Hi Jim,
Thanks for the info!? It appears that I was replying when you were and then, I left the computer sitting without pushing the "SEND" button!? So you can see my what I discovered experimenting? below!
I absolutely did (first) power it up using only the existing bleeder !? I of course discovered exactly what you're talking about!?? The NE51 was not installed at the time.? Everything is disconnected? and standing alone.? I am using 2 SEMTECH 5000v diodes in place of the old 866A's and the filament transformer is also gone.
Again, I am still concerned that the 40ma of additional current draw due to the tube will not result in enough current to make the choke work but I will try it.? If I have to add a little more bleeder, I can easily add another 100K.? The NE51 I have is in fact an NE51H
I do have a good tube (actually I have 3!!)?? I tried all of them in my L-4B and they all do at least as good as the 3-500's I have in it now.? (same roughly 1300w out)?
As an aside, the Eimac 3-500's I have fit perfectly (slightly shorter than the plate choke)? in the HT45 so I am tempted to use one of them and just use the 3-400's in the L-4B but that's another thread to discuss!!
Anyway, I am going to do exactly what you're suggesting.? I am going to try it with the HT45.? If the voltage is "ok", I'll leave it alone.? If the voltage is still high, and an additional 100K doesn't work,? (maybe the choke is NOT actually the original choke, or it's defective) ? I may just see if I can get another swinging choke.? If I cannot find one, I am going to use the extra Drake L-4PS I have.? (it's less than ONE HALF the size of the PS-2V!!)
The downside of using the L-4PS is the 2700 no-load voltage.? I think the 3-400 (or 3-500)? will work pretty good with 3200-3400v?
73/Rick
WA6III
__________________________________
No critters were injured transmitting with Hallicrafters transmitters except
the ones that wandered into the final amp cage Bug-Motel!!
Bugs check-in, but they don't check-out!
|
Howdy,
Thanks for the reply
Well, since the voltage across the choke is dependent on the current through the choke, it shouldn't make any difference. Position of the choke in the circuit, positive or negative doesn't really affect the voltage "across" the choke.? It only changes the actual voltage on the windings referenced to the grounded iron core
Putting it in the negative lead would only take the high voltage off the windings (which is certainly desirable).... but I don't think the "snapping" is due to "winding-to-core" arcing.? If it was, it would likely be continuous.? I.E., it would short, stay shorted and pop the fuse.?
This is more a "clicking", snapping", ticking that I think is due to internal arcing across windings (or the arc "gap" depicted in the schematic) and that voltage is directly related to the (pulsating) current in the windings.
Either way, my original question is more related to the the idling current when the amplifier is in the STBY mode.? (I know what it should be in the transmit mode.....It should be around 120ma, and that's more than enough current for the choke)
And in fact, I went back to the manual and read a little closer and actually found what I was looking for!
I guess I should just RTFM? before asking questions!!? But at 40ma, I'm thinking it's not going to be enough unless I add an additional bleeder.
I found that using only the power supply bleeder resistor of 210k Ohm (with only an 18ma draw) , the voltage was high at around 3750+ volts.? (and there was "ticking")?
When I added an additional 100K in parallel,? I still had around 3750+ volts ,? total resistance around 68K,? resulting in a total 55ma draw (still ticking!!)
When I added an another 100K in parallel, I saw a significant voltage drop.? Voltage was 3460v, no ticking, with a combined resistance of about 40K.
Total current draw due to the total 40K (210K + 100K + 100K parallel) was around 86ma.
I know choke input power supplies have a lower limit of current that must be present to prevent the voltage from "soaring" (ARRL handbook term!)
The part that I am concerned about is that since the tube will draw 40ma (according to the instruction above) when the T/R "jumper" is removed, that's only going to be a total of about 18ma + 40ma? =? 58ma.
If you note above that I still had "ticking at 55ma, I am having a hard time believing that 3 additional ma will be the "break-point" of where the choke starts to "choke"
Maybe it will.?? This is where my lack of experience with high voltage (swinging) choke input supplies is somewhat lacking.?
