1960s JTM 45 key changes

[granttg83]

Conscious a lot of spec changes to the JTM 45 throughout the mid 60s.

Am curious about a few things.

Roughly when did the power light shift from circular to square?

When did the Aluminium end blocks come in?

Would you expect to see a grey RS caps instead of blue Hunts in 66 or where they used interchangeably?

Thanks!

 

[TAZIN]

Roughly when did the power light shift from circular to square?

I would say early '66 (Feb.-Mar.).

When did the Aluminium end blocks come in?

I'd say mid '66. The 100w amps were a bit later.

Would you expect to see a grey RS caps instead of blue Hunts in 66 or where they used interchangeably?

Are you referring to filter caps? If so, then they were used concurrently. Remember, Hunts also had caps without the blue sleeve too.

 

[London John]

I would say early '66 (Feb.-Mar.).


I'd say mid '66. The 100w amps were a bit later.

I’d suggest early ‘67 for both.

 

[TAZIN]

I’d suggest early ‘67 for both.

Any insight as to why you're thinking early '67? For the 100w amps I'm thinking April - May '66 for the intro of the square light, and November '66 for the aluminum block ends. The 50w seem a bit earlier probably due to the higher number of units produced. The introduction of the 100w JTM black flag amps with the steel chassis is around March '67.

 

[Trouserpress]

Roughly when did the power light shift from circular to square?

An article in the reputable German magazine, 'Gitarre & Bass': "at the end of 65" -> same what Tazin sais

And they point out that every now and then when boxes with circular lights popped up in 66 or 67 they would use them - just like on my 67 JTM.

 

[London John]

Any insight as to why you're thinking early '67?

My perspective is based solely on unaltered amps I've owned over the years. Granted, the majority of these have been combos and, of those, mostly 18w. I've also owned a lot of JTM45s, a few of which were relatively late production, but pre block-end chassis. The amber round neon lamps were certainly used into early '67, I've had them on both the above models. I'd go as far as to say that I'd look quite suspiciously on an amp (stand fast JTM45/100, which I know nothing about) from Q3 '66 or earlier that didn't have an amber lamp (also stand fast early 18w, which have a different lamp altogether). What I can say for certain is that is was a very long way past the end of '65.

 

[London John]

And they point out that every now and then when boxes with circular lights popped up in 66 or 67 they would use them - just like on my 67 JTM.

I'm not sure what you mean here. Do you mean lamps on chassis? FWIW, I can't remember ever seeing an amber lamp in a '67 amp. Perhaps it's a replacement, which is easy to determine as the holes are different.

 

[Trouserpress]

I'm not sure what you mean here. Do you mean lamps on chassis? FWIW, I can't remember ever seeing an amber lamp in a '67 amp. Perhaps it's a replacement, which is easy to determine as the holes are different.

Yes, the power-on lamp on the chassis. On my amp it is not amber but (not transparent) red. One could argue it may not be original but I think it is.

 

[drewtlh]

I have grey RS signal caps in a 1967 black flag 50W instead of the mustards.

 

[London John]

Yes, the power-on lamp on the chassis. On my amp it is not amber but (not transparent) red. One could argue it may not be original but I think it is.
View attachment 155213

I’ve never seen another like it on any Marshall amp.

 

[TAZIN]

My perspective is based solely on unaltered amps I've owned over the years. Granted, the majority of these have been combos and, of those, mostly 18w. I've also owned a lot of JTM45s, a few of which were relatively late production, but pre block-end chassis. The amber round neon lamps were certainly used into early '67, I've had them on both the above models. I'd go as far as to say that I'd look quite suspiciously on an amp (stand fast JTM45/100, which I know nothing about) from Q3 '66 or earlier that didn't have an amber lamp (also stand fast early 18w, which have a different lamp altogether). What I can say for certain is that is was a very long way past the end of '65.

I don't have any data on the 18w & 20w amps since my focus has always been on the 50w & 100w stuff. Perhaps the 18w amps retained the round lamp longer?

