Geez!!!!
JTM50 Black Flag build, finally under way.
- Thread starter ivan H
- Start date
Geez!!!!
OP
ivan H
Ambassador of Tubes & Grooves
OMG is right. First I've heard of this model, thanks for posting Mr Plexi. Beautiful amp, I can only imagine that it sounds glorious.Marshall did make a 4 x 10" combo called a model # 1961 built in 1964 through 1965
The Elusive, Vintage, Marshall Super Tremolo
***CALL FOR PRICE*** Whenever a discussion turns to how the circuit for the first JTM45 was lifted nearly point for point from that of Fender’s 5F6-A Bassman combo, it seems there’s always a caveat about how it ended up sounding slightly different as a head through a closed-back 4x12" cab. Oh...www.truetonemusic.com
A micro would be a great project, I've been thinking of doing one for a while but haven't got around to. I've got suitable iron sitting on the shelf. I'm imagining you mean this Robrobinette version
Would be a great home use amp, or could be mic'd up for gigging (or re-amp the output). Sylvania's are excellent tubes, I've got three Sylvania 12AX7's in another amp & have used many, including 6CA7's in the past. Great US made tubes & the pre amp tubes can still be had NOS at good prices. Cheers
I'd love to downsize a 4x10 to where the speakers almost touch in the middle
ChasFred
Ambassador of Smooth Operations
I am not sure if that would be sonicly beneficial. There are formula to calculate cabinet size vs speaker configuration.
Fantastic work Ivan.
Few amps are as tidy inside.
I agree with Drumoid about that wire lacing. It's mind blowing detail.
You sir, have a true gift. Old school craftsmanship with modern practicality.
Few amps are as tidy inside.
I agree with Drumoid about that wire lacing. It's mind blowing detail.
You sir, have a true gift. Old school craftsmanship with modern practicality.
Oh, I am sure there is, so I am thinking only of how to get it in a S197 Mustang Trunk....
Don't worry you can follow along with your hot glue gun and Fisher Price amp kit.
I think I can build an E-Z Bake Oven now....
jtcnj
Ambassador of the Crossroad
Exactamundo!
syscokid
Ambassador of War & Peace
I'm not sure, when you say "scratch chassis", if you mean a blank and undrilled chassis or repurpose an old chassis into a new circuit?
If you go with a blank chassis: Due to my total lack of experience with drilling out a blank chassis, I'm having some major ups and downs with precision and layout of just about everything on the chassis of my current build. A predrilled chassis is obviously much easier to deal with if you can find one that'll jive with the circuit and components that you want to use. Good luck with this...
Dave Sloven
Ambassador of DOOM!
Very clean and awesome build!
Also IEC connectors are the shizz; Americans wish that they would be forced to use them so that they would be more available instead of those stupid wired-in AC power cables.
Also IEC connectors are the shizz; Americans wish that they would be forced to use them so that they would be more available instead of those stupid wired-in AC power cables.
syscokid
Ambassador of War & Peace
I also prefer IEC connectors for the AC, but with the old school hardwired AC cable method, it is so much easier and less time consuming to drill out the chassis hole needed for the old method and slightly easier in connecting the AC cable leads. However, if I had a fancy shmancy computerized surgical cutting machine, then an IEC style is a no-brainer!
ChasFred
Ambassador of Smooth Operations
I did the IEC on a previous amp build. I had to use a Dremel to do it and it was a steel chassis. It would be a lot easier with your aluminium chassis, if you had a Dremel.
OP
ivan H
Ambassador of Tubes & Grooves
That is exactly how I did this one, a Dremel cut-off wheel. I cut it slightly undersized, then filed it to size. By doing the two longer cuts first, the cut-off wheel is then worn down a little & so will do the shorter two cuts without over cutting.
Chassis punches are available for both valve socket cutouts & IEC socket cutouts. You could use the manual "bolt & nut" type with an aluminium chassis, but would need hydraulic for steel.
So, the ARS 16uf/32uf PI filter cap still hasn't arrived yet (well over 3 weeks, hope it isn't lost in the mail), so I've decided that if it doesn't arrive today I'll use the one that's in it at present (32uf/32uf) & condition/form the filters, then install tubes, bias power tubes etc on Saturday. I'll post a couple of pics. Cheers
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syscokid
Ambassador of War & Peace
I have a sort-of-Dremel. Didn't even think of using it as a cut-off tool...