I would REALLY like to hear from someone else that actually has or has played with one of these power supplies hooked up to an HT45? so I can compare notes!
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On Sun, Oct 23, 2022 at 02:16 AM, D. Platt wrote:
<!doctype html>
Just a thought but if it is indeed choke input, you might consider putting the choke on the negative side if a bridge, or the center tap if otherwise. That way, way less voltage across the choke.
Jeep K3HVG
--
On Sun, Oct 23, 2022 at 02:16 AM, D. Platt wrote:
K3HVG
? -- 73/Rick WA6III __________________________________ No critters were injured transmitting with Hallicrafters transmitters except the ones that wandered into the final amp cage Bug-Motel!! Bugs check-in, but they don't check-out!
|
Hi Rick!
?? In looking over the power supply schematic and in view of my own experience with a PS-500 power supply, I think I can safely say that Hallicrafters did not know how to design power supplies.
?? First, a caution:?? This PS-2A power supply is not intended to be operated without a load and in the absence of proper connection to the HT-45 amplifier.?? If you do so, all bets are off.?? Note that with the power supply disconnected from the amplifier, there is no negative return for the high voltage.?? The high voltage should therefore be about 1700 volts positive with respect to the chassis and the negative lead (Pin 7 on TB2) should be about negative 1700 volts with respect to ground.?? However, this assumes that the insulation all the way around is perfect, which it likely isn't.?? There is supposed to be 1/2 ohm of at least 2 watts power rating between this negative lead and chassis ground.?? This is formed by the plate current metering shunt resistors in the amplifier when it is connected to the supply.?? Absent the amplifier being connected, who knows what is arcing where and what is causing your noises.
?? According to the manual, the idling current with the extra resistor in place is about 40 mA.?? Since this will change the output voltage of the power supply, we are dealing with one equation in two unknowns, so experimentation would be required to discover what sort of external resistive load would draw 40 mA.?? Until you figure this out and connect a suitable external load and a suitable ground to the negative of the HV supply you cannot determine the operating parameters of the power supply.?? The best test is to operate it with the amplifier as a load.... however, this assumes that the 3-400 is good and at least the DC portions of the rest of the amplifier circuitry are correct.
?? The circuit calls for an NE51 to be connected across the 10K bleeder in the power supply.?? Using Hallicrafters figures for the B+ (3,000 volts) the rated current of the lamp would be exceeded and the lamp should be destroyed.?? For higher voltages such as you are experiencing, the condition is even worse.?? An NE51H MIGHT survive here, but is not specified in the parts list.
?? I wish you the best of luck in getting the thing working; hopefully you will not have to do too much re-engineering.
Regards,
--
Jim T.
KB6GM
|
Re: SR-75 transceiver notes
I wasn't able to UL the Magazine but did see a copy of service manual and operator's manual for the SR-75 in the files section.
Jeff
K7AIL
|
Re: SR-75 transceiver notes
Thanks John, I will hang on to this for awhile and make some contacts, maybe we will work. ? 73, Roger, NJ2R ?
