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Re: HT-44 noise on SSB
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How and where are you sampling when you see the noise.
Walt Cates, WD0GOF
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From: [email protected] <[email protected]> on behalf of Floyd - K8AC <floydsense@...>
Sent: Friday, April 26, 2024 2:23 PM To: [email protected] <[email protected]> Subject: Re: [HallicraftersRadios] HT-44 noise on SSB ?
Well, the AALC idea didn't pan out.? I disconnected one end of the diodes and also removed the plate supply from the AALC amplifier stage.? No change whatever.? Also played with the mic? connector lead and there was no difference in the noise level or
pattern with both ends of the cable grounded vs. just one end.
Floyd |
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Re: HT-44 noise on SSB
Well, the AALC idea didn't pan out.? I disconnected one end of the diodes and also removed the plate supply from the AALC amplifier stage.? No change whatever.? Also played with the mic? connector lead and there was no difference in the noise level or pattern with both ends of the cable grounded vs. just one end.
Floyd |
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Re: HT-44 noise on SSB
On Tue, Apr 23, 2024 at 10:09 PM, Paul Christensen wrote:
I don't own an HT-44 but looking at the manual, it uses AALC like some other Hallicrafters gear.? Possibly part of what you're experiencing is a low-threshold AALC.? Temporarily disabling it may help in localizing the noise source. From the manual:Interesting idea - thanks, Paul.? Will look into that. 73, Floyd - K8AC |
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Re: HT-44 noise on SSB
Floyd,
I don't own an HT-44 but looking at the manual, it uses AALC like some other Hallicrafters gear.? Possibly part of what you're experiencing is a low-threshold AALC.? Temporarily disabling it may help in localizing the noise source. From the manual: "An outstanding feature of the HT-44 is the amplified Automatic Audio Level Control (AALC). The AALC circuitry virtually eliminates splatter commonly caused by excessive audio gain and its?
resultant 'flat-topping."" This is accomplished by providing up to 12 DB of compression..." Paul, W9AC |
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Re: HT-44 noise on SSB
On Tue, Apr 23, 2024 at 06:18 PM, Jim Whartenby wrote:
In the HT-44 manual, specs page, there is no information on that.? They list carrier suppression, unwanted sideband rejection, thrid and fifth order distortion products and unwanted beat output, that's it.? I've restored a total of 15 old transmitters (this is first Hallicrafters) and I've never seen a transmitted noise floor this high.?? |
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Re: HT-44 noise on SSB
Floyd I see that the noise is about 40 dB down in the SA displays.? What is the spec for the HT44? Regards, Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Tuesday, April 23, 2024 at 04:16:20 PM CDT, Floyd - K8AC <floydsense@...> wrote:
On Tue, Apr 23, 2024 at 03:03 PM, Jim Whartenby wrote: I used polypropylene film caps when replacing the discs.? There really was no change in the noise compared to the original caps.? All of the replaced caps had broken ceramic where the leads entered the body and Walt previously mentioned that failed caps often had that characteristic.? I think it's safe to say that any modern cap is going to be at least as good as the ones used 62 years ago.?? |
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Re: HT-44 noise on SSB
On Tue, Apr 23, 2024 at 02:38 PM, W7WRX wrote:
Yes, I originally went through the unit using Walts HT-44 Repair Manual.? I have no idea what you mean by spec AN.? I readjusted the carrier null and unwanted sideband suppression again after taking the screen captures I posted.? The carrier null is greater than 50 dB and both the LSB and SSB suppression shows greater than 50 dB.? I suspect both of those could be improved if the prominent noise weren't there.? I was using the spectrum scope on my IC-7610.? The screen can be captured to an SD card by just pressing a button and then I edited out the unnecessary areas of the screen with a photo editor.? An oscilloscope probe connected to the receive-only antenna inputs works great for seeing what's going on in the transmitter or other receiver.?? 73, K8AC |
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Re: HT-44 noise on SSB
On Tue, Apr 23, 2024 at 03:03 PM, Jim Whartenby wrote:
I used polypropylene film caps when replacing the discs.? There really was no change in the noise compared to the original caps.? All of the replaced caps had broken ceramic where the leads entered the body and Walt previously mentioned that failed caps often had that characteristic.? I think it's safe to say that any modern cap is going to be at least as good as the ones used 62 years ago.?? |
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Re: HT-44 noise on SSB
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From:[email protected] <[email protected]> on behalf of Jim Whartenby via groups.io <old_radio@...>
Sent:?Tuesday, April 23, 2024 2:03 PM To:[email protected] <[email protected]> Subject:?Re: [HallicraftersRadios] HT-44 noise on SSB ?
Floyd
What type of disc capacitor did you use as a replacement?? See:
It might be worth the effort to use metalized film caps in place of the ceramics for use in the audio stages.
Regards,
Jim
Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
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Re: HT-44 noise on SSB
Floyd What type of disc capacitor did you use as a replacement?? See: It might be worth the effort to use metalized film caps in place of the ceramics for use in the audio stages. Regards, Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Tuesday, April 23, 2024 at 01:29:42 PM CDT, Floyd - K8AC <floydsense@...> wrote:
HT-44 - one last query for ideas before moving on.? ?The problem is a lot of "noise" within the audio passband when in LSB and USB modes.? I previously had thought the problem was in the mic amplifier stages, but it seems that's not true.? The nature of the noise is best seen in the attached spectrum pictures.? These were all taken from a tap on the dummy load with the HT-44 adjusted for about 10 watts output.? The first two photos show the output in CW and AM mode.? The second and third show LSB and USB mode.? The noise appears in the active sideband and shifts to the other sideband when changing from LSB to USB or vice versa.? The mic gain is set to 3-4 with somewhere around 5 mv sine wave audio input at 1400 Hz.? Before discovering the noise, I made one SSB QSO and the report was excellent audio but with some noise in the background.
