3H choke in JTM 45

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F#m7
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3H choke in JTM 45

Post by F#m7 » Tue Apr 07, 2009 3:04 pm

Is this the size choke found in most of the old 45's? What difference am I gonna hear when replacing the 7H that came with the kit? I'm guessing George favors the 7H because of ghosing issues, but I'm really curious to see what the tonal differences are gonna be with the 3H. Anyone have experience in this area?

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Re: 3H choke in JTM 45

Post by shakti » Wed Apr 08, 2009 5:12 am

I read somewhere that the first ones had a 20H RS choke. This is the one found in the earliest JTM45/100 amps as well.

I think the info on chokes in early (pre-'69) Marshalls is a bit sketchy, I'd also love to hear about people's experiences with different types. When you look at photos of old amps, it's usually hard (for me, anyway) to tell which type of choke the amp had.

Seems the ones in use were:

20H RS choke (early JTM45s and JTM45/100s)
3H choke (brand? years of use?)
5H Drake 352-114 (later JTM45/100s like George's own)
JTM45 RS OT, 1973 18W, JTM45/100, JTM50, JMP50 1986, JMP100 "West Coast", AC15, AC30, BF Super Reverb, Boogie Mk 1, Hiwatt CP103, DR103

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Re: 3H choke in JTM 45

Post by F#m7 » Wed Apr 08, 2009 12:03 pm

I know the early schematic shows a 20h. Brian Wallace makes one. Maybe Brian could shed some light on the subject.

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Re: 3H choke in JTM 45

Post by paulster » Wed Apr 08, 2009 8:06 pm

I don't know if Brian's around just at the moment. I've emailed him about this question and about potentially getting some of his iron and haven't heard back yet.

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Re: 3H choke in JTM 45

Post by Brian Wallace » Wed Apr 08, 2009 9:22 pm

I'm around. :D

Send me another email.
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Re: 3H choke in JTM 45

Post by Dejoblue » Thu Apr 16, 2009 2:26 am

MM has a multichoke:

http://www.MercuryMagnetics.com/pages/mainframe.htm" onclick="window.open(this.href);return false;

"Mercury's exclusive multi-tap choke -- tolerance +/-10%
10 Henry (DCR = 100Ω),
15 Henry (DCR = 125Ω),
20 Henry (DCR = 148Ω),
25 Henry (DCR = 169Ω) and
30 Henry (DCR = 188Ω)"

Dunno if there are any tone disadvantages to it. Might give that try and see what you like best.

It's not the 3H your speaking of, however.

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Re: 3H choke in JTM 45

Post by thousandshirts » Thu Apr 16, 2009 3:03 am

Not only do they have a 10H - 30H choke in 5H increments, they have other multi-chokes on the way.

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Re: 3H choke in JTM 45

Post by Brian Wallace » Thu Apr 16, 2009 5:48 am

The choke you are going to find in 99% of all Marshall's is the 3H 100 ohm choke.

I find that raising the value causes the amp to become stiff and have less breakup.
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Re: 3H choke in JTM 45

Post by F#m7 » Thu Apr 16, 2009 7:18 am

Well I have one of Brian's 3h chokes on the way, so I'll see very soon what difference it makes. :D

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Re: 3H choke in JTM 45

Post by shakti » Thu Apr 16, 2009 9:16 am

Brian Wallace wrote:The choke you are going to find in 99% of all Marshall's is the 3H 100 ohm choke.

I find that raising the value causes the amp to become stiff and have less breakup.
Brian,

do you mean 99% of JTM45s, or any Plexi Marshall? The history of chokes is hazy to me...the 3H choke was a Dagnall, wasn't it? In which case, isn't it more likely that this was introduced around the time of the Dagnall OT, i.e. late '67?

The 20H RS choke - what does it look like? I've been poring over photos at Amp Archives trying to figure out what type of choke the early '65-'67 JTM45, JTM45/100 and Black Flag amps had. It's not easy to distinguish many different chokes. There is one which looks quite different though, like this:

Image

Is this the 20H RS choke? This is an early JTM45/100, SN7412, probably not '65 as the photo says since it has the Drake 1204-43 PT. I can only see this choke in a very small number of amps, whether they are JTM45s or JTM45/100s. Which choke did all those other '65-'66 amps have? Is it a Drake, or other brand? Specs?

Further on, the Drake 352-114, when was that introduced? Drake transformers usually had codes stamped on them, but I've only seen a few amp photos where you can see this code on the choke, like the amp below (SN SL10007, one of the earliest EL34 amps, still with JTM45 front panel, but gold back panel and early 10-series SN)

Image

The majority of amps in the '65-'67 era appear to have a choke which looks like this (from the "Hendrix" amp, SN7026):
Image
However, are they all the same type choke? I'm confused on this matter...
JTM45 RS OT, 1973 18W, JTM45/100, JTM50, JMP50 1986, JMP100 "West Coast", AC15, AC30, BF Super Reverb, Boogie Mk 1, Hiwatt CP103, DR103

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Re: 3H choke in JTM 45

Post by jerrydyer » Thu Apr 16, 2009 1:37 pm

yeah what tonal differences does it make? I buy a replacement from CE and it was like a 20h but the one I use most is the Mercury 7h. But I dont know what they do. what are the tonal difference ?
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Re: 3H choke in JTM 45

Post by thousandshirts » Sat Apr 18, 2009 2:47 pm

jerrydyer wrote:yeah what tonal differences does it make? I buy a replacement from CE and it was like a 20h but the one I use most is the Mercury 7h. But I dont know what they do. what are the tonal difference ?
As Brian pointed out above, the bigger the choke's rating (for example, going from 3H to 7H with similar current ratings) will make the amp more stiff in feel. The smaller the choke, more loose. While it is a tonal difference more people will characterize it as a "touch sensitivity" or "feel" difference.

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Re: 3H choke in JTM 45

Post by Brian Wallace » Sat Apr 18, 2009 10:08 pm

Shatki,

The first picture shows the 20H RS choke. The others are 3H Drakes. The Dagnall choke would be the C1999.
thousandshirts wrote:
jerrydyer wrote:yeah what tonal differences does it make? I buy a replacement from CE and it was like a 20h but the one I use most is the Mercury 7h. But I dont know what they do. what are the tonal difference ?
As Brian pointed out above, the bigger the choke's rating (for example, going from 3H to 7H with similar current ratings) will make the amp more stiff in feel. The smaller the choke, more loose. While it is a tonal difference more people will characterize it as a "touch sensitivity" or "feel" difference.
That's how I look at chokes. The 10H will make the note attack faster and therefore make the amp feel stiffer to play. It will also tend to clean the amp up and make the amp cleaner at 10 than if it had the 3H in it.
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Re: 3H choke in JTM 45

Post by shakti » Sun Apr 19, 2009 4:39 am

Brian Wallace wrote:Shatki,

The first picture shows the 20H RS choke. The others are 3H Drakes. The Dagnall choke would be the C1999.
So the 352-114 is actually 3H? I think George's 352-114 is 5H, 100mA. Which is correct?
JTM45 RS OT, 1973 18W, JTM45/100, JTM50, JMP50 1986, JMP100 "West Coast", AC15, AC30, BF Super Reverb, Boogie Mk 1, Hiwatt CP103, DR103

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Re: 3H choke in JTM 45

Post by Brian Wallace » Sun Apr 19, 2009 7:36 am

The factory spec for the 352-114 is 3H but they can vary due to tolerance and manufacturing.
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