Amps with Chokes

Guitar Toad

Guitar Toad

Toadily Stratologist
What does a choke do? Is it basically a voltage regulator? Why do some designs use a choke? If I recall correctly the Mr. Soldano's amp designs use chokes.

I found this description? http://www.kk5dr.com/chokes.htm

Is the bottom line that a choke reduces amplifier hum and helps an amp work more efficiently?
 
Re: Amps with Chokes

I am uncertain exactly what is going down - but a choke is just jive-talk for an inductor. And as such it passes low frequencies down to DC real easy but progressively blocks higher frequencies.

My understanding of the choke in a tube amp is that it blocks nearly everything but the DC in the power supply - and since we WANT a DC supply that is a good thing - and does so more efficiently and effectively than a circuit using capacitors to ground alone. This applies more so to tube rectifier circuits because of the difference in impedance between tube rectifiers and the more recent semi-conductor diodes. But even in a diode circuit - the choke / capacitor circuit is more effective than just caps alone.

A tube circuit guru will come by shortly and explain things.....:notworthy
 
Re: Amps with Chokes

A choke is used to "de-couple" the various stages of a tube amps power supply. That is, it keeps AC ripple and noise from passing from one stage to the next. A choke is usually used in large amps, and is placed between the B+ supply for the output stage, and the subsequent power supply stages for the preamp stages.

Why large amps? Simple resistors can do the same thing, but they drop the voltage in proportion to the current going through them. So, if you need a lot of decoupling, use a large resistor - but then your preamp stages get lower voltage. If you want higher voltage in your preamp, decreasing the decoupling resistor will help, but then more noise gets through.

A choke uses inductanace in addition to resistance to decouple the stages and keep out the noise. So, you get more noise rejection, and higher preamp voltages.

As an added benefit, the voltage in the preamp stages is more stable with a choke, because the voltqage drop across is doesn't swing as much with load (how loud you're playing) as it would with a resistor. So, amsp with chokes tend to be less "saggy" than those without. Not better or worse, just different.

In little amps, the lower current involved as well as economics dictate that resistors are "good enough"

My Marshall 18-Watter clone uses a decouipling resistor, 50- and 100-watt Marshall ead uses a choke.

Fender Champs and Princetons use resistors, Super Reverbs, Twins, and even Deluxe Reverbs use chokes.
 
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Re: Amps with Chokes

A capacitor stores voltage. A choke stores curent.

When you hit a low bass note, a lot of current tries to flow to make the speaker move. A choke releases that power, giving a bigger bottom end than a resistor.
 
Re: Amps with Chokes

Thanks Rich for your greatly informative response. I'm planning to building a 5E3 with 6L6 tubes. I was curious if a choke mod to this build schematics would be desireable. From your response, there's no need in this little amp build for a choke. A resistor will be good enough.
 
Re: Amps with Chokes

A choke in a 5E3 upgraded to 6L6 fixed bias is a good idea---more like a E series Pro or Bandmaster in the 30 watt range, if that's what you want. But you will lose a lot of the 5E3 character...and a choke in a cathode bias 6L6 tweed is kinda a waste of iron IMHO...
 
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