Need a bit of help....(solved)

[kidjan]

Okay, I have my kit all together, and I flipped the heater switch--no problems. All tubes glow, everything looked good.

Flipped the main switch, everything still good. Throws out a bit more heat, but AOK otherwise.


Thing is, when I hook up speakers and a source to the amp, I get no sound. I did notice if I turned the volume up on my pre-amp, I got a very faint noise of the music out of just the left speaker. I also noticed that the Output transformers were cold (not sure if those typically throw out heat, but they were stone cold compared to the rest of the amp). If I unplugged either of the rca jacks, I got no music out of anything....I need to check various voltages when I get home--will post results when I can and also a picture of the amp to see if anyone can see anything.


I'm thinking perhaps I have a cold solder joint, but....


I'm using a PA774 for the power tranny, and Hammond's for the output trannies. Anyone have any ideas?

[kidjan]

On a side note - so far I'm really happy with the kit. :D

[nineno]

Don't worry about the output trannies being cold. They're always cold.

This probably isn't the greatest help, but just be sure to check all of your connections. Make sure the primary side of the transformers are hooked up right, etc.

As for the cold solder joints, they shouldn't <necessarily> prevent it from working, but you should still fix them up.

Also, make sure you've got the tubes plugged into the right spots. I'm not entirely sure what flipping the phase splitter and pre-amp tube whould do, but that *could* be the culprit.

Hope that helps a little. I'm sure