1962 Marshall JTM45 Offset Reissue

[andrewsrea]

My best friend in PA has three of these. This one had never been played and is in like-new condition. He asked me to take it back to St. Louis, bias the tubes and break it in. I asked him when he wanted it back and he said 'whenever.' So pretty much on loan as long as I like.

In 1962, this type was the first ever made by Jim Marshall and Ken Brian, who followed the Fender Bassman F5A schematic. Only 3 were ever made and this amp is #41 of a total of 300 of the year 2000 reissues. The head and cab are a matched set, with the same serial number. About 1/3 came to the US, 1/3 went to Japan and 1/3 to Europe and all were sold by pre-order. I think the MSRP was $8000, but the actual sale price was around $5,500.

With exception of the power plug, speaker selector and export voltage capability, these are exact replicas of the originals. The Partridge company (transformers) and Celestion (speakers) had to research the old parts and manufacturing techniques to build these. Even down to the paper-pulp used for the speaker cones! The transformers are heavy-duty compare to the modern-day Drake transformers. All hand-wired using turret board.

This has a few component values which are different from the 1959 Fender Bassman. Most notably 4x12 vs. Fender's 4x10, Golden Dragon KT66 (MO Valve) output tubes vs. Fender's 6L6GC (GE) and last, Mullard ECC83 preamp tubes vs. GE 12AX7.

So this is a conservative 35 watt RMS (clean), all tube amplifier head, on top of a 4x12 loaded with Celestion Silver Alnico 15w, 8 ohm speakers (60w & 16 Ohm total). These are exceptionally efficient speakers, so on '2' it is still clean and almost as loud as my 100w Mixmaster. On '3' it brings in the dirt and gets louder. It stops getting painfully loud at '5' and just gets more harmonic (but painfully loud). When broken in, the speakers sound very harmonic.

I biased his first JTM45 Offset and rehearsed with it from 2010 to 2014. These amps are heavenly when broken in. They take pedals pretty well to boot. If you can imagine throwing a 1959 Bassman into a blender with a Vox AC30 and a Marshall Plexi, that would be the sound that this amp makes!

It is very-very good to have friends!

[Chocol8]

That’s a pretty sweet amp. I remember the Marshal fans hating them because, well, they don’t sound like a Marshal. It really is a very slightly modified Bassman head with Celestion Alnico speakers.

Do you know if the cab is historically accurate? I thought they initially had 2x12’s and 4x10’s and didn’t develop the 4x12 until later when the amp wattages went up.

[Partscaster]

very nice to see and read about.

[mozz]

Remember, the Fender also had a 12AY7 in the V1 slot and Marshall changed that to a 12AX7, so you have a gain increase right there. Built a JTM45 once on a very hacked/ gutted Fender silverface head, the guy loved it.

Very nice amp but a lot of $$$$$$$.

[golem]

I had a chance to hear it. Sounds great at volumes I can't deal with personally. That might sound like I'm dissing it but it's just insanely loud to get it to where it sounds best.

[andrewsrea]

That’s a pretty sweet amp.

Agreed! Thank you!

It really is a very slightly modified Bassman head with Celestion Alnico speakers.

I've played and repaired genuine 5F6A Bassmans and have just played this amp through a 4x10 loaded with (2) Weber 20w Blue Pups and (2) Weber 20w Jensen clones. IHMO, they are kissing cousins using 5F6A type speakers.

As @mozz said, the Offset uses a 12AX7 preamp and the Bassman uses a 12AY7 (less gain). Accordingly, the Offset goes to distortion faster and also tops out around' 7' on the volume. The negative feedback circuit is taken off the 16 ohm tap vs. 4 ohm, making a tighter bass response and making the presence control a little more extreme. The Offset KT66 output tubes generate a lower bass frequency than the Fender's 6L6. Making the Offset richer and clearer in the low-end, with a mid-range growl and a creamy top end. The Bassman is alike in the midrange and treble frequencies, but is more wooly in the low-end.

IMHO, the Offset is louder than the 5F6A Bassman given the same speakers, which I attribute to the transformers. Marshall rated the Offset (basically model 2245) at 30w. I need to bench test it, as I think it is more like 45w to 50w.

I will try a less gainy preamp, like a GE5751 or a 12AY7, to get more usable range from the volumes.

Do you know if the cab is historically accurate?

I have not found anything definitive yet on the historical accuracy of the cabinet, but it is a great question. Keep in mind there were only 3 of the Offset prototypes and 3 of the 'centered' porotypes made, before they started what we know as the Plexi production models. These prototypes still exist and Marshall has a few which they used to create this reissue. I do know Marshall put extraordinary efforts into digging through early records to ensure this reissue would have historic relevance. I also believe they lost money on this, as the R&D had to be expensive for only a run of 300.

This is the best info so far: https://guitar.com/features/marshall-amp-history/ . From this and other sites, it is clear the first models were piggy back and they first tried it with a 2x12 open-back cab w/ 15w Celestions. The settled on a 4x12 closed-back Celestion loaded cab for the Plexis', so this might have been an evolutionary in between step (semi-open back 4x12, asymmetrically arranged).

[mozz]

Once read that Pete Townshend was one of the reasons for the 4x12. This might have been a few years after the JTM45. He wanted a 8x12 cabinet and a few were made, they were loud but way too heavy. They cut it down to 4x12 and allowed them to be stacked.

[andrewsrea]

They cut it down to 4x12 and allowed them to be stacked.

Thank god!

Carrying one is bad enough. I was in a band that was playing big places, in which I had to rent (2) Marshall JCM800 100w full stacks to compliment my Marshall Jubilee 50w full stack. All my earnings went straight into the roadies pocket to carry the damm things.

I have the aforementioned Marshall 1965A 4x10 loaded with (2) Weber 20w Blue Pups and (2) Weber 20W Jensen clones. It is a great sounding cab and is a whole lot easier to get from place to place with. @golem likes it and has been casually searching for one.

[Chocol8]

My understanding, “confirmed” by Marshall’s website is that the 4x12 cab was created for the first 50 watt heads because the speakers were rated for 15 watts each and 2 would blow.

Pete came in with the Introduction of the full stack. The WHO wanted more powerful 100 watt heads which then required 8 speakers (at the time). Jim wanted to make two 4x12’s but Pete insisted on an 8x12…until he tried it and the roadies bitched. He went back, admitted he was wrong, and the Marshall stack was born.

BTW, I am surprised the reissue uses KT66 tubes. I thought the first ones had 6L6 tubes before they tried various other due to availability in the UK. Could be wrong on that too though.

[andrewsrea]

BTW, I am surprised the reissue uses KT66 tubes. I thought the first ones had 6L6 tubes before they tried various other due to availability in the UK. Could be wrong on that too though.

No - you are correct. I think the 6L6 was still in the experimenting stage. They eventually produced about 100 of the 'centered' JTM45's which looked like this, except they had a red coffin logo. These came with KT66s.

This one came with exceptionally nice KT66 - Marshall stenciled Golden Dragons, which are audiophile MO Valve replicas. I am thinking the 6L6's may sound more crunchy in this amp.