Delay Line Issues

[Jon1967us]

This CTC16 has recently displayed symptoms of delay line failure. The even spaced ringing is a sure sign of ringing in the line, as verified by shorting the line (and disconnecting its ground lead)

Schematic




Shorted:



I've since replaced the original DL with one from a spare CTC10 chassis, but to no avail. The ringing is still there. Very odd.

Now, I'm thinking an out of tolerance resistor could be the cause of the issue.

I measure 45-48V on the plate of V4B (should be 35), so I'm wondering if this excess voltage is driving the DL too hard. The excess voltage perhaps being a symptom of R62 dropping out of tolerance? Or could it be R63, 64 drifting? Hmm

[old_tv_nut]

I think likely an open termination on the delay line. Check L14, in series with R64, 2200 ohms. If L14 is not open, check R64 itself.

[Jon1967us]

L14 was dead open. Highly likely I could have scraped where the invisible to the naked eye wire connects to a terminal on top when taking a measurement. Anyway, I resoldered that connection and we’re back in business. This is actually the first open coil I've found. Something to be aware of now when testing this type of coil!

[old_tv_nut]

[bluenorm]

my ctc 16 (gf629) has displayed the same symtoms as of jon 1967us. i purchased this set about 20 years ago. high hours and with a zenith tube and the has the same issue since day first.
upon recomendations from old-tv-nut the following discoveries are;
R65 factory @2200ohm currently at 1.9k (ok )
R66 factory @150K currently 140K (ok)
L14 factory @ 6 ohm currently@ 7.3ohm (not open, pass.
and the surprice is R64 factory @ 10K currently is 1.9 (not pass as stated by old tv nut)

next is to remove the chassis and check L13 right after delay line. check post electrolitic voltage and R102 and other resistors. replace parts.

is there something that i overviewing please let me know.