MISCELLANEOUS SR-2000 NOTES BY K9AXN
||MISCELLANEOUS SR-2000 NOTES BY K9AXN
By Jim Liles, K9AXN
MISCELLANEOUS SR-2000 NOTES
METER CKT We have received numerous inquiries regarding SR-2000 S-Meter insensitivity. First, the procedure for adjusting the S-Meter included in the operator's manual is a bit lacking. The correct procedure is to turn the S-Meter pot, R-120 fully clockwise, zero the meter with the meter zero pot, and then turn the S-Meter pot CCW until the meter just moves. This is a three step process and you are finished. Before doing anything, check the resistors R-118, 119, and 121. They are critical, especially R-118. Bear in mind that the AGC/S-Meter tube is a 7059 which is a 13.5V tube running at 12.6V if all is well and 90V on the plate. After you perform the adjustment above, remove the S-Meter tube V8A and see what the S-meter indicates. It should be above +60Db, pegged. Whatever it reads with the tube removed is the highest possible reading. You will probably wonder why the meter is pegged when you first turn it on. When first fired up, the B+ will be approximately 320V until the tubes warm up and draw plate current. Then it will drop back to 280V (The meter is driven with a bridge). Tube V8 is the one tube in the SR-2000 that must be hand selected for S-Meter performance. If the meter does not peg with V8 removed replace it and do the above adjustment then pull the tube and repeat until its right. The S-Meter will be quite accurate when you are finished.
POWER SUPPLY A while back we started chasing an intermittent high voltage tick in the SR-2000 that occurs at about 1/2 second in low power mode and about every 1/4 second when high power is enabled. The culprit was the plate/screen plug that connects to the SR-2000. Disassembled and cleaned it and voila it is history. I tried it on another with the same result. Another issue with the P-2000 is the tendency to replace the high voltage capacitors with much higher values of capacity --- more is better. Not so. The manual calls for 90uf capacitors which are difficult to find but 100's or 50/50's are common and can be used. Anything higher can cause damage to the tubes if a flashover should occur. The 8122 specs call for no more than 10uf in the plate filter for that reason. Lastly, if you are restoring a P-2000 check that the overload relay trips out at 120 to 140ma isolated or 850 to 980ma with the 4 ohm resistor across it --- might save tubes one day. We have found a few with open coils that simply couldn't trip, fall back goes to the main fuses which is usually to late. Don't let em smoke! ADDENDUM:::: We posted a note on the Hallicrafters reflector some time ago regarding a tick when the high voltage is applied with the SR-2000 - P2000. We successfully cleared the problem by cleaning the P-2000 connector. Since then it has reappeared. We now have a definite fix. Both the P-2000 and SR-2000 connectors have a metal jacket. The P-2000 connector has a plastic insert that is held in place by a screw. The screw, when inserted, contacts the metal jacket and apparently is too close to the 2700 volt pin. This causes a static voltage to build on the jacket that finally arcs to the jacket in the SR-2000 causing a tick and noise of varying duration. The fix is simply to replace the metal screw with a nylon version. The absence of the tick and reduced noise level is worth the five minute change.
TRANSMITTER DISCUSSION I would not worry about the ALC, it only responds to grid current flowing which is exactly what it attempts to dampen. An SR-2000 that is operating properly and has a pair of good 8122's will deliver 1200/1000 watts to the antenna 80/10 meters. What is important is whether you can drive the finals into the positive zone of the control grid when in tune mode. This will be apparent as you increase the rf drive, the plate current will increase then decrease before reaching maximum drive. If you can not get adequate drive in tune mode, one of two things must be done. Fix the radio or alter the tune up process. The SR-2000 was designed to drop the carrier frequency 100 Hz into the filter band pass and force enough signal through to drive the finals in tune mode. The insertion loss at this point is 30 to 40db and if the filter terminators are not aligned properly, adequate drive will be impossible. So what is the consequence? Here is what will happen to an SR-2000 that has inadequate drive in tune mode if you foll ow the tune up process from the manual. Conditions: you have a pair of 8122's that are capable of 500 watts in tune mode but have only enough drive to provide 300 watts. You tune it up for 10ma of screen current and switch to sideband. The voice frequencies pass through the filter with significantly less than the 30 to 40db of attenuation --- more like 10db. The added drive will send the screen current soaring and you may hear the insidious prink of death from an 8122. A good test is to a short whistle in sideband mode while monitoring screen current. If it is high, retune for a lower screen current. It's better to chance a whistle rather than talk for an hour driving an 8 watt screen to its demise.
