70/71 Spec 1987.

[revolver1]

So I've made a start on the next one.

I wanted the cans on top and after info gained through the usual suspects soon realised I would be building more of a 70/71 spec rather than a 69.

(Again a big thanks to everyone for all the knowledge).

So filtering wise I've opted for 50/50uf mains, 50uf screens, 50uf phase inverter and 32/32uf pre amp.

[revolver1]

I cut the pre-amp filter hole out with a 32mm hole saw. I later found you can get the hole saws in 1mm increments and so a slightly smaller hole would have been more appropriate.

It worked out alright though, I then protected the cut steel with a dab of galvafroid paint.

The face plates are from Valve storm. I sent them off to Modulus amplification in Scotland (UK) to have the JMP logo put on the front and the blurb on the back.

The back blurb was supposed to be stacked as in 3 separate lines. Not sure why but it didn't work out that way.

I think Michael did a great job, it looks pretty good anyway.

[revolver1]

So again here is about as far as I can go with out the iron.

Good news the iron should be here in the next couple of weeks.

[revolver1]

I made the board from Carp brand Tuffnol, I'm quite happy with the way it's turned out.

Big thanks to neikeel for the tip off on the snubbers.

[revolver1]

So after much thought and looking at the info and pics on the excellent Marstran site and amp archives I opted for the .68uf/820R combo.

I only have experience with a 69 100watt.
With the last one I went with 2.7k but with a 4700pf brghtcap.

I really liked the way that turned out so for this one I want to go with a 5000pf dog bone bright cap. I'm trying to second guess things a little here but maybe the 820R will get me in the zone.

Either way it'll make it a little different from the rest.....

[revolver1]

[revolver1]

So here's a sneak preview before the iron goes in.

Gotta say a big thanks to neikeel for the help with the diodes and snubbers.

It has definitely been more of a challenge getting the info on the 50watt.

And so I wait.....

Oh, I've got the head shell coming from John Wheeler at Stone Age Custom Cabs. He has been showing me pics as they are being made and they look amazing. I'll be sure to post some pics when they turn up. Shouldn't be too long now.

I was going to do a Superbass next but I think I'm going to redo the board so I guess it's going to be the Superlead next.

There's a couple of points I need to 're address on the 2203 and this build and then I guess I'll see you all over in the 100watt section. Of course I'll be back to Finnish this one when the iron showes up.

[neikeel]

Huge pics but very nice neat work.

Top notch so far

[danman]

Looking great so far!!

[bill bokey]

Looking great ! Nice work !

[NoMasterVol]

cant see photos

[RockinRocket]

Looking good !

[rockinrod'67]

Hi there guys. What are these “Snubbers” and please describe their purpose, values, and implementing. I did not see these on the Valvestorm 50 w instructions. I assume they are optional.

[revolver1]

Hi rockinrod. Sorry I haven't checked in for a while. I need to finish off these posts now that the amp is done.

To answer your question snubbers were used to eliminate the hash from the diodes and popping when powering down the amp. As I understand it diodes are pretty good these days so there isn't really any need for them, I just did it as a historical thing.

100w amps had 2x .22uf 1000v caps in parallelle and I've seen that set up on 70's 50watters but the earlier 50watters had 1x .5mfd cap but it's not on the board. The diodes are wired from the P.T tags directly to the HT fuse carrier and the cap goes on the other side of the carrier to ground along with the wire that takes the H.T voltage.

Original caps were Hunts brand but they have a reputation for being not so good reliability wise.
I found this out the hard way. I had some RS caps that looked great but after powering down a few times when I was working on it it went bang and scared the cr@p out of me....

[rockinrod'67]

thanks for the info.