 

[guitarzan2525]

I would like to chime in and ask these additional questions regarding JTM-45's:

1) When did Marshall start using Drake PT in place of RS (my guess is early '65)?

2) When did Marshall start using Drake OT in place of RS (my guess is mid to late '65)?

3) When did Marshall start using Orange peel black tolex in place of the smooth black tolex (my guess is early '65)??

 

[TAZIN]

I would like to chime in and ask these additional questions regarding JTM-45's:

1) When did Marshall start using Drake PT in place of RS (my guess is early '65)?

2) When did Marshall start using Drake OT in place of RS (my guess is mid to late '65)?

3) When did Marshall start using Orange peel black tolex in place of the smooth black tolex (my guess is early '65)??

Those sound-like pretty good guesses to me.

 

[neikeel]

Marshall kept the RS Deluxe OT, 20H choke and RS PT (with selector on top) well into 65. The smooth levant ended when the silver/maroon block logo amps ended late 64.
I’m pretty sure Autumn 65 saw the move to selectors on side Drakes, script logo and more familiar levant. The fat gold strip on front panel can be found on some of these amps before the thinner string we see on most plexi era amps. Also these Drake versions had the smaller gold capped knobs as the Clapton knobs were phased out.
66 saw the later Drake iron with rear panel selectors and the square red lamps.
Never seen an original untouched JTM45 with round red RS logo.

 

[TAZIN]

Marshall kept the RS Deluxe OT, 20H choke and RS PT (with selector on top) well into 65. The smooth levant ended when the silver/maroon block logo amps ended late 64.
I’m pretty sure Autumn 65 saw the move to selectors on side Drakes, script logo and more familiar levant. The fat gold strip on front panel can be found on some of these amps before the thinner string we see on most plexi era amps. Also these Drake versions had the smaller gold capped knobs as the Clapton knobs were phased out.
66 saw the later Drake iron with rear panel selectors and the square red lamps.
Never seen an original untouched JTM45 with round red RS logo.

So, the PT with the selector on top of the end bell which has self-leads and the lead identification text on the coil wrap is an RS? The Drake version PT also has the selector on the end bell but has solder lugs; correct?

 

[guitarzan2525]

So, the PT with the selector on top of the end bell which has self-leads and the lead identification text on the coil wrap is an RS? The Drake version PT also has the selector on the end bell but has solder lugs; correct?

So is this PT Drake or RS??

This amp originally came with Clapton style knobs (which I'm looking for replacements)..

 

[TAZIN]

So is this PT Drake or RS??

This amp originally came with Clapton style knobs (which I'm looking for replacements)..

View attachment 155259View attachment 155260

I would say it's a Drake. Usually the RS PT has RS written on the selector and I believe the circle index/placement for the input voltage taps is different.

 

[TAZIN]

Here's an example of a RS PT. The end bell has a hammerite paint along with and additional fold which caps the laminate stack. The selector doesn't include a 105-115v tap so the layout is indexed like a impedance selector.

 

[London John]

So is this PT Drake or RS??

This amp originally came with Clapton style knobs (which I'm looking for replacements)..

View attachment 155259View attachment 155260

The witches hat tube retainers aren't original to this amp, they would have been the thin braid variety. I have quite a few sets if you need a couple for your power tubes. Rectifiers didn't generally have retainers. I also have a set of original Pekalit knobs. Check your pot shaft diameter to determine which knobs were original to the amp.

 

[guitarzan2525]

The witches hat tube retainers aren't original to this amp, they would have been the thin braid variety. I have quite a few sets if you need a couple for your power tubes. Rectifiers didn't generally have retainers. I also have a set of original Pekalit knobs. Check your pot shaft diameter to determine which knobs were original to the amp.

I do believe the tube hats are original. I got this amp from Julian Marsh in 1990 (on trade) He found this amp (complete stack) in London as it is. The owner used it as a bass amp (from what I remember Julian telling me). The amp came with replacement black AC-30 pointer knobs which I replaced (using knobs from another JTM-45 that I sold). Your Pekalit knobs are original, not the repro Coopers??