I'm requesting the help from Norm Leal or Thomas Dermody, or both, on this problem. They've been recommended to me. My set is a Zenith 7S657R...nom
And do ‘dis reeeeeealy be ‘dat mro , or is someone just surreptitiously aliasing with his I.D. ?
As per the voltage being too high….what is the voltage being read currently?
In tracing the routing of that supply voltage.... and it being too high at the 7B8….. that seems to be attributable to two series
resistors inline possibly being of too low of values.
Starting from its sourcing at the cathode of the power rectifier tube shown as the red buss , it is initially dropped by the
series resistor R16, an 8.2k unit rated at 2 watts and then the flow goes up the red buss upwards and over to the left to the
R10 dropping resistor of 27K at 1 watt rating. That reduced voltage then feeds your specified 7B8 grid along with the
screen grids of the IF and RF amplifier tubes on that same buss.
Additionally....in the past....Seems like some time back that you were having trouble with the screen grid of that same 7B8 and supposedly had too low of a value of resistor for that R7 10K resistor ?
Marky Mark-up Reference:
73's de Edd
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:And do ‘dis reeeeeealy be ‘dat mro , or is someone just surreptitiously aliasing with his I.D. ?
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:Bless you Edd for responding...Yeah it's me...Neal.
Let me bring you up to date. I got this set off ebay. First thing right out of the box it had low volume. I left the house with it powered up and the transformer failed and about burnt the house down. My wife was very pleased with me. Since then I have replaced the transformer. (and apologized to my wife).
I have a problem with it eating up 6X5's so I've added some protection suggested by Doug and Norm. I have a CL-90 inrush suppressor on my line input. It's holding down my input current to .4amps and I'm fused at 1/2amp there. Without that I think I would blow another 6X5.
As for the protection of my new power transformer, I have the CT fused and I have a #47 bulb in series with each secondary transformer leg and the 6X5 pins.
I'm using a pm speaker. I have a 7 henrie coil to replace the field coil and I have the extra resistance in line in the form of 2 25Watt resistors to achieve the 1250 ohm requirement. That being 100 ohms coil resistance and a 1k resitor along with a 150 resistor. I have quite a hummmm! I've added some filter capacitance but it didn't make much difference.
So much for the background. You asked me about the voltage at pin3 on 7B8. It's 190 vdc.
I have replaced R7 and R10, but I've overlooked R16. That was some time ago and it wouldn't hurt to check them again. However, they don't look like they've been hot. I will check that tomorrow morning. I've found several resistors in the set that have been cooked long enough to significantly increase their resistance. Some were doubled.
I think if I can get the right voltage on pin3, 7b8, I can get rid of alot of this extra current and possibly improve the hummmmmmmmmmmmm! I need to also have better channel reception. I can only pick up a few low volume stations. Lotsa hum but no reception. And as opposed to the last set I worked on that had BC and not SW. This has better SW and very little BC.
I thought this post was going to flunk out and I want to tell you again how much I appreciate your response....Neal and thanks for the schematic mark up especially.
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:As per the voltage being too high….what is the voltage being read currently?
:
:In tracing the routing of that supply voltage.... and it being too high at the 7B8….. that seems to be attributable to two series
: resistors inline possibly being of too low of values.
:
:Starting from its sourcing at the cathode of the power rectifier tube shown as the red buss , it is initially dropped by the
: series resistor R16, an 8.2k unit rated at 2 watts and then the flow goes up the red buss upwards and over to the left to the
: R10 dropping resistor of 27K at 1 watt rating. That reduced voltage then feeds your specified 7B8 grid along with the
: screen grids of the IF and RF amplifier tubes on that same buss.
:
:
:Additionally....in the past....Seems like some time back that you were having trouble with the screen grid of that same 7B8 and supposedly had too low of a value of resistor for that R7 10K resistor ?
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:Marky Mark-up Reference:
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:73's de Edd
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