RECEIVER SENSITIVITY ON 15 METERS Forgot to mention the check and work around for the 15 meter problem. If the receiver is not as sensitive or lacks drive in the 15 meter band --- check the entire band, switch to 20 and move the 14.0 Meg dial slightly above or below the 20 meter scale start point and re- adjust the 20 meter coils. This will move the resonant point out of the 15 meter band.
REGARDING THE 7059 The 6U8 is an exact replacement with a 6 volt filament --- simply wire two in series. I have done this with my SR-2000, SR-400, and SR-400A. For the 7056, the 12DK6 works well as a replacement. It is a better solution in that the 7059 and 7056 are 13.5 volt tubes and if your feed is 114 volts they are running at 12.0volts which is the minimum for those tubes. The Hallicrafters designers had mobile use in mind when they put these radio's to pen.
S METER AND 15 METER INSENSITIVITY The SR-2000 should be capable of moving the S-Meter to S5 with a 3uv signal and S1 with 1uv and S9 with 50uv. Also, you should be able to distinguish a two tone .05 uv signal. If you can clearly distinguish a .1uv two tone or carrier and sidebands on an AM signal, look at the S-Meter tube and circuitry otherwise start at the 6.5MHz IF strip. T1 and T2 cannot be adjusted without a sweeper --- tried and wore the slugs out. If you have a problem with the 15 meter band, there is a design booboo that may be present. The 20 meter coils for the in and out of the first rf amp resonate in or very close to 21MHz when switched to any other band than 20 meters. Also, being directly adjacent and unshielded, couples to the 15 meter coil and imparts resistance to the 15 meter tank --- the grid dip effect. For some strange reason, they fixed the problem in the 12BY7 final drive circuits (18pf rather than 47pf) but forgot the other two. One other question, can you overdrive the finals in tune mode? ---
RECEIVER DISCUSSION For your other issue, receiver sensitivity. The most sensitive band in receive mode for an SR-2000 will almost always be 20 meters followed by 15 then 40, 80, and 10. This is true with few exceptions and has a lot to do with the design of the first carrier oscillator and the gating through the 1N295. If 20 meters is not the star performer, the 15 ohm resistor that is in series with the 20m carrier osc coil will be high, in most cases above +50%. When I stated that the 15 m band could be affected by the adjacent 20m coil being resonant in the 15m band, I failed to mention that the other coils are not resonant in other bands. Also, the 20m problem only appears if you happen to have the preselector knob slightly off when adjusting the 20m coils. One other thought on output. Neutralization problems can make an SR-2000 squirrelly and or cripple the output. In the past I have destroyed a neutralizing tab or two with so many bends trying to get it right on. Well, I took a ball point pen apart and commandeered the s pring along with a longer screw and washer. With these I spring loaded the tab so that I could test, turrn off the hv, and with an insulated screwdriver move it a bit and re-test (Careful with the length of the mounting screw --- too long will hit the opposing ground mounting screw, tab has 280v). CAUTION, that tab has 280 v on it any time it is powered up. Finally, disconnect all power, measure and restore the original mounting --- DO NOT LEAVE THE SPRING IN PLACE. I was hesitant to put this last tip to pen and only a lunatic would do such a thing but for me, it works. Lastly, if the peak output occurs on the higher capacity side of the plate current dip, you have too much neutralizing capacity and if it occurs on the lower capacity side, not enough.
