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

[Electronic M]

Originally Posted by Penthode

The isolation transformer won't help.

Look at it this way: you want to differentially measure a small dc voltage that is not referenced to the chassis ground. A three pronged plug on your VTVM, one os hot, one is neutral and the round pin is case ground. The metal case is grounded via the third pin to protect against you getting a shock if the case is not at ground potential.

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I know this is a settled matter, but there's one thing I find odd. Your assumption that an isolation transformer will pass it's plugs ground through to its outlet and that the VTVM would have a 3 prong cord... While I wouldn't doubt there are ones that do out there somewhere, I've never seen an isolation transformer built that way out of better than half a dozen I've had. Most isolation transformers I've seen don't have 3 prong cords and many that do don't ground the outlet or use a 2 prong outlet.
Likewise the vast majority of VTVMs made are only 2 prong...It wouldn't surprise me if some lab or mil spec units or some last gasp 80s units might have been built with 3 prongs, but that seems like assuming the exception rather than the rule.... Better to assume the rule and warn to check for the exception in most cases.

[Chris K]

What I think I’ll do is wait for the 250K pot that’s coming tomorrow. I took a 6SN7 that has shorts and broke it up and cleaned out the base and pins. I stripped out 2 wires long enough that I could solder them in pins 2 and 5. When the pot comes, I’ll attach it to the wires and mount it on or in, space permitting, the socket. I’ll then have a dedicated tool to align RCA sets with this circuitry.

[Chris K]

Thanks for your thoughts on this Tom. I don’t know enough about my isolation transformer to say anything about its ground protections but all of the VTVMs I’ve used have had nonpolarized 2 prong plugs. They’ve all been from the 1950s.

[Electronic M]

Originally Posted by Chris K

Thanks for your thoughts on this Tom. I don’t know enough about my isolation transformer to say anything about its ground protections but all of the VTVMs I’ve used have had nonpolarized 2 prong plugs. They’ve all been from the 1950s.

When you've had an old isolation transformer developed a primary to secondary short (which also acted as a step up winding) that you accidentally found with your bodys internal volt meter or a persistent ground loop in an agile modulator or ever got zapped connecting a 50s stereo component to a 80s stereo component with a grounded cord you start to learn to check exactly how much your gear is grounded or isolated as well as whether it's hot from line to chassis "safety"/RF line filters despite having a power transformer... Mistakes can be powerful lessons/impetus to learn and check things.

It is important to check grounding between any devices you interconnect even if they're designed to be internally isolated as that can fail. I often measure voltage between devices with my battery powered DMM to prevent sparks flying on interconnection.

BTW metal cone CRTs aren't terrible to handle if you work smart. Always discharge the HV with a HV meter (to prevent dielectric bounce back in the caps) and get a glass test CRT (most metal cone sets a all glass 5AXP4 is the right one) so you can make it run well with the test tube, then at the end reinstall the metal and do width, height, linearity, centering and focus touchups.

[Chris K]

I appreciate the effort to keep me safe. Penthode knows what a novice I am and doesn’t want me to get hurt and with good reason. Very appreciative of that.

[Penthode]

Originally Posted by Electronic M

I know this is a settled matter, but there's one thing I find odd. Your assumption that an isolation transformer will pass it's plugs ground through to its outlet and that the VTVM would have a 3 prong cord... While I wouldn't doubt there are ones that do out there somewhere, I've never seen an isolation transformer built that way out of better than half a dozen I've had. Most isolation transformers I've seen don't have 3 prong cords and many that do don't ground the outlet or use a 2 prong outlet.
Likewise the vast majority of VTVMs made are only 2 prong...It wouldn't surprise me if some lab or mil spec units or some last gasp 80s units might have been built with 3 prongs, but that seems like assuming the exception rather than the rule.... Better to assume the rule and warn to check for the exception in most cases.

You unfortunately misinterpreted what I said. Look at the instructions in manual for adjusting traps. I said the isolation transformer will not prevent the measurement from being a shock hazard.

And my Heathkit VTVM I bought new in 1971 was provided with a power plug third prong or ground. My three earlier VTVMs (two RCA's and a 1950 Heath) did not have the ground connection but my later Heathkit one did.

I only had to emphasize that the dangerous measurement using a VTVM with a metal case at 120 volts B minus potential can cause quite a jolt and one must be aware.

[Chris K]

Originally Posted by Penthode

You unfortunately misinterpreted what I said. Look at the instructions in manual for adjusting traps. I said the isolation transformer will not prevent the measurement from being a shock hazard.

And my Heathkit VTVM I bought new in 1971 was provided with a power plug third prong or ground. My three earlier VTVMs (two RCA's and a 1950 Heath) did not have the ground connection but my later Heathkit one did.

I only had to emphasize that the dangerous measurement using a VTVM with a metal case at 120 volts B minus potential can cause quite a jolt and one must be aware.

...and I appreciate that very much!

[jr_tech]

Why use an ancient VTVM? A modern multimeter has about the same input resistance (usually 10megohm) and is not grounded

jr

[Kevin Kuehn]

Originally Posted by jr_tech

Why use an ancient VTVM? A modern multimeter has about the same input resistance (usually 10megohm) and is not grounded

jr

Or if you prefer an analog meter there's any number of FET input VOM meters available that run on batteries. But they are all good to have.

[Chris K]

I have a decent DMM. Probably use that as Penthode suggested about 100 posts ago! It’s accurate enough

[Electronic M]

Originally Posted by Penthode

Look at the instructions in manual for adjusting traps.

I don't have time to read any manual.... I'm very close to ghosting videokarma for the next few months. Dieseljeep died back in January. I bought up most of his monochrome sets and a few color ones that his family didn't send to the dump. I've got borderline too many projects to complete before winter and reorganize.

[Penthode]

Originally Posted by Electronic M

I don't have time to read any manual.... I'm very close to ghosting videokarma for the next few months. Dieseljeep died back in January. I bought up most of his monochrome sets and a few color ones that his family didn't send to the dump. I've got borderline too many projects to complete before winter and reorganize.

I understand. I only wish to point out the pitfalls of aligning this particular chassis. Done right the picture and sound is amazing. Done poorly, the picture is difficult to even watch. I have done a number of these ones and can help prevent the pitfalls. That is all.

[Chris K]

And I thank you for that. Probably be Thursday before I can get back on this. Busy week but I’ll post as I move along. Thanks to everyone for their guidance and suggestions

[Chris K]

Close enough to continue?

[Penthode]

Cool. I always wanted to get around to putting the pot in an octal socket. And you did it!

Now on to the trap alignment. You need an analog metering device because you are tuning to a minimum. I have very gotten around to getting a digital analog display device because I had the VTVM and it does the job well. You just have to be careful.