I measured the HV with a B&K 0-40kv range test probe with the kilovolt meter on the probe, grounded to the chassis...actually I tried grounding to the chassis and the HV cage and the readings were the same.

Yes, the dark dominos are paper but, I changed the micas for 2 reasons...they were a bit out of spec and Phil, who graciously chimed in above, changed the micas in his restoration. The micas I replaced were in the horizontal trimmer area for frequency, output and lock. Is it possible to change the HV output by moving the horizontal output adjustment?

The micas were primarily in the horizontal frequency, output and lock trimmer section. They were out of tolerance but not by much. Phil changed his so I changed mine!! :D

Here is the B&K

Just a thought, if the CRT is not connected, it can't act as a capacitor (aquadag coating). Could that cause the voltage to appear lower? You know, if you have an open filter capacitor, the unsmoothed voltage would be lower.

I changed all the filter caps...all new electrolytic caps (Nichicon)

He knows. He was posing it as an example of what happens when you don't have a filter cap.

The outer coating of the CRT should be ground. It allows the CRT itself to act as a filter capacitor for the high voltage.

I bought one of those to try a while ago. I can't recommend it because the one I got would regularly black out and come back to normal. Maybe I got a rare defective unit, but if a good portion are like mine (likely for no-name Chinese stuff) it's not a great gamble.

Also IIRC the ad claims it will transmit...It doesn't seem to have the power for anything other than a direct connection and even then was going dark regularly.

Hey there...thanks so much for chiming in. I've been watching your restore on this unit over and over. Yes, the graphite coating on the CRT contacts 2 wire loops on the yoke frame when the CRT is pushed all the way in. I'm not going to obsess over the HV reading. The picture is OK at this point and I'm going to turn my attention to getting some sound.

I've been working backwards from the speaker in the troubleshooting. Speaker pops and moves on contact with a 9v battery. AOTrans ohms out ok and there's continuity all the way back to the AOTube sockets but that's where it gets dicey. Filament voltages are OK and the tube is new but there's all sorts of out of spec voltages on the other pins. I was going to get a read on them last night and post but I never got off the couch and YouTube all night!!!

OK I guess I'll stay away for now and rely on the pattern/sound generator and the crappy over the airways digital, converted to analog, signals. On these projects, I try to maintain a conservative, step by step diagnostic and analysis approach but sometimes, at a point of "problem solved!", I want to race to the end game finish line ASAP. I need to concentrate on getting sound next. :scratch2:

That HV meter looks OK. I haven't seen that model before. Yeah, it could be the capacitor smoothing effect.

A quick and dirty way to check the audio output circuit is to touch the wiper on the volume control with a screwdriver with a finger touching the blade. Don't have the volume control turned down however. You should hear a hum. If this was a hot chassis set you definitely want it plugged into an isolation transformer to do this.
You would need a FM modulated 4.5MHz audio signal to inject to trace the signal further up (from the volume control towards the tuner).
A oscilloscope could enable you to trace the audio from the tuner toward the volume control.
Without those you are left with checking voltages, resistors and tubes, etc.

I'll check the HV with the CRT in place, grounded and plugged in. I managed, after a 6 month wait, to get my hands on some Aquadag graphite with binder spray from Ted Pella Associates and I can spray any chipped or scratched areas although the coating on this CRT is pretty complete and undamaged.

I do have a scope and a signal generator. I can give those a try. Maybe Mr. Andersen would know if this is a hot chassis but I do have the hot and neutral blades of the power cord marked so I can be sure it acts as a keyed plug.

On the topic of the power cord, it's in terrific condition. Is there anything I can do or a treatment I can apply to help preserve the rubber and keep it from becoming hard and brittle?

Thanks
Chris

It is not a hot chassis. I believe the original cord would by vinyl not rubber.

BTW less expensive and more readily available Slip Plate graphite coating works well on CRTs.

