I've been blessed!

[etype2]

I’m getting the bug for resuming my Television DX addiction. I live in the Phoenix NW valley. Las Vegas, LA and San Diego are easy day trips. Thinking about a 35 foot tower with a Televes Boss Mix on a rotor. Heard good things about the antenna. 90 miles is the theoretical limit but I’ve seen exceptions under certain atmospheric conditions. This antenna is supposed to be exceptional for long range. At the same time it removes the noise and won’t overload on strong signals.

Edit: My elevation is 1200 feet.

[old_tv_nut]

Originally Posted by etype2

I’m getting the bug for resuming my Television DX addiction. I live in the Phoenix NW valley. Las Vegas, LA and San Diego are easy day trips. Thinking about a 35 foot tower with a Televes Boss Mix on a rotor. Heard good things about the antenna. 90 miles is the theoretical limit but I’ve seen exceptions under certain atmospheric conditions. This antenna is supposed to be exceptional for long range. At the same time it removes the noise and won’t overload on strong signals.

Edit: My elevation is 1200 feet.

You do realize the specs on that antenna are fudged? The unamplified gain should be measured with respect to a tuned dipole, not a 1-meter dipole.

Also, adding the amplifier gain to the antenna gain and calling it the amplified antenna gain is bogus. The amplifier gain is useful to compensate downlead loss. The apparent 15 dB gain of their amp (reading their graph) is more than enough, but the important amplifier spec is noise figure, which they don't give. If their amplifier noise figure is worse than your TV tuner noise figure, it can actually be a detriment.

Another important amplifier spec is overload level. At least they have an option to shut it off if it suffers overload from local signals.

"Removing the noise" is an odd sounding claim - there is no way to "remove noise" from a signal - but this seems to refer to the amplifier shielding, which will help keep unwanted strong local signals that the antenna is not directly aimed at from getting into the system.

[etype2]

Originally Posted by old_tv_nut

You do realize the specs on that antenna are fudged? The unamplified gain should be measured with respect to a tuned dipole, not a 1-meter dipole.

Also, adding the amplifier gain to the antenna gain and calling it the amplified antenna gain is bogus. The amplifier gain is useful to compensate downlead loss. The apparent 15 dB gain of their amp (reading their graph) is more than enough, but the important amplifier spec is noise figure, which they don't give. If their amplifier noise figure is worse than your TV tuner noise figure, it can actually be a detriment.

Another important amplifier spec is overload level. At least they have an option to shut it off if it suffers overload from local signals.

"Removing the noise" is an odd sounding claim - there is no way to "remove noise" from a signal - but this seems to refer to the amplifier shielding, which will help keep unwanted strong local signals that the antenna is not directly aimed at from getting into the system.

The build quality looks amazing. https://youtu.be/4jFfVEN-gFM

The antenna in the video is a smaller version, but a good representation of the one I’m looking at. Do you have any recommendations for ultra long range reception?

I have a small roof mounted antenna and one day, I rescanned, got lucky and a bunch of stations locked in from outside Phoenix valley. Tucson and a bunch of others I didn’t identify. So with a tower, rotor and a really good antenna, I’m hopeful of reaching further.

Edit: current antenna has no rotor pointed at the Phoenix transmitter towers.

[old_tv_nut]

Sorry, no recommendations to give, too hard to find companies that don't give hyped specs. That antenna may do just fine, (I'm guessing the 20 dB gain in the chart may be real for at least one frequency) but there's no real hard comparison possible.

[old_tv_nut]

Reopening this "I've been blessed" CTC-5 thread to cry about the brightness control drift getting worse and worse. Sarts out with brightness way high and over 5-10 minutes warmup drops down to the point where the maximum control setting is not quite high enough.

Right now, I don't know what's drifting, cathodes, G1's, G2's?
I replaced the luminance output back when I first saw it, and didn't get any improvement.

The thing is, as I have gotten older, it's become difficult or impossible for me to pull the chassis to work on.

I'm thinking I will open the back and measure what I can, voltages and resistor values, to see if I can determine what it is that's doing the drifting, and hope it's something easy to get to.

Don't know if I will get to it before the holidays.

Wish me luck!

[old_tv_nut]

If anyone has a good guess, let me know!

[Penthode]

A brightness drift? I have a few questions.
I recall the old rule of thumb to pinpoint drift how long does it take to occur from switch on? If the drift is within the first few minutes after powering up, I would suspect a vacuum tube. If over 10 to 20 minutes a resistor and after 20 minutes a capacitor. Is there a reliable timeline?

Looking at the schematic, there is limited DC coupling to the input of the 12BY7. So the drift we can be 80% certain is the from the 12BY7 through to the 21AXP22A and it's surrounding components.

You did not report blooming so we can assume it is a bias change.

My first focus would be measuring the voltages and checking was changes from start up to running when the screen goes dark.

So first three questions:

How long a period does the darkening occur?

Have the capacitors been replaced around the 12BY7?

Has the contrast control 12BY7 cathode modification been made?

[Penthode]

Futher thoughts.

I would think it less likely the problem is with the voltages to the 12AX22A screen or control grids unless you saw a hue change as the picker got darker.

The gradual dimming will be most likely due to the plate voltage of the 12BY7 rising gradually. Depending upon how long it takes, it will be the 12BY7 heading to cut off. It may be the control grid potental changing. Chief suspect would be R407 180K drifting upward.

