Authentic JTM 45/100 build diary. Clips added.

Detailed assembly steps separated into threads.

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Authentic JTM 45/100 build diary. Clips added.

Post by VintageCharlie » Sun Jun 06, 2010 8:42 am

Dear forum members,

i received my metro package recently and i've also hunted down almost all of the NOS parts for the build (the hunt was obsessive, with highs and lows and lasted 3-4 months). I thought i'd go over my stuff to see if i haven't forgotten something, so i put the parts on the boards to see if everything's there. I didn't want to miss the opportunity to show off and share some close-up vintage-parts-porn with you here. So this is sort of "Part I" of the build - still looking for some parts and checking if everything else is there.

As you see i still don't have 2x 8uF or 10uF @ 150v Hunts electrolytics and the 250uF Wima has one very short lead that has to be extended (so i hope to find one with better leads). Also the Erie 32+32uF is not "vintage correct" and from a tad later era - maybe i will find a good substitute for this one too. The 68k's are the only ones i couldn't find NOS - so these are used and looks like they've been pulled of a JTM-45 - for what ever reason ( i still don't know if they are any good though). And of course i'm short of 7x 32uF arced RS logo electrolytics @ 450v. Maybe i'll hunt these and add one by one during the next year(s) when the amp is built.
Almost everything else is there. BrianH's boards are fantastic, but i still hope to get some original RS turret board material somewhere for this build, as almost every single part is era correct (including even date codes for the most part). So please let me know if you have some of it or know where i might get some. (as i've stated earlier - i have loads of nos Marshall parts to trade for the RS boards - lot's of them can be seen here and there is more - i'll make pics of the rest sometime next week). Almost anything can be added later on, but it's, of course, different with the turret board itself :roll: - so this is what keeps me back from starting the build right away.
Ah, and the last thing i'm still hoping to find are the era correct, black, not brown, colored impedance and voltage selectors - that would be the only parts really indicating a non-vintage 45/100. I think i even got the switches right, including the ring, that looks pretty much spot on to me.

I haven't decided yet if i want to go with Dickinson specs or not and i'm open to suggestions either way. I have all the needed parts for that and i think, if i dig deep in my parts box, i should find also EXACTLY the same differing parts - the iskras, except 470r and 100k, i have the 500pF RS mica (though the leads are crappy short), etc.

I also haven't decided which parts to choose at the positions where i have put some parts close to the board - should i go with the corresponding pihers instead of carbon comps? If i go with carbon comps, shall i choose the standard ones or the mil spec ones (i suppose they mught have slightly different characteristics?)? Also i've heard that the wimas actually sound crappy - so maybe go with the BC cap instead. And when we're taling BC caps - maybe better changing them alltogether to Rifa?

I'm very interested in your opinions and suggestions guys, so please let me know if you have anything to say about these questions.

I haven't ordered the KT66's yet, but as NOS is out of question because of $ right now, i think i will order TAD KT66's - i've read here on the forum, mostly in Re's posts, that these are the best from the chinese and russian ones - even better than Valve Art, which actually makes these, but afaik they are selected and tested to better tolerances or something.

Ok, cut to the chase, here are the pics:
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02.jpg
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03.jpg
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04.jpg
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05.jpg
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DSC_0142.jpg
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And here's a link to the whole album with more and higher res pics:
http://s802.photobucket.com/albums/yy30 ... S%20Parts/" onclick="window.open(this.href);return false;

Kind regards,

VintageCharlie
Last edited by VintageCharlie on Sat Nov 26, 2011 6:08 am, edited 3 times in total.

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Re: Authentic JTM 45/100 build diary

Post by Roe » Sun Jun 06, 2010 8:49 am

its a good idea to use new caps for the bias supply unless you want to risk output tubes
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Re: Authentic JTM 45/100 build diary

Post by VintageCharlie » Sun Jun 06, 2010 8:55 am

Thanks for the advice! - i've read that on many occasions and that probably has it's reasons - so i suppose i might ditch the idea of the 10uF Hunts. But as far as modern caps go - would you recommend BC or Rifas, or would there be no considerable difference?

Thanks!

