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Re: SX-28A Hum
开云体育Jim, that waveform is what I previously commented on. Looks like a base frequency of 60 with third harmonic. ?the 3rd harmonic is generated by the PT magnetizing current and it ?along with the 60 HZ coupled ?to wires in the choke circuit somehow; wiring being most likely. The location of the choke ?makes it unlikely that it is directly from the transformer. ? From: [email protected] [mailto:[email protected]] On Behalf Of Jim Whartenby via groups.io
Sent: Wednesday, February 19, 2025 10:14 PM To: [email protected] Subject: Re: [HallicraftersRadios] SX-28A Hum ? I am not sure that the problem is resolved.? CH2 was replaced with a similar value choke with less winding resistance so it will have higher Q.? Higher Q will affect the audio filter curve so there will most likely be more ripple in the audio bandpass in the bass out switch position.? This may not be that noticeable to the ear but the scope will see it. ? In Tom's first video, at about the 45 second mark, the scope shows a strange waveform.? The main peaks are of a 60 cycle waveform.? The center peak is at 120 cycle but it's peak is negative, the two remaining peaks are at 240 hertz and positive.? There must be some nonlinearity to cause these harmonics to be generated.? This nonlinearity is acting like a diode and causing the second and forth harmonics of the 60 cycle waveform. Regards, Jim ? ? -- don??? va3drl |
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Re: S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!
Jim, we were working on the same idea.
Here is my resonance frequencies table give the measured values. I added 10pF to count for min capacitance of the BS variable (estimated) as per Don's suggestion.
Rounding a part, it fully matches with your calculation.
?
Having L3 out of circuit I was able to detect the ACTUAL signal paths in bands 1&2 (neither theoretical nor from schematic: ACTUAL).
I think they are identical to what you expressed in words and, at the end, matches with Don's drawings (many posts ago).
?
Give this arrangement it appears clear to me that the alignment sequence is very important as setting on band 2 interacts with setting in band 1 and vice versa.
?
Now I need to hunt for the hidden capacity that's moving all responses down,? ...but I really can't find it.
--
Emanuele (IU1KNR).
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Re: S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!
开云体育Jacques, it is not much maybe but where is the min cap of the BS? What is the dial frequency at the very top of the band [min cap] ?is !.6kc ?really min capacitance. Agree, even with a small change it still looks like come hidden cap ???? Emanule re Jim’s .. at 1360 or 1380 there is no breathing room on the trimmer like one would expect. ? Also many variable caps have the min cap below 10% of the max, so we can wonder what this one was intended to be ? From: [email protected] [mailto:[email protected]] On Behalf Of Jacques_VE2JFE via groups.io
Sent: Thursday, February 20, 2025 10:57 AM To: [email protected] Subject: Re: [HallicraftersRadios] S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak! Importance: High ? Hi Emanuele, ? From your measurements: BAND 1: C7A = 450pF, L3(C&D) = 200?H Fr = 530.5kHz (1/(6.2832 x SQRT(L x C))) C7A = 50pF, L3(C&D) = 200?H Fr = 1591.5 kHz ? BAND 2: C7A = 450pF, L3(A&B) = 26?H Fr = 1.47 MHz C7A = 50pF, L3(A&B) = 26?H Fr = 4.414 MHz ? From a mathematical point of view, that should work on both bands, or be very close to ! Unless there is a hidden capacitance in the assembly somewhere, like a connecting wire that should stand in free air, but that is pushed close to the GND along it’s path instead.? (I have seen that before: too long story to tell here). Hard to verify because the radio is not right in front of me …. I also believe that the schematic is right: on band 2, the A+B section of L3 is connected to C7A, but the antenna signal is fed to L3 C+D and coupled using mutual inductance between the coils. On band 1, L3 C+D section is connected to C7A, antenna signal fed to L3 A+B section with a 1k resistor in series and fed by mutual inductance again. I believe that the 1k resistor is there to “balance” the Band 1 sensitivity to the one of the other bands (more or less). ? Sorry to repeat feats or opinions that were mentioned before on the thread, but I caught this boat late… ? 73, Jacques, VE2JFE in Montreal ?
