First post!
I'm considering building a PP stereo amp using DHT's. I was going to use 2a3's, but my One Electron BFT-1B power transformer has a beefy (9.6A) 6.3 volt secondary for output tubes and it would be a shame to waste it, so I think it'll be 6B4G's instead.
My question is: with directly heated power tubes, do you need separate filament supplies for each channel of a stereo amp? And if so, why? (I'm new at this, so I'm trying to learn).
Thanks!
I'm considering building a PP stereo amp using DHT's. I was going to use 2a3's, but my One Electron BFT-1B power transformer has a beefy (9.6A) 6.3 volt secondary for output tubes and it would be a shame to waste it, so I think it'll be 6B4G's instead.
My question is: with directly heated power tubes, do you need separate filament supplies for each channel of a stereo amp? And if so, why? (I'm new at this, so I'm trying to learn).
Thanks!
Hi,
Need, no. Not really but...
To avoid crosstalk between channels.
Cheers,
P.S....Hadn't noticed this is your first post straightaway...
Welcome to the forum.
My question is: with directly heated power tubes, do you need separate filament supplies for each channel of a stereo amp?
Need, no. Not really but...
And if so, why?
To avoid crosstalk between channels.
Cheers,
P.S....Hadn't noticed this is your first post straightaway...
Welcome to the forum.
BHD,
The scheme I outline below will take care of your 6B4G filaments. A cautionary note, there is plenty of talk about "washed out" sonics when "ordinary" DC is used to energize DHT filaments.
Use the 9.6 A. filament winding to feed a full wave voltage doubler made from 2X Schottky diodes. 50 A. rated parts are not overkill, as the turn on surge will be massive. The doubler cap. stack consists of 2X 22000 muF. 'lytics. The doubler feeds a pair (1/channel) of 7812 3 terminal regulators. The regulators are being used at their limit; so, BIG heatsinks, insulating washers, and thermal compound are a must. Follow the regulators with 20 muF. 'lytics in close physical proximity. Wire the 6B4G filaments in series. The junction point of the 2 filaments is where the RC bias network (1/channel) gets connected. An enhancement is to add a 4PDT switch to periodically (once a month) reverse the polarity the filaments "see". Reversing the filament's DC polarity compensates for the effects of the voltage gradient on them.
The scheme I outline below will take care of your 6B4G filaments. A cautionary note, there is plenty of talk about "washed out" sonics when "ordinary" DC is used to energize DHT filaments.
Use the 9.6 A. filament winding to feed a full wave voltage doubler made from 2X Schottky diodes. 50 A. rated parts are not overkill, as the turn on surge will be massive. The doubler cap. stack consists of 2X 22000 muF. 'lytics. The doubler feeds a pair (1/channel) of 7812 3 terminal regulators. The regulators are being used at their limit; so, BIG heatsinks, insulating washers, and thermal compound are a must. Follow the regulators with 20 muF. 'lytics in close physical proximity. Wire the 6B4G filaments in series. The junction point of the 2 filaments is where the RC bias network (1/channel) gets connected. An enhancement is to add a 4PDT switch to periodically (once a month) reverse the polarity the filaments "see". Reversing the filament's DC polarity compensates for the effects of the voltage gradient on them.
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