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Show quoted text
From: [email protected] < [email protected]> On Behalf Of John K5MO Sent: Friday, October 21, 2022 9:22 PM To: [email protected]Subject: Re: [HallicraftersRadios] SR-75 transceiver notes ? That is a great story and I've never seen one of those in person either. It certainly does sound like it was "meant to be" with your ownership. 7050 is a good spot for such a radio and I have no doubt you'll be successful there. Id love to work your station! ? I’d known of the SR-75 for a long time as is it shown in the Chuck Dachis book but I’d never seen one though possibly passed them at swaps and thought, “just another S-38B”. ? So, at the Chelsea, Michigan swap in May of this year, there it was on a table. While I do not need any more radios, this one was worth the fun to see if it could get going. ? The SR-75 as I mentioned is a S-38B but cleverly a 10 watt crystal controlled transmitter is incorporated by adding a 12BA6 crystal oscillator and using the 50L6 audio amplifier as a RF amplifier. It has a keying relay to key the cathode of the 50L6 and unlike many keys of that era only 3 volts is present on the key because two D cells are used to provide the relay voltage. On the back of the radio is Plate tuning, Antenna loading, a switch to change the oscillator to allow 11/10 meter operation and a 5 pin jack for monitoring plate current and attaching the key. There is a single pigtail antenna wire that as shown in the manual that connects to a random wire or a balanced line to a resonant dipole. ? The SR-75 uses 4 different plug-in coils and uses crystals, 3.5 MHz for 80 meters or 7 MHz for the remaining bands. I was fortunate that mine came with the 80 meter coil and a crystal on 3555 KHz ? I brought up the SR-75 on a Variac and to my surprise it received pretty well since it appeared to have never had a part changed except for the volume control since new. The transmitter was another story and it did not work. Oddly, half of the 117Z6 rectifier was not working so there was no negative bias supply. Suspect too, though there was only minor hum, ?were the multiple electrolytics in two waxed paper cases. After getting a new rectifier I had bias voltage but decided to change the electrolytics which actually resulted in more space under the chassis. The outcome was having nearly exact tube voltage readings everywhere. ? ? Next was to wonder where in the world I’d find the phenolic 5 pin plug for the key and plate current. Lo and behold it’s really 4 pins and a 4 pin connector ( the center pin was not used) was found new on eBay to my surprise. It was a sign that this was “meant to be” as was an original manual also on eBay. ? So what was I going to do for additional coils? I’d put out a message here, on QTH, and heard from others who own the SR-75 and almost all had no coils or information except for Chris Farley KC9IEQ who had the 40. 20. and 10 meter coils. Chris graciously provided me with pictures, turn counts and even measured the inductance. With that information I went about finding the correct phenolic coil forms, spreaders and banana plugs to reproduce the coils. I made a coil winder and lucky enough had enough enamel covered wire to make the coils. Later I remade them using the original tinned copper just for appearance sake.? I sent Chris an 80 meter coil to complete his set otherwise I have had no information on the coils had it not been for him. ? Though the radio received OK enough I went ahead and recapped the whole thing, checked resistors, did the alignment and it now receivers really well for an S-38B. ? I had a hard time getting to” know” the transmitter. What would I do to be able to read power besides measuring RMS volts on my HP-410C. I wanted to see power into a dummy load which Hallicrafters describes for the transmitter. Eventually I was seeing some power as evidenced by burning my finger from the resistor in the dummy load! With a bit of experimentation, I was able to connect a piece of RG-58 though a wattmeter and was able to get 6 to 10 watts output into a 50 ohm dummy load. The next step was to see if my off center fed dipole would be liked by the radio. On 80 meters not so much with only 2 watts output shown but on 40 meters I have a solid 10 watts with about 1 watt SWR. ? Back when I was a novice as KN8AJF, using a S-53A and Globe Scout, crystal controlled on 40 meters with a 75 foot long wire, I’d call CQ and listen all over the band for a reply. I did manage to work quite a few stations including the FCC when my second harmonic ended up on 20 meters.? My sense is that in today’s world few stations would tune off frequency and if so I’d be told I was off frequency! Another drawback of the SR-75 is there is no side tone. I admit to not being very good with a straight key anymore so I used another receiver to provide side tone. The “band” around 7050 KHz is very narrow and the bandspread of the SR-75 is pretty narrow as well so it is easy to miss a caller. I have made one contact so far just to be sure everything worked as I thought. Certainly, back in the day this could have and probably did serve as a complete novice station. Even so I am somewhat intimidated to be using it today. ? The outward condition of the radio is not at all mint though I prefer to say it has some patina with a few touchups here and there. Someone cut a hole perhaps to mount a SO-239 socket in the side but it was done so neatly I thought at first it was original. I don’t know what I will do with this now though I will likely sell it at some point. I hate to see things like this sit on a shelf. ? I still have some coil forms and a few spreaders as well as that scarce 4 pin plug for the back if anyone wants them at a small cost. I can wind coils though while they are close to original they are not as nice looking as Hallicrafters made them ? Thanks to all who have shared their SR-75 stories with me! ? 73, Roger, NJ2R ? ?
|
Just a thought but if it is indeed choke input, you might consider putting the choke on the negative side if a bridge, or the center tap if otherwise. That way, way less voltage across the choke.
