Building a JTM45/100 clone (#7026 type) - There's sound and some Q's!

[BlueX]

Started to build a JTM45/100 clone, based on the Marstran schematics by BKW, 5/12/07 (the so called "Hendrix/Dickinson" amp, Marshall #7026). This wont be a faithful replica. Instead, I will make some up-dates to the circuit (safety, reliability). The exterior I plan to keep close to original, with modern parts.
- Marstran trafos (still waiting for delivery, x-mas gift in best case, but probably next year)
- MetroAmp chassis from Valvestorm
- Boards, turrets, sockets, selectors, pots, etc. from Modulus
- Standard parts from Mouser and Digi-Key
- Still haven't ordered valves. Matched TAD quad seems reasonable, together with Psvane ECC83.

Got most part and dry-fitted what I've got. Octal sockets don't fit the chassis. Need to get a 30 mm step-drill to make the holes about 1 mm bigger. There will be some more work to layout bias sampling points, fit the IEC socket, etc. Some pictures below.




Prelude

Help me specify a JTM45/100 clone

I would like some help to specify a JTM45/100 clone, “Hendrix” circuit. Been searching Internet, and I see some of the frequent usernames here coming up, but some info is no longer available and there seems to be changes in availability for e.g. trafos from different suppliers. Therefore, I’m...

www.marshallforum.com

Coda
Some related/relevant links:
https://www.marshallforum.com/threads/my-45-100-jh-clone.101156/
https://www.marshallforum.com/threads/not-another-jtm-45-100.124630/
https://www.marshallforum.com/threads/building-a-jtm-45-100-malcolm-young-kt66.117350/
https://www.marshallforum.com/threads/dc-or-ac-standby-switch-for-jtm45-100-clone.135476/
https://www.marshallforum.com/threads/questions-on-bias-sampling-resistors-jtm45-100-clone.135600/
https://www.marshallforum.com/threads/nfb-resistor-for-jtm45-100-clone.137042/

Volume drop at 10 (DIY clone)

There's a sudden volume drop right before I hit the max stop end on the High Treble volume pot on my newly built JTM45/100 clone. It's been consistent the few time I tested. Volume increases as expected when I turn the pot, until this drop happens. It's also independent of guitar input volume...

www.marshallforum.com

Schematics, voltage chart, component list, and bias calculations and measurements for the completed amp:

 

[playloud]

Exciting! That's a good selection of parts

I'm glad I'm not the only one that finds a step drill adequate for octal sockets...

 

[Sigs]

That was quick, a lot faster than me..........I'm just waiting on two parts.

 

[playloud]

That was quick, a lot faster than me..........I'm just waiting on two parts.

It's not a race. I'm still looking forward to seeing your build!

When it comes to clones, there's a vast spectrum from "following the schematic with modern parts" to "1-to-1 using vintage parts" but you can make a great 45/100 anywhere along it.

 

[william vogel]

Started to build a JTM45/100 clone, based on the Marstran schematics by BKW, 5/12/07 (the so called "Hendrix/Dickinson" amp, Marshall #7026). This wont be a faithful replica. Instead, I will make some up-dates to the circuit (safety, reliability). The exterior I plan to keep close to original, with modern parts.
- Marstran trafos (still waiting for delivery, x-mas gift in best case, but probably next year)
- MetroAmp chassis from Valvestorm
- Boards, turrets, sockets, selectors, pots, etc. from Modulus
- Standard parts from Mouser and Digi-Key
- Still haven't ordered valves. Matched TAD quad seems reasonable, together with Psvane ECC83.

Got most part and dry-fitted what I've got. Octal sockets don't fit the chassis. Need to get a 30 mm step-drill to make the holes about 1 mm bigger. There will be some more work to layout bias sampling points, fit the IEC socket, etc. Some pictures below.

Here's the prelude:

Help me specify a JTM45/100 clone

I would like some help to specify a JTM45/100 clone, “Hendrix” circuit. Been searching Internet, and I see some of the frequent usernames here coming up, but some info is no longer available and there seems to be changes in availability for e.g. trafos from different suppliers. Therefore, I’m...

www.marshallforum.com

View attachment 139211View attachment 139212View attachment 139213View attachment 139214

Be very careful with a step drill. On holes less than 3/4 inches, they work well. Those holes are really difficult to drill. The aluminum galls and it is very grabby. I have Greenlee punches and man, that’s the ticket. Please don’t ruin the chassis.