The other chief suspect to me would be the screen resistor R410 22K drifting upwards lowering the 12BY7 screen voltage.

[old_tv_nut]

Originally Posted by Penthode

Futher thoughts.

I would think it less likely the problem is with the voltages to the 12AX22A screen or control grids unless you saw a hue change as the picker got darker.

The gradual dimming will be most likely due to the plate voltage of the 12BY7 rising gradually. Depending upon how long it takes, it will be the 12BY7 heading to cut off. It may be the control grid potental changing. Chief suspect would be R407 180K drifting upward.

The other chief suspect to me would be the screen resistor R410 22K drifting upwards lowering the 12BY7 screen voltage.

Thanks.

I may not get to this until January, but will put these on the list of things to check first. Hope these are on the top of the boards.

[Penthode]

Yes looks like a fun troubleshooting project!

I think for a start you at least won't have to pull the chassis. The prime suspect resistors I believe are both on the Video PCB.

A can of freeze spray with a stream aimed precisely at the resistors in question when the dimming occurs should instantly reveal if they are bad.

[old_tv_nut]

Originally Posted by Penthode

...So first three questions:

How long a period does the darkening occur?

Have the capacitors been replaced around the 12BY7?

Has the contrast control 12BY7 cathode modification been made?

Thanks.

The darkening continues over 5 to 10 minutes, but fast enough that you can see a change in under 30 seconds to a minute.

I gave the set had a total recap when I first got it.

Yes, the contrast modification was made. In the category of full-disclosure of dumbness I accidentally wired the contrast control backwards, so max contrast has been CCW ever since, but I think this can't have anything to do with the problem because it's capacitively coupled in the rewired configuration, and besides, it worked fine after reconfiguring.

[old_tv_nut]

Update: No joy yet.
I started chasing the brightness drift this afternoon The suspect resistors measure OK cold, and after the brightness has drifted, freeze spray shows no effect on any components on the video board.

Cathode voltages drift by 10-15 volts, and adjusting the brightness control for the same variation shows the same brightness variation as the drift.

I noted that the far end of the brightness control goes to a negative grid bias voltage developed by the horizontal output tube, but changing the HO tube and/or the H driver made no difference.

I backed up and measured the 385 V supply, and it is low (as low as 330) and varies with beam current. If I understand the HV regulator properly, it should keep a constant load on the HV with brightness changes and therefore the 385 supply should not vary drastically. So, the regulator may be wonky or just acting wonky because the B+ is low.

I think my next move is to replace the 5U4's in the power supply, but I don't have any at the moment.

[old_coot88]

Maybe tack four Si diodes, each with proper series resistance, across the 5U4s(?). Just a thought for a quick&dirty test. That'd also stiffen the B+ against sag.

[EDIT.] Interesting vid here on a CTC-5 resto. https://www.youtube.com/watch?v=3GPrCym5qXw

[Penthode]

Originally Posted by old_tv_nut

Update: No joy yet.
I started chasing the brightness drift this afternoon The suspect resistors measure OK cold, and after the brightness has drifted, freeze spray shows no effect on any components on the video board.

Cathode voltages drift by 10-15 volts, and adjusting the brightness control for the same variation shows the same brightness variation as the drift.

I noted that the far end of the brightness control goes to a negative grid bias voltage developed by the horizontal output tube, but changing the HO tube and/or the H driver made no difference.

I backed up and measured the 385 V supply, and it is low (as low as 330) and varies with beam current. If I understand the HV regulator properly, it should keep a constant load on the HV with brightness changes and therefore the 385 supply should not vary drastically. So, the regulator may be wonky or just acting wonky because the B+ is low.

I think my next move is to replace the 5U4's in the power supply, but I don't have any at the moment.

If the variance of the +385v supply is that great, something is wrong. On my CTC5, upon inspection before I even powered it up, the ground to the transformer center tap was not properly soldered from new! I never had the opportunity to find if it affected the B supply! But a drop to 330 volts can mean a few things eg bad 5U4 tubes, bad fuse holder of a leaky electrolytic. But if it varies with beam current that would suggest the series power supply resistance is too high: bad weak 5U4 tubes seem the most likely candidate.

The voltage sag for a 5U4 at 250mA is about 50volts per plate. The seiers resistor would be 50/0.25 = 200. Two plates in parallel son 1 100ohm 50W resistor per would work.

To test I would simply replace the two 5U4 tubes with a pair of of 2A 1500 PIV diodes.

[old_tv_nut]

Originally Posted by Penthode

If the variance of the +385v supply is that great, something is wrong. On my CTC5, upon inspection before I even powered it up, the ground to the transformer center tap was not properly soldered from new! I never had the opportunity to find if it affected the B supply! But a drop to 330 volts can mean a few things eg bad 5U4 tubes, bad fuse holder of a leaky electrolytic. But if it varies with beam current that would suggest the series power supply resistance is too high: bad weak 5U4 tubes seem the most likely candidate.

That's what I'm thinking - both the time that it takes to drift and the fact that it always comes back to the same starting condition when cold points to tubes.
I ordered a couple, should be here in a few days.

By the way, dragging it from the corner revealed that the convergence plug was not making good contact, and exercising it a bit seems to have restored it.