AUDIO IMPROVEMENT The SR-150 and the SR-2000 use a 2.7 kHz and 2.1 kHZ filter respectively. A common complaint for the SR-150 is that it is too wide for contest operations and the SR-2000 can sound pinched or tinny. These filters 049-000216 and 049-000324 can be exchanged along with the carrier crystals. The carrier crystals for the SR-2000 are 1648550 and 1651550 kHz and the SR-150 1648100 and 1651700 kHZ respectively. I have tried the SR-150 filter in the SR-2000 and it works perfectly. The warp cap that brings the USB crystal 90 Hz down into the filter window for tune and CW works flawlessly also. What you get is great sounding audio, transmit and receive, and a radio (2.7 kHZ) that would be a little wide for contest use. If you are an SR-150 owner who likes to contest and is willing to give a little audio quality for a skinny filter, it's a good solution.
GENERAL PERFORMANCE ISSUES Just want to pass along a heads up regarding radios that include an aluminum or other than steel chassis. We just finished restoring and de-bugging an SR-2000 finding two things that seem to be a problem on the SR-2000 and all of the radios that are built with a non-steel chassis. The use of the mounting ring for the tube socket for a ground is risky, even though they used a star washer between the ring and chassis. We found three rings with resistance readings to ground of from 3 to 10 ohms. This caused low level ripple on all circuits that used the ring for ground reference. In our case, the noise blanker performed poorly at best and was intermittently non-functional. We sprayed oxy on the washers and tapped them just enough to turn slightly and 0 ohms was the result with no ripple. The second problem was that the 20 meter band seemed to under perform the 15 and 10 meter bands. The SR-2000 and SR-400 use a 15 ohm resistor in series with the 56PF capacitor in the heterodyne oscillator output tank. We have f ound this resistor to be significantly high in all cases usually 25-30 ohms. The specs on that resistor should be ~<15ohms. We found 9 other manufacturing bugs that were simply sloppy workmanship. Is there an SR-2000 interested parties list anywhere?
TUBES 8122 RCA or any others will deliver 1000+ watts to the antenna but only in high power and SSB mode. You have to use an oscilloscope or peak reading watt meter to measure it. If you use an oscilloscope like the 475 or most others, use a 10X probe and set ground on the lowest graticule line. They usually read only 600V peak to peak which is 300 X .707. There is nothing wrong with RCA tubes, other than they are not marked with bias levels like the Burle red, blue, green, and black. If you are using RCA tubes or for that matter any. Check the match by setting the bias to 200ma then remove one tube and power it up. should be 100ma. Then install both and set the bias to 200ma and turn the idle to 400ma and power down and remove one tube power up and check that one tube will idle at 200ma. The last test is using both, tune it up into a dummy load and go to about 1kw for 30 seconds and shoot both tubes with an infrared gun to determine the temp. All measurements within 7% are a good match. At 1kw they will be loafing --- about 85 degrees centigrade. I have reservations regarding the RCA tubes because of the vast spread of specs. Burle added color codes to the plate caps --- Red, Blue, Green, and Black indicating bias levels Red 8.0 to 10.9V, Blue 11.0 to 13.9, Green 14.0 to 16.9, and Black 17.0 to 19.0. What does that tell you? Two things, if you find a pair with the same color code they will be close enough to a match to work in most cases. Second, the Red ones will generate ALC too early and reduce output and the Black will generate ALC late and introduce distortion. The ALC is generated solely from grid current caused by driving it above 0V.
More on tubes: I see a pair of Black tip 8122's for sale on ebay. The Black version is a good tube but almost universally needs to be used in an amplifier that is forgiving regarding neutralization --- low input impedance/swamping resistors and has a very broad bias range --- the NCL-2000. They need more than 30 volts of bias to idle at 100ma, over 60 volts of drive, and an incredible amount of neutralization feed back. If you use an SR-2000 and plan to replace the 8122's because of low output, look for a pair of Blue or Green Burle tubes or a profiled pair of RCA's. The RCA version can be equal to any of the four Burle defined tubes, Red, Blue, Green, or Black, and there is no way to know without profiling the tube. We have found in most SR-2000's with low output, alignment or trying to use 8122's whose characteristics fall outside reasonable limits to be the reason. For what it's worth, a pair of 8122's running frequently at high power in an SR-2000 --- 1000+ Watts out, will out last most of us if the radio is tuned prop erly.
Note: We profile an 8122 by applying 1700 Volts to the plate and 300 to the screen. Then we measure the bias required to provide 100 ma, 550 ma, and momentarily what the tube will deliver at -2 Volts of bias. This tells us whether the tube will work in AB1 radios with high impedance drive systems, how difficult they will be to neutralize, what output can be expected, and verify matching attributes.
