Just to confirm, with nothing connected to the VTVM and it set to 5 volts, it still goes off scale?

The brightness control goes from 135 volts fed by a 12 K resistor going thru the control to ground. If it does pull a short to ground, the 12 K would overheat and possibly pull the 135 low. This 135 volt source feeds the I F screen grids also. If the control is grounding, check for tin whiskers on the control. Changing the 135 source in relationship to ground will, thru the screen voltages changing, affect the amplification factor of the I F and cause quite a change in the I F.
I would monitor the brightness control to ground as I rotate it for a drastic voltage change.

Just to confirm, with nothing connected to the VTVM and it set to 5 volts, it still goes off scale?

Not sure I understand the question. Do u mean is there an issue with the meter? No there’s no issue. It works fine. I’ve tested ac dc and resistance with it and it’s dead on

The brightness control goes from 135 volts fed by a 12 K resistor going thru the control to ground. If it does pull a short to ground, the 12 K would overheat and possibly pull the 135 low. This 135 volt source feeds the I F screen grids also. If the control is grounding, check for tin whiskers on the control. Changing the 135 source in relationship to ground will, thru the screen voltages changing, affect the amplification factor of the I F and cause quite a change in the I F.
I would monitor the brightness control to ground as I rotate it for a drastic voltage change.

Check the 135V correct?

So you are saying the VTVM is across R119 and reading off scale on the 5v range? What if you remove the probe ( hot) lead? Does the meter go to zero?

I checked step 6 and see the problem. The instruction manual has an error. The table gives an incorrect connection of the VTVM to the junction of L104 and R126. You need to measure across R119 with the case of the VTVM at -120vdc.

Please explain because you were talking as if the VTVM was faulty.

I have an alternative procedure which is safer and more precise. I will follow up once I see your reply. Can't recall seeing the error before but it explains what you are seeing.

Check the 135 v as you rotate the brightness control. If it varies widely, suspect a problem with it.

Ok guys thanks for everything tonight. Gonna get back on this tomorrow morning and I’ll report in and answer all questions

I may not be available in the morning so here goes. The table measuring at the junction of L104 and R126 is impossible because on my diagram there is no junction.
The reason your VTVM goes off scale is because there is a DC bias of at least 10vdc there.
To adjust the traps do this:
Connect the VTVM to pin 1 of V106 and ground.
Switch the VTVM to the 5vac range. Not DC.
Next switch the HP8601a AM modulation on to 1kHz.
Adjust input RF until you see about 3 volts AC on the VTVM
Adjust the traps null at frequency specified.
Raise the RF level as necessary to keep the null at no less than 1 vac.
Repeat this for each of the trap frequencies.

Wow. That’s so different and really helpful. I’ll give it a try. Not exactly free as I thought this morning myself! Sitting in the car in a he parking lot outside the salon while my wife gets her hair done! I’ll let cha know later today.

I checked step 6 and see the problem. The instruction manual has an error. The table gives an incorrect connection of the VTVM to the junction of L104 and R126. You need to measure across R119 with the case of the VTVM at -120vdc.

Please explain because you were talking as if the VTVM was faulty.

I'm going to get set up shortly to start with step 6 in the alignment again as per your instructions but I'm a bit concerned whether or not we are on the same page...literally on the same page and chassis. I don't see a mention of L104 and R126 anywhere in the Riders documentation I'm using. I know there was some confusion before as to what chassis this thread was about so I just want to clarify with a few words and pictures. My chassis is the KCS28B in the 9TC240 model and below are pictures of the alignment instructions and the table of alignment steps.

https://imagizer.imageshack.com/v2/1024x768q70/922/EmPcUx.jpg

https://imagizer.imageshack.com/v2/1024x768q70/923/WnF4RQ.jpg

https://imagizer.imageshack.com/v2/1024x768q70/924/1FMXtw.jpg

Mine was a 1948 publication. They fixed it in yours.

Makes no difference in my suggested procedure. I think mine better as it eliminates the DC offset to the meter and you can measure an actual signal and not just carrier amplitude.

I'll check it out just for fun. I have the first 4 volumes. Gonna get on the adjustment tonight. Will I get the 1KHz tone through the speaker and will monitoring it during the tuning process provide any additional guidance?