-- don??? va3drl |
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Re: S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!
开云体育Hi Emanuele, ? From your measurements: BAND 1: C7A = 450pF, L3(C&D) = 200?H Fr = 530.5kHz (1/(6.2832 x SQRT(L x C))) C7A = 50pF, L3(C&D) = 200?H Fr = 1591.5 kHz ? BAND 2: C7A = 450pF, L3(A&B) = 26?H Fr = 1.47 MHz C7A = 50pF, L3(A&B) = 26?H Fr = 4.414 MHz ? From a mathematical point of view, that should work on both bands, or be very close to ! Unless there is a hidden capacitance in the assembly somewhere, like a connecting wire that should stand in free air, but that is pushed close to the GND along it’s path instead.? (I have seen that before: too long story to tell here). Hard to verify because the radio is not right in front of me …. I also believe that the schematic is right: on band 2, the A+B section of L3 is connected to C7A, but the antenna signal is fed to L3 C+D and coupled using mutual inductance between the coils. On band 1, L3 C+D section is connected to C7A, antenna signal fed to L3 A+B section with a 1k resistor in series and fed by mutual inductance again. I believe that the 1k resistor is there to “balance” the Band 1 sensitivity to the one of the other bands (more or less). ? Sorry to repeat feats or opinions that were mentioned before on the thread, but I caught this boat late… ? 73, Jacques, VE2JFE in Montreal ? ? Jim, great job! Don, remember: 1600-500=1100 so we have 110KHz/DIV; 1600-220=1380 .. close enough. So Jim's peak stay exactly where it should: dial @1400KHz !! peak at 1380KHz. His tank works as expected! Jacques, C7 is halli original with the correct prt. no. 048-300341. It measures 50-450pF (LCR). L3 has nothing, null, nope, vacuum inside. NO CORE. L3 coils as measured by the LCR: the first coil (pins A and B) measures 26uH, while the second (pins C and D) measures 200uH. ? -- Emanuele (IU1KNR). _._,_._,_ |
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Re: SR-500 Tornado
开云体育
There is no socket conversion needed. The 6DQ5 is a direct "plug and play".
Walt Cates, WD0GOF
?
From: [email protected] <[email protected]> on behalf of Scott WA9WFA via groups.io <whitebear1122@...>
Sent: Thursday, February 20, 2025 12:17 AM To: [email protected] <[email protected]> Subject: Re: [HallicraftersRadios] SR-500 Tornado ?
Thank you Walt for your SR-160 and SR-500 information, weak points, and the finals. ?I think I've read an early post of yours talking about converting the 8236 tube socket to 6DQ5. ?I didn't have a clue about tube height though. ?Also didn't know about
the temperature compensation capacitor failure. ?I will download your SR-500 repair manual. ?I've seen your other repair manuals before and they are a godsend! ?
?
I'm going to keep my eyes open for an SR-500 Tornado to satisfy a nostalgic urge for the SR-160 and the long time desire to own one of the premium transceivers like the Tornado, Cyclone, Hurricane. ? If someone on the list knows of a nice condition Tornado
for sale, I'd appreciate hearing about it. ?
?
Thanks.. ?73, Scott WA9WFA
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Re: S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!
Jim, great job!
Don, remember: 1600-500=1100 so we have 110KHz/DIV; 1600-220=1380 .. close enough. So Jim's peak stay exactly where it should: dial @1400KHz !! peak at 1380KHz. His tank works as expected!
Jacques, C7 is halli original with the correct prt. no. 048-300341. It measures 50-450pF (LCR).
L3 has nothing, null, nope, vacuum inside. NO CORE.
L3 coils as measured by the LCR: the first coil (pins A and B) measures 26uH, while the second (pins C and D) measures 200uH.
?
--
Emanuele (IU1KNR). |
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Re: S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!