Jeep K3HVG
On 10/22/2022 7:49 PM Rick WA6III <myr748@...> wrote:
Ok,
I am going to probably show my ignorance of choke input power supplies but here goes!!
I am rebuilding my HT45 power supply.? My HT45 is Hallicrafters branded but probably like many, has the Radio Industries PS-2A power supply. I am guessing that Hallicrafters probably had a LOT of them laying around and used them until the supply was exhausted and then started putting their own name on them.? No matter, there doesn't appear to be any electrical difference.
Testing mine, I have noticed that if I use only the existing 210K ohm total bleeder resistors (series 100k + 100k + 10K), I hear what is best described as a faint "clicking" sound in the choke!? And the voltage is upwards of 3750V.? (too high in my book)
Although I don't see any discussion of it in the manual, the schematic shows the 4-16H (swinging) choke with what I would call an "arc-gap" (maybe internal) for protecting the choke (I guess) .
With no load (but with the 210K resistors) on the power supply the voltage is a little more than 3700V.? If I add some load (an additional 50K like an idling 3-400) drawing a total of 87 ma, The voltage drops to about 3460v and the clicking stops!
And before someone tells me how a choke input power supply works (needs a minimum load etc)? I did read the handbook discussion on choke input power supplies!
My question (and I'm hoping Walt jumps in here) concerns the jumper on the back of the HT45.? This terminal allows "shorting" across a 150 OHM resistor in the 3-400 cathode circuit that is there to increase bias and reduce cathode current during STBY.
The manual talks about using a T/R relay controlled by PTT from the exciter with additional contacts for this purpose.? This is also done with the HT33 I have and many other amplifiers. (Note 5.)
I am just wondering what to expect with the reduction?? I have experimented with the power supply a little and have discovered that with the current swinging choke I have, the existing 210K ohms aren't enough, an additional 100K isn't enough, and I had to put another 100K in parallel to get the choke to stop "ticking"
210K + 100K + 100K? all in parallel (about 40K) produced enough current to stop the ticking and clicking and put the output at 3460V with 122VAC on the primary.
Anyone have experience with one of these?
--
73/Rick
WA6III
__________________________________
No critters were injured transmitting with Hallicrafters transmitters except
the ones that wandered into the final amp cage Bug-Motel!!
Bugs check-in, but they don't check-out!
|
Re: SR-75 transceiver notes
That's where my file came from. ?I tried to upload it a couple of times but was unsuccessful. ?It's about 18MB in size. ?Is the size fine?
|
Re: SR-75 transceiver notes
I have not looked? but suspect it's on worldradiohistory.org? perfectly enormous amount of stuff there?
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-------- Original message -------- From: Jeffrey Benedict <raoul@...> Date: 10/22/22 6:37 PM (GMT-08:00) Subject: Re: [HallicraftersRadios] SR-75 transceiver notes
[Edited Message Follows]
Looking around, I found a contemporaneous review of the SR-75 from "Radio and Television News" of April 1951. ?The whole magazine isn't too big so I'm going to UL the whole the . ?The review is in the middle of the magazine and there is other cool stuff. There is an article about the "new" ham tickets of 1951 including Novice, Technician, General (and Conditional), Advanced and Extra. It's an interesting look back in time. I will UL it to the file section. Jeff K7AIL
|
Re: SR-75 transceiver notes
Looking around, I found a contemporaneous review of the SR-75 from "Radio and Television News" of April 1951. ?The whole magazine isn't too big so I'm going to UL the whole the . ?The review is in the middle of the magazine and there is other cool stuff. There is an article about the "new" ham tickets of 1951 including Novice, Technician, General (and Conditional), Advanced and Extra. It's an interesting look back in time. I will UL it to the file section.
Jeff K7AIL
|
Ok,
I am going to probably show my ignorance of choke input power supplies but here goes!!
