Crosley 1949 - Horizontal Linearity Issue

[SteveMartin]

Working on a 1949 Crosley model 9-407M-1 (12” 1949). I’ve got a picture, but the horizontal linearity is poor and I can't adjust it out (see CRT pic). All the tubes test good, fully recapped and I’ve replaced several out-of-spec resistors in the horizontal circuit. I’ve attached the schematic of the circuit and the scope traces I’m getting at various points. The tube & pin numbers are labeled above the waveform. I don’t have a lot of experience looking at the horizontal sweep signals so I’m not sure what to expect. I was expecting to see a sawtooth at the damper tube (V23 pin 4-6). Instead, this signal seems to have a lot of ringing and an extremely fast rise. I’m hoping someone can help me isolate where the horizontal drive signal is going bad. I had many more scope traces from different tubes/pins but am limited to upload only 6. If there are any other probe points I should post, let me know. The schematic is an attached file to maintain reasonable resolution. All ideas are greatly appreciated.

[old_tv_nut]

Which side of the CRT pic is left and right? Trying to correlate that to the voltage on the yoke/damper tube.

I don't know what V15 pin 4 should look like, but I don't see any ringing.
v21 pin 4 looks like a highly filtered and therefore low amplitude signal, which I'd guess is OK.
V22 pin 5 and V23 pin 4,6 both have ringing, which I didn't expect, and I guess that corresponds to the linearity getting wide then narrow then wide then narrow. The problem is finding what is causing (or not preventing) the ringing when so many things are interconnected.

I guess I would try checking capacitors, starting with the bigger vlaues first - C8, 100 uF across the H centering; C89, .1; and also whatever is connected to the circuit, like the line from R11 and R112 that goes of the upper right of the schematic.
Also, do you have any info on what the switch that is lower left of R115 is supposed to do?

[SteveMartin]

Thanks for the reply. I updated the images so only the schematic is a pdf (for resolution). The crt pic was taken with the chassis on it’s side and then rotated so the left is the left side of the horizontal sweep. The switch on the schematic selects the audio source for the set’s audio amplifier and speaker. It can be tv, phono or FM radio. I’ll continue checking the surrounding components. You’re right about the ringing. No ringing at V15 but ringing at V22. I’ll check every component between those two tubes.

[Penthode]

Wow it uses the original RCA synchrolock oscillator control used on the earliest post WWII RCA sets. It is not a common circuit and I would refer to earlier television books like Grob.

The schematic should have waveform diagrams. If not refer to the RCA 630TS service literature which can be found on the Early Television Foundation website.

[SteveMartin]

After much troubleshooting I believe the most likely component failure is L28, the horizontal linearity control coil. Even though the resistance measures good (37 ohms), the adjustment has no effect on the linearity or the signal waveform. Crosley lists this as part# AW-160281. Does anyone know where I can get a replacement part? Thanks.

[Penthode]

Originally Posted by SteveMartin

After much troubleshooting I believe the most likely component failure is L28, the horizontal linearity control coil. Even though the resistance measures good (37 ohms), the adjustment has no effect on the linearity or the signal waveform. Crosley lists this as part# AW-160281. Does anyone know where I can get a replacement part? Thanks.

I would be very suspicious suggesting the coil is bad if it measures the correct resistance. Did you examine the coil to see if the core is intact? Or why it is not adjusting?

Have you confirmed the correct 0.035uF and 0.05uF capacitors are properly connected? Is R113 across the 5V4 Damper okay?

I would refer to the RCA 630TS service data for the synchrolock circuit waveforms. So far the waveform input to the horizontal output tube appears to match between your waveform and the RCA service data. This suggests the nonlinearity is from the horizontal output stage and after.

Phil Nelson kindly put the manual on line for our reference.

https://www.antiqueradio.org/art/RCA630TSService.pdf

[Yamamaya42]

I agree that you should look very closely at the resistor across the damper, for it has a direct impact on the left side linearity.
I had (still have) the same issue with my Magnavox Brittany, which I could not get the right FBT for.
This is what I was told by someone who knows the circuits well, the horizontal linearity will have little to no visual effect on the screen, I was told to set it with a meter across the 100 ohm resistor on the HOT cathode and to adjust for the lowest reading, thus setting lowest current on the 6BG6.
As for your horizontal linearity issue, that damper resistor is suspect :O

I really need to touch up mine someday, it's still too wide, and I need to try to add said damper resistor

[SteveMartin]

Thanks very much for the feedback. Since my first post, I did find the damper resistor (R113) was open. I thought for sure it was the smoking gun but replacing it with a new 6 Kohm wire wound resistor only improved the linearity slightly. I’ve replaced and double checked the .035 uF & .05 uF caps. What I did find that helped significantly is adding a 250 ohm resistor across the linearity control coil. I tried different values but 250 seemed to work the best. The two attached pics show the difference. Without the resistor, center is compressed. With the resistor, right side is compressed. I also swapped the damper tube with a solid state replacement but that provided no change. Adjusting L28 or L29 has no visual effect. At this point, I’m going to go through all the waveforms again and compare with the RCA630TS service manual. I’ll also re-check the tube voltages. If I still don’t find anything I’m thinking of buttoning it up and calling it “good enough”. If anyone has any other ideas, I’m all ears. Thanks again.

[Penthode]

One thing you did not mention is the horizontal drive. The stretch to the left of the image suggests the drive to the horizontal output may be high.

I would confirn the drive pot and the 680pf cap is good. Perhaps reducing the series resistance in half by bridging the 10k resistor with another 10k?

[Yamamaya42]

Just a quick note, I have been told and seen in a few places that the solid state 5v4g is fine for amps and radios and so on, BUT NOT for dampers in TVs, they won't hold up to the pounding of the Horz pulses and will soon fail and are a risk to the HOT & FBT, so stick with the classic glass type.

[Yamamaya42]

If you REALLY want to GO solid state, may wanna try a SF5408-TR , but that's getting a bit silly, there is no shortage of NOS damper tubes!

[SteveMartin]

Yes, I'll stay with the tube. I tried the solid state damper just to see if it changed anything. It did not.

[Penthode]

Steve have you tried reducing the horizontal drive?

[SteveMartin]

Yes. I confirmed the pot is working and the 680 pf cap checks out good for capacitance and leakage. Bridging the 10k resistor with another had negligible effect. The best linearity seems to be with the pot adjusted to 0 ohms. I replaced a few resistors that were a bit out of spec but no real improvement. More checking to do do.


Sent from my iPhone using Tapatalk

[Penthode]

If the pot is at zero, it could mean the drive to the output is excessive. Typically too much drive leads to stretching on the left and compression or actual drive line on the middle.

I would check the plate resistor of the discharge tube and resistances and capacitances around the output tube.