You won't hear the tone or it will be pretty weak. First it is AM. Second the 19.75MHz and 27.25MHz traps are pretty remote from the 21.25MHz sound IF.
You could see it on a scope. But just be sure you detect the tone on the VTVM by varying slightly the RF level. When you tune for the notch, the null should appear pretty obvious.

Seems this thread has gone dead! I wonder what happened?

Just haven't had a chance to work on it. Life happened. It's not forgotten or given up on...I just haven't had any time over the last 10 days. Fe:thmbsp:ar not!!!

Hi all. Lots going on here but that's life. All the traps and transformers have been nulled and peaked according to the new testing scenario laid out by Penthode. I'm now at the point of adjusting T-1 and T-101 with a sweep from 20-30 mc symmetrically around 25mc. It's kinda a mess. Amplitude is low and it doesn't look anything like the two peak response curve in figure 15. I'll post some pictures shortly. I hate to start thoughts of feeding composite video in this but I'm starting to consider that option. I have checked the multiburst bar sweep and the resolution isn't much better than it was when I started all of this. Maybe this TV was too much too soon for me. I did get further than I ever have in the past and I've learned so much about how these circuits work. Right now, the challenges of this are blocking work on other projects I want to get into. Other than holes in the chassis for the RCA plugs, there's nothing irreversible about cutting in with a signal at the video and audio amplifier section. I'm willing to give this process one more shot...start to finish. I mean all the way back to de-tuning T-113 in step 1. Despite Penthode's helpful suggestion with the alternate method for tuning of the video section and being pretty confident in getting the correct responses on the VTVM, there's still no change in the quality of the picture and, as I said, the T-1 T-101 tuning step is a mess on the scope despite hooking up the 330ohm resistor shunts correctly and feeding in a sweep signal at a number of different amplitudes correctly. Like I said, I'll give it one more comprehensive shot but if it fails, well, I have some decisions to make. Thanks all.

Show some pictures of the response with markers and we will set you straight. Forget about doing it any other way. Feeding in composite video and trying to adjust to to that will not work. You are getting there and all you need is patience and perseverance. And the results when done right will amaze you because this set delivers superb pictures.

The signal level will be low because of the shunts across the IF stages. You must turn the RF level up. The main thing is you must ensure is when varying the RF level, there should be no change to the shape of the RF response curve. Only the amplitude of the response curve will change. Make sure the ground connections are good. And show a picture of the sweeper generator panel so we may see the settings.

Patience!

I believe he is considering injecting composite video directly into the video amp and bypassing the IF entirely.

Thanks. I only realized that after the post.

Feeding in composite video is crummy on this set because you will lose the DC component unless you create a clamp circuit at -120 volts. Think about it. It is messy.

Hi all. Lots going on here but that's life. All the traps and transformers have been nulled and peaked according to the new testing scenario laid out by Penthode. I'm now at the point of adjusting T-1 and T-101 with a sweep from 20-30 mc symmetrically around 25mc. It's kinda a mess. Amplitude is low and it doesn't look anything like the two peak response curve in figure 15. I'll post some pictures shortly. I hate to start thoughts of feeding composite video in this but I'm starting to consider that option. I have checked the multiburst bar sweep and the resolution isn't much better than it was when I started all of this. Maybe this TV was too much too soon for me. I did get further than I ever have in the past and I've learned so much about how these circuits work. Right now, the challenges of this are blocking work on other projects I want to get into. Other than holes in the chassis for the RCA plugs, there's nothing irreversible about cutting in with a signal at the video and audio amplifier section. I'm willing to give this process one more shot...start to finish. I mean all the way back to de-tuning T-113 in step 1. Despite Penthode's helpful suggestion with the alternate method for tuning of the video section and being pretty confident in getting the correct responses on the VTVM, there's still no change in the quality of the picture and, as I said, the T-1 T-101 tuning step is a mess on the scope despite hooking up the 330ohm resistor shunts correctly and feeding in a sweep signal at a number of different amplitudes correctly. Like I said, I'll give it one more comprehensive shot but if it fails, well, I have some decisions to make. Thanks all.