I am rebuilding my HT45 power supply.? My HT45 is Hallicrafters branded but probably like many, has the Radio Industries PS-2A power supply. I am guessing that Hallicrafters probably had a LOT of them laying around and used them until the supply was exhausted and then started putting their own name on them.? No matter, there doesn't appear to be any electrical difference.
Testing mine, I have noticed that if I use only the existing 210K ohm total bleeder resistors (series 100k + 100k + 10K), I hear what is best described as a faint "clicking" sound in the choke!? And the voltage is upwards of 3750V.? (too high in my book)
Although I don't see any discussion of it in the manual, the schematic shows the 4-16H (swinging) choke with what I would call an "arc-gap" (maybe internal) for protecting the choke (I guess) .
With no load (but with the 210K resistors) on the power supply the voltage is a little more than 3700V.? If I add some load (an additional 50K like an idling 3-400) drawing a total of 87 ma, The voltage drops to about 3460v and the clicking stops!
And before someone tells me how a choke input power supply works (needs a minimum load etc)? I did read the handbook discussion on choke input power supplies!
My question (and I'm hoping Walt jumps in here) concerns the jumper on the back of the HT45.? This terminal allows "shorting" across a 150 OHM resistor in the 3-400 cathode circuit that is there to increase bias and reduce cathode current during STBY.
The manual talks about using a T/R relay controlled by PTT from the exciter with additional contacts for this purpose.? This is also done with the HT33 I have and many other amplifiers. (Note 5.)
I am just wondering what to expect with the reduction?? I have experimented with the power supply a little and have discovered that with the current swinging choke I have, the existing 210K ohms aren't enough, an additional 100K isn't enough, and I had to put another 100K in parallel to get the choke to stop "ticking"
210K + 100K + 100K? all in parallel (about 40K) produced enough current to stop the ticking and clicking and put the output at 3460V with 122VAC on the primary.
Anyone have experience with one of these?
--
73/Rick
WA6III
__________________________________
No critters were injured transmitting with Hallicrafters transmitters except
the ones that wandered into the final amp cage Bug-Motel!!
Bugs check-in, but they don't check-out!
|
Re: SR-75 transceiver notes
YES, it was an exciting time to be a new ham. The war was over, television was just getting a good start, telephone service to a home was sparse as it was usually a party line, private phone service was rare. So here comes Ham Radio as an Unlimited method to contact the world at any time of day or night, using that special method of communication “Morse Code”. The common excited comments were “I worked California, I worked Canada, I worked Maine! YES, it was very exciting and provided a lifelong love for Ham Radio! It was a Great Time to be a new Ham.
|
Re: SR-75 transceiver notes
C. 1951 the S 38B was about $40 and the SR 75 about $80.? I don't know what that included in the way of accessories, extra coils, etc.? I got a brand new S 38b when I was a kid,? I don't remember it came with anything except an instruction book.
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Show quoted text
-------- Original message -------- From: Jeffrey Benedict <raoul@...> Date: 10/21/22 10:59 PM (GMT-08:00) Subject: Re: [HallicraftersRadios] SR-75 transceiver notes
That's kinda cool! ?Those days were kinda different for starting hams.
?
Does anyone know the difference in price between a S-38 and this radio? Depending on price, it may have been cheaper to use and S-38 and make some sort of a 10 watt transmitter. But, again, that might be a little bit out of the ability range of a teen aged novice, especially one without a club or elmer.
Jeff K7AIL
|
Re: SR-75 transceiver notes
That's kinda cool! ?Those days were kinda different for starting hams.
?
Does anyone know the difference in price between a S-38 and this radio? Depending on price, it may have been cheaper to use and S-38 and make some sort of a 10 watt transmitter. But, again, that might be a little bit out of the ability range of a teen aged novice, especially one without a club or elmer.
Jeff K7AIL
|
Re: SR-75 transceiver notes
Hi Roger
That is a great story and I've never seen one of those in person either. It certainly does sound like it was "meant to be" with your ownership.