VintageCharlie

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Re: Authentic JTM 45/100 build diary

Post by Vegard » Sun Jun 06, 2010 10:04 am

Nice! Lots of NOS goodies you've got there! :)
When do you start the build?
Metroamp builds : 68` 50w (x2), 69` 100w, 68` 100w 12xxx (x3), JTM45/100, JTM50(x2), 2203

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Re: Authentic JTM 45/100 build diary

Post by VintageCharlie » Sun Jun 06, 2010 10:52 am

The build could start right away, but what's holding me back is that i still hope to find the original RS turret board material, as you can't just exchange the board later on like you can do with all the other parts.

Yes, there's really a lot of stuff, even more stashed away in my holy NOS-parts-shoe-box :) - it took quite some time and effort, but luckily it was worth it as i got everything together that i hoped to get and even more. It's a silly feeling when you're starting to take the plunge for nos parts, as you never know how much you'll be able to find (and hence, if it's worth the effort at all). I think i had lots of luck too, but the "luck" had to do a great deal with the friendly and helpful people on the forum and many others - most of them i mentioned in my post "double checking parts for 45/100 build" in the 45/100 section. The parts are from about 10 or more countries, including Japan :D

I won't build it myself as my soldering skills top out at making some cold looking solder joints in my guitars and i'd also probably electrocute myself out of stupidity at some point :D - i'll take it to a local pro. But, if he won't mind, i'll try to document it as good as it goes with a proper SLR and a tripod.

Regards,

VintageCharlie

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Re: Authentic JTM 45/100 build diary

Post by Roe » Mon Jun 07, 2010 4:27 am

VintageCharlie wrote:Thanks for the advice! - i've read that on many occasions and that probably has it's reasons - so i suppose i might ditch the idea of the 10uF Hunts. But as far as modern caps go - would you recommend BC or Rifas, or would there be no considerable difference?

Thanks!

VintageCharlie
I dont think it will make a considerable difference. these caps should stabilize the bias voltage, thats about it
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Re: Authentic JTM 45/100 build diary

Post by neikeel » Mon Jun 21, 2010 5:59 am

Do you want a 8k2 Iskra or Piher 2 or 5 watt for the first dropper resistor.

Marshall used carbon comps there in the early amps.

I would go Dickinson spec for your amp :wink:
Neil

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Re: Authentic JTM 45/100 build diary

Post by VintageCharlie » Mon Jun 21, 2010 6:23 am

Thanks Neil!

I have piher in 8.2k, but i'm not sure if it's 2w, i think rather 1w - looks quite a bit smaller than the beefy AB 2w cc's.

"First drop resistor" is the one near the big filter cap, right? Is this considered part of the power supply line or are the big resistors near the bias section the ones which are in the power supply? Roe suggested against CC's in the power supply. Almost all Marshalls from that era have CC's there and it doesn't seem like they've been changed in the amps i've seen (so i suppose there have not been that many issues because of cc's?) - hence i'd like to go with these, unless there's really a big possibility of issues due to this choice. Which one would you suggest? In regard to this build - as you know i aim at the highest authenticity level possible, but i've seen pihers appear in the same era in JTM-45's for example.

At the moment i do levitate towards the Hendrix (Dickinson) spec amp. Afaik it gives out more bass and lower mids and is like a halfsie between a 45/100 and a Super Lead, in regard to the board components, right? What else differs in tone between standard and Dickinson spec?

The only thing that makes me doubtful about that Dickinson amp is that there's afaik actually no real proof that it was modded while Hendrix really used it - it might have happened afterwards, which i actually think is quite possible - what do you guys think about this?

Regards,

VintageCharlie

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Re: Authentic JTM 45/100 build diary

Post by neikeel » Mon Jun 21, 2010 6:44 am

VintageCharlie wrote: I have piher in 8.2k, but i'm not sure if it's 2w
You need 2w. In the pic below I replaced mine like for like but have since added a 2w Piher for safety.
VintageCharlie wrote: are the big resistors near the bias section the ones which are in the power supply? Roe suggested against CC's in the power supply.
Yes the first dropper is the first one from the filter caps. It sees the most action and they do get hot and may fail. A 2w is the minimum there. ccs are not flame proof like the modern MO which is what I would use in an amp for the road.
Although Marshall seemed to use 1w (smaller than you have there) as it is quite tight to fit the 10k under the filter cap running along the board, mid board and some people hang it over the side of the board. Both my plexis ('67 and '68) had them on the board tucked under the can.