MYSTERIOUS OSCILLATIONS C198 and C208 in most SR-2000's are flat back to back. Look at the schematic and you will see that it was an oversight. It causes an oscillation that is composed of a 1Kc note barely distinguishable that modulates a 289MHz pulse that appears everywhere in the radio. It only occurs when the mike is unplugged and the switches are in receive and usb or lsb. When I upload the photo's, I'll send them to you. We have found this in many radio's but were able to isolate this only as we were able to keep it in failing mode. Simply move the bodies of the two capacitors and angle them apart.
280MHZ SPUR We have chased an intermittent anomaly in the SR-400 and SR-2000 for some time and finally got a snapshot. When aligning the radio we would occasionally see a significant high level overtone at about 280MHz throughout the radio. Originally thought it was from outside. Put a spectrum analyzer to work and found it to be 280MHz pulses at 1KHz intervals. We had seen this in several radio's and traced it to component placement. Look in the schematic for C198 and C208. You will find them back to back on a terminal strip --- simply separate them 1/4 inch and the problem will not occur. I have snapshot's of the scope and spectrum analyzer if there is any interest.
8122 testing The 8122 is a close spaced high power tube --- can't be dropped. The method that I use to test for a good tube and match follow. First check continuity with a capacitor checker that can deliver 350 Volts or better --- not across the filament, between elements. Then we apply 1700 Volts to the plate and 300 Volts to the screen with full bias 70 Volts. If the tube has not been used for a few years, leave the HV on at full off bias for an hour --- gets rid of any gas which can cause a flash over. Best way is to use the SR-2000 and P-2000. Why, because they were designed to survive a flash over sparing the tube or power supply destruction. We attach a 50K pot to pin 7 of the 11 pin connector and one side of the pot to ground. This gives you the ability to vary the bias to ground. Measurement of the bias will be at the center leg of the bias pot on the front panel. We remove one 8122 and plug the empty hole to sustain air flow. With HV off and the hi/lo power switch set to lo, go to transmit and verify that you un derstand how to vary the bias from 2 to 30 volts. Set the bias to 30 Volts, go back to receive, turn on the HV, go to transmit, and set the bias for 100ma of plate current while also checking for positive or negative screen current. if you detect more than 2ma of + or - screen current, call me that's another subject. Record the bias level and go back to receive. Now set the bias pots up so that you can vary the bias from 8 to 15 Volts from the panel pot. set it to 15Volts and go to transmit, while quickly decreasing the bias until 550ma of plate current flows and go to receive immediately. turn the HV off and go to transmit and record the bias level --- should between 9 and 12 Volts. Now we have to be quick. With HV still off, go to transmit and set the bias to 5 Volts. Back to receive. HV on. Go to transmit for only a moment recording the plate current. If it was 850ma we stop, if less we Turn HV off, go to transmit and set the bias to 2 Volts. Back to receive, turn HV on, and go to transmit momentarily rec ording the plate current. The whole process is performed while being vigilant of any screen current --- normally none. This finishes the profile of an 8122. You know it's idle bias which is one part of the match process. You know the bias level that results in 550ma, and you know that the tube will peak at 850ma. If the tube will reach 850ma a pair in an SR-2000 will provide 1000 watts + to the antenna 10 through 80. This is sounding like it should be in a book. The next process is to install a matched pair in the radio load it up to 1kw for 15 seconds and measure the individual tubes with an infrared gun to verify temperature parity. Lastly, the characteristics of the 8122 vary vastly. When Burle bought the RCA line they color coded the tubes Red, Blue, Green, and Black to describe bias levels. The Red, Blue, and Green are useable in the SR-2000 with the Blue being preferred. A pair of the Red or Blue will almost always be close enough to a match to use in the SR-2000. The green will work but you have to mo dify the radio to accommodate the higher bias and neutralization requirements. The black tubes require so much negative feed back that you will have the feed back tab 1/8 inch from the tube and bias system has to be modified to deliver -36 volts to the tubes. This is a long winded description of tube management but well worth the time. I had some hand written notes from the Hallicrafters engineers complaining that they had to order a barrel of 8122's to get a handful of matches that would also work in a high impedance drive system.