7050 is a good spot for such a radio and I have no doubt you'll be successful there. Id love to work your station!
Best 73 John k5mo
I’d known of the SR-75 for a long time as is it shown in the Chuck Dachis book but I’d never seen one though possibly passed them at swaps and thought, “just another S-38B”. ? So, at the Chelsea, Michigan swap in May of this year, there it was on a table. While I do not need any more radios, this one was worth the fun to see if it could get going. ? The SR-75 as I mentioned is a S-38B but cleverly a 10 watt crystal controlled transmitter is incorporated by adding a 12BA6 crystal oscillator and using the 50L6 audio amplifier as a RF amplifier. It has a keying relay to key the cathode of the 50L6 and unlike many keys of that era only 3 volts is present on the key because two D cells are used to provide the relay voltage. On the back of the radio is Plate tuning, Antenna loading, a switch to change the oscillator to allow 11/10 meter operation and a 5 pin jack for monitoring plate current and attaching the key. There is a single pigtail antenna wire that as shown in the manual that connects to a random wire or a balanced line to a resonant dipole. ? The SR-75 uses 4 different plug-in coils and uses crystals, 3.5 MHz for 80 meters or 7 MHz for the remaining bands. I was fortunate that mine came with the 80 meter coil and a crystal on 3555 KHz ? I brought up the SR-75 on a Variac and to my surprise it received pretty well since it appeared to have never had a part changed except for the volume control since new. The transmitter was another story and it did not work. Oddly, half of the 117Z6 rectifier was not working so there was no negative bias supply. Suspect too, though there was only minor hum, ?were the multiple electrolytics in two waxed paper cases. After getting a new rectifier I had bias voltage but decided to change the electrolytics which actually resulted in more space under the chassis. The outcome was having nearly exact tube voltage readings everywhere. ? ? Next was to wonder where in the world I’d find the phenolic 5 pin plug for the key and plate current. Lo and behold it’s really 4 pins and a 4 pin connector ( the center pin was not used) was found new on eBay to my surprise. It was a sign that this was “meant to be” as was an original manual also on eBay. ? So what was I going to do for additional coils? I’d put out a message here, on QTH, and heard from others who own the SR-75 and almost all had no coils or information except for Chris Farley KC9IEQ who had the 40. 20. and 10 meter coils. Chris graciously provided me with pictures, turn counts and even measured the inductance. With that information I went about finding the correct phenolic coil forms, spreaders and banana plugs to reproduce the coils. I made a coil winder and lucky enough had enough enamel covered wire to make the coils. Later I remade them using the original tinned copper just for appearance sake.? I sent Chris an 80 meter coil to complete his set otherwise I have had no information on the coils had it not been for him. ? Though the radio received OK enough I went ahead and recapped the whole thing, checked resistors, did the alignment and it now receivers really well for an S-38B. ? I had a hard time getting to” know” the transmitter. What would I do to be able to read power besides measuring RMS volts on my HP-410C. I wanted to see power into a dummy load which Hallicrafters describes for the transmitter. Eventually I was seeing some power as evidenced by burning my finger from the resistor in the dummy load! With a bit of experimentation, I was able to connect a piece of RG-58 though a wattmeter and was able to get 6 to 10 watts output into a 50 ohm dummy load. The next step was to see if my off center fed dipole would be liked by the radio. On 80 meters not so much with only 2 watts output shown but on 40 meters I have a solid 10 watts with about 1 watt SWR. ? Back when I was a novice as KN8AJF, using a S-53A and Globe Scout, crystal controlled on 40 meters with a 75 foot long wire, I’d call CQ and listen all over the band for a reply. I did manage to work quite a few stations including the FCC when my second harmonic ended up on 20 meters.? My sense is that in today’s world few stations would tune off frequency and if so I’d be told I was off frequency! Another drawback of the SR-75 is there is no side tone. I admit to not being very good with a straight key anymore so I used another receiver to provide side tone. The “band” around 7050 KHz is very narrow and the bandspread of the SR-75 is pretty narrow as well so it is easy to miss a caller. I have made one contact so far just to be sure everything worked as I thought. Certainly, back in the day this could have and probably did serve as a complete novice station. Even so I am somewhat intimidated to be using it today. ? The outward condition of the radio is not at all mint though I prefer to say it has some patina with a few touchups here and there. Someone cut a hole perhaps to mount a SO-239 socket in the side but it was done so neatly I thought at first it was original. I don’t know what I will do with this now though I will likely sell it at some point. I hate to see things like this sit on a shelf. ? I still have some coil forms and a few spreaders as well as that scarce 4 pin plug for the back if anyone wants them at a small cost. I can wind coils though while they are close to original they are not as nice looking as Hallicrafters made them ? Thanks to all who have shared their SR-75 stories with me! ? 73, Roger, NJ2R ? ?