What's been done so far:? All new NOS tubes.? Replaced .01 and .001 caps in the area of V1, V2, V3, V4.? That was done after finding one defective disc cap in the audio chain output.? Biased off the audio chain by using a jumper between the bias line and the first mic amp stage as is done for CW mode.? The noise remained, so I assume that the problem is in the balanced modulator stage.? ?Looked at the output of T2 with the spectrum scope and the noise is present there, so ruled out a problem in subsequent RF stages.
The balanced modulator section is at least working as I can minimize the unwanted sideband fairly well, and CW and AM modes don't look bad.? I suppose it's possible that there's a noisy resistor or capacitor and will look more closely at that in the next few days.? Years ago I ran into a difficult problem in an HA-1 keyer and it turned out to be a poor ground through one of the riveted tube sockets.? Hopefully this isn't that problem.
Here's how the output looks on CW and AM.?? The horizontal lines are 10 dB, so pretty clean down to 50 dB or so.? Now for SSB: LSB.? Carrier point under the red M, LSB to the left, USB to the right.? Audio input was 1400 Hz sine wave USB.? Noise shifted with selected sideband. Ideas? 73, Floyd - K8AC |
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HT-44 noise on SSB
HT-44 - one last query for ideas before moving on.? ?The problem is a lot of "noise" within the audio passband when in LSB and USB modes.? I previously had thought the problem was in the mic amplifier stages, but it seems that's not true.? The nature of the noise is best seen in the attached spectrum pictures.? These were all taken from a tap on the dummy load with the HT-44 adjusted for about 10 watts output.? The first two photos show the output in CW and AM mode.? The second and third show LSB and USB mode.? The noise appears in the active sideband and shifts to the other sideband when changing from LSB to USB or vice versa.? The mic gain is set to 3-4 with somewhere around 5 mv sine wave audio input at 1400 Hz.? Before discovering the noise, I made one SSB QSO and the report was excellent audio but with some noise in the background.
What's been done so far:? All new NOS tubes.? Replaced .01 and .001 caps in the area of V1, V2, V3, V4.? That was done after finding one defective disc cap in the audio chain output.? Biased off the audio chain by using a jumper between the bias line and the first mic amp stage as is done for CW mode.? The noise remained, so I assume that the problem is in the balanced modulator stage.? ?Looked at the output of T2 with the spectrum scope and the noise is present there, so ruled out a problem in subsequent RF stages.
The balanced modulator section is at least working as I can minimize the unwanted sideband fairly well, and CW and AM modes don't look bad.? I suppose it's possible that there's a noisy resistor or capacitor and will look more closely at that in the next few days.? Years ago I ran into a difficult problem in an HA-1 keyer and it turned out to be a poor ground through one of the riveted tube sockets.? Hopefully this isn't that problem. Here's how the output looks on CW and AM.?? The horizontal lines are 10 dB, so pretty clean down to 50 dB or so.? Now for SSB: LSB.? Carrier point under the red M, LSB to the left, USB to the right.? Audio input was 1400 Hz sine wave USB.? Noise shifted with selected sideband. Ideas? 73, Floyd - K8AC |
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Re: Vintage
gr8 big thnx----73
tom NU2W
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5T restoration - IF cans and R4 toasting
Working on adding #18 to the collection.? Picked up this 5T no-Boy dial receiver that matches up with the Rider drawing attached.?
Completing preliminary checks and metering out the IF cans showed: ? First IF, primary and secondary each at 8.5 ohms.? ? Second IF primary at 95 ohms and secondary at 30 ohms.? (?)? Physically it looks fine. I've searched and found no data and have nothing to compare against to verify the Second IF coil measurements. I read where a S-19 may be a close comparative model but I don't have one and the S-19R I do have is a different beast. Power transformer metered out OK.? Field coil is open, dang it.? Tubes tested - The 80 tube had an open filament which was resolved by re-flowing solder into the pins, the 6F7 fails "very weak" a portion on the pentode side but no shorts.? Caps done, electrolytic 4 and 8mfds replaced with 10mfds each.? Some dogbones out of tolerance and one 100pfd mica replaced.? Subbed in a 1500 ohm for the open FC.? At initial power up on the variac and at 40vac input the 5 and 6vac reached enough that the 80 kicked in and a low B+ came up, lamps and filaments glowed.? Bringing up to 60vac sound was heard and at 80-90vac I could clearly tune in a BC station.? B+ at 250-255v.? Then, as if you threw a switch, a dominant "power" hum kicked in and the clear sound became garbled under that hum, the hum being constant despite volume position.? The power transformer began to heat up excessively, I heard a crackle or two coming from it.? And R4 (25K replaced with a 27K 1W, off B+ / screen of 6A7 in drawing) gets VERY hot. R6 is also replaced with a 27K.? The rig is now on a test bench transformer for its supply (320-0-320), a test speaker with audio transformer, the field coil subbed by a 1500 ohm 10W wire-wound. No change in the operation, symptoms, all supply voltages come up as expected, the B+ remains pretty steady at 245-250v even when the hum kicks in 10-15 seconds after power up.? The hum may drop out and reception is clear for a few seconds before it returns, its present most of the time.? I do have a 6F7 on order as its hum suspect #1 but doubting its the root of my problem with R4 heating up.? Also, an appropriate replacement transformer is on order. ? -- Dan K1DTS |
waltcates
Floyd - K8AC
Paul Christensen
Jim Whartenby
Thomas K. Lanieri