[jbloudg20]

I thought it might be fun to have a worklog for the construction of my new amplifier. I'll try to update it with all the progress I made, and I'll include plenty of pictures.

Background (abridged version

): It all started last summer. I built my first amp, a CMOY "optimized for Grados". It sounded beautiful with my SR80, and since I've always been a DIY electronics freak, I decided to go deeper. I next built a Millet Hybrid. This was done on the old board, before the new revision. That was it... I was hooked on tubes. I next built a YAHA. Then last fall I began researching to build a Morgan Jones. That amp was the absolute best sounding amp I'd ever heard playing through my HD600's. I then aquired my beloved AKG K340 (see signature for pics), and sold my HD600. Although the MJ was a great amp, it didn't have the oomph to drive the K340 very well. I lived with it for about 5 months. Then, about 3 months ago I began research on the VanWaarde OTL amp. I liked the massive output tube, and decided that was going to be my next amp. However, I wanted better than the 6922 gain tube. I began my intensive modifications.

The amp will now use a 6SN7GT for gain, and the same 6AS7G for output. The output stage on my amp is also a little different, I have modified it to put out about 3 times as much current. I am sacrificing some serious tube life, but I don't mind.

The other big difference: I am running this amp balanced. I have a Zhaolu on the way, and I wanted even more power for my thirsy K340.


Now that most of the introduction is finished, here is how far I got today:

The Postman delivered the final part I was waiting on, my Hammond 269AX transformer, so I began the layout for the enclosure:

You can see the holes for all four tube sockets, and for the one large JJ cap I am using. I am heading out to the hardware store to pick up the screws I need to mount everything tonight, and I'll hopefully finish the casing tomorrow.

Random shot of the transformers I am using:

 

[philodox]

Nice, can't wait to see how this turns out.

 

[jbloudg20]

Quote:

Originally Posted by philodox Nice, can't wait to see how this turns out.

Shouldn't have to wait long, I plan on finishing it by next week

 

[Thaddy]

What kind of case are you using? I don't think I've ever seen one like that. It looks nice and simple

 

[sbelyo]

I love mine... It was by far the easiest build I've done in a while. Mine has about 50 Hours on it and it sounds great with high impeadence headphones.

 

[jbloudg20]

Quote:

Originally Posted by Thaddy What kind of case are you using? I don't think I've ever seen one like that. It looks nice and simple

It is a plastic Pac-Tec enclosure. I used the same one for my Morgan Jones buid, and I really liked it.

 

[jbloudg20]

Quote:

Originally Posted by sbelyo I love mine... It was by far the easiest build I've done in a while. Mine has about 50 Hours on it and it sounds great with high impeadence headphones.

I'm just a little worried because the design has not actually been built yet. FASchmidt over at headwize hooked me up with the simulation of the amp with the 6SN7GT, but I'm just scared that I'll get this far into it (Money wise) and have it not work out so good. I guess if it gets that far, I could just rebuild with a 6922, the way it was meant to be. Funds are low, and I have no amps to drive my K340, so im laying it all on the line. I sure hope it pays off.

 

[Voodoochile]

Cool! Thanks for the pics. Looking forward to the finals when you finish.

 

[philodox]

Quote:

Originally Posted by jbloudg20 I'm just scared that I'll get this far into it (Money wise) and have it not work out so good.

I know how that is... I am out ~$400 from my failed amp build. I hope you have better luck. At least you seem to know what you are doing... that should help.

It looks like Peter will be able to use all my tubes and most of my caps and maybe some of the other stuff though, so a lot of that $400 is going to be 'reinvested' in my McAlister amp.

 

[jbloudg20]

Quote:

Originally Posted by philodox I know how that is... I am out ~$400 from my failed amp build. I hope you have better luck. At least you seem to know what you are doing... that should help. It looks like Peter will be able to use all my tubes and most of my caps and maybe some of the other stuff though, so a lot of that $400 is going to be 'reinvested' in my McAlister amp.

Yeah that's what I'm scared of. I couldn't get a job this summer because my mother needs me to take care of her after surgery. So the money I have in this amp is from the sale of my other amps. I have no cashflow, so all my chips are in on this amp. I might not even be able to afford a rebuild if it fails. The smart thing would have been to build it the proven way, but I began collecting parts before I really learned how hard up for cash I would be. Oh well.

I'm off to get some heavier gauge cable for all the power wiring, and then I'll finish casing this up today (hopefully).

 

[motherone]

Do you have a schematic reflecting the changes that you're making? I've thought of going with a 6SN7 instead of the 6922 as well, though in my amp, I was going to parallel the 6080/6AS7 triodes to double the current (i.e. use two 6080's instead of one). I have like 12 of them sitting around in a box, so I figure what the hey.

 

[jbloudg20]

Quote:

Originally Posted by motherone Do you have a schematic reflecting the changes that you're making? I've thought of going with a 6SN7 instead of the 6922 as well, though in my amp, I was going to parallel the 6080/6AS7 triodes to double the current (i.e. use two 6080's instead of one). I have like 12 of them sitting around in a box, so I figure what the hey.

I have a schematic I can share with you, but its not all in one right now. They are kind of all over the place. It might be easier to just make the same changed I made to the output stage, as my modifications brought the output from 15ma to about 50ma. This will work out even better than if you were to parallel the 6AS7G, which, btw, I don't know if you can just parallel them. The stages are directly coupled, and that might mess things up. I'm not really sure about that though.

 

[dsavitsk]

Quote:

Originally Posted by jbloudg20 This will work out even better than if you were to parallel the 6AS7G, which, btw, I don't know if you can just parallel them.

You can (http://www.atma-sphere.com/papers/6as7.html) and in fact this is the way to get the output impedence lower. However, keep in mind that this is a noisy beast of a tube. I built a preamp using it and after trying just about everything could never get it to quiet down sufficiently to use it. It's also a very hot tube, so if you use more than one use plenty of ventelation -- and make sure your transformer can keep up with all the heaters, it is a lot of power to supply.

-d

 

[jbloudg20]

Good to know, and a very interesting read. Thanks!

Update: Mid-day,
I finished the to of the chasis, and I might call it a day for today. I have a wicked headache, and I'd rather not goof something up by working too much. I picked up all the screws yesterday, but it didn't go so well. The hardware store I went to for some reason didn't have much in stock for round head machine screws. So I grabbed a bunch of the angled ones, and I'll just change them at a later date. Also the four screws I got for one of the transformers were too small, so I found 4 here that work, but do not match. Oh well it will work temporarily.

This is what the top of the amp should look like:

Next come the rear layout, including the IEC, power switch, fuse holder, and XLR input.

 

[motherone]

Looking good! Is that two transformers, or a tranny and a choke on there? Also, if you're gonna burn out tubes, maybe you should use some Russian/Chinese 6N5Ps instead of sacrificing RCA (I think I can make that out in your pics) NOS tubes? Looks like you can get them for about $5.50/each on Ebay