Perhaps the best thing is indeed to make a non-invasive direct video feed (without opening holes in cabinet or chassis), playing with that, and other things. Then, some time ahead, you can return to this issue with "not loaded mind" ("not tired mind" (I forget what the term for that in English).
Sometimes for me, for example, heavy projects (for the mind) I end years after the starting, after some big pause.

As I said a direct video feed will lose the DC component of the video.

Honestly, the problem I see here is proceeding with the alignment without understanding how the set works. The alignment although long is being wrongly interpreted. I see the same problem attempting to introduce composite video feed.

Now that the correct test equipment is being applied, the alignment will be quite straight forward.

Let us see what the problem is here. I suspect it is a trivial mistake of adjusting equipment.

It could be a trivial thing. I injected a composite signal directly into my RCA 721 with no issue and ended up with a high quality picture...an order of magnitude better than through the tuner.
I do have a pretty good idea of how the signal is going through the IF and being filtered and modified but there are certainly aspects of getting a decent picture I don't understand.
I'm getting 3 KCS28 parts chassis in about a week plus a NOS 10BP4. I definitely want to replace the brightness control and I want to proceed carefully knowing I have a ready supply of replacement parts. Two of the traps I got from Bob are like most of these...stuck slugs that need a bit of mineral spirits to get them working but even with lubrication, they don't turn all that easily. The other issue with the slugs is a lack of robustness in that the iron slugs are solid but the threads, and I use that term lightly, in the coil tube are very susceptible to damage. They're not really threads but more like cuts in the inside walls of the tube every 90 degrees and it doesn't take much to strip them out. I can see why manufacturers quickly went to sticking a threaded rod in the slugs and made it ride up and down in a metal channel in the top of the can.

It is not as simple inserting composite video in this set compared to the 721. I have a 721 and the picture is excellent through the tuner and IF. The set you are working on is better but if all you are interested in is getting a picture on the screen, yeah that will work.

It is not as simple inserting composite video in this set compared to the 721. I have a 721 and the picture is excellent through the tuner and IF. The set you are working on is better but if all you are interested in is getting a picture on the screen, yeah that will work.

Gonna keep on keepin on!

Gonna keep on keepin on!

Great! You mentioned the trap null adjustments were okay?

What does the sweep look like on your scope? It can be made to match the published curve. I have done it with the equipment you are using. Can you detail what you are getting?

I’ll be working on it Thursday night.

:banana:

:banana:

I picked up the spare chassis today...3 of them. I want to swap out the brightness control first thing then do a quick reassessment of all the steps. I'm starting to know all of them from memory! I may not be able to get what I should but I sure as hell know the procedure by now. That's a big advancement for me.

The parts pieces have the fabric fine tuning/pulley strap intact. I wonder if there's a way I can make it more supple and less prone to breakage when I remove it? I've rigged a rubber replacement for my TV but because it stretches, there's backlash when you fine tune the set.
EDIT: Actually it looks like leather.

I used a leather strap. Bought some thin leather from Hobby Lobby. Cut a long strip of correct with a razor blade. Pre-stretch it then cut the strip a slightly longer than needed. Then with the razor blade cut taper (sloping) ends and then lap the ends together with a dab of white glue or super glue and clamp until glue is hard with a pair of pliers. Belt still working fine on my KRK5 tuners (three of them) with no slip after 20 years.

The same method was used for the mandrel drive belts on the earliest Edison cylinder phonographs from 1888 thru 1912 except they used fish glue. ( I have a 1900 Columbia AT, 1901 and 1903 Edison Model A Standards, a 1906 Edison Model B Triumph and a 1910 Edison Fireside which have belts made this way and play faultlessly).

Here is a YouTube video of the process.
https://youtu.be/NF9A-_xMBck?si=3yBpeNXUjuekhMDD

Very cool. I replaced the brightness control and there’s still intermittent full brightness even when it’s turned all the way down. Something else going on with that. Anyway I got into the alignment process and the damn HP 8600 Digital Marker went all wonky again and wouldn’t display frequencies. I’m not going to be able to keep using the screwdriver tap method on this anymore to get it to work. I’ll do some troubleshooting but does anyone know of a similar instrument that would work with the HP sweep generator I’ve been using? No 8600s on eBay at the moment.

