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previous: ADM I've noticed that some Ampeg's have... -- 4/19/2000 5:25 PM

Re: Ampeg Heater Circuit Questions

4/20/2000 12:36 AM
Ray Ivers	Re: Ampeg Heater Circuit Questions Andrew, Supposedly, biasing the AC heater voltage with a positive DC voltage (such as that available at the bypassed common cathode resistor of the output stage) reduces hum. I have experimented with this and not had too much luck with it, although it was common enough practice in the 50's and 60's to reduce hum levels in amps and preamps. A 100 ohm balance pot would perhaps be more effective at 'zeroing out' the hum, although in my book it's hard to beat a center-tap; and those 100 ohm pots are both hard-to-find and prone to burnout. Regulated DC is the way to go, but it's a lot easier to design it in at the git-go than add it later. Ray Ivers

4/20/2000 12:36 AM

Ray Ivers

Re: Ampeg Heater Circuit Questions

Andrew,

Supposedly, biasing the AC heater voltage with a positive DC voltage (such as that available at the bypassed common cathode resistor of the output stage) reduces hum. I have experimented with this and not had too much luck with it, although it was common enough practice in the 50's and 60's to reduce hum levels in amps and preamps. A 100 ohm balance pot would perhaps be more effective at 'zeroing out' the hum, although in my book it's hard to beat a center-tap; and those 100 ohm pots are both hard-to-find and prone to burnout.

Regulated DC is the way to go, but it's a lot easier to design it in at the git-go than add it later.

Ray Ivers

Replies:

andy fuchs Keep in mind that the DC available ... -- 4/20/2000 1:14 PM