开云体育Jim? thanks from us! so both are similar, peaking too low Poor low band may be due to No “C 62” as in the S40B ?? ? From: [email protected] [mailto:[email protected]] On Behalf Of JThorusen
Sent: Wednesday, February 19, 2025 9:51 PM To: [email protected] Subject: Re: [HallicraftersRadios] S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak! ? Greetings to the Group: ? ?? I attempted to replicate Emanuele's measurement of the RF tank circuit.?? This required that I construct an RTMA dummy antenna, which turned out to be a bit of a chore; I had to make the 20 uH coil as I didn't have anything close in stock.?? Since Emanuele used a spectrum analyzer with tracking generator, I decided to do the same.?? The tracking generator output was connected to the antenna terminals (with the low side jumper to ground in place) through the RTMA dummy antenna.?? The signal was taken from the RF amplifier (V1, 6SG7) control grid, pin 4 with a 10:1 oscilloscope probe.?? The receiver main tuning dial was set to 1.4 MHz.?? The tracking generator level was set to 0 dbm to obtain adequate signal for display.?? The sweep range was from .5 MHz to 1.6 MHz.?? 10 db/division vertical scale. ? Here are the results: ? This is the response with C4 set to minimum capacity. ? This is the response with C4 set to maximum capacity. ? ?? Incidentally, my receiver also displays considerable sensitivity change over the broadcast band.?? At the high end, there is considerable 60Hz hash and noise as one would expect in a suburban environment.?? As one tunes to the bottom of the band, the receiver becomes virtually quiet.?? I live a fair distance from the nearest AM broadcast station and I was unable to hear anything on the pair of clip leads I was using for an antenna; only the above mentioned noise. ? 73, -- Jim T. _._,_._,_ -- don??? va3drl |
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Re: SX-28A Hum
I am not sure that the problem is resolved.? CH2 was replaced with a similar value choke with less winding resistance so it will have higher Q.? Higher Q will affect the audio filter curve so there will most likely be more ripple in the audio bandpass in the bass out switch position.? This may not be that noticeable to the ear but the scope will see it. In Tom's first video, at about the 45 second mark, the scope shows a strange waveform.? The main peaks are of a 60 cycle waveform.? The center peak is at 120 cycle but it's peak is negative, the two remaining peaks are at 240 hertz and positive.? There must be some nonlinearity to cause these harmonics to be generated.? This nonlinearity is acting like a diode and causing the second and forth harmonics of the 60 cycle waveform. Regards, Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Wednesday, February 19, 2025 at 02:13:41 PM CST, Richard Knoppow via groups.io <1oldlens1@...> wrote:
Thank you. Since its a different choke it doesn't explain why the original was humming. Doesn't matter if the problem is solved but would be interesting to know. Its possible there is a leak between the winding and core or frame in the original. A sensitive ohm meter would probably tell. I had thought of suggesting putting the old choke on an insulator (just a sheet of paper) temporarily to see if the hum stopped. Not worth taking the new choke out to try. The SX-28 is an interesting receiver, an attempt by Hallicrafters at advanced engineering that didn't quite come off. The Lamb noise blanker was a very good idea but was not well implemented. Eventually, Drake and others, did a better job with it. This type of blanker works well on pulse type noise, like ignition noise, but hardly at all on the more common (now) power line noise. Hallicrafters eventually published a modification (on BAMA) to disable it and replace it with a conventional series limiter. I hope not many SX-28s were mutilated this way. On 2/19/2025 11:57 AM, thoyer via groups.io wrote:
Yes, I replaced the original CH2 with another 4hy one I had from an -- Richard Knoppow Los Angeles WB6KBL SKCC 19998 |
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Re: S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!