 

[Marcomel79]

Excited to see this build. One tip about using a step drill: carefully enlarge your holes from both sides. That way youll have a clean hole and no need for deburring.

 

[playloud]

Be very careful with a step drill. On holes less than 3/4 inches, they work well. Those holes are really difficult to drill. The aluminum galls and it is very grabby. I have Greenlee punches and man, that’s the ticket. Please don’t ruin the chassis.

That's definitely the sensible approach. To be fair, I've only ever done it with old aluminium project chassis that were already littered with scratches and unused holes (although they've always turned out cleanly).

Those Greenlee punches look very nice. Pity about the international shipping.

 

[BlueX]

That was quick, a lot faster than me..........I'm just waiting on two parts.

Let's see how fast. Won't do any permanent wiring until I've got the trafos, and that can take some time. I enjoy the design and trouble-shooting phases as well, so I will take my time.

 

[BlueX]

Be very careful with a step drill. On holes less than 3/4 inches, they work well. Those holes are really difficult to drill. The aluminum galls and it is very grabby. I have Greenlee punches and man, that’s the ticket. Please don’t ruin the chassis.

Good advice, thanks! I've used such "punch and die" tool for installing faucet in kitchen sink sheet metal. Works well.

In the case of the octal sockets the holes are 28,2 mm but need to be 30,0 (sockets 29,7). This means I will "shave off" 0,9 mm on the radius. Could be a risk that I just bend the edge of the hole with the punch and die. I will make some tests on scrap sheet metal first before attacking the chassis.

 

[Sigs]

It's not a race. I'm still looking forward to seeing your build!

When it comes to clones, there's a vast spectrum from "following the schematic with modern parts" to "1-to-1 using vintage parts" but you can make a great 45/100 anywhere along it.

I never said it was a race, I only came across BlueX's other post when he was looking for info on building a JTM45/100, so its only from this post I realised he had a fair number of parts already, when you consider I have been sourcing parts for the last 3 years, so my build will be rather long and slow.

 

[Sigs]

Good advice, thanks! I've used such "punch and die" tool for installing faucet in kitchen sink sheet metal. Works well.

In the case of the octal sockets the holes are 28,2 mm but need to be 30,0 (sockets 29,7). This means I will "shave off" 0,9 mm on the radius. Could be a risk that I just bend the edge of the hole with the punch and die. I will make some tests on scrap sheet metal first before attacking the chassis.

I'd go find a workshop who has something like this, otherwise you could destroy the chassis. A deburring tool would take considerable time but would not cause any damage, I'd look at filing it out as you don't have a lot of material to remove.

 

[william vogel]

Good advice, thanks! I've used such "punch and die" tool for installing faucet in kitchen sink sheet metal. Works well.

In the case of the octal sockets the holes are 28,2 mm but need to be 30,0 (sockets 29,7). This means I will "shave off" 0,9 mm on the radius. Could be a risk that I just bend the edge of the hole with the punch and die. I will make some tests on scrap sheet metal first before attacking the chassis.

I’ve had to enlarge the aluminum Valvestorm chassis for the sockets just like what you’re doing. I’ve had to do it on the steel 12000 series chassis also. The punch works beautifully with no issues, carefully center the punch in the hole and tighten. I stopped using drills a long time ago because I mangled some bare chassis’s. Bought the 3/4 punch and the 30mm and now it’s fast and easy. If you think you’ll do this several more times in the future, it’s a solid investment and the cost will be offset by time and grief, trust me. The advantage is comparable to the scope purchase for building amps. If you’re being patient with the build and really looking for perfection, buy the punches.

