It's not possible to optimize the filament offset in this amp as the penthode section has filament in commonSo I now have 39VDC to the hum pot wipers on the ASR-433 due to the circuit modification.
I am going to see how this works out on tube longevity.
Or, would it be worth the trouble to install a separate filament transformer for the 6U8A's, remove the current circuit modification, and increase the DC voltage to the 6U8A heaters only?
Heater transformers are inexpensive and small, and that way all the tubes are within limits.
It's not possible to optimize the filament offset in this amp as the penthode section has filament in common
Sort of like anti-skate, it's an approximate compromise, and some is better than nothing.yes but ....
so the best you can really do is compromise. I believe all of the commonly used triode/pentode tubes have the same situation with a single heater connection for both elements.
It's not possible to optimize the filament offset in this amp as the penthode section has filament in common with the triode that is used as cathodyne. The penthode has it's cathode only a few volts above ground, the triode has ( according to the schematic i have ) 70V above ground. Thus 39V seems to be a very reasonable compromise in this case.
I checked the schematic for my Silvertone/ Warwick console amp, they tie the heater chain to the output tube cathode bias.
There was some bypass I replaced substantially more low esr capacitance with film augmentation to each channel during the upgrade.Since I don't have the schematic in front of me, some minor speculation which needs validation.
If the elevation voltage is pulled from the cathode bias resistor the voltage slightly fluctuates, even with a capacitor. Removing the degeneration is the purpose of the capacitor, but it cannot be fully removed.
Any fluctuation in heater voltage modulates the heater winding and thus the cathode. True, this may be minor, but it can still inject noise. Any foreign signal in this context is noise.
Since I don't have the schematic in front of me, some minor speculation which needs validation.
If the elevation voltage is pulled from the cathode bias resistor the voltage slightly fluctuates, even with a capacitor. Removing the degeneration is the purpose of the capacitor, but it cannot be fully removed.
Any fluctuation in heater voltage modulates the heater winding and thus the cathode. True, this may be minor, but it can still inject noise. Any foreign signal in this context is noise.
It must be amazing and impossible then to have a @100% quiet (common inobtrusive PS ripple/ear to the speaker hum excluded) amp with AC heaters lifted by only 7v of DC from output tube cathodes with minimal bypassing.
One of the advantages of the paraphase front end (Magnavox) is the cathodes being nearly 0 volt bias.