why would somebody prefer to remove the choke?

Roe · Post by **Roe** » Tue Jun 13, 2006 9:50 am

does it give a more hollow sound?

According to a person on the plexipalace who claimed he bought some old marshalls from ac/dc their tech had removed the chokes on the marshalls. the amps were pretty much stock otherwise (with possible exception for installed fans).

guitronics · Post by **guitronics** » Mon Dec 18, 2006 7:01 am

That doesn't make sense to me...the choke is in there to add inductance to the power supply, in order to filter it better.

As I understand it...the cleanest power would be a battery...the first amplified radios had batteries,probably because a lot of people didn't have Electrical service in their homes,and secondly;power supply filtering probably wasn't sufficiently advanced.

That's why the high voltage transformer output is called B+. (Battery)

I know of only 3 things that are used to filter the rectified DC : Capacitance (Electrolytic's),Resistance , and Inductance.

Tech's call these L - C - R (L = Inductance, C = Capacitance, and R = Resistance).

So the circuits to filter out the artifacts of AC from the DC are called L-C,or L-C-R.

I LOVE AC/DC (The Band)...have most everything they made on CD,and Vinyl.

If the tech took out the Choke (Inductor)...that would give you some voltage boost, but at the expense of 60 HZ or multiples of 60 HZ noise.

Maybe THAT's the Point! Maybe they wanted the noise! LOL

mightymike · Post by **mightymike** » Mon Dec 18, 2006 9:00 am

I thought they replaced that choke with a resistor though. Probably to keep the volatege the same, by matching the equivelent resistance of the choke. I wouldn't be suprised if it was a 100 ohm resistor.. Unless I have them confused with someone else.

So yes the B+ would be filtered less without a choke, but that lower filtering is part of their sound.

guitronics · Post by **guitronics** » Tue Dec 19, 2006 5:58 am

I don't know,mike.

100 ohms seems like a lot of resistance,chokes are usually kinda heavy wire,especially in Power Supply circuits.

If the chokes were just bypassed,you'd get a bit more voltage...

But a Variac would do the same thing, and you just need to plug it in, instead of desoldering/unbolting/resoldering the supply wire and the output wire.

There may be more to this than we know

In any event, I sure hope somebody posts the "What was done,and why"...'cause I'm

Billy Batz · Post by **Billy Batz** » Tue Dec 19, 2006 6:39 am

Ive done this a lot with fenders. The result is a bit more liquid OD. Not as much punch to it. I guess a lack of linearity. I guess you could liken it to a tube recto vs a SS. Not exactly but a similar difference. Its not something I was ever tempted to try in a marshall.

robert · Post by **robert** » Tue Dec 19, 2006 6:56 am

More compression at "full tilt", especially with EL34 or 6550 (because their relatively high screen grid current). One can use also a 450 R or 1K power resistor to try this out. The amp gets an other dynamic bevavior than with a choke, more "bluesier" IMO.

Regards

Robert

mightymike · Post by **mightymike** » Tue Dec 19, 2006 9:00 am

Would a welkin 1k 5watt be enough power rating?

I have some laying around here.

908ssp · Post by **908ssp** » Tue Dec 19, 2006 10:38 am

Robin Ford runs a resistor rather then a choke on his Dumbles. My Glaswerks amp has a switch that allows you run either one.

wadeberglund · Post by **wadeberglund** » Tue Dec 19, 2006 12:10 pm

Mike-

Hiwatts use a 100Ohm 5W resistor here (instead of a choke), so that power rating should be just fine.

-WA

novosibir · Post by **novosibir** » Tue Dec 19, 2006 1:43 pm

mightymike wrote:Would a welkin 1k 5watt be enough power rating?

wadeberglund wrote:Hiwatts use a 100Ohm 5W resistor here (instead of a choke), so that power rating should be just fine.

5W @ 100 ohms is ok!

but 1K (= 1,000 ohms) would require at least a power rating of 25W, better 50W

Larry

wadeberglund · Post by **wadeberglund** » Tue Dec 19, 2006 1:48 pm

Oops, thanks for the correction Larry.

mightymike · Post by **mightymike** » Tue Dec 19, 2006 3:53 pm

Wow the Dumbles used that, holy crap Robben Ford, Hiwatts, and I bet SRV's Dumble SSS had that then too.
I bet that extra compression full tilt, would be awesome with a strat to thicken it up a little with that compression.

Oh man I have to experimentwith this.

Thanks for the heads-up on the wattage rating Larry.

robert · Post by **robert** » Tue Dec 19, 2006 5:13 pm

Hi Mike,

I believe that most of the Trainwrecks use a power resistor instead a choke, too?

For testing, make it switchable: Choke, 100R, 470R, 1K etc.
Those nice power resistors (the ones with the gold anodized aluminum case) are optimal, IMO.
25 Watts or even better, 50 Watts, like Larry said- so you don't need a heat sink.
And then report what you prefer, please!

Regards

Robert

JD · Post by JD » Tue Dec 19, 2006 5:19 pm

What would happen (sound wise or potential damage) if you ran a resistor in parallel with the choke?

novosibir · Post by **novosibir** » Tue Dec 19, 2006 6:24 pm

robert wrote:For testing, make it switchable: Choke, 100R, 470R, 1K etc.

Or adjustable - with a 1K/50W rheostat:

http://www.larry-amplification.de/briti ... pur091.jpg

Larry