Park JTM 45/100

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Re: Park JTM 45/100

Postby cerrem on Wed Mar 09, 2016 11:58 am

mitchell colby wrote: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.


Mitch... These amps do not put out that much power.... figure 85 Watts clean at most, depending on the transconductance of your particular KT66 tubes being strong or weak...
The plate load was way to big for the given circuit....
It appears they raised the voltage to make up for the large plate load in order to achieve more power output...while instead if they simply lowered the plate load they would have achieved higher power output without having to resort to use such high voltages..,,
Keep in mind that I am referring to "CLEAN" output power.... The full distorted output power will be roughly the same regardless of plate load within reason....
Also keep in mind that 3" power transformer has 108 V tap for US .... So putting 120V US mains on that tap will make for some crazy high voltages inside the circuit... So a variac set at 105V would be a safe bet...
When that amp is set-up properly figure 550V to 560V B+ range at idle .... The power supply is weak, so it will have a huge droop when playing....So the tubes are not really operating at those high idle voltages...


C.E.R.R.E.M.
1969 SVT Bass Amps x2 + 4 8x10 cabs...
1964 JTM-45 (GEC KT66)
1965 JTM-45/100 Super-Amp100W(GEC KT66)
1965 JTM-45/100 100W SuperPA (GEC KT66)
1967 Super Lead 100W (Mullard EL34)
1968 Super Bass 100W (Mullard EL34)
Various cabinets
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Re: Park JTM 45/100

Postby mitchell colby on Wed Mar 09, 2016 2:11 pm

Chris,

Thanks for confirming. The OT on this one is 1202-119 for EL34s and measured 1.7k primary. Should the power be around 75 watts? That's what I'm getting clean. B+ is around 560V.
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Re: Park JTM 45/100

Postby cerrem on Wed Mar 09, 2016 6:25 pm

mitchell colby wrote:Chris,

Thanks for confirming. The OT on this one is 1202-119 for EL34s and measured 1.7k primary. Should the power be around 75 watts? That's what I'm getting clean. B+ is around 560V.


Mitch... you have a "Wacky" situation there...
Is it a 3" power?? It has a 108V tap..... So best to use a VARIAC set to 105V .....
Confirm by checking the heater voltage at the transformer....
As for the 75 Watts...... a couple of things could make the power run low...

1. Your output tubes may be really weak ..low gm (transconductance) and or biased way to cold...
2. Check impedance selector wired for the correct -119 color codes.... ORANGE=COMMON, GREEN=16 Ohms, Yellow = 8 Ohms, BLUE=100V
3. Make sure the signal coming out of the Phase Inverter is not clipping too soon ...ie if it clips simultaneously with the output of the amp, not good...
4. A filter cap may not be bypassing the audio efficiently...
5. Get rid of those resistors on the output tube CATHODES ...they can make problems...
I am having Deja Vu, did you buy this from a guy in LA ??

CERREM
1969 SVT Bass Amps x2 + 4 8x10 cabs...
1964 JTM-45 (GEC KT66)
1965 JTM-45/100 Super-Amp100W(GEC KT66)
1965 JTM-45/100 100W SuperPA (GEC KT66)
1967 Super Lead 100W (Mullard EL34)
1968 Super Bass 100W (Mullard EL34)
Various cabinets
100% EVH free
*****SEMPER FI*****
cerrem
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Re: Park JTM 45/100

Postby mitchell colby on Thu Mar 10, 2016 3:03 am

Mystery solved!!!!!!!!!!!!!!!!!!

(I got this amp about three years ago. It didn't sound great but I figured I would get it up and running properly some day. Also it would be cool to have as a Park reference amp along with my other vintage Park amps)

Here is the story..........I what I assume to be an effort to lower the voltages someone disconnected the common and connected the 240V tap in it's place! So for the amp to reach the proper voltages it needed to see approx. 130V at the primary. I reconnected the common and 240V tap to the correct places and the amp works and sounds like it should. Maxes out at 110 watts clean and sounds stellar!
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Re: Park JTM 45/100

Postby buttshaker on Fri Mar 11, 2016 1:22 pm

Great news here Mitch !!