Hallicrafters SR-2000 Note: Over time we have found that the SR-2000 generally lacked adequate transmit drive to saturate the 8122's. Is that a problem? Absolutely! If you load the transmitter up with inadequate drive it will be too lightly loaded when full drive is applied causing screen current to soar. The design of the SR-2000, in tune mode, forces the carrier through the filter somewhere between the -30 and -40db points on the skirt. If the filter, alignment, and components are close to perfect, you will have adequate drive in tune mode. In most cases you won't. Full drive will occur when voice/audio is applied because the center 2.1kc of the filter will lose only 6db, not 30 to 40db. Minimum drive on all bands and all modes must be capable of driving the 8122's grid positive which is required to generate ALC.
Another issue. The receiver when properly aligned and with reasonable components will deliver a 10db SN/N ratio with 1/2 watt of audio when .25uv is applied to the antenna lead. These are good numbers. Can it be better, yes, With a small easily removable change, a 10db SN/N ratio at .15uv can be had. The SR-2000 was designed for civilian and military mobile use but never left the desktop. It uses 8122, 7059, and 7056, 13.5v tubes as well as the 6AQ5, 12BA6 and 12AT7. The 7059 is simply a 13.5 volt 6U8. The pentode in the 6U8 and 7059 have a mu of 5200. Was the 6U8 the best choice? Probably at the time. We changed V3 and V7 to 6GH8's. The mu is 7500, a significant gain, wiring them in series. Re-aligned the 1.65Mc and 6.5Mc systems and now the radio has more than adequate transmit drive on all bands and modes. Also the receiver now has a 10db SN/N ratio at .15uv and a noise floor close to -140dbm. You can clearly hear the carrier and sidebands of a .03uv signal modulated at 1Kc AM signal using a calibrated HP 8662A with a 20db coaxial attenuator. If you want to remove the change install 6U8's rather than 6GH8's, or remove the series wiring and go back to 7059's --- you won't go back.
MORE ON TUBE REPLACEMENT We replaced V3 and V7 both 13.5 volt 7059's with 6GH8A's. We wired the filaments of V3 and V7 in series because there is no 6 volt source in the SR-2000. Also added a .01 cap where the V3 and V7 filaments connect to prevent any regen loops. The SR-2000 and for that matter every radio that was discrete wired in that era including Collins had significant and unique personality problems caused by both positive and negative feed back and wire coupling. Wire and component placement cause numerous anomalies in the SR- 2000, i.e. a positive feed back loop precluding correct alignment of the 6.5 Mc I.F. system and the radio being racked by 290Mc bursts spaced at 1Kc intervals. I believe that some are in the SR-2000 archives already and there are many more to come. This in no way means that the SR-2000 is anything but one of the finest instruments ever built. It simply states that very few complex electronic devices are immune to improvement. The best example is the Run 1 SR-2000 was a mandatory recall. serial #'s 45 2000 -*. The risk of that radio going up in flames as a result of simultaneously going into transmit and receive mode was absolute --- just a mater of time. If you have an SR-2000 please send the serial # and history if you can, I am collecting as much info on the series as possible. If you have any other questions, please call me at 847-571-8420.
LOW LINE VOLTAGE Running an SR-400, SR-400A, or SR-2000 specifically, on lower line voltage, and some other vintage radios will result in a myriad of disappoint results especially in transceivers where gating is done with diodes. The SR-400, 400A, and SR-2000 were designed with mobile use in mind using a significant number of 13.5 volt tubes. If you lower the voltage to 110 v for the SR-2000, the 8122's filaments are well below the 12v minimum design specs, and performance changes are unacceptable. Also, these transceivers use diode gating for T/R functions. If the gates are run out of center range, a whole plethora of feed back loops and spurs develop. The SR- 400, 400A, and SR-2000 need 115 to 120 volts to function properly. Can't speak to others but if it is a transceiver, check the logic. We use a Variac and keep the bench at 117V. They are not expensive and will keep the voltage where it belongs.