No the HP 8601a/HP8600a are a unique pair. The HP8600a is a very reliable unit. What do you mean it is not reading frequencies? How are the switches set?

It’s not a setup or connection issue. This is an intermittent issue where all the frequencies read zero or when in CW more an inability to lock in on frequency. The cure for this has been shock to the unit with a tap with a screwdriver or picking up the front and dropping it an inch etc. it’s something inside that’s very subtle and is going to be a SOB to run down. It’s been an issue since I got the thing. This issue has been more frequent since I put the unit in a stack of other equipment so I’m going to pull it out, get it working again and have it just stand alone. But this kind of issue isn’t going to be easy to run down. It’s a fault somewhere in one of the boards. I’ve tried cleaning the plugin contacts and making certain they are seated well but that’s about as far as I’ve gone. I don’t think it’s an issue I can fix. I’ll just have to live with it until I can get another unit.

It sounds like a intermittent solder joint. Requires opening things up and applying pressure to various areas with a length of wood dowel in attempt to isolate it to a smaller area. Eventually you can hone in on it, but often takes a lot of time.

It sounds like a intermittent solder joint. Requires opening things up and applying pressure to various areas with a length of wood dowel in attempt to isolate it to a smaller area. Eventually you can hone in on it, but often takes a lot of time.

Yes that’s what I think. More than likely in the main board and not one of the modules. The main board is more susceptible given it’s a horizontal board and will flex. I’ll be working on it tonight

It uses cards on connectors. It is made by HP and should be nearly bullet proof.

I would simply open the box and reset the connectors and cards and VOILA it will work again.

It uses cards on connectors. It is made by HP and should be nearly bullet proof.

I would simply open the box and reset the connectors and cards and VOILA it will work again.

I did and cleaned the connectors again and made sure everything was seated firmly. I reassembled it after pulling off the 30 lbs of equipment on it and it's working fine. Time will tell but as long as it's operating, I'll get back on it tonight.

I may not be available in the morning so here goes. The table measuring at the junction of L104 and R126 is impossible because on my diagram there is no junction.
The reason your VTVM goes off scale is because there is a DC bias of at least 10vdc there.
To adjust the traps do this:
Connect the VTVM to pin 1 of V106 and ground.
Switch the VTVM to the 5vac range. Not DC.
Next switch the HP8601a AM modulation on to 1kHz.
Adjust input RF until you see about 3 volts AC on the VTVM
Adjust the traps null at frequency specified.
Raise the RF level as necessary to keep the null at no less than 1 vac.
Repeat this for each of the trap frequencies.

So I'm starting the trap adjustments over again. Just to confirm the procedure outlined above is after removal of V107 substituting the potentiometer I made and adjusting it to -4.5V DC at resistor R135/R136 junction?

Let me describe what's going on with the very first "null" of the top slug of T-103. I have the HP 8601A set as follows. Frequency is 21.25 MHz continuous. The output is 1KHz AM modulated at 10mV. It is being fed through a 1500pf cap into pin 1 of V2. The coaxial ground lead is clamped to the chassis. The VTVM is set to AC 5V range and was zeroed prior to connection. Probe is connected to pin 1 of V106 and grounded to the chassis. The 10mV RF output is the minimum output strength that can be adjusted to 3V AC but strong enough that interference, like touching the coaxial lead, doesn't cause deflection of the VTVM needle. Tuner is between channels 2 and 13.

I've turned the upper slug in T-103 a couple of turns clockwise and counter-clockwise from the initial position is resulting in no change on the VTVM.

I've checked and rechecked the connections and they are all correct. Is the RF output voltage too low? Shouldn't I get some VTVM deflection with those slug adjustments I made?

...there is another adventure I might propose and I can do it anyway even if this one goes down too many rabbit holes. I have two identical untouched chassis to this one. I might start a separate thread where I take one and do a dim bulb run up to reform the caps and with guidance from Penthode and others, do the minimum to get it working well...or at the least, as well as Penthode says his TV works on mostly original components.

Because it is a trap, it is sucking energy. Try cranking up the RF level until you see and indication.

It is a good idea to get a signal indication on the VTVM before you touch anything.

