Park JTM 45/100

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Re: Park JTM 45/100

Postby mitchell colby on Thu Mar 03, 2016 6:57 am

Here's mine. I'm sure paid a lot more than you did!

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Re: Park JTM 45/100

Postby LD50 on Thu Mar 03, 2016 10:39 am

That is really interesting Mithc as yours has the cream chickenhead knobs, early 45/100 type cap board and bent alloy chassis, ie 66 specs yet has a 1202-119 OT to run EL34s. I thought the white chicken heads were earlier than the barrel with white pointer ones) Mitch - do you know if your OT is original. My slightly later (early Spring 45/100 has same OT but blockend chassis and 8 cap board and dual rectifers.

buttshaker do you know for sure that yours is the 1202-84 OT for KT66s?
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Re: Park JTM 45/100

Postby buttshaker on Thu Mar 03, 2016 10:52 am

"For sure" not yet, but everything in that amp is strictly the same as my others Marshall 45/100 running KT66s.
I will have to calculate the OT primary impedance. Also, no numbers on trannies - I've seen that on a few 45/100 too.

Mitch, what is your serial # ? Are your banana knobs original? Now I'm confused :-) Mine for sure has had the barrels, as I still have two on it.
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Re: Park JTM 45/100

Postby mitchell colby on Thu Mar 03, 2016 11:52 am

I'm not sure about anything on this amp. I bought it a few years ago on eBay as you see it. In fact those are the pictures the seller took. I would imagine that the knobs are original. It wouldn't have been easy to find six matching old ones. I'll check the serial number later today.
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Re: Park JTM 45/100

Postby mitchell colby on Thu Mar 03, 2016 12:14 pm

The OT and knobs in my amp could be original even though It seems that people believe that Marshall could have used different transformers (and why not knobs) than what we expect for certain series amps. It might have to do with what they had in stock at the time. I found this on a forum:

"and have come to the conclusion that at times Marshall was just putting trannies based on what they had on hand. A good example is he has removed factory installed 10,000 series PTs from amps as late as 69. That's 2 years past what is documented on paper, or what everyone takes as gospel. I take from that you could pretty much expect a odd combination to occur at any time. A 2.2k OT could easily end up in a stock 12000 series, as could a 10,000 series Drake PT."
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Re: Park JTM 45/100

Postby buttshaker on Thu Mar 03, 2016 1:00 pm

You're right Mitch.
Now, i knew Marshall standardisation and classification in the 60's era was a mess; but it seems on Park it's a nightmare :mrgreen:
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Re: Park JTM 45/100

Postby buttshaker on Thu Mar 03, 2016 5:22 pm

All right, I took the Variac, and did my maths.
I have roughly 3.8K impedance on my OT primaries. This is the 4 x kt66 OT.
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Re: Park JTM 45/100

Postby buttshaker on Thu Mar 03, 2016 8:21 pm

And here are the trannies in close-up.

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Re: Park JTM 45/100

Postby Tread on Fri Mar 04, 2016 12:54 am

Wow! that is really nice .
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Re: Park JTM 45/100

Postby mitchell colby on Fri Mar 04, 2016 12:35 pm

3.8k would be for four KT66s.

I measured the one in mine and its 1.7k, EL34s

The serial number is 214.
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Re: Park JTM 45/100

Postby buttshaker on Fri Mar 04, 2016 1:12 pm

Ok thanks Mitch.

So. If yours is #214 and mine #117, we can at least guess mine is earlier. And the important info here is, you can't trust cosmetic details to date a Park...Park seems to have used at the same time barrel knobs and banana white knobs. Same for jacks and jack nuts. Mine are white and fully original. A lot of early plexis have the standard black / metal jacks, I see white jacks nuts on later amps also, etc.

You know the song "You can't judge a book by looking at the cover" ? Here would be "You can't judge a Park by looking at the cover" :mrgreen:

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Re: Park JTM 45/100

Postby LD50 on Sat Mar 05, 2016 9:06 am

mitchell colby wrote:The OT and knobs in my amp could be original even though It seems that people believe that Marshall could have used different transformers (and why not knobs) than what we expect for certain series amps. It might have to do with what they had in stock at the time.


I am sure there was a significant amount of pragmatism to use up what was around. We know when certain transformers only became available after a certain period (the 1202-119 was only available after February 1967) but we see odd things like the RS 20H choke appearing mid 68 or the weird block end alloy chassis JMPs that were more like JTM45s (except for 50w trannies).

I am more intrigued by the repair work under the OT of Mitch's on why is otherwise a clean amp, sure quite a few caps etc replaced but all part of the story.

ps buttshaker the knobs are in the post as of this am.
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Re: Park JTM 45/100

Postby Ned B on Sun Mar 06, 2016 5:34 am

I wonder if Mitch's amp isn't from early '67 even with the folded chassis. The -117 OT came out February of that year.
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Re: Park JTM 45/100

Postby mitchell colby on Sun Mar 06, 2016 1:46 pm

I am more intrigued by the repair work under the OT of Mitch's on why is otherwise a clean amp, sure quite a few caps etc replaced but all part of the story.


The chassis is not in great shape. There are big cracks in the side bends (it needed end blocks!). The repair work was done because of the failing/bending chassis under the OT
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Re: Park JTM 45/100

Postby mitchell colby on Tue Mar 08, 2016 10:59 pm

How much power should these amps put out? This ones seems light and maximum power is achieved with impedance different than the the marked settings.
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