[QUOTE=bandersen;3242720]It is not a hot chassis. I believe the original cord would by vinyl not rubber.

BTW less expensive and more readily available Slip Plate graphite coating works well on CRTs.[/QUOTE

Great...one less shock hazard! I'll google SP and check price and availability. I've got a Zenith and a Philco Seventeener where the dag is flaking off in big chunks!

This is a early post war split sound set so the sound IF is 21.25MHz NOT 4.5MHz that intercarrier sound sets use.

Also he may be able to get away with a tube AM modulated signal generator...Most tube TV/radio repair grade generators distort the the RF carrier enough to create FM/PM modulation that TV audio systems can detect. I've done this with 2-3 different generators so far.

I have an old Knight Model KG-650 RF generator with an output range from 100 kilocycles to 100 megacycles. We might be getting into territory here where my comprehension database is running full throttle and losing ground! :saywhat:

If it's a working generator odds are it will work for audio IF signal injection...IIRC a friend of mine has the same generator and has used it for FM work. You can check it by using an FM radio set to a dead channel in the 88-95MHz range and trying to tune the generator to make a signal in that range. If the FM radio tunes it then there should be enough FM slop in the generator for it to work with TV audio.

Before you start with IF injection first try audio injection at the first audio stage grid. That knight generator should have an audio output you can use. If the set passes audio from the 1st audio grid decently then IF injection is the next troubleshooting step. If it doesn't pass audio injected at the 1st audio grid then troubleshoot the audio stages and make them work before messing with the audio IF.

We can walk you through audio IF injection if you end up needing to do it.

I get what EM is saying, that most tube frequency generators ( like my Eico324) and so on, will have just enough intermodulation / distortion in them to trigger the sound discriminator circuit in the TV when you feed the generator via input AM modulation.
IE, you should hear some pretty weird stuff when you get it right! :D

Excellent...I have a Channel Master Super Fringe (Sanyo inside I think) AM/FM I restored that has a great speaker and makes terrific sound for a 1962 tube set. I'll try using that and the Knight. Yes, I will probably need some seeing eye dog aid in crossing these audio output tracing streets! Thank you so much for the help. It is so appreciated as is everyone's input in this thread. Thank you all!:music:

So my RF generator is set at 21.25MHz. The grid on the 1st audio tube, 6AT6, is pin 1. Do I need to ground the black generator output lead or just touch pin 1 of the 6AT6 with the red lead from the Knight? Sorry for the very basic questions here but this is virgin soil for me!

Nice loud tone on the FM radio BTW from the Knight

...and here's the schematic...half of it anyway

this set is very close to my FADA 895, which is a RCA630TS clone.

the 6AT6 is the 1st audio level amp, it also serves as a bias clamper ( diode ) as this set is pre-AGC and has a " picture control" like my FADA,

like someone mentioned above to test the audio out section, you can simply clip on to the center wiper of the volume control, and feed in any sine wave in the audible range, to test it. this will also insure that you are on the isolated side of the grid via the .01 cap , no risk of loading loading thing down hooking up to that point.

I'm using this! :)
https://www.earlytelevision.org/pdf/..._rider_tv1.pdf

OK...more idiot me on display...my Knight's lowest output frequency is about 160 kilocycles...out of audible range. Is there something else I can do???

I'm not getting anything...even poking a screwdriver around and across the volume control's 3 terminals there's not a sound...no snap, crackle or pop...nothing. There isn't even a hum.

as was mentioned before, you should be able to crank it up and touch the center terminal of the volume cont with a screwdriver while touching the metal shaft and hear the telltale 60 cycle hum, like touching the unconnected end of an audio cable.


https://www.youtube.com/watch?v=r-WCPDdn9mk
My FADA in action! :D

That's the one. Sam's has one too that's a little different. It's this chassis and a radio in a combo cabinet unit. I've found the Sams helpful but it's too different to follow verbatim

The FADA is so crisp and bright. Just beautiful! I left a comment on YT! My 721 is audio dead from the volume control to the speaker. Volume control ohms out at 1 meg and the audio output transformer ohms out at 0.5k.

