Using proper choke

[dude]

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

[PRR]

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.

[jjasilli]

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.

[TIMBO]

SO, what if the choke supplies the preamp only.....

[shooter]

You pick an affordable lump of iron with enough current rating for this load

[sluckey]

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.   

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.

[TIMBO]

Thanks sluckey,

This many valves in the preamp....

[Colas LeGrippa]

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.

[shooter]

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

[dude]

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.

[DummyLoad]

the choke will help with PS buzz in SE amps. filament string hum is separate noise article.


--pete