Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on May 05, 2019, 01:38:04 pm
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Does the type of rectifier used determine the Henries value of a choke used..? Not finding much info on this. Will I usually find the choke value needed in the rectifier tube data?
thanks,
al
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Nearly all guitar-amp power supplies are cap-input, so the rectifier isn't facing the choke directly.
Nearly all push-pull amps omit any choke to the OT's B+ feed.
So the choke normally only has to feed screens and preamps. You pick an affordable lump of iron with enough current rating for this load. It has less DC drop for a load and more filtering than a simple resistor. The exact value of inductance is not real critical because if the filtering is insufficient it is much cheaper to use larger caps than a bigger coil.
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The tube charts spec the choke for a choke input circuit. This is not applicable when the choke is used downstream (after the plate supply node on the B+ rail.)
A R can be used in place of a choke; so why use a choke. For design criteria, a choke reduces ripple without dropping voltage to the screen under signal conditions. Also, because a choke is a reactive device, it sounds and feels different from a R.
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SO, what if the choke supplies the preamp only.....
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You pick an affordable lump of iron with enough current rating for this load
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SO, what if the choke supplies the preamp only.....
Take a 1/4-20 x 3/4" long bolt and wrap 200 turns of #30 magnet wire around it. :icon_biggrin:
Actually, why would you need a choke with such a light load? It's very easy to obtain almost perfectly smooth dc with just a CRC filter when the load is only a few mils.
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Thanks sluckey,
(https://i.imgur.com/9KQq35y.jpg)
This many valves in the preamp....
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SE amps need a choke before the OT B+ supply for hum free operation. In all my builds a 5H choke is good, PP or SE. , 12 W or 100W. Chose the mA rating acording to what the circuit is drawing, times 2.
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SE amps need a choke
I agree, but IF you make a "stiff" PS they can be "worked around", I have 2 11lb-ers
as book ends for now. You need a CRC with BIG C's before the OT tap, AND a big Ck.
saves money, saves weight, but WILL loose about 20% of the guitar players
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SE amps need a choke before the OT B+ supply for hum free operation. In all my builds a 5H choke is good, PP or SE. , 12 W or 100W. Chose the mA rating acording to what the circuit is drawing, times 2.
So, you're saying a Vibrochamp would benefit from a choke..., less hum? I changed the filament wiring on mine (later BF design) and the hum left.
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the choke will help with PS buzz in SE amps. filament string hum is separate noise article.
--pete