Ok. Let’s try this again…RCA 9TC240 Alignment

[Penthode]

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.

[Chris K]

Originally Posted by Penthode

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?

[Chris K]

So here is the baseline setup:









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.

[Chris K]

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?

[Chris K]

VIF? Video if?

[Penthode]

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.

[Penthode]

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

[Chris K]

+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.

[Penthode]

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

[Chris K]

Me too

[Kevin Kuehn]

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.

[Chris K]

Originally Posted by Kevin Kuehn

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.

Thanks Kevin...hangin' in with it.

[Chris K]

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.

[Penthode]

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

[Chris K]

Originally Posted by Penthode

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?