SR-2000 S Meter Discussion We have received numerous inquiries regarding SR-2000 S-Meter insensitivity. First, the procedure for adjusting the S-Meter included in the operator's manual is a bit lacking. The correct procedure is to turn the AGC threshold pot, R-46 fully clockwise, zero the meter with the meter zero pot, and then turn the AGC threshold pot CCW until the meter just moves. This is a three step process and you are finished. Before doing anything, check the resistors R-118, 119, and 121. They are critical, especially R-118. You can find R119 the 82K resistor directly below L15, R121 3.3K under the plate that holds the Meter zero pot, and R118 5.6K at V8B. Disconnect one S-Meter lead and measure all three after unscrewing the pot plate and isolating it from ground, you won't have to unsolder anything. Bear in mind that the AGC/S-Meter tube is a 7059 which is a 13.5V tube running at 12.6V if all is well and 90V on the plate. After you perform the adjustment above, remove the S-Meter tube V8A and see what the S-meter indicates. It should be above +60Db, pegged. Whatever it reads with the tube removed is the highest reading possible. You will probably wonder why the meter is pegged when you first turn it on. When first fired up, the B+ will be approximately 320V until the tubes warm up and draw plate current. Then it will drop back to 280V (The meter is driven with a bridge). Tube V8 is the one tube in the SR-2000 that must be hand selected for S-Meter performance. If the meter does not peg with V8 removed replace it and do the above adjustment then pull the tube and repeat until its right. The S-Meter will be quite accurate when you are finished.
HIGH NOISE I have received the fifth call in as many Months regarding a high noise level that occurs under several conditions. 1. Switching the HV on or switching to Hi power 2. Resonating the pre-selector. 3. You think the radio is really hot because without an antenna resonating he pre-selector results in a significant rushing noise --- it's not hot just broken. 4. Makes a lot of noise when going from transmit to receive. The fix is simple. Replace CR1 a 1N458 with a 1N459A. What's happening is CR1 has been punctured and leaks causing current to flow in R146 --- a great noise generator. CR1 is used to quench any RF that breaches the T/R relay from getting into the receive front end and is gated off with back -90V in receive mode. The 1N458 was a bad choice for that component. The 1N459A will not fail. If this is not clear or you have questions call home 847-913-8576 or cell 847-571-8420
ANOTHER TUBE DISCUSSION Good morning: Here is an experiment that will pique your interest: The SR-150, SX-117, SR-400/A, and SR-2000 use 6U8A, 6EA8, 7059 tubes. The 7059 is a 6U8A with a 13.5 volt filament. The 7059 and 6U8A have a transconductance of tetrode 5200 and triode 8500; the 6EA8 tetrode 6400 triode 8500; and the 6GH8A tetrode 7500 triode 8500. All have the same pin out's. We have used the 6GH8A in the SR-2000 V3 and V7 positions, rewiring the filaments in series with great results. The innate low transmit drive problem is fixed so normal standard tune up procedures can be followed and receiver gain produces an MDS below -140 Dbm with 10Db s+n/n of less than .15 uv. The SR-150 change that is worth while is to replace the 6EA8's V3 and V17 with 6GH8A's. In both cases you will be quite happy. The next tube with even more gain is the 6HL8 but beware it's transconductance figure is 10,000. If you try this tube you will have to modify the circuit to stabilize it and it can be a bit noisier than the 6GH8A. The 6U8A, 6EA8, 6GH8A, and 7059 have the same pin outs. The SX-117 can also be made to b e significantly more sensitive with tube change out. Final note: Any radio using the 6U8A can and will be a better performer when using the 6EA8 or 6GH8A and any using the 6EA8 will improve with the 6GH8A. Also, we do not change out mixers only amplifiers. Hope this piques your interest ---
CAPACITOR OVERHEATING We have discovered a design flaw in the final configuration of the SR-2000. Capacitor C156A is the solo loading cap, bearing 100% of the unloaded current when using the 10 meter band and bears more than 1/2 the load when using the 15 meter band. Every SR-2000 that we have inspected has experienced over heating at that connection. To check your SR-2000 simply use a mirror and flashlight to confirm that the connection has actually melted the solder or worse. This connection is used on all bands but solo on 10 meters. The best description of the effect is the radio is squirrely when loading and tune up as a result of the unreliable solder joint. The fix is to remove the capacitor by clipping the wires which can be spliced using #16 id copper tubing from a hobby shop, sliding the lock ring back on the tuning shaft --- it is not in a groove, slide the coupler to the front, remove three mounting screws and tip the rear of the cap to the left of the radio. The existing wires in the final cage will not solder withou t sanding, too many years on the tin. I would replace those on the cap and sand the partners before inserting into the copper couplings when reinstalling. To fix the connection, find a short, I believe 10/32 screw, a piece of copper strap, and some silver base solder. Tin the strap then gently screw the copper strap to the phenolic holding it to the stator phalange. Reinsert the removed or new #16 wire into the original tab and wrap the copper strap over the wire and silver solder all. It will be clear when you see the connection up close. We made this change and after several hours of operation on 10 meters the joint was cool. If you need clarification or photo's please email or call 847-571- 8420
We sent a note regarding the SR-2000 final loading capacitor heating problem and need to add a step to the fix. Anytime the final loading capacitor is removed, replaced, or unscrewed and after it is re-secured, all three sections must be hi potted to 600 volts with the wires separated. If it fails, it must be shimmed to relieve the tension caused by tightening the screws. The SR-2000 is designed to enable idle bias, final drivers, and keying only after the antenna relay is confirmed closed. If the loading capacitor shorts, the radio will think that relay transfer has occurred and can go to transmit before the relay actually closes with significant risk of damage.
CHIRP We've had several queries regarding a chirp during the transition from transmit to receive and receive to transmit. The chirp will be present on the second to last run of the SR-150, the last run of the SR-400, and any SR-2000 that installed the following service note that we wrote about two years ago. We recommended the installation of a 5uf capacitor to ground on the line that runs from the VOX relay to VFO. The problem that it corrected was a very slightly fuzzy sounding audio both receive and transmit at the lower audio frequencies. This was caused by low level 60 cycle modulation/sidebands being present on the VFO output. The origin of the problem is resistance build up in the line between the RIT/CAL pots and the varactor diode in the VFO. The high impedance created allows 60 cycle crossover in the wiring harness. Cleaning both the RIT switch and VOX relay will correct the problem. That line carries no current and will develop resistance over time unless a conditioner like Deoxit is applied. Once you have cleaned the path and checked for zero ohms, remove the 5uf capacitor which was added to the VFO line. We recommend the cleaning of the switch and relay in all SR-150, SR-400 400A, and SR-2000's and the removal of the capacitor work around, if it is present. You will be pleased with clearer audio. Spectrum analyzer photos of the VFO and audio distortion are posted on the SR-2000 reflector. Any questions call 847-571-8420
I have swept a number of SR-150 filters and they indeed average 2.7kc. I can find no reason for Hallicrafters to have printed misleading data in the operations manual. A good reference is page 11 of the SR-150 Performance specifications document i.3. (-3 db limit at 400 cps to 600 cps) and (-3 db limit at 2700 cps to 3200 cps). There were no filter variations from the "A" to "C" level which is the most current. The following information will clarify the installation of the SR-150 "2.7 kc filter into SR-2000 which uses a "2.1 kc" filter. First, if you are a contester, don't do it. It sounds great but 2.7 kc is a bit wide. The difference between the filter circuits is as follows. L14 and L15 in the SR-150 are adjustable from 40uh to 240uh. L15, the filter source in the SR-2000 is the same inductor as used by the SR-150 but L16, the terminating inductor is 17uh to 39uh and the capacitor that parallels it is 300pf --- much higher Q and different impedance than the terminating circuit in the SR-150. You can go two ways here. Simply drop the SR-150 filter into the SR-2000 and accept approximately 3db to 6db of filter ripple or replace the terminating inductor with the one removed from the SR-150, copying the capacitor and resistor. Leave the input termination alone, it does not appear to affect the filters performance. The termination is the cause of the filter ripple. I believe my post a few years back did not reference the termination or filter ripple. The filter ripple was measurable but quite undetectable to the ear.
Kindest regards, Jim K9AXN
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