70 3.89120.00 172.50 191.20
27.10 3.27 170.70 189.20 26.80
4.06125.00 178.60 197.80 28.00 3.37
178.00 197.30 27.90 4.23130.00 186.80 207.20
29.20 3.52 185.60 205.70 29.10
4.41Average Average Average Average Average Average
Average Average Average115.00 164.36 182.09 25.87
3.12 163.30 180.97 25.73 3.90 ±
± ± ± ± ±
± ± ±13.04% 13.65% 13.79%
12.87% 12.87% 13.66% 1 3.66% 13.10% 13.10%23 ºF total
transformer temperature rise after 2 hours 32 ºF total transformer
temperature rise after of operation
additional 2 hours of operationΔ B+
with FR207 is 11.4 volts higher then 26Z5 @ Δ B+ with FR207 is 13.2
volts higher then 26Z5 @120V line
@120V line
The FR207 diodes are equivalent to the standard 1N4007 in this test. The FR207
has a better reverse recovery time and are rated for 2 amps but this should
make no real difference. They were just at hand and I expect the same results
with the standard 1N4007 diode. There is no difference in the R-390/URR and
R-390A/URR power transformers with respect to the high voltage specifications.
The bottom line is that going solid sate makes little difference in B+ but it
significantly lowers the temperature in the power transformer besides removing
some 80 watts of waste heat in the R-390/URR. The last data run was with the
heater load lowered from 8.3 to 6.6 ohms to stress the power transformer to the
published specification on the transformer. Happy to respond to any technical
questions.
Regards,Jim
Logic: Method used to arrive at the wrong conclusion, with confidence. Murphy
On Monday, October 6, 2025 at 12:59:05 PM CDT, Jacques Fortin
<[email protected]> wrote:
Hello Jim,
This is a very good solution too.
The only values that are missing is the current rating and the DC resistance of
your 6H chokes...
I presume that 200mA rated parts will be needed but the DC resistance also play
a role in the output voltage.
Do you have a maker/model for your 6H chokes ?
73, Jacques, VE2JFE in Montreal
Since the R-390A/URR cost reduction program deleted the high heat generating
regulated power supply used in the R-390/URR, has anyone considered removing
the regulated power supply circuit from the audio module and installing two 6H
chokes and suitable electrolytic capacitors in place of the 6082 tubes?
The end result will be very close to the 180 or so volt B+ seen in the
R-390A/URR. Also solid-stating the power transformer rectifiers will reduce
more waste heat generated in the receiver. Total savings is close to 80 watts
doing a back of the envelope calculation which is almost half of the power
consumed by the R-390/URR. Thoughts?
Jim
Logic: Method used to arrive at the wrong conclusion, with confidence. Murphy
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