Zenith 2250R

[Kevin Kuehn]

Originally Posted by Zsuttle

I'm using Sams Set:114 Folder:13 Replacing the damper did improve the voltage slightly, to around 7.5kv. Doing so improved the Screen voltage to around 115v. The cathode voltage was sitting around 11v (Sams lists 10v) before and after replacing the damper.

So your HV increased from 2kv to 7.5kv? Thats quite an improvement in my book. Did you see the Horizontal Sweep Circuit Adjustments on page 10 of your Sams? Also check R103 (470k under the HV rectifier socket) to make sure it hasn't drifted high, as that can really drop your high voltage if you're measuring at the CRT HV anode.

[Kevin Kuehn]

If you have them, try a few other 6BQ6 horizontal output tubes. Riders calls out 10kv for high voltage. 12v on horizontal output pin 8, 141v on pin 4, and 12v on pin 5. Nothing magical about those numbers, they're just ball park and vary from tube to tube.

[Zsuttle]

Well, I've checked all of the voltages on both the horizontal output and the damper and everything matches up except the screen voltage on the horiz out. I tried a spare 6BQ6 that tested NOS and it didn't change. R103 on the anode lead tested about +8% but it's noted as a 20% resistor on the datasheet.

[Kevin Kuehn]

Riders also calls for 15k screen grid. I suppose you've already changed the HV rectifier and checked it's 1.2 ohm filament resistor?

[Kevin Kuehn]

Interesting that Sams calls for a 3.3 ohm HV rectifier filament resistor, but Riders shows 1.2 ohm. And I don't see any notes in the Sams parts list specific to model type variations.

*Edit* Oops, I do see a note in Sams that says some sets use a 1.2 ohm. The Riders schematic is specific to your model/chassis.

[Zsuttle]

Yeah, changed the HV rect and checked the resistor, mine is the 3.3ohm variant

[Kevin Kuehn]

I'm not sure if 3.3 is correct for your set, it's not according to my Riders schematic that lists your specific model. But I also don't know if that alone could account for your 35% lack in high voltage, I kind of doubt it.

I guess it's time for someone smarter than I to step up and make a suggestion.

[Zsuttle]

Someone just check this and my logic. Assuming that the screen on the 6BQ6 doesn't provide any voltage, the resistor (R15) faces the whole 340v of the B++. Given this, we can determine the "should be" resistance of R15 based off of the given voltage drop from the Sams voltage chart. If I did my math correctly, the resistance should be about 8K ohms. Why isn't it 8K ohms then?