http://s76.photobucket.com/albums/j2/ne ... Superlead/
http://s76.photobucket.com/albums/j2/ne ... c09008.jpg" onclick="window.open(this.href);return false;
http://s76.photobucket.com/albums/j2/ne ... Superlead/
VintageCharlie wrote: Almost all Marshalls from that era have CC's there and it doesn't seem like they've been changed in the amps i've seen (so i suppose there have not been that many issues because of cc's?) - hence i'd like to go with these, unless there's really a big possibility of issues due to this choice. Which one would you suggest? In regard to this build - as you know i aim at the highest authenticity level possible, but i've seen pihers appear in the same era in JTM-45's for example.
The ccs do fail, they drift and can give you wind/whistling noise whebn they do. Depends how much action the amp is going to see.
VintageCharlie wrote: At the moment i do levitate towards the Hendrix (Dickinson) spec amp. Afaik it gives out more bass and lower mids and is like a halfsie between a 45/100 and a Super Lead, in regard to the board components, right? What else differs in tone between standard and Dickinson spec? The only thing that makes me doubtful about that Dickinson amp is that there's afaik actually no real proof that it was modded while Hendrix really used it - it might have happened afterwards, which i actually think is quite possible - what do you guys think about this?
The tone stack will give more upper mid bite - I do not find it hard to believe JH used that set up. The additional node in the filtering/droppers will lower the V1 voltages and add a little more gain to the front end.
To have authentic early JTM45/100 you would be using a single 16uF can on the preamp board, just like a twin pot 45, ie not the dual 32uF you have in the pics :wink:
Neil

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Re: Authentic JTM 45/100 build diary

Post by VintageCharlie » Mon Jun 21, 2010 1:25 pm

Thanks a lot for the info, Neil!

I'll dig in my stash and will try to find out if they are 1w or 2w pihers i have. And most probably go with these then. But what i'm wondering about is that George uses cc's in his plexi replicas, and it even looks like 1w.

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Re: Authentic JTM 45/100 build diary

Post by Roe » Mon Jun 21, 2010 3:10 pm

does george use 1w CCs? :shock:
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Re: Authentic JTM 45/100 build diary

Post by VintageCharlie » Mon Jun 21, 2010 6:58 pm

If my eye isn't lying, then looks like 1w cc's to me. Unless they're metal oxides or other in a 1w cc disguise. 2w cc's are quite a bit bulkier than .022uF mustards. Afaik Goerge uses Allen Bradleys, but might be the bigger ones are some modern cc's that ar smaller than AB's? But they do look like AB's to me.
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Re: Authentic JTM 45/100 build diary

Post by Roe » Tue Jun 22, 2010 3:04 am

yes, indeed. thats a 1w AB CC. the amps I've seen pics of have all used metal oxide or flameproof resistors
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Re: Authentic JTM 45/100 build diary

Post by VintageCharlie » Tue Jun 22, 2010 4:49 am

Well, Goerge probably has a few tricks up his sleeve why he can pull it of with 1w cc's without issues. 2w's are pretty easy available still and not much more expensive than 1w's, so i suppose George does it in a way that there's no need to go up to 2w? Or maybe he has realized that it's not the cause of issues associated with these resistors? George (in case you can find a moment to chime in), could you maybe enlighten us about the cc thing in the power supply?

Best regards,

VIntageCharlie

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Re: Authentic JTM 45/100 build diary

Post by VintageCharlie » Tue Jun 22, 2010 6:07 am

And it looks like George is in good company, as all Germino amps on the site have also 1w cc's - probably AB. Afaik George and Greg are two of the most or maybe THE most respected plexi style amp builders around, so i suppose they have a good reason for trusting the cc's. But i suppose they also measure and test them well before they are being used.

Oh, and when Larry improved the JTM-45 he was sending to Pipper for testing, one of the first things he did was going with cc's, also in these spots that put a big stress on the resistors. It may have contributed to the improvement in tone, as Pipper said the amp sounded really close to the original after Larry made the mods (a lot of other components were changed along with the resistors though).

Could the reduced voltage of these amps be a reason why 1w cc's are ok? The originals were at about 560v or even more, and if i'm not mistaken, George and Greg build their amps with voltages slightly under 500v (which is what will be also the case with my build - 490v tap on the Marstran PT).

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