开云体育Hello Emanuele, ? Did you see any part number on the Main Tuning Capacitor ?(C7) ?? It should end with 341… ? As you seems to have a LCR meter, can you also measure C7A (the section of the main tuning capacitor that tunes the Antenna Coils ?? It can be easy with L3 being removed. Please measure the fully meshed and fully open values. ? And, being there, can you also measure the inductance of the two L3 windings, please ?? From those measures, we can try to make sense of what is happening. ? It will be also good if you can take pictures of the L3 coil, seen from the top, and also from the bottom. Can you see something in the center hole, or not ? ? 73, Jacques, VE2JFE in Montreal ? De?: [email protected] <[email protected]> De la part de Emanuele Girlando via groups.io ? Don, no idea about the run of this unit. The serial on paper is almost impossible to read; looking carefully it seems read "serial. 196479". No other info. Here is an info briefing: As arrived, the radio looked fully original. I recapped it following this rule: do not touch anything in RF sections (ANT, MIX, OSC) unless something proves to be really faulty. Main filter caps were retained as they measured good and perform well. Checked all resistors and replaced when out of value (above the required tolerance). At the end of the job all voltages where very close to the ones indicated in the service manual. One exception: V1pin6 measures 140V instead of 125Volts. V1 and V2 measured "good" and "very good" respectively on my simple emission tube tester. As I said multiple times the radio works, but:
Furthermore, it appears that no one here can fully understand how these strange RF ANT and MIX circuits really work, making fault finding process close to impossible - really frustrating. What surprises me a lot is that in more than 70? years no one has ever raised a hand on the subject: we all were not able to find any reference to the problem... IMHO, the best way to represent what's going on is the following picture: ? Today I torn down L3/C4 assembly. Here it is. ? In DC, using 4 wire measurement procedure, the first coil (pins C and D) measures 5ohm, while the second (pins A and B) measures 1.5ohms, all in line with what is reported in the S-40B service manual for the same L3 (even if the part numbers differ...). The TRIMCAP, measured with an LCR meter, ranges from 1.7pF to 30pF - good to me. ? ? ? Now I have to go. Tomorrow I am going to check the ANT and MIX wiring... and S1 wafers positioning... -- Emanuele (IU1KNR). |
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Re: S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!
开云体育Emanuele Real good pics! The knowledge that it looks original helps reduce speculation that it has been modified and that is causing the problem.. good to know about that. The trimmers for band 4 have a range of 20 to 1 while the others are 10 to 1. ? About L3 ?just thinking out loud, when in band 1 the incoming signal arrives at the top coil, where there is a tendency for it to peak at say ??4Mcs due to its trimmer ?but that should not hamper the signal on band 1. ?The tuning of the lower coil is mostly done by the main tuning cap in resonance with that lower coil[schematic view not physical], then the signal is passed thru the switch to the V1 grid. We expect some interaction? between c4 and c3 but ?L3 lower for band 1 ?is likely using the top coil just to transfer the signal, and maybe isolate this tuning from the antenna. when the dial is at the top it resonates at 1.6 ? mc while the upper coil remains near 4mc , still well away from 1.6. It is the same idea for band 2. But swap all the stuff. Here the lower coil has only its trimmer connected and wants to resonate ??at 1.6 or whatever which is not much lower than band 2 bottom? so I wonder about that Note I hate using all these “I’s” but it is how I am thinking for good or bad, its far from a law. The Mixer has similar coils and caps but the switching seems more normal BUT ?the big mystery of V1 v2 coupling The S-85 ?Mixer tank area seem to be identical to the S-40B, except for the C62 which maybe does enough coupling at resonance [] So I am convinced that the antenna tank might work in general but but why it wont peak high enough remains a big mystery. ? Maybe put L3 back but don’t connect the variable caps, and try a sweep to see how high the frequency goes, then perhaps connect the variable one at a time and contemplate that. Hope you get the gist of this stuff, but don’t quote me! From: [email protected] [mailto:[email protected]] On Behalf Of Emanuele Girlando via groups.io
Sent: Wednesday, February 19, 2025 5:59 PM To: [email protected] Subject: Re: [HallicraftersRadios] S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak! ? Don, no idea about the run of this unit. The serial on paper is almost impossible to read; looking carefully it seems read "serial. 196479". No other info. Here is an info briefing: As arrived, the radio looked fully original. I recapped it following this rule: do not touch anything in RF sections (ANT, MIX, OSC) unless something proves to be really faulty. Main filter caps were retained as they measured good and perform well. Checked all resistors and replaced when out of value (above the required tolerance). At the end of the job all voltages where very close to the ones indicated in the service manual. One exception: V1pin6 measures 140V instead of 125Volts. V1 and V2 measured "good" and "very good" respectively on my simple emission tube tester. As I said multiple times the radio works, but: 1.???? IF aligned seamlessly; 2.???? bands 1 & 2 trimcaps don't peak during alignment; 3.???? sensitivity close to zero in the lower part of band1; can hear stations on the higher part of the band; 4.???? bands 3&4 work much better and the trimcaps peak during alignment (even if we have seen the ANT and MIX peaks behave like the ones in band 1&2. May be the trimcaps range is much larger allowing the tanks to reach the alignment frequency. Still I have to check if sensitivity remains constant all over the bands.. 5.???? while keeping reasoning about the RF circuits I replaced R26 as you can see in my previous posts pictures; 6.???? once again I can assure C5 was fully OPEN while performing all test; 7.???? both the variable capacitors seems in good shape; nothing prevent them from traveling the entire route, in one direction or the other. Furthermore, it appears that no one here can fully understand how these strange RF ANT and MIX circuits really work, making fault finding process close to impossible - really frustrating. What surprises me a lot is that in more than 70? years no one has ever raised a hand on the subject: we all were not able to find any reference to the problem... IMHO, the best way to represent what's going on is the following picture: ? Today I torn down L3/C4 assembly. Here it is. ?