|
I’d known of the SR-75 for a long time as is it shown in the Chuck Dachis book but I’d never seen one though possibly passed them at swaps and thought, “just another S-38B”. ? So, at the Chelsea, Michigan swap in May of this year, there it was on a table. While I do not need any more radios, this one was worth the fun to see if it could get going. ? The SR-75 as I mentioned is a S-38B but cleverly a 10 watt crystal controlled transmitter is incorporated by adding a 12BA6 crystal oscillator and using the 50L6 audio amplifier as a RF amplifier. It has a keying relay to key the cathode of the 50L6 and unlike many keys of that era only 3 volts is present on the key because two D cells are used to provide the relay voltage. On the back of the radio is Plate tuning, Antenna loading, a switch to change the oscillator to allow 11/10 meter operation and a 5 pin jack for monitoring plate current and attaching the key. There is a single pigtail antenna wire that as shown in the manual that connects to a random wire or a balanced line to a resonant dipole. ? The SR-75 uses 4 different plug-in coils and uses crystals, 3.5 MHz for 80 meters or 7 MHz for the remaining bands. I was fortunate that mine came with the 80 meter coil and a crystal on 3555 KHz ? I brought up the SR-75 on a Variac and to my surprise it received pretty well since it appeared to have never had a part changed except for the volume control since new. The transmitter was another story and it did not work. Oddly, half of the 117Z6 rectifier was not working so there was no negative bias supply. Suspect too, though there was only minor hum, ?were the multiple electrolytics in two waxed paper cases. After getting a new rectifier I had bias voltage but decided to change the electrolytics which actually resulted in more space under the chassis. The outcome was having nearly exact tube voltage readings everywhere. ? ? Next was to wonder where in the world I’d find the phenolic 5 pin plug for the key and plate current. Lo and behold it’s really 4 pins and a 4 pin connector ( the center pin was not used) was found new on eBay to my surprise. It was a sign that this was “meant to be” as was an original manual also on eBay. ? So what was I going to do for additional coils? I’d put out a message here, on QTH, and heard from others who own the SR-75 and almost all had no coils or information except for Chris Farley KC9IEQ who had the 40. 20. and 10 meter coils. Chris graciously provided me with pictures, turn counts and even measured the inductance. With that information I went about finding the correct phenolic coil forms, spreaders and banana plugs to reproduce the coils. I made a coil winder and lucky enough had enough enamel covered wire to make the coils. Later I remade them using the original tinned copper just for appearance sake. ?I sent Chris an 80 meter coil to complete his set otherwise I have had no information on the coils had it not been for him. ? Though the radio received OK enough I went ahead and recapped the whole thing, checked resistors, did the alignment and it now receivers really well for an S-38B. ? I had a hard time getting to” know” the transmitter. What would I do to be able to read power besides measuring RMS volts on my HP-410C. I wanted to see power into a dummy load which Hallicrafters describes for the transmitter. Eventually I was seeing some power as evidenced by burning my finger from the resistor in the dummy load! With a bit of experimentation, I was able to connect a piece of RG-58 though a wattmeter and was able to get 6 to 10 watts output into a 50 ohm dummy load. The next step was to see if my off center fed dipole would be liked by the radio. On 80 meters not so much with only 2 watts output shown but on 40 meters I have a solid 10 watts with about 1 watt SWR. ? Back when I was a novice as KN8AJF, using a S-53A and Globe Scout, crystal controlled on 40 meters with a 75 foot long wire, I’d call CQ and listen all over the band for a reply. I did manage to work quite a few stations including the FCC when my second harmonic ended up on 20 meters.? My sense is that in today’s world few stations would tune off frequency and if so I’d be told I was off frequency! Another drawback