Not sure what's going on here but I'll tell you what I'm seeing...and hearing.
Let's be certain we are on the same page. I'm trying to do step 6 in the alignment table, the adjustment of the top of T-103. I have the VTVM connected to pin 1 of V106 and set to the 5V AC scale. I'm using my AC probe and ground lead from the VTVM. The 8601 is set for a CW of 21.25MHz. I tried what you suggested about turning up the RF gain. At 30mV through 300mV, I hear the 1KHz tone very clearly through the speaker with 100mV being the sweet spot for best undistorted tone. Anything lower than 30mV or higher than 300mV, I hear no tone through the speaker. At none of these RF output voltages can I see deflection on the VTVM of any significance when I turn the slug. What the hell is going on with this possessed thing?

Oh and just as an infuriating aside...the frequency counting issues previously were NOT the 8600. The switch on the 8601 that changes the frequency scale from 11 to 110 was wonky. I opened that unit and hit the inside of the switch with some contact cleaner and it seems to be stable. I figured this out when the counter was reading 0.000 with the 8601 set to 21.25MHz and for the hell of it I flipped the switch to the 11 scale and got a stable reading of 2.125 on the 8600. I went through all of the frequencies on that scale and it was rock solid. Now the 110 scale seems to be working after the cleaning but who knows what's next with these old components?????

Don't try to listen to the tone. It is AM. The sound discriminator is for FM.

Is the VTVM set to AC? Is the bias pot set correctly? Is the video IF, video detector and video amplifier working properly? Is the VTVM attached properly? You need to systematically go through things.

When setting up to adjust the traps, slightly mis tune the generator. Look for a deflection on the VTVM that goes up and down when the generator output level is adjust up and down. And the deflection must increase as you increase the RF level. I suspect you are going to have to increase the RF level to see a deflection. Again do not adjust things until you see the needle deflect with signal.

Also make sure you are not overloading. Overloading is as bad as no signal: it will distort your results.

Once you see the needle deflecting with signal, then fine tune to the trap frequency. Adjust the RF level until you see just enough to adjust the trap for a dip.

Don't try to listen to the tone. It is AM. The sound discriminator is for FM.

Is the VTVM set to AC? Is the bias pot set correctly? Is the video IF, video detector and video amplifier working properly? Is the VTVM attached properly? You need to systematically go through things.

When setting up to adjust the traps, slightly mis tune the generator. Look for a deflection on the VTVM that goes up and down when the generator output level is adjust up and down. And the deflection must increase as you increase the RF level. I suspect you are going to have to increase the RF level to see a deflection. Again do not adjust things until you see the needle deflect with signal.

Also make sure you are not overloading. Overloading is as bad as no signal: it will distort your results.

Once you see the needle deflecting with signal, then fine tune to the trap frequency. Adjust the RF level until you see just enough to adjust the trap for a dip.
Ok I will forget about the tone. I’ll answer your questions one by one…The VTVM is set to AC and the range is set to 5V as you said.
The 250K pot is in place and the voltage at R135/136 was adjusted to -4.5V DC
When I have fed a video signal through the antenna from my pattern generator I get an image. The multiburst pattern is ok but the high resolution bands are not sharp. Anyway I’m assuming this means the video IF circuit is working?
The AC probe of the VTVM is connected to pin 1 of V106. The needle on the VTVM does deflect sharply to being pegged if I raise the frequency on the 8601. I get lost with what you say after that. Should I slightly mistune the generator and then do something after that? I got confused because you started talking about signal gain and levels and not changes based on mistuning.

Ok I will forget about the tone. I’ll answer your questions one by one…The VTVM is set to AC and the range is set to 5V as you said.
The 250K pot is in place and the voltage at R135/136 was adjusted to -4.5V DC
When I have fed a video signal through the antenna from my pattern generator I get an image. The multiburst pattern is ok but the high resolution bands are not sharp. Anyway I’m assuming this means the video IF circuit is working?
The AC probe of the VTVM is connected to pin 1 of V106. The needle on the VTVM does deflect sharply to being pegged if I raise the frequency on the 8601. I get lost with what you say after that. Should I slightly mistune the generator and then do something after that? I got confused because you started talking about signal gain and levels and not changes based on mistuning.

