Silvertone CTC15/16: attack of the clone!

[miniman82]

If I remember output circuit theory right, low drive would lead to higher bias voltage on the grid since the bias is developed in part because of the waveform going through the cap, and the coupling cap itself. So Dave might be right about the drive being a little off.

[ctc17]

Keep this in mind, the whole thing is kind of a loop. IF the fly were shorted the voltages behind it wouldnt all be perfect because the HOT would be overloaded, the feedback pulses would be missing and the phase correction would be missing.

I was talking to Dave about this and he mentioned that maybe the screen resistor has increased in value. On a 16 its a 13K at 7watt.

You did sub the HOT??

The thing that stumps me here is the lack of smoke. If the drive is missing the HOT would be red plating unless it failed, if the fly was bad the HOT would be red plating or the fly would be smoking.

If the damper was bad, the effency coil open or the screen supply resistor bad it could cause this but were assuming you subbed/checked all that stuff.

If you dont have a 4k resistor you could put 4 25watt bulbs in series and see if they light up fully. (can you even buy 25 watt incandescent bulbs any more?)

If the yoke or the focus coil was twacked it wouldnt develop full HV but that should result in high cathode current.

Low cathode current equils, bad hot, low screen voltage or low supply to plate.

If you dont have an adapter you really need to break into the cathode ground lead and check it.
You can check the plate current if you have a stand alone plate current meter. There are huge pulses on the plate (or should be) that will creamate a multimeter.

You can check the boost diode and focus rectifier with you cap tester using leakage test. With the tester on 450v the diode should read full leakage one direction and no leakage reversed.

Those are a bunch of random thoughs, im looking the the 16 sams in a trance so take what you can from it.

[bgadow]

Just wanted to say, I'm paying close attention here. I'm currently fighting an earlier bw set with no HV and the suggestions are very helpful.

[ctc17]

My 4k resistor or light bulb test is based on the ohms law of the plate voltage and the cathode current so dont apply that to your bw set
Im going on 400 volts at 220ma.

One thing I coulldnt recommend enough is a bk 1077 for these issues. It pretty much instantly isolates the problem.

Not to hijack the thread but I would be interested in hearing about your bw set.
We really cant have enough discussion on HV issues. It has always been the biggest issue with sets and looking through old trade mags verifies that.

[Electronic M]

Well I have 100mA on the cathode with the yoke connected and ~170 with the yoke disconnected.

I probably don't have an exact 4K ohm resistor, but should have some 2 watt units that are close. I'm too tired to do the wattage calc right now to see if that will work.

The screen is at about 90V, and seems to jump up if I disconnect the .1 cap on it, but the HV dies when I do that.

I'm going to call it a night.

[DaveWM]

double check the screen resistor value, both the large one and the 47 ohm one.

[Electronic M]

The closest replacement I could make up for the 13K was a 12.5K and it still reads at approximately 12.5K as of last night. The 47ohm is down around 41 I want to say.
The voltage is at about 90V both at the screen and at the junction of the 47 and 13K resistors. There is voltage across the 47, but it is only around a volt or so.

[ctc17]

That shure sounds like
a weak hot
bad damper
low b+
open in the flyback

[bgadow]

Originally Posted by ctc17

Not to hijack the thread but I would be interested in hearing about your bw set.
We really cant have enough discussion on HV issues. It has always been the biggest issue with sets and looking through old trade mags verifies that.

I'll post a new thread in B/W.

[Electronic M]

It is working again!

I had subbed all the tubes except the damper (which tested good the first time around) well I subbed all the horizontal stage tubes from the bad set in to the good set and the good set would not light. So next I went and put the horizontal tubes from the good set in the Silvertone and it got TONS of HV (I for got to connect the top of the HV reg.) very fast. I then started plugging the original tubes in one by one until it went bad again. I retested the bad damper and it is in the "?" zone on my tester unless I let it sit for a while.

I really need to keep a spare damper with that set with a sign that reads "In case of HV issues: don't do anything until you try this."

I still need to readjust the horizontal stage, and the deflection in general. As well as fix the no color issue (I'm hoping I did not blow anything when I accidently shorted one of the color pots to ground). Here is a picture of it in action.

[Electronic M]

I fixed the color issues there were two. The one that killed the color was a lead breaking loose from the color level pot. This set's leads tend to break of their terminals easily (especially the ones going to the tuner sub chassis). The second issue, which has been there since I knocked off the color osc coil during a previous post restoration repair, is that the color lock occasionally gets disturbed. The effort I put in to getting it right after discovering the slug was stuck almost deserves it's own thread (meaning I don't have time to go into it now).

I had little time after fixing the color lock issue, but I managed to do a quick and dirty static convergence, and readjust the horizontal stage, but totally for got to check the purity and rotate the yoke to a give a more perpendicular raster. Hopefully it is good enough that I won't be tempted to mess with it again for awhile.

Well as I was writing this I powered it up for a purity check and lost color synch again (this time it is clear I need to carefully redo the color osc alignment).

This is a picture of what it did when it worked right last night.

[Electronic M]

Well I finally redid the color osc. adjustment last night, and this time it held synch for over 2.5 hours without issue. It also has good color lock from power up onwards which it lacked before this iteration of adjustments. I decided that the position it was in from the first botched readjustment (the slug half sticking out the top) did not look right so I kept turning it in to the coil until it it was on the edge of lock with the burst reference disabled (if I turned it closer to lock the screen would go green) then I re-enabled the burst reference and and checked if it would lock to a weak signal which it did. Aside from yellows and pinks being a tad weak all seems like it has returned to normal so I'm going to focus on other things for the present.