Isn't there 2 outputs on that knight (one audio one radio frequency)? There should be a fixed frequency audio output (something like 400Hz) that you can use to inject audio.

If there isn't an AF output on the Knight, do you have a junky (something won't be sad if you accidentally break it) radio or audio player (battery powered is preferable) with a working headphone or line output? You can make a cable that plugs into the output of your audio test source and has alligator clips on the other end. Put a roughly .1uF cap in series with the audio hot lead and feed that to the grid, clip audio ground to the chassis.

Alternately if you want even simpler just use a roughly .1uF capacitor to connect the heater hot lead to the grid...All you'll get is 60Hz hum, but it's a simple method to use when you don't have test equipment or sacrificial audio gear on hand.

Hi Tom...you're right about the Knight. There's an RF out and an audio in/out as well. Anyway, I ran the heater voltage to the grid through the capacitor and nothing. The only noise this speaker has made is when I connected the audio output transformer leads to a 9v and the speaker crackles and pops as I touch the battery poles. So the fault, or the first fault, is somewhere between the first audio and the output leads of the AOT I would think.

That should be a start point then in tracking down the lack of sound, even though the linked Rider's may or may not be exact to what you have, the voltages shown should be close enough to give you a hint of the problem.

be it a bad tube, or resistor or cap or what ever.
the voltages on the 6K6 and 6AT6 should be pretty close to matching what you see in the schematic.

So looking at the Riders and the audio output 6K6, I'm looking at 6.3 AC on pins 8, 7 and 2, -14 volts DC on pin 5, 185 volts DC on pin 3 and 200 volts DC on pin 4? Do you concur?

pins 8 & 7 are tied to gnd so they are 0v , pin 2 is heater at 6.3v AC, pin 4 (ctrol grid) is tied to bias & the red wire of the output via 1k resistor to +225, should be about 200v, pin 3 is hooked to pin 3, plate and will be lower because of the 500 ohms of the output @ 185v, or so they say.
pin 5 is pulled negative via 470k

Learning so much here...thank you very much. I'll get to work!

that 1k feeding power to the plate should be a rather big one, 5w or larger, and they tend to fry easily.

Reads 1152 ohms

as mentioned, make sure the voltages are OK, AND, if the paper caps in the area have not been replaced, DO IT...

Leaky caps are the fastest way to kill audio output, and they are hard to test w/o a leakage tester.

Um.. small nit, but pin 4 is screen grid, pin 5 is control (signal) grid.

All of the wax/paper caps in the set have been replaced with new film capacitors throughout the TV. The only place I changed out the micas is in the horizontal adjustment section so any micas in the audio circuits are still in place.

The voltages you measured around the 6K6 seem pretty good. Have you tested and replaced tubes in this set?
What about the voltages on the 6AT6 pins.

A bit of clarification on how the sound stages work. 6K6 is the audio output tube, it is responsible with developing the power to operate the speaker. Most of the 6AT6 is used as a audio amplifier, it increases the voltage size (amplitude) of the audio signal. The 6AL5 is the FM discriminator (detector or demodulator). Before the 6AL5 the signal is 21.25 MHz with FM audio modulation, after the discriminator the sound is in the audio range. That makes the volume control a good place to try injecting audio. The audio stages are easier to troubleshoot than the IF.
You need a bigger audio signal at the grid of the 6K6 than the 6AT6 grid to hear the same volume.
The general way to determine the wattage required for a resistor is to use the resistor value and the voltage difference across it. That 1K resistor that feeds the screen of the 6K6 and then feeds the plate through the output transformer has 25 volts across it. Voltage squared, divided by the resistance is the wattage given off (dissipated), that come out to 0.625W. You always want to use a resistor rated two or more times the dissipated wattage so it stays fairly cool. So a 2W should be OK.