In DC, using 4 wire measurement procedure, the first coil (pins C and D) measures 5ohm, while the second (pins A and B) measures 1.5ohms, all in line with what is reported in the S-40B service manual for the same L3 (even if the part numbers differ...). The TRIMCAP, measured with an LCR meter, ranges from 1.7pF to 30pF - good to me. ? ? ? Now I have to go. Tomorrow I am going to check the ANT and MIX wiring... and S1 wafers positioning... -- Emanuele (IU1KNR). _._,_._,_ -- don??? va3drl |
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Re: S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!
Don,
no idea about the run of this unit. The serial on paper is almost impossible to read; looking carefully it seems read "serial. 196479". No other info.
Here is an info briefing:
As arrived, the radio looked fully original.
I recapped it following this rule: do not touch anything in RF sections (ANT, MIX, OSC) unless something proves to be really faulty. Main filter caps were retained as they measured good and perform well. Checked all resistors and replaced when out of value (above the required tolerance).
At the end of the job all voltages where very close to the ones indicated in the service manual. One exception: V1pin6 measures 140V instead of 125Volts.
V1 and V2 measured "good" and "very good" respectively on my simple emission tube tester.
As I said multiple times the radio works, but:
Furthermore, it appears that no one here can fully understand how these strange RF ANT and MIX circuits really work, making fault finding process close to impossible - really frustrating. What surprises me a lot is that in more than 70? years no one has ever raised a hand on the subject: we all were not able to find any reference to the problem...
IMHO, the best way to represent what's going on is the following picture:
?
Today I torn down L3/C4 assembly. Here it is.
?
In DC, using 4 wire measurement procedure, the first coil (pins C and D) measures 5ohm, while the second (pins A and B) measures 1.5ohms, all in line with what is reported in the S-40B service manual for the same L3 (even if the part numbers differ...).
The TRIMCAP, measured with an LCR meter, ranges from 1.7pF to 30pF - good to me.
?
?
?
Now I have to go.
Tomorrow I am going to check the ANT and MIX wiring... and S1 wafers positioning...
--
Emanuele (IU1KNR). |
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Re: SR-500 Tornado
开云体育Hi Scott,
Talk about timing...
I have an SR-160 (upgraded to
SR-500), an SR-400, and matching P-500 power supply that I would
like to find a good home for (all in good working order and
condition).
The SR-160 is a bit of an oddball in
that the original VFO had been replaced with a solid state VFO
when I got the rig. I don't know if this was something done by a
previous owner, or as a factory experiment or prototype. Because
this rig was already non-standard, I made the changes to upgrade
it to be functionally equivalent to the SR-500. Walt Cates (who
replied to you earlier and whom I consider the expert on these
rigs) had put together a list of differences/changes between the
two rigs.
As I only have the one power supply
(which works for either rig), I don't want to break up the set.
By the way, I also have an SR-2000
and matching P-2000 power supply. All of these are great rigs,
even by today's standards (especially for someone who likes to
fiddle with real knobs instead of a computer screen).
