'New' Rev a Build Completed!

a DIY, modified Mullard 5-20 monoblock design

'New' Rev a Build Completed!

Postby Kojak » Mon Mar 17, 2008 11:49 am

Here's an edit of my previous 'progress' post, because now I am finished!

I recently scored these basically complete 'kits' consisting of two Ike Rev a boards and nearly all components less tubes and chokes to complete the amps- it included all new transformers, chassis, and basically all components one would order from Mouser. I've had my share of good and bad ebay deals as both a buyer and seller. This was one of the good ones- $210.50 plus shipping. I ordered C354 chokes from Triode and tubes from a couple sources. I picked up some Mullard El34 Russian repro's- they were cheap, why not? I also ordered the few extra components from Mouser to bring these up to Shannon's latest rev B standards. Including a cheap DMM and all shipping charges, I have everything I need at a budget just shy of $400 including shipping, tools, odds n ends, etc.

Side notes: I like the Radio Shack 62/36/2 solder- very easy to use and very clean, flux is clear. Radio Shack is what it is- they do a good job servicing their intended market, which probably doesn't fit most on this forum. However, you can still pick up a few things for the hobbyist. Since I already have my share of decent multimeters for AC work and misc analog meters, I picked up a cheap Harbor Freight DMM that worked very well for this. I used my old basic 25W Weller iron with a pencil point for most connections and a 40W chisel point iron for the larger connections and ground plane connections. This worked fine for me- though of course as noted some of the ground plane connections required touch-up on the opposite side of the board. The 62/36/2 solder doesn't seem to stay in a plastic phase at all which probably helped to keep me from botching connections.

The only problem with my 'score' was that the 'pre-cut' chassis holes for the octal tube sockets were slightly undersize and out of position. I tried re-cutting with a 1-1/16 hole saw, but the existing holes made for a bad cut. I did a little hand grinding to move the holes to where they needed to be and used appropriate sized O-rings to hide my hack job. Actually, it did not look too bad before the O-rings.

It took a little research and some answers from members of this forum to work through a couple of the rev A to rev B issues, but overall this was not too difficult of a project. The boards seem to be very high quality and were easy for neophytes such as I to solder. I have repaired some tube radios and a couple control boards in my Land Rovers- that's about the limit of my experience w/ PCB's. Despite being my first DIY audio project, most everything went according to the manual and schematics- I was pleasantly surprised that I didn't muck up something.

This is a great forum with quite a bit of good info and some very astute and pragmatic contributors. I have found answers to many questions simply by searching through the posts. I picked away at completing the amps when I had a little spare time in the evenings. If I can do this, almost anyone can. I hope to post pics of the completed amps later. I do have a link to the boards.

Link to pic of Rev A board:

http://www2.snapfish.com/slideshow/AlbumID=217934697/a=22158302_22158302/PictureID=4662990454/t_=22158302
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Postby Kojak » Sun Jun 22, 2008 10:32 am

Mullard repro EL34's in the IKE's- long exposure in the dark pics of the tubes at work. Blue dot on 12ax7 is probably a reflection from my preamp. I don't normally sit in the dark Yellow_Light_Colorz_PDT_09 but of course wanted to see what they would look like. The blue is somewhat faint to the eyes but comes out better in a long exposure pic. Amps are sitting side by side- I didn't combine in one chassis.

Image

Very happy with the IKE's, though I need to do a little more work to clear up some faint hum from one of them. Doesn't bug me much & all I have to do is what I have already done on the other amp- better routing and isolation of the input.
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Postby Marshman » Wed Sep 10, 2008 8:14 am

Hey Kojak,

I get that same blue glow with the KT88's in my Ike. Kind of cool looking if you ask me!!

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Postby Kojak » Sat Sep 13, 2008 6:31 am

I have to admit the visual effect of tubes is part of the attraction for me. Yes, that blue glow is cool- maybe a sign that I am running these a little aggressive but I don't think I'm way out of line biased at 550 mV at TP1 and TP2.

I had two of the Mullard repro's go bad- plates started to go thermal & after shutting them down would not bias up correctly. Wish I had kept the purchase info- they were from an older lot than the others & I have had no problems with any of the other tubes or replacements of the bad ones. Incidentally, I tried the regular EH EL-34's and think the main difference between those and the Mullard repro's are cosmetic. If they are not made in the same plant they are made in sister plants and share many components. Mullards have a larger bottle but internally appear very similar to the EH's. Oh well, you get what you pay for and the Mullards were bought cheaper than usual. I guarantee that for every good deal I can brag about there's an offsetting bad deal- all a wash in the end. At least the Mullard repros look cooler than the plain jane EH's...

Before building the Ikes I bought a couple relatively inexpensive 6L6 converted organ amps to try out tubes. I was impressed by the sound and immediately hooked on tubes. Being my first project like this it made sense to not spend a lot of dinero on tubes. Next step is to try a set of KT-88's or 6550's - something with a little more cajones than the EL-34's. The EL-34's already produce from my perspective 'live concert' volume levels through my KLF-20's, so more is simply an exercise in excess Yellow_Light_Colorz_PDT_07 .
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