ChasFred
Ambassador of Smooth Operations
I have seen them before but never realized who made them.
OP
ivan H
Ambassador of Tubes & Grooves
Well, the 16uf PI filter cap still has not arrived, so tomorrow I'll solder the wiring to the 32uf that is in there & proceed, then change it out if & when the 16uf does turn up.
Just a quick point of attention, normally these had a single 32uf (or 40uf) main cap mounted above the chassis between the rectifier tube & power tubes, with a dual cap can 32uf (screen) 16uf (PI) mounted internally on the sidewall.
As the ARS caps only come as dual cap cans, I have a 32uf/32uf in the main filter position. With the "Larry's Grounding" system that I've used it makes more sense to ground the screen filter along with the main filter, rather than with the PI filter, so my screens are wired to the "above chassis" main dual capacitor.
I'll get the filters conditioned then hopefully tubes up & running by tomorrow night. Cheers
Just a quick point of attention, normally these had a single 32uf (or 40uf) main cap mounted above the chassis between the rectifier tube & power tubes, with a dual cap can 32uf (screen) 16uf (PI) mounted internally on the sidewall.
As the ARS caps only come as dual cap cans, I have a 32uf/32uf in the main filter position. With the "Larry's Grounding" system that I've used it makes more sense to ground the screen filter along with the main filter, rather than with the PI filter, so my screens are wired to the "above chassis" main dual capacitor.
I'll get the filters conditioned then hopefully tubes up & running by tomorrow night. Cheers
syscokid
Ambassador of War & Peace
Did you already look into ordering any ARS caps directly through ARS? They're actually located in Van Nuys, California, which is just north of Los Angeles.
Also, do you know if ARS actually makes their own caps? They look identical to the F&Ts or Sprague Atoms.
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OP
ivan H
Ambassador of Tubes & Grooves
No, I haven't, but will, thanks for the heads-up on their location. I've been getting them through Valvestorm in the US & Watford Valves in the UK (which is where the 32uf/16uf is coming from).
I don't know if ARS manufacture the electrolytic capacitors themselves or have them made for them (think the later), but do know that they introduced them in 1990 as a replica of the old UK made LCR capacitors that stopped production around that time. They have been used by Marshall (supposed to replicate the l "feel" of the LCR's that Marshall had previously used). They differ from the F&T's dimensionally, the ARS are 60mm in length whereas the F&T's are 50mm in length.
If anyone has any more info on these (ARS capacitors) I'd be interested in hearing. Cheers
Edit: Using a 32uf in place of a 16uf for the PI node will only be noticeable when pushing the amp. The supply to the PI will be "stiffer" & not "sag" as much, so it will slightly affect the"feel" of the amp under overdrive conditions. Cheers
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syscokid
Ambassador of War & Peace
Ha ha… I forgot the size difference between the ARS and F&T. Here's a couple pics of my old JCM800 showing just that:
The Mains cap, the shorter one, is the F&T. The F&T has been there since 2010. I installed the two ARS caps about two years ago. I'm also a firm believer in forming new caps. Even old filter caps that have not been used in a while can be reformed as long as they ain't leaking.
OP
ivan H
Ambassador of Tubes & Grooves
Yes, if the amp has not been powered up in more than a few months it pays to reform the filters.
I'm using a new production (JJ) GZ34 rather than the Mullard for the first power up & conditioning the filters. As such I have put a UF5408 diode in series with (before) the 100k current limiting resistor, just in case the JJ rectifier tube fails. Rather than break the HT rail to insert them I simply jumpered across the standby switch, which is left in the standby position. On power up the meter rose to show a 216VDC drop across the resistor (when the GZ34 started conducting), quickly dropping to around 100V & continued falling. After a little over ten minutes it showed a drop of 40.5V
In the time it has taken to type this it has dropped to 26.4V
so shouldn't take long to get below a 5V drop. Then I'll put the NOS Mullard tubes in (including GZ34) & get the power tubes biased up. I usually bias to around 65% of maximum dissipation, rather than 70%. Probably have to wait until tomorrow to play through it. Cheers