NAD - 1965 JTM 45

[Nick1234]

Are those KT66 though, or rebadged imports? These look like Soviet 6P3S for example.

I propose we start referring to GECs as the "worst KT66s ever made". Might help keep the prices reasonable!

These are NOS KT66s. I got a matched quad recently, in their original boxes.

 

[playloud]

These are NOS KT66s. I got a matched quad recently, in their original boxes.

Sorry, I didn't mean you! Was asking @neikeel about those "Bentley" branded 70s valves. Apologies for the confusion

 

[Nick1234]

No problem - sorry for not reading all the replies!

 

[Seanxk]

When you had the monopoly, indeed they were the worst also

 

[Whatwhatringrang]

Yeah interested in those Bentley ones as I dont think I have seen these. Probably junk also lol.

Yeah ceg kt66 the worst tubes on the planet.
https://ibb.co/mcy4VQY

Seriously those tube will last many years in there. Then 20 years down the will still sell online somewhere lol.

 

[Derrick111]

Claptons famous crossroads stripped amp was 1178, I previously owned 1185 and I’m aware Joe Bonamassa recently purchased one although I can’t get the serial of it. Then this one being 1213 fits in with that. All of them being PA spec. Don’t know if anyone else has known serials of such amps from this period?

I couldn't see the circuit well enough on my phone to tell... Are we sure this one and the others being referred to are really PA spec amps, or do the panels just say "PA"? I have seen some Park and other plexis that were lead spec that had PA on the crude back panel yet seemed all factory original. These all appear to have 4 inputs as opposed to the traditional PA amps that had 8. Were there any actual PA 4 input plexis?

I propose we start referring to GECs as the "worst KT66s ever made". Might help keep the prices reasonable!

About 20 years too late 😉

 

[guitarzan2525]

Y

These are NOS KT66s. I got a matched quad recently, in their original boxes.

You must have paid a nickel for those!

 

[neikeel]

This one is PA spec.
No mixer bypass on the 270k channel 1 resistor, no cap on vol 1 pot.

 

[Derrick111]

This one is PA spec.
No mixer bypass on the 270k channel 1 resistor, no cap on vol 1 pot.

Most lead model plexis by now have lost the bright cap on the vol 1 pot, but good catch on the 556pf mixer bypass cap in the 270k resistor! Funny that the only real difference between most pre-1968 PA model and lead model plexis is basically a 556pf cap. I always thought that all 50w and 100w PA models had 8 inputs but not true!

 

[StuC]

PA spec JTM45s also had two output jacks; lead and bass only one as standard.

 

[Derrick111]

S

PA spec JTM45s also had two output jacks; lead and bass only one as standard.

Interesting... are you sure about that? I have one with and one without, and they are both factory lead amps. Both are from 1966.

 

[neikeel]

Stu is right the PA amps were (AFAIK) always two output jacks. The lead and Bass amps frrom 63-65 (at least) only had one output jack. When the transition two output jacks occurred I suspect late 66.

 

[Derrick111]

Stu is right the PA amps were (AFAIK) always two output jacks. The lead and Bass amps frrom 63-65 (at least) only had one output jack. When the transition two output jacks occurred I suspect late 66.

Wow, perhaps it was a few months earlier than originally thought... My block end chassis '66 has one output, and the other '66 which presumably is earlier because it doesn't have block ends does have two outputs. The 2nd jack doesn't seem to have been added because the "speaker" silkscreen is above and "centered" between the two jacks, and the 556pf cap is definitely factory. Ah Marshall... you hold so many mysteries!

 

[TAZIN]

If memory severs me correctly there's also a label difference on the rear panel for Lead & Bass amps compared to PA's....The PA's state "SPEAKERS" while the others have "SPEAKER".

 

[Nick1234]

On this note, (and I wouldn’t modify to lead or bass spec, regardless), what are the tonal differences you would expect from the difference in hardware between this PA and a lead or bass spec from the same era? If A-B blind tested, would it be easy to tell the difference? And does anyone know if Claptons PA JTM45 was modified to lead or bass spec?

 

[Nick1234]

Y

You must have paid a nickel for those!

I paid a few nickels. To rub salt into the wounds, they had their original price stickers on them: 50 South African Rands. Currently 2GBP.

 

[Derrick111]

If memory severs me correctly there's also a label difference on the rear panel for Lead & Bass amps compared to PA's....The PA's state "SPEAKERS" while the others have "SPEAKER".

Unfortunately, I don't think it is possible to identify in that manner. Below are two examples of 1966 JTM-45s with back panels labeled "Speakers" but having only a single output.

 

[neikeel]

There will have been a transition to using up old panels (they were batch made - hence the variability in serials/specs so you will see a typical batch spec and some oddities). Remember in 65 they went from all selectors on the Drake transformers (post RS supply) to both selectors on the back with transition ones just having the voltage selector until the OTs with selectors were used up. Note that these do not have the type (BASS. LEAD. PA) silkscreened and will have had the Dymo stickers instead.

 

[AML]

Stu is right the PA amps were (AFAIK) always two output jacks. The lead and Bass amps frrom 63-65 (at least) only had one output jack. When the transition two output jacks occurred I suspect late 66.

My '67 PA (4 input) has two output jacks.



My guess is that this was a slip-stream change once bands came back to the Marshall shop and said that they wanted a PA speaker for each side of the stage. A related Q would be: when did Marshall start to make the pairs of vertical column speakers? Those obviously necessitated two speaker outputs.

 

[Derrick111]

My '67 PA (4 input) has two output jacks.

View attachment 130997

My guess is that this was a slip-stream change once bands came back to the Marshall shop and said that they wanted a PA speaker for each side of the stage. A related Q would be: when did Marshall start to make the pairs of vertical column speakers? Those obviously necessitated two speaker outputs.

Wow, window type serial number on a cream back panel... either I never paid much attention to this detail or this is rather rare and I don't recall being aware of it's existence. Pretty cool either way.