If you swing the generator away from 21.25MHz and both sides the amplitude increases, then the trap is working. Remember there are two 21.25MHz traps.

You may have to raise the RF signal at the trap frequency sufficiently until you see the nedle deflect. I am only suggesting you slightly swing the generator away from 21.25MHz to test for the trap presence because the trap will cause a big dip. It seems that you are not applying sufficient RF at 21.25MHz to make the adjustment.

I’ve gone pretty high on the RF signal. I mean several people have posted going to 500mV is a HUGE rf signal. I’ve gone as high as 300mV and can’t get any deflection at T-103. Should I just move on to another trap at another frequency? No deflection adjusting T105 either at 21.25mc. That’s the sound trap correct?
What do you think of my idea of going back to square one with one of the other KCS28 chassis I have and resurrecting it on mostly original components?

I’ve gone pretty high on the RF signal. I mean several people have posted going to 500mV is a HUGE rf signal. I’ve gone as high as 300mV and can’t get any deflection at T-103. Should I just move on to another trap at another frequency? No deflection adjusting T105 either at 21.25mc. That’s the sound trap correct?
What do you think of my idea of going back to square one with one of the other KCS28 chassis I have and resurrecting it on mostly original components?
Can you get a signal thru at 22MHz? If so then the trap is attenuating. Because you offset the stagger tuned stages, likely there is less gain around 21.25MHz.

Tell us if you get anything at 22, 23 or 24MHz. If so, you are not getting sufficient signal thru at 21.25MHz. raise the signal and reduce the bias from -4.5v. adjust the pot until you get a signal.

How are you injecting the RF out from the HP8601a?

Signal is being injected from the 8601 rf out through a coax terminating in a red signal alligator clip and a black ground clip. The signal is going through a 1500pf cap into pin 1 of V2. Ground is clipped to the chassis

Can you get a signal thru at 22MHz? If so then the trap is attenuating. Because you offset the stagger tuned stages, likely there is less gain around 21.25MHz.

Tell us if you get anything at 22, 23 or 24MHz. If so, you are not getting sufficient signal thru at 21.25MHz. raise the signal and reduce the bias from -4.5v. adjust the pot until you get a signal.

How are you injecting the RF out from the HP8601a?

What do you mean by "get anything"? Do you mean deflection on the VTVM or do you mean the ability to tune the trap and see deflection at those alternate frequencies?

What do you mean by "get anything"? Do you mean deflection on the VTVM or do you mean the ability to tune the trap and see deflection at those alternate frequencies?

I mean can you see the needle deflect if you set the generator to another frequency? Is the signal from the generator getting through at all?

I mean can you see the needle deflect if you set the generator to another frequency? Is the signal from the generator getting through at all?

Yes it does deflect

Yes it does deflect

Does the deflection change when you rotate the RF level? If the level changes at 23MHz but not at 21.25MHz, it means the bias is too high and you will have to rotate the bias control to increase the VIF gain.

So now I interpret there is a level at 23MHz and the level goes up if you increase the 8601a output level.

Look at my CT-100 IF response. See how low the 41.25MHz level is with the trap set to suck away the energy at that frequency. If you adjust the generator to say 42MHz at the peak of the curve, the gain is much higher and a lower RF level is required to easily see that frequency.

At 41.25MHz there is hardly any gain. So you will have to increase the RF level AND increase the gain of the VIF stages.

Does the deflection change when you rotate the RF level? If the level changes at 23MHz but not at 21.25MHz, it means the bias is too high and you will have to rotate the bias control to increase the VIF gain.

So now I interpret there is a level at 23MHz and the level goes up if you increase the 8601a output level.

OK let me check. By the bias control you mean the 250K pot I have installed correct?

So here is the baseline setup:

https://imagizer.imageshack.com/v2/1024x768q70/923/zWQ5fP.jpg

https://imagizer.imageshack.com/v2/1024x768q70/922/SM2IKV.jpg

https://imagizer.imageshack.com/v2/1024x768q70/923/FhLKjz.jpg

https://imagizer.imageshack.com/v2/1024x768q70/924/HOcmLU.jpg

When I change the frequency to 23.0 MHz or to 24, the needle deflects slightly above and below where it is in the baseline setup. When I turn up the gain using the detent steps on the output level, the needle deflects off scale but then returns to the original position and it doesn't matter if I go up or down in gain. Maybe the input at V2 is a problem. I'll check it and the tube. The DMM is the bias but the 250k pot is turned up to max.

