JTM50 Build

[Marcomel79]

So I'm gonna start a JTM50 build with solid state rectifier. Got the transformers from another amp, bought a Hammond 3H 250mA choke, and I'm building my own chassis and turret board. I'm also building a dual bias circuit so I can use tubes that are not matched. Here are a few pics from the fabrication of the chassis, although not finished yet.

 

[Marcomel79]

Here are a few pics of the progress on the turret board. I bought it blank so i could drill my own template.

I used a piece of an old sewing machine that had the hole of just the right size to hammer down the turrets.
Care must be taken when doing this as a few of the holes were a hair too tight and i got a few cracks underneath. Thankfully it was something superficial, but it would suck to break the board and having to wait for a new one.

Also a massive thank you to a gentleman by the name of @AndyD, for providing me with the measurements of the spacing of the sockets AND the front plexi panel for my build, FREE OF CHARGE. He even paid for postage. Im truly humbled.

 

[AndyD]

Looking good!

 

[Marcomel79]

Here is the layout of the turret board. I started posting pics in another thread but i thought it would better to have one here, in the proper section. No under board wiring, i dont trust myself🤣

 

[Marcomel79]

Looking good!

Thank you Andy, i really hope to finish the chassis next week. It always takes longer than expected...

 

[AndyD]

Looks like a very well thought out layout. Nice to see a hand drawn layout! I agree that over board connections are a good idea. Helps with trouble shooting.

 

[StingRay85]

Looking great!

 

[Pete Farrington]

With such board layouts, the placement of 10k preamp HT dropper and board mounted associated ecap troubles me a little. As heat is a significant stress factor with ecaps especially, if drilling a blank board (ie rather than using a pre drilled matrix board), I suggest to nudge the turrets for resistors alongside them etc over a half step or so, so that there’s some free air between the resistor and cap bodies. To allow for convection cooling / prevent heating by direct conduction.

 

[Marcomel79]

With such board layouts, the placement of 10k preamp HT dropper and board mounted associated ecap troubles me a little. As heat is a significant stress factor with ecaps especially, if drilling a blank board (ie rather than using a pre drilled matrix board), I suggest to nudge the turrets for resistors alongside them etc over a half step or so, so that there’s some free air between the resistor and cap bodies. To allow for convection cooling / prevent heating by direct conduction.

Funny you say this, i actually thought about doing something like this, to not have that resistor under the ecap.

and bending the 56K slope resistor on the inside of the board. That should keep things cool?

 

[Pete Farrington]

Yes, that would work.
Or alternatively, mount the 10k by the first 10k HT dropper, between it and the 47k nfb resistor.

 

[Marcomel79]

I see that in this schematic, in the bias circuit, the diode is a 10D8, 1,5A 800V. I have a bunch of 1N4007s, is that ok to use?
http://www.marstran.com/JTM50.gif

 

[neikeel]

1N4007 is the diode of choice in the bias circuit

 

[Marcomel79]

1N4007 is the diode of choice in the bias circuit

Ok great, thanks Neil

 

[shakti]

Here are a few pics of the progress on the turret board. I bought it blank so i could drill my own template.

View attachment 123089

I love your DIY approach. I like your taste in wine even better.

 

[Marcomel79]

I love your DIY approach. I like your taste in wine even better.

Thanks man! But its not a wine i buy every weekend...

 

[AndyD]

Thanks man! But its not a wine i buy every weekend...

We believe you!!!

 

[_Steve]

Awesome. It will sound that little bit sweeter knowing you drilled every hole and fastened everything yourself

 

[Marcomel79]

Awesome. It will sound that little bit sweeter knowing you drilled every hole and fastened everything yourself

I think you might be right, and hopefully it will make sound!

 

[playloud]

Fantastic work so far!

Very cool of @AndyD to help you out like that too

My first thought when I saw the thread title was ‘no tubes at all’! This is much better

 

[Leonard Neemoil]

Awesome, thanks for posting!