New Vista/Philco

[Kalamazoo-DJ]

Does anyone know what HV tube can be substituted its a 9 pin.
I noticed my 63/64 Philco combo has the same chassis as my 65 Rca New Vista combo but I have focus troubles and was told a higher output tube can replace the standard one. Is this a dangerous fix?

[old_tv_nut]

If you're talking about a focus rectifier, a bad tube can cause problems, but a good one cannot raise the voltage above normal.

[Kalamazoo-DJ]

We adjusted the HV and made an adjustment on focus I am not totally familiar with this procedure, it did clear the problem I assume a HV should be measured? and if so what should a good reading be?

[marty59]

I believe you're talking about the Horizontal Output? If it's the 6JE6 there is a higher rated sub for that but it's only going to perform the same as the circuit is designed. What you may be thinking of is the 6MJ6 which is a much more rubust tube with a plate cap that resembles that on a HV Rectifier or Regulator tube. Pricey when you can find them!

[kx250rider]

Something's fishy. If it's the focus rectifier (1V2 or 2AV2, I think you can swap those, but the filament voltage is 1.1 on the 1V2, vs. 2 volts on the latter. Being a simple diode, it has no bearing on the focus voltage.

Please be kind to you flyback! Measure that high voltage, and set it at 21KV or whatever the manual says. The biggest risk is overburdening and burning out the flyback! I've seen more 60s color TV flybacks killed by misadjusted high voltage than any other failure cause.

If the focus voltage (or high voltage) is low, so probably is the B+ throughout the chassis, and you need to troubleshoot and find the cause (leaky filter cap, horizontal problem, etc etc).

Charles

[nasadowsk]

Ok, shouldn't a higher HV be less of a burden to the flyback because he shunt regulator's not holding it down as much?

[DaveWM]

I wonder about that too, higher current due to loading down vs. HV breakdown of insulation and possible Xrays....

FYI, I have found a happy medium, setup up the set with the correct voltage, and then operate it from a variac to drop the line down to about 110.

[old_tv_nut]

Originally Posted by nasadowsk

Ok, shouldn't a higher HV be less of a burden to the flyback because he shunt regulator's not holding it down as much?

The HV regulator works by sampling the total current in the HV suppply, and keeping that current constant. Based on the equivalent resistance of the HV supply, setting a particular total current will set a particular voltage. So far, you have it right - a higher voltage means there is less (constant) current draw.

1) if you go too far towards low current and higher voltage, you will run out of range and out of regulation on bright pictures sooner. This is more of an issue with sets that have full DC coupling (which no early roundies had).

2) running insulation beyond its rated voltage is asking for leakage and eventual breakdown

So, higher voltage setting is probably easier on the horizontal output tube, but harder on the flyback.

My opinion is to follow the specified setting, unless you are willing to gamble.

[Kalamazoo-DJ]

So a 6MJ6 would be ok to add?

1) if you go too far towards low current and higher voltage, you will run out of range and out of regulation on bright pictures sooner. This is more of an issue with sets that have full DC coupling (which no early roundies had).

Would that be the case if it would lose focus on bright pictures to begin with? darker pictures were in focus please remember I am learning here.

[oldtvman]

As others have stated the problem isn't in the rectifiers but the regulator or power supply circuits. I always check the basics and in this case the HV regulator is more suspect than anything, but don't overlook the power supply voltages.

[Zenith26kc20]

Have you checked horizontal output tube cathode current? This is very important for flyback health. Too high can slowly roast the flyback and kills Horizontal outputs in fairly short time.
I have been checking this for years on my sets and since a early shop owner/employer insisted this always be checked, we cut down on flyback failures dramatically.

[kx250rider]

Originally Posted by old_tv_nut

2) running insulation beyond its rated voltage is asking for leakage and eventual breakdown

So, higher voltage setting is probably easier on the horizontal output tube, but harder on the flyback.

My opinion is to follow the specified setting, unless you are willing to gamble.

My concern exactly. Thanks for the detail on that. It's the higher voltages, closer to the failure point of the insulation of the windings, that causes the arc-over and burnout of the FBT.

Charles

[DaveWM]

Good to know, thanks for the input.

[old_tv_nut]

Second on checking the HO current. Agree it's a common cause of overheating the flyback and more likely to kill it quickly than any other cause.

Horizontal circuits are designed very close to actual planned usage due to the difficulty of handling high currents and voltages. Flyback transformers are a balancing act between staying within the safe limits of the horizontal output device, producing the desired output, having suitable fire-retardant properties (which affects the dielectric constant, distributed capacitance, and dissipation factor of the winding), etc. etc.

[Kalamazoo-DJ]

Originally Posted by Zenith26kc20

Have you checked horizontal output tube cathode current? This is very important for flyback health. Too high can slowly roast the flyback and kills Horizontal outputs in fairly short time.
I have been checking this for years on my sets and since a early shop owner/employer insisted this always be checked, we cut down on flyback failures dramatically.

We have not done this as of yet I also have not ran it since until I make sure it is within correct limitations.