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previous: Ray Ivers Andy,Thanks for the... -- 4/22/2000 8:09 PM

Re: Scott Heaters for PA Cathode Resistors

4/22/2000 10:27 PM
andyfuchs	Re: Scott Heaters for PA Cathode Resistors I would doubt the heaters have any preference,as far as their order goes. I recall that there was a capacitor across the series string. I don't remember if they were setup as 6 or 12 volt either, but that would be a function of the required bias for the power tubes anyway. 4 12AX7 could be potentially wired up to produce a pretty decent spread of voltages, with series and/or parallel tubes. Even if you needed to, a small 5 watt resistor to make up the difference (if you only had 2 or 3 tubes and needed a higher bias voltage) wouldn't be a big deal. As far as turn-on's go, it would also be a "free" slow turn-on, as the power tubes warmed up ! I've used surplus power supplies (Fair Radio Sales and similar outlets sell them), which produce a reasonably high current (3 A or more) output, and are self contained. They are even built into a thick aluminum housing, that acts as a heatsink. Some extremely sick audiophiles even run their power tubes with them ! I only found this as an advantage in single ended triode outputs, where the DC filaments really can reduce output noise levels. When you are using 95 and 100 db (horn) speakers, every noise source is looked at. These can be found for cheap, if you shop around. There are also some nice kits from Velleman and others, that produce an amp or two of adjustable DC output. While it's not imperitive to use DC, It can't hurt (at least at the first or second tube stages in an amp). GOod Luck !

4/22/2000 10:27 PM

andyfuchs

Re: Scott Heaters for PA Cathode Resistors

I would doubt the heaters have any preference,as far as their order goes. I recall that there was a capacitor across the series string. I don't remember if they were setup as 6 or 12 volt either, but that would be a function of the required bias for the power tubes anyway. 4 12AX7 could be potentially wired up to produce a pretty decent spread of voltages, with series and/or parallel tubes. Even if you needed to, a small 5 watt resistor to make up the difference (if you only had 2 or 3 tubes and needed a higher bias voltage) wouldn't be a big deal. As far as turn-on's go, it would also be a "free" slow turn-on, as the power tubes warmed up !
I've used surplus power supplies (Fair Radio Sales and similar outlets sell them), which produce a reasonably high current (3 A or more) output, and are self contained. They are even built into a thick aluminum housing, that acts as a heatsink. Some extremely sick audiophiles even run their power tubes with them ! I only found this as an advantage in single ended triode outputs, where the DC filaments really can reduce output noise levels. When you are using 95 and 100 db (horn) speakers, every noise source is looked at.

These can be found for cheap, if you shop around.
There are also some nice kits from Velleman and others, that produce an amp or two of adjustable DC output. While it's not imperitive to use DC, It can't hurt (at least at the first or second tube stages in an amp).

GOod Luck !

Replies:

Ray Ivers Andy,Thanks again f... -- 4/22/2000 10:55 PM