Exact value parts

[electra225]

Working on the Imperial stereo, the schematic gives a 15% tolerance on readings and parts values. I read a comment on another forum that if you use lower-tolerance parts, say, 5%, there is a danger of "breaking it", making the device under repair so it won't work right. That doesn't make sense to me. Why specify a component value or a voltage value if that value is unimportant? Just say "whatever you have in your junk drawer will work", or "if the tubes light and if the plates don't get red hot, you're good" instead of specifying a value? I'm trying to troubleshoot a fault. I don't want to introduce another one. This might be a good topic for conversation......

[TC Chris]

I've always figured that the tolerance reflected the parts standards--the inexpensive varieties were low-tolerance, so there was some variation. The device was engineered to function with component parts anywhere in that range. There's no reason whatsoever why "right-on" parts would cause a device to fail. What might break is your bank account of you got fixated on exact values. Or the company's warranty budget if service techs expected a 2K resistor to measure 2K exactly. Note that when exact values mattered, the designs specified high-tolerance parts. Being right-on does not make the device silent.

If the right-on theory were correct, none of our vehicles would start or go, because they are built to vastly higher tolerances than 50 years ago.

Chris Campbell

[19&41]

If I have a concern about a component operating close to the maximum specified power or voltage, I will use a higher voltage capacitor or higher power rated resistor.

[hermitcrab]

Any receiver that uses tubes needs to be bench tested under power for up to a few hours ... then check components like resistors and caps ....they check OK while cold but as soon as they warm up all bets are off.... My RCA is a great example.... plays great for 1/2 hour then drifts off channel and the stereo light refuses to work, I have a 1963 Zenith that actually does not drift or wander off channel ... and I have never touched the chassis, all original except for the tubes...why some are more susceptible to this IMO is poor ventilation with hot and cold cycles taking their toll on components.. where finding this problem in a solid state is almost unheard of...

[electra225]

I think you may be on to something with your comment about ventilation. Magnavox is NOTORIOUS for having horrible cabinet ventilation. That may be why I found so many resistors that had drifted high between 2015 and now. The Imperial gets warm enough to bake bread in the changer compartment. They hang the poor Multiplex adapter in the warmest part of the cabinet, right over the output tubes. It might be a good idea to design a new back with better ventilation like I did for the CG and the Stereo Theater.

[hermitcrab]

If you don't have any kids or pets to worry about , I would leave the back off ... When the RCA has played for a time, you can feel a slight temp change when you enter the room and the tell tale faint odor of hot components, tubes, etc .

[electra225]

I have a black girl cat who will be camping out amongst the 6V6's just to show us she can and can get by with it. This is down the road a ways, but I need to consider better cabinet ventilation of some kind.

[19&41]

There are muffin type fans that move a good bit of air and are quiet. You could set one up with a foam or scotch brite filter to push air into the cabinet.

[electra225]

The cavern where the amp and tuner are located has a solid bottom with no provision for getting air into the compartment. They left the speaker enclosures open on the bottom, but not where the heat is produced. I have considered using those little fans. Maybe I can figure something out in that regard.