Like you, I started in ham radio
early in life, getting my novice license in 1957 at the age of
12 (KN7DYB). Since then, I have been in and out of ham radio
depending upon the demands of real-life. When I retired from the
computer industry, I had enough time (and money) to nurture my
interests in vintage tube-type ham radios. I am more of a
restorer and tinkerer rather than operator, although I do get on
the air occasionally, mostly to check out whatever project I am
working on at the time.
If you are interested, I can send you
more information (photos, etc.). My email is good on QRZ.com.
Bob,? K7DYB
- - - - - - -
On 2/19/2025 1:21 AM, Scott WA9WFA via groups.io wrote:Hi, Lately I’ve been waxing nostalgic about the old Hallicrafters transceivers. ?A friend loaned me his SR-160 for several months back in 1971 while I was in Senior in High School and I used it for that summer before heading off to the Vietnam War. ? It was a wonderful transceiver! ?
|
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Re: SR-500 Tornado
开云体育Hi Scott,
Talk about timing...
I have an SR-160 (upgraded to SR-500),
an SR-400, and matching P-500 power supply that I would like to
find a good home for (all in good working order and condition).
The SR-160 is a bit of an oddball in
that the original VFO had been replaced with a solid state VFO
when I got the rig. I don't know if this was something done by a
previous owner, or as a factory experiment or prototype. Because
this rig was already non-standard, I made the changes to upgrade
it to be functionally equivalent to the SR-500. Walt Cates (who
replied to you earlier and whom I consider the expert on these
rigs) had put together a list of differences/changes between the
two rigs.
As I only have the one power supply
(which works for either rig), I don't want to break up the set.
By the way, I also have an SR-2000 and
matching P-2000 power supply. All of these are great rigs, even by
today's standards (especially for someone who likes to fiddle with
real knobs instead of a computer screen).
Like you, I started in ham radio early
in life, getting my novice license in 1957 at the age of 12
(KN7DYB). Since then, I have been in and out of ham radio
depending upon the demands of real-life. When I retired from the
computer industry, I had enough time (and money) to nurture my
interests in vintage tube-type ham radios. I am more of a restorer
and tinkerer rather than operator, although I do get on the air
occasionally, mostly to check out whatever project I am working on
at the time.
If you are interested, I can send you
more information (photos, etc.). My email is good on QRZ.com.
Bob,? K7DYB
On 2/19/2025 1:21 AM, Scott WA9WFA via
groups.io wrote:
Hi, Lately I’ve been waxing nostalgic about the old Hallicrafters transceivers. ?A friend loaned me his SR-160 for several months back in 1971 while I was in Senior in High School and I used it for that summer before heading off to the Vietnam War. ? It was a wonderful transceiver! ?
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Re: SX-28A Hum
开云体育Thanks Jacques, well that seems to pour cold water on the magnetic coupling theory. If the trace I copied is typical {I don’t know}… ie; assuming? that hum is 60 cps with third harmonics at /I n /close to the choke, there can be electrostatic coupling by close parallel wires from AC incoming wires being too close to the? choke ??wires. ??? Moving stuff might mean moving wires and coupling. I worry more about long wires running to the switch. ?Another long shot.? … but the old stories of just moving stuff raises its head. I’m dried out. ? From: [email protected] [mailto:[email protected]] On Behalf Of Jacques_VE2JFE via groups.io
Sent: Wednesday, February 19, 2025 3:04 PM To: [email protected] Subject: Re: [HallicraftersRadios] SX-28A Hum ? In a SX-28A, the CH2 is as far as it can be from the power transformer: ? ? ? The black “core” at the left is the CH2. You can see the bottom of the power transformer and the filtering choke at right. The closest transformer to the CH2 is the audio output. ? ? 73, Jacques, VE2JFE in Montreal ? De?: [email protected] <[email protected]> De la part de don Root ? Tom and/or anybody still tuned in. Still looking for what really failed and how. For anyone wondering about the details and possible source, I copied a bit of your first Video so I could take a closer look. I see 60 Hz and strong third harmonics, and no visible high harmonics. It reminds me of core saturation. Power transformer magnetics and primary is the only source I can think of. Any comments?
_._,_._,_ -- don??? va3drl |
don Root
Emanuele Girlando
Jacques_VE2JFE
waltcates
Jim Whartenby
Robert Kembel