I like the JTM's because they are not aggressive, giving a full round 3D halo of sound around the stage, without the very directive and piercing highs...but they are very loud indeed !

I received the original barrel knobs from LD. I'm so glad. I will update pictures soon.
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Re: Park JTM 45/100

Postby mitchell colby on Fri Mar 11, 2016 1:35 pm

They are great amps indeed! You found something very special.

Sorry for hijacking you post!
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Re: Park JTM 45/100

Postby buttshaker on Fri Mar 11, 2016 2:18 pm

Oh no, you're very welcome, and i feel honoured having you here on this thread.
I know you since my teenage years, since i read "AMPS!" by Ritchie Flieger, and than Pittman's book...etc. It's been a while.

At first, I was glad and excited I found a Park plexi amp, but really didn't know what i had on hand. You know...I looked at it maybe 5 seconds, no more. No eye on the back, no nothing. I then put it against the wall, and recovered it with piles of various garbage stuff "I may be interested in". And then everybody in the flea / pawn shop was a suspect..the old lady with her bag...I'm sure she knows what a Park is...this guy...pretty sure he plays guitar...this one...too clean to be trusted...etc etc. You get really crazy / paranoid.

And so I was pretty amazed finding it is a jtm 45/100, and i didn't know park produced that many (well, in a sense of course). I'm very glad I found other owners. This is the collaborative Park 45/100 thread ! :cheers:
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Re: Park JTM 45/100

Postby buttshaker on Mon Mar 14, 2016 4:15 pm

An updated pic with complete knobs set (thanks to LD!) . They are engaged, not screwed and not aligned here. Have to clean them up a bit to have an even look.

Image

Image
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Re: Park JTM 45/100

Postby pckpat on Tue Mar 15, 2016 12:03 am

Awesome score buttshaker...and yes, I can appreciate that feeling you describe when you finally come across something incredibly rare in a most unlikely spot. :lol: Although for me it wasn't quite as impressive as a mid-sixties Park 45/100. :shock: So what city was this vintage r&r beauty hiding out in?
"Who does not work,is heavy to the earth" (Albanian proverb)
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Re: Park JTM 45/100

Postby buttshaker on Tue Mar 15, 2016 9:25 am

A kinda small 20.000-people town in the middle of nowhere, centre-east of France, no that far from my hometown of Lyon, but not that close neither.
Nothing special there, no music festival, not known for its r&r scene, nothing.

I really don't know how the hell did a mid 60's Plexi-Park, built for obscure northern english stores, get there.
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Re: Park JTM 45/100

Postby mitchell colby on Thu Mar 17, 2016 1:37 pm

All you need are some nuts for the input jacks.........!
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Re: Park JTM 45/100

Postby buttshaker on Thu Mar 17, 2016 1:56 pm

mitchell colby wrote:All you need are some nuts for the input jacks.........!


They are on their way. :wink: Some RIFA grey 33uf's are too, shouldn't be long. Then I'll be able to work on it. Some of the yellow replacement power caps have broken legs right now. I'm waiting for the full set of parts to slowly fire it up !
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Re: Park JTM 45/100

Postby buttshaker on Sun Mar 20, 2016 9:11 pm

So, I received a few things, and began the work.

Some power caps were out of order, some broken legs..

Image

I replaced and cleaned the area a bit.

Image
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Re: Park JTM 45/100

Postby buttshaker on Sun Mar 20, 2016 9:14 pm

Slowly pumpin' the juice through the Variac :

Image

It works 8)

Image

Power supply is good. Correct voltages everywhere.
I worked on switches & nuts too. More to come !
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Re: Park JTM 45/100

Postby JeffH on Sun Mar 27, 2016 12:32 pm

Love this thread - it's like amp archaeology!
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