I got two Carver TX-11 tuners and I got them both to work, but power supplies seem to run hotter than a solid state tuner ought to. I recapped one of them, replaced the 22 ohm 2W power resistor with a new 3W wirewound Vishay PAC series. Still, that resistor heats up to 200-210 deg F (93-100 deg C) in normal use.
The 2SD330 power transistor runs about 140 deg F at the heatsink. All other PS components run at near room temperature.
If anyone out there still owns a Carver TX-11, I would like to know how hot it's supposed to get in normal operation, just so I don't go chasing a fault that does not exist.
Schematics attached, PS is at bottom right, R701 is the hot resistor. Unfortunately I am not skilled enough to calculate the as-designed resistor's power dissipation from looking at the schematics.
All feedback is welcome. Thank you in advance!
The 2SD330 power transistor runs about 140 deg F at the heatsink. All other PS components run at near room temperature.
If anyone out there still owns a Carver TX-11, I would like to know how hot it's supposed to get in normal operation, just so I don't go chasing a fault that does not exist.
Schematics attached, PS is at bottom right, R701 is the hot resistor. Unfortunately I am not skilled enough to calculate the as-designed resistor's power dissipation from looking at the schematics.
All feedback is welcome. Thank you in advance!
The resistor is being operated within its power rating, so if the ventilation is adequate, it should be ok.
Check its value. The actual surface temperature at max power will vary with the resistor design and use.
Nevertheless, you still could replace it with a higher power resistor, or several in parallel.
Perhaps two 43 ohm 3W metal oxide resistors in parallel, spaced apart, would work better.
Check its value. The actual surface temperature at max power will vary with the resistor design and use.
Nevertheless, you still could replace it with a higher power resistor, or several in parallel.
Perhaps two 43 ohm 3W metal oxide resistors in parallel, spaced apart, would work better.
@rayma
Thanks for the suggestion of 2 // resistors it makes a lot of sense.
Factory-spec resistor was 2 watt carbon. Replaced with a 3 watt 1% wirewound, so dissipation is already 150% of factory spec.
What I would like to know is if 210 degrees is "normal" for this tuner. If it had been running at 210 degrees for the past 40+ years, wouldn't signs of heat be visible? Yet the PCB solder joints etc all look like new, and the old resistor's color bands are nice and bright.
Vishay PAC series' data sheet says operating temp = -55 to 275 deg C, so at 100 deg C we're well within safety. Am I overthinking this?? Thanks!
Thanks for the suggestion of 2 // resistors it makes a lot of sense.
Factory-spec resistor was 2 watt carbon. Replaced with a 3 watt 1% wirewound, so dissipation is already 150% of factory spec.
What I would like to know is if 210 degrees is "normal" for this tuner. If it had been running at 210 degrees for the past 40+ years, wouldn't signs of heat be visible? Yet the PCB solder joints etc all look like new, and the old resistor's color bands are nice and bright.
Vishay PAC series' data sheet says operating temp = -55 to 275 deg C, so at 100 deg C we're well within safety. Am I overthinking this?? Thanks!
Power resistors can run surprisingly hot but without problems if you stand them off the board.
Some infrared temperature meters can be fooled by the surface of the resistor if it's not flat black.
If the solder joints were good, they probably knew what they were doing. A mfr can't afford a grossly derated part.
This is the hardest working resistor in the chassis, being just after the rectifier with ripple voltage across it.
Some infrared temperature meters can be fooled by the surface of the resistor if it's not flat black.
If the solder joints were good, they probably knew what they were doing. A mfr can't afford a grossly derated part.
This is the hardest working resistor in the chassis, being just after the rectifier with ripple voltage across it.
I am using a thermocouple probe with my DMM so I think the temperature reading is pretty accurate.
I guess the concern I am dealing with is that some fault / condition elsewhere in the circuit is causing this resistor to run abnormally hot.
If it runs hot by design I'm good with that. I just would like to get some kind of comfort level that it is normal, if that makes sense 🙂
I guess the concern I am dealing with is that some fault / condition elsewhere in the circuit is causing this resistor to run abnormally hot.
If it runs hot by design I'm good with that. I just would like to get some kind of comfort level that it is normal, if that makes sense 🙂
The specs from Carver say 110 / 220V, but the voltage selection switch inside the unit says 115V. AC is pretty stable at 121-122V around here.
Specs also say that max power consumption is 15W.
I recapped the PS, all brand new electrolytics (interestingly, many of the 40-year-old Rubycons measure better - lower ESR - than the new Nichicons!).
Specs also say that max power consumption is 15W.
I recapped the PS, all brand new electrolytics (interestingly, many of the 40-year-old Rubycons measure better - lower ESR - than the new Nichicons!).
I have 28.95V on one side of the resistor and 23.95V on the other, so 5V across it instead of 4V. Is that potentially a problem?
@stocktrader200
It'is a brand new 1% resistor. I measured it before installing it too, it was 22 ohm on the nose.
As far as current goes there is 0.145A across the resistor.
It'is a brand new 1% resistor. I measured it before installing it too, it was 22 ohm on the nose.
As far as current goes there is 0.145A across the resistor.
OK, so I have two of these Carver tuners. The above write-up was about - let's call it tuner B
I since reworked tuner A to the same standard as tuner B
I powered tuner A, everything worked fine, but R701 shot right up to 320 degrees! That's definitely not normal. On the other hand, Q701 ran much cooler than in tuner B, only 80-90 degrees.
I dug into it and found D707 shorting to ground. That prompted me to test Q702, which was shot too.
I'll update the thread after my new parts arrive
After some experimenting, it looks like the Fluke does not like curved surfaces like the resistor's. On flat surfaces the two track pretty close.
I think I need a thermal imaging camera 🙂
I since reworked tuner A to the same standard as tuner B
I powered tuner A, everything worked fine, but R701 shot right up to 320 degrees! That's definitely not normal. On the other hand, Q701 ran much cooler than in tuner B, only 80-90 degrees.
I dug into it and found D707 shorting to ground. That prompted me to test Q702, which was shot too.
I'll update the thread after my new parts arrive
I have both a Fluke infrared, and a thermocouple that plugs into my Brymen DMM. The Fluke measured only half as high a temperature as the thermocouple did.
After some experimenting, it looks like the Fluke does not like curved surfaces like the resistor's. On flat surfaces the two track pretty close.
I think I need a thermal imaging camera 🙂