 

[BlueX]

I’ve had to enlarge the aluminum Valvestorm chassis for the sockets just like what you’re doing. I’ve had to do it on the steel 12000 series chassis also. The punch works beautifully with no issues, carefully center the punch in the hole and tighten. I stopped using drills a long time ago because I mangled some bare chassis’s. Bought the 3/4 punch and the 30mm and now it’s fast and easy. If you think you’ll do this several more times in the future, it’s a solid investment and the cost will be offset by time and grief, trust me. The advantage is comparable to the scope purchase for building amps. If you’re being patient with the build and really looking for perfection, buy the punches.

Thanks, again! This addresses my concern.

 

[BlueX]

A deburring tool would take considerable time but would not cause any damage

Thanks! I didn't even think about this tool. Just a couple of minutes for one hole in the 2 mm aluminium sheet (and replacement blades are just some USD 3 each, if it wears out).

 

[BlueX]

Test assembly of the boards, but no soldering and turrets not yet pressed in placed. Might move around a bit. General layout follows the pictures I've seen, with some exceptions:
- Still not decided on secondary fuses (one HT CT, or one in each live HT)
- Moved two first dropping resistors to power board (next to nearest filter cap)
- Moved FB resistor next to PI grid caps (where it actually connects)
- Added both 33k/560pF "Lead" and 56k/250pF "Bass" for the tone stack. Will decide later if I will add a switch to select, or just hardwire one option.

The tiny MF resistors don't look right in the turret board (better on a tightly packed PCB). Might get CC or CF instead. Missed to order 10k resistors, so there are 2x20k instead (for now).

This is probably as far as I will get without trafos. Need them to make sure everything fits, including wiring.

 

[Sigs]

Are you planning to use Larry's grounding ?

Test assembly of the boards, but no soldering and turrets not yet pressed in placed. Might move around a bit. General layout follows the pictures I've seen, with some exceptions:
- Still not decided on secondary fuses (one HT CT, or one in each live HT)
- Moved two first dropping resistors to power board (next to nearest filter cap)
- Moved FB resistor next to PI grid caps (where it actually connects)
- Added both 33k/560pF "Lead" and 56k/250pF "Bass" for the tone stack. Will decide later if I will add a switch to select, or just hardwire one option.

The tiny MF resistors don't look right in the turret board (better on a tightly packed PCB). Might get CC or CF instead. Missed to order 10k resistors, so there are 2x20k instead (for now).

This is probably as far as I will get without trafos. Need them to make sure everything fits, including wiring.

View attachment 139415View attachment 139416View attachment 139417View attachment 139418View attachment 139419View attachment 139420View attachment 139421View attachment 139422View attachment 139423

 

[Marcomel79]

Looking good! Maybe trim the scocket screws?
I agree with those tiny resistors looking wrong, but you havent soldered anything yet..... its definitely a big boy build, id be nervous starting one. Look forward to your progress

 

[BlueX]

Are you planning to use Larry's grounding ?

Haven't decided yet. On my 18W build I used three separate (all three with dedicated screws):
- Input jacks, preamp, and pots, near the input jacks.
- Power supply and power amp near PT
- Protective earth
That amp has very little noise, and I can understand the principle behind.

I've read Merlin's book, and many forum threads. Seems like it's possible to get good results in different ways, but I would prefer to understand the method I will use.

Looking good! Maybe trim the scocket screws?

Thanks!

I'm using M3x20 screws, and will cut to measure with this Knipex multi pliers (clean cuts, fast) once ready to assemble.

Still waiting for trafos. Delivery maybe early next year.

 

[Sigs]

Are you planning to use Larry's grounding ?

Nice images, I'm working on a retro build of a JTM45/100 , I'll keep an eye out for how your progressing as I'm still learning.

 

[BlueX]

Nice images, I'm working on a retro build of a JTM45/100 , I'll keep an eye out for how your progressing as I'm still learning.

Thanks! Be sure I'm looking at your posts, as well.

I plan to follow the original "#7026" schematics, but with some up-dates. I'm using current production components. Here are some more pic's on test lay-out, and areas where I'm still thinking about how to do.
- Fuses
- Rectifier
- Standby switch
- Dropping resistors
- Bias sampling
- Switching for "Lead" or "Bass" resistor/cap for tone stack

I'm using nylon spacers close to significant voltage to fasten the boards.