choke for plexi suggestion needed

[mightymike]

3H and I've seen some schematics with 20h if memory seves me right. I've also heard the 20h was wrong.
It will be cleaner, which some (Like Sergio and Paul) would interpret as vintage but really it cleaner in high filtering stiff way. Like Brian says.

There are some meters that Measure Henries, I don't know if they measure it live at 400 Volts or more though. I measure everything else and solve for the Henrys.

I measure the voltage drop across the choke dived that by the Amps measured in series with the choke. Once you have those 2 measurements then use ohms law solving for resistance V/I =R
But in this case, it's a coil, and that resistance is equivelent resistance of a coil
better known as inductive reactance XL =2PIFL

All that formula means is that Inductive reactance "XL" is equal to 2 times PI times the Frequency times the Henrys "L"

Now here's where you combine the 2 equations to find out how many Henries your Choke is putting out.,

First off you already know what XL is becasue you measured earlier and solved for it with ohms law.

second: You already know what 2 PI F is becasue the the Frequency in a full wave rectifier would be double the 60hz comming out of the wall.
So f = 120hz

Once you get to this point you have every number in that equation except L which is your Henries.

Let;'s simplify this further:
If F = 120, then 2 times PI times F = 753.98

so XL = 753.98 times L

that same equation reararranged

XL/753.98 =L


So all this shit boiled down to 4 simple steps goes like this.

1) measure the Voltage Drop Across the Choke
2) measure the Amperage by placing your meter in series with the choke
3) Divide the voltage reading, by the Amperage reading to get XL
4)* Divide XL by 753.98 = Henries


*or Divide XL by 376.99 = Henries if it's a half wave rectifier

[Flames1950]

3H and I've seen some schematics with 20h if memory seves me right. I've also heard the 20h was wrong.
It will be cleaner, which some (Like Sergio and Paul) would interpret as vintage but really it cleaner in high filtering stiff way. Like Brian says.

The 20 henry choke did show up -- otherwise Brian wouldn't have had the specs to repro for my Super PA. But as always, Marshall grabbed whatever they could get and more often than not that seems to have been something other than the 20H.

And remember that it was 20H measured at only 70mA -- where did that drop to when you were diming your 100-watt amp? It is not stiff at all in my Super PA.

[mightymike]

There was a thread somewhere, where they were calling that into question. Probably because somebody saw one that didn't have a 20H. It was probably made that way because of the reasons you cite. Makes perfect sense now.

Because of that thread I didn't feel so bad when I couldn't find any 20H chokes laying around that fit the 2/78 spaced holes in my Metro Aluminum chassis. Like Marhsall, I used what I had. Plus I was trying to keep it looking clean, and not swiss cheese the chassis.

What is the price, spacing mount, and part # if any on that 20H repro choke? I've had a regular plexi choke in my JTM 45/100 until now and love the way the amp sounds, but I want to try them all.



This discussion has me thinking that maybe because the JTM 45/100 is 60hz half wave, it needs more Henries to achieve the same smoothing as a 3 Henry in a 120hz full-wave plexi.
Because of longer release time needed in between peaks in a Half wave



Plexi Full Wave Rectifier 120hz
XL =753.9L
L = XL/753.98

With a 3 Henry

753.98 x 3 = 2261.94 Ohms of Inductive reactance

JTM 45/100 Half Wave Rectifier 60HZ
XL/376.99 = L
L = XL/376.99

With a 20 Henry

376.99 x 20 = 7539.8 = Ohm of inductive reactance


It makes sense that higher XL would be needed for a JTM 45/100, but since I like the way a plexi feels on the bottom end, I'd like to try the equivent XL which would be a 12 Henry in the JTM 45/100. Here's how I came up with 12H, you tell me if the math is right.

A 12H would be double the 2261.94 Ohms of inductive reactance of a 3H full-wave circuit, so I doubled the 2261.94 because it's going into a half wave circuit.

I don't know if this is right, but I noticed 376.99 goes into
2261.94 six times, so 6H is needed to get 2261.94 in a half-wave JTM 45/100, but then I doubled it because you have twice the space in between the peaks to filter in a half wave, so with 12H in a JTM 45/100 you end up 4523.99 Ohms of XL which is double the 2261.94 Ohms of XL in a Full Wave Plexi.

Because of this I had originally wanted to try a 10H Merc in there (closest to 12), but it was too wide of a mount, then I saw that thread challenging the 20h, so then I used a Metro plexi choke.

It sounds killer as is, but I'll be getting a 20H eventually.
A little tightening would hurt, as long as it doesn't get too stiff.

[rgalpin]

awangotango,

That choke would be a 3H one. Also, if you raise the Henry value, you will not only "clean" the amp up, you will also make it stiffer on the feel and note attack. This is really not a vintage feel as most chokes used by Marshall are the 3H rated ones.

bingo! this is the info i am looking for! thank you for that input.

[Flames1950]

What is the price, spacing mount, and part # if any on that 20H repro choke? I've had a regular plexi choke in my JTM 45/100 until now and love the way the amp sounds, but I want to try them all.

Mount spacing is 3 1/8". Brian would have to help you with the other info, I've never seen him list this choke on his site yet. It does not have a part number sticker like a lot of Heyboer stuff does.

[mightymike]

Was 3 1/8 what your PA Chassis already had, or did you drill that/

[Flames1950]

It was close enough to what it had that it worked. The spacing was part of the reason Brian thought the RS 20H choke was originally on that chassis.

[Brian Wallace]

Mightymike,

Even though the early schematics show a 20H choke, most did not have this RS part, they came with the Drake 3H choke.

I may I have one left in stock, I think they are $28 I'll have to check, and I did send George one to check out.

[mightymike]

I'm ready
Can I send the $28 to you paypal?
All I need is the account to send it to.

[Brian Wallace]

Send me an email, Info@marstran.com, I need some info from you first.

[bluze81]

Brian would it be correct that the lower the choke henry rating= softer,less clean, less stiff, but possibly more ghosting notes? thanks bluze

[Brian Wallace]

bluze81,

Yes, the combination of a lower henry choke and lower filtering will give you ghosting but the amp sounds so good.

[joshwilson3]

bluze81,

Yes, the combination of a lower henry choke and lower filtering will give you ghosting but the amp sounds so good.

What about high filtering and a lower henry choke?

I've been trying to figure out what choke to put in a Marshall master volume (2203) clone I plan on having built.

[Necrovore]

bluze81,

Yes, the combination of a lower henry choke and lower filtering will give you ghosting but the amp sounds so good.

What about high filtering and a lower henry choke?

I've been trying to figure out what choke to put in a Marshall master volume (2203) clone I plan on having built.

Josh, my suggestion would be to use the stock value at first. You are already using upgraded componants for your build. See how they react to the stock valued choke first, then start messing with your filtering and choke, as those parts are not that expensive.

[Brian Wallace]

Josh,

The original choke is a 3H in a 2203. I personally would rather see a higher value, maybe 10H, since you are really using the preamp for all your distortion and compression. This will make the power amp tight and solid to bring back some umph to the amp. Maybe this is why some people choose the 6550 and KT88 tubes in these amps. Kind of the same thing.