choke on speakers??

[punkykatt]

What would be a reason for using a choke on speakers?

[FYL]

Never seen that arrangement.

A choke connected in series would act as a low-pass filter akin to a treble cut, in parallel as a high-pass, treble boost.

[PRR]

> reason for using a choke on speakers?

Short-out bass.

SilverTone out-cheaped themselves. They got a carload of cheap OTs, then a load of even cheaper speakers. The bass power of the amp slapped the cheap cones and made rude noises.

The best answer is better speakers, but.....

The next fix is actually a cheaper OT, to short-out the bass to a level the cheap cones can tolerate politely.

In this case, it seems they could buy some chokes cheaper than they could get new speakers or new OTs. A lot of mass-production decisions are not "ideal", but "how can we move this crap we already bought?"

I believe it is unique.

[bigsbybender]

I see it often in PA speakers, as it's a cheap way to make sure the subwoofers are doing most of the bass work by rolling lows out of the mid/high cabinets. That's a new one for me in a guitar amp.


j.

[punkykatt]

Thanks for the explanation guys.  I`am I correct for thinking the choke will lower the speaker impedance too?

[FYL]

The best answer is better speakers, but.....

The pictured speakers look like Jensen P12Q's, which are some of the best vintage guitar speakers.

They got a carload of cheap OTs, then a load of even cheaper speakers. The bass power of the amp slapped the cheap cones and made rude noises.

Sure, but lowering the value of a couple of caps gives the same results and is even cheaper.

[Frankenamp]

Thanks for the explanation guys.  I`am I correct for thinking the choke will lower the speaker impedance too?

Nuh-unh!

A choke or coil will have a rising impedance depending on the value of the coil (in Henrys) which depends on the impedance of the loudspeaker. The speaker also has a rising impedance due to VC inductance and the coil in series compounds the impedance. This has the effect of rolling off the highs when used in series with the driver. I would not use an inductor in parallel with the speaker VC. Yes you can shunt off some of the bass, but at lower frequencies it can look close to a dead short to your amp which is not necessesarily a good thing.

EDIT for clarity: the coil does not make the driver impedance lower- it takes the lower frequencies through, depending on the inductance of the coil. A low DCR coil could be dangerous.

[PRR]

Amps like these can face a dead-short, no harm. They run roughly constant-current. They certainly won't pump a lot of excess current into a short.

Those speakers are probably not original. Even if ST was using a Jensen frame, it surely was not Jensen's best coil/cone assembly. Even though this is a high-price SilverTone, it was still a bottom-price amp for its power.

> lowering the value of a couple of caps

Changes frequency response, NOT power response. Or not so neatly.

Change coupling caps, roll-off some bass, OK. Now play harder. The driver generally has ample headroom to push 6L6 hard, even with considerable bass loss in the coupling network.

Under-size the OT (or shunt a choke across an existing OT), low inductance, bass current is shunted away from the speaker. Large bass current can't flow in speaker, excursion is limited.

RCA patented this in the dawn of home loud-speakers. Same problem: their speaker could not handle full bass power without slapping. Theirs was an SE amp, so the OT size was picked for good small-signal bass response. A correct proportion of shunt-choke would limit bass excursion without much harm to the sound.

Whatever. I'm sure nobody wants to do it this way, unLESS your production buyer has already bought OTs and speakers which don't play well together. Most modern speakers will handle self-bias 2*6L6; if not, DIYers have choices. If this amp's speakers have already been replaced, snip the chokes and see how it sounds.