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Eric's Bluesbreaker Marshall Combo: new pictures.

F-Hole

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Well, I was talking to one of the UK's best repair guys last week, shooting the breeze as you do. He was a player back in the day, lots of cool memories. Anyway, we started talking about an old Marshall he sold me some time ago, and we get onto Clapton's infamous amp.

This is where is gets interesting. I told him that we'd probably never find out what it was, and he pipes up with......."it's a JTM45 chassis in a 2x12 cabinet, we chatted about it at a gig with maybe 20 people there, Lewisham, 1966".

This chap was an early Marshall user (per the amp he sold me), and remembers specifically discussing his rig. They both played 'bursts at the time.
 

TM1

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Well, I was talking to one of the UK's best repair guys last week, shooting the breeze as you do. He was a player back in the day, lots of cool memories. Anyway, we started talking about an old Marshall he sold me some time ago, and we get onto Clapton's infamous amp.

This is where is gets interesting. I told him that we'd probably never find out what it was, and he pipes up with......."it's a JTM45 chassis in a 2x12 cabinet, we chatted about it at a gig with maybe 20 people there, Lewisham, 1966".

This chap was an early Marshall user (per the amp he sold me), and remembers specifically discussing his rig. They both played 'bursts at the time.

So.. Not a Tremolo chassis?
Cheers!
 

TM1

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I'm seeing him next week, so will get more details.

That is really great! Thanks for sharing! Are you familiar with the article that "Guitar & Bass" magazine did a couple years back on BB combos? It had an interesting theory on EC's amp using an RS output with "Reflective Matching" in the output section to achieve his sound..I'll find out which issues it is as I have it on my ipad.
Cheers!
 

goldtop0

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That is really great! Thanks for sharing! Are you familiar with the article that "Guitar & Bass" magazine did a couple years back on BB combos? It had an interesting theory on EC's amp using an RS output with "Reflective Matching" in the output section to achieve his sound..I'll find out which issues it is as I have it on my ipad.
Cheers!


What is Reflective Matching?
 

F-Hole

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What is Reflective Matching?

I think TM1's referring to an article by Dave Petersen, where he suggests that Clapton's amp was wired 16 ohms output into 8 ohms at the cabinet. He suggests that this mismatch is the basis for Clapton's sound, as primary load was halved to around 3.3k, allowing the amp to increase output to around 45W with lower bias current. The "negative", he argues, was less bass (because of lower primary inductance) and more distortion, particularly with KT66's which have an "individual sound" under these conditions.

He reached this conclusion from looking at photos of old Series 1 Bluesbreaker wiring and extrapolating. I think it's a bit of a long bow to draw, but a guy I know wired a genuine BB this way and says the difference was night and day, and that it nailed the Beano sound.

I'm not convinced, but I guess it may be true.
 

corpse

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My understanding is that's exactly what kills OT's- right?
The old story "man, my amp sounded the best I ever heard it, right before it blew up."
 

efk

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No, running into a lower impedance generally is most harmful to tubes. Running into a higher impedance sets the stage for potential flyback spikes and arcing, which can puncture OT insulation. Most OT are built tough enough to handle a bit of mismatch, however since guitar amps are typically driven into oblivion, if an OT is going to fail it typically manifests in a guitar amp as opposed to a hi-fi amp.

I don't think there is any way of knowing how Claptons amp was wired but I can indeed verify from personal experimentation that running a RS style OT into a 1-step-lower mismatched load does indeed make for a very audible difference. It will with a Drake style OT also.
 

springhead

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I'd like to see that article if it's available somewhere.

I don't think you'll ever get 45W out of a pair of KT66's. Pentode connected, Class AB1 pretty much 30W max. Clean that is. Pretty hard to quantify what the output would be under gross distortion.

Looks from the datasheet that the output power will fall and distortion will rise for a pair running below about 5K5 a-a.

Not disputing that the distortion will increase/change in nature in a good way and that could be what we're hearing!
 

TM1

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8k tap on the RS o/p tranny primary, 16 ohm tap on the secondary and an 8 ohm speaker load if I remember right. It was in the G & B magazine in March 2013 issue. I tried it on mine and it pretty well nailed the sound using my 2002 R-0, Historic Makeovers Les Paul. I have ThroBak pickups in it and Monel strings (Gibson called them "Mona Steel"). the only one making these for electric guitars are Pyramid in Germany. Martin has a really stiff acoustic/Tony Rice set with Monel but they used a Hex core wire which was not used in 1965/66. should be a silver plated German Steel round core/plains, not that awful tin plated Swedish steel junk!
 

springhead

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So effectively 4K a-a primary. My JTM 45 head is wired 6K6 at the moment and runs into a 16 ohm 2x12 cab, on it's 16 ohm winding. Don, if you've got a pdf or scan of the G&B article I'd love to read it.
 

goldtop0

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No, running into a lower impedance generally is most harmful to tubes. Running into a higher impedance sets the stage for potential flyback spikes and arcing, which can puncture OT insulation. Most OT are built tough enough to handle a bit of mismatch, however since guitar amps are typically driven into oblivion, if an OT is going to fail it typically manifests in a guitar amp as opposed to a hi-fi amp.

I don't think there is any way of knowing how Claptons amp was wired but I can indeed verify from personal experimentation that running a RS style OT into a 1-step-lower mismatched load does indeed make for a very audible difference. It will with a Drake style OT also.


So maybe Eric's 1962 combo blew up! Losing it's OT.
I've had it happen in my amps.
 

F-Hole

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So maybe Eric's 1962 combo blew up! Losing it's OT.

I very much doubt it, these early RS Deluxe transformers are extremely robust, and are wound like no other.

There's another thread on this amp forum that talks to the minutiae, and very much worth reading.
 

E-Rock

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Dec 11, 2002
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I very much doubt it, these early RS Deluxe transformers are extremely robust, and are wound like no other.

I thought the general consensus over the years was that EC's amp likely had Drake transformers. No? Still very much up for debate?
 
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