Should I just do the 20-30MHz sweep and look at the IF response in total? Can adjustments be made looking at that without all this VTVM stuff that's been driving me crazy?

VIF? Video if?

You have to be careful here. there are many hidden things that may be going on here. Increasing the gain of the IF amplifier to max with the pot may induce the IF amplifier to oscillate. I would reduce the gain and increase the RF generator to +10 or +20 if necessary to force a signal through.

What you must confirm is that when you see a deflection on the meter, always confirm you cange vary the level properly eg a smal increase in input yields an increase in the output and vice versa. If you overload an amplifier, sometimes you will find the change of input yield no output change. Or increasing the input may reduce the output. Always make sure increasing the input will increase the output.

You have to understand and get a feel what the circuit is doing. Instead of the VTVM, you could use an oscilloscope on pin 1 of the 12AU7 to see the 1kHz sine wave amplitude. I sometimes like to check things visually to confirm there is actually a sine wave there and I am not just measuring noise. Additionally if the amplifier is overloading, you will see the sine wave clipped. And if the amplifier is oscillating, you will see that too.

I think you need to go to +10 on the HP 8601a.

+10dBm got it. I like the idea of using the scope as an addition to the analysis and I will attempt to employ your suggestions. I appreciate all of the time you have generously provided. I might end up not being able to get this working right but I’ve learned a lot about IF signals as well as design and what engineers in the late 1940s were thinking and trying to achieve.

We have gone so far. I would like to see you finish this and make it work! 😄

Me too:yes:

Considering the level of commitment, so far, along with your spare parts chassis, there's no reason to expect anything other than complete success. Slowly and methodically it will happen. :thmbsp:

Considering the level of commitment, so far, along with your spare parts chassis, there's no reason to expect anything other than complete success. Slowly and methodically it will happen. :thmbsp:

Thanks Kevin...hangin' in with it.

I put the scope on pin 1 of the video amp and I’m not getting a signal through. I tried it at +10dBm. Something in the tv hardware may be amiss. Tube testing and socket check up next. Strange that when I inject an fr signal through the tuned I see a fairly decent quality image. Sound is way off…picture on channel 3 and audio on 4.

But it was working before? I would check the generator. Is that range switch still wonky?

But it was working before? I would check the generator. Is that range switch still wonky?

Yeah but I checked the output on my scope and the frequency is spot on and varies with changes as does the amplitude. The 8600 has the frequency output as stable and correct. I’ll make sure the tubes are good and seated in their sockets. If I’m getting a signal through using my video generator through the antenna please, the signal should be at V106 right?

Yeah but I checked the output on my scope and the frequency is spot on and varies with changes as does the amplitude. The 8600 has the frequency output as stable and correct. I’ll make sure the tubes are good and seated in their sockets. If I’m getting a signal through using my video generator through the antenna please, the signal should be at V106 right?
Is the 1kHz modulation selected? The VTVM on pinn 1 of the 12AU7? What is the bias pot set to? You and see the RF on the scope at +10?

Yes, yes, -4V DC and I see it coming out of the 8601...I just don't see anything at the 12AU7. Don't spend any mental sweat thinking about this right now until I get everything checked out and make certain I'm not doing something stupid. Can't get back on it tonight but maybe tomorrow or Friday. Stand by!

Hi folks. Just a brief update. Gonna need to take a break from this for a bit. Family stuff has come up and my time priorities have shifted for the time being. I'm not talking about months, just a few weeks until after the Thanksgiving holiday. As I've mentioned before, I have a 95 year old dad suffering from dementia. He's in a facility and has taken a recent turn for the worst so my wife and I need to reboot his situation and ours to deal with his needs. In some ways, this KCS28 has been a refuge from the storms so I hope to be back on it and reactivate it in a few weeks. Thanks everyone. Just didn't wanna leave y'all hangin'!

Thanks for letting us know.

Thanks for letting us know.

No thank you for your help and sharing your experience and knowledge…and for your patience!