of the SR-75 is there is no side tone. I admit to not being very good with a straight key anymore so I used another receiver to provide side tone. The “band” around 7050 KHz is very narrow and the bandspread of the SR-75 is pretty narrow as well so it is easy to miss a caller. I have made one contact so far just to be sure everything worked as I thought. Certainly, back in the day this could have and probably did serve as a complete novice station. Even so I am somewhat intimidated to be using it today. ? The outward condition of the radio is not at all mint though I prefer to say it has some patina with a few touchups here and there. Someone cut a hole perhaps to mount a SO-239 socket in the side but it was done so neatly I thought at first it was original. I don’t know what I will do with this now though I will likely sell it at some point. I hate to see things like this sit on a shelf. ? I still have some coil forms and a few spreaders as well as that scarce 4 pin plug for the back if anyone wants them at a small cost. I can wind coils though while they are close to original they are not as nice looking as Hallicrafters made them ? Thanks to all who have shared their SR-75 stories with me! ? 73, Roger, NJ2R ? ?
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Re: SX-110 Dial Lamp Mystery
An update on this.? I removed the stripping and as far as I'm concerned the lighting looks just fine now. Will button up the front panel and call it good. That was really quite bizarre -- I was being overly-cautious because I don't like taking any pieces out of a boat anchor that look like they belong there. This appears to have been most likely a factory error, left by a Hallicrafters worker decades ago, because the petrified strip and the glue were definitely vintage. The other possibility is that the strip was originally meant to block some, but not all of the light, creating a more somber glow -- and it expanded and hardened over the years. Usually, though, these things contract with time rather than expand, so I'll put that in the category of less likely. ? Back to re-capping, etc. ? 73 – Steve, KW4H ? No.? The strip is mounted below the glass. ? 73 – Steve, KW4H ? Could the bulbs push further in?? To maybe get beyond the edge of the glass...
73,
Gary
WB6OGD
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Re: SX-110 Dial Lamp Mystery
No.? The strip is mounted below the glass. ? 73 – Steve, KW4H ? Could the bulbs push further in?? To maybe get beyond the edge of the glass...
73,
Gary
WB6OGD
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Re: SX-110 Dial Lamp Mystery
Gary, ? Very good points, thanks!? I took another close look at the dial, the markings, and how it’s mounted.? It seems to be original.? I can’t find any evidence that the bandspread window has been disturbed since the SX-110 was manufactured.? In any event, this will be resolved by installing some thin weatherstripping in a manner that provides a break for the dial lamps.? What would be very helpful to see is what someone else’s panel looks like (from behind) who does have the lights shining through.? However, that would require some disassembly. ? 73 – Steve, KW4H ? Its been a long time but I remember my SX-110 was lit and Bill's looks really correct to me.
I know these dials have fragile white markings after all these years and I am pretty sure I have seen repros.
Could it be that yours Steve is a repro and could it be that the bottom edge is painted black whereas it should
be open to let the light "edge light" like Bill suggests?
73,
Gary
WB6OGD
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Re: SX-110 Dial Lamp Mystery
Could the bulbs push further in?? To maybe get beyond the edge of the glass...
73,
Gary
WB6OGD
|
Re: SX-110 Dial Lamp Mystery
Its been a long time but I remember my SX-110 was lit and Bill's looks really correct to me.
I know these dials have fragile white markings after all these years and I am pretty sure I have seen repros.
Could it be that yours Steve is a repro and could it be that the bottom edge is painted black whereas it should
be open to let the light "edge light" like Bill suggests?
73,
Gary
WB6OGD
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Rick W7IMM