[R-390] R-392
Jim Whartenby
old_radio at aol.com
Mon Oct 6 14:48:06 EDT 2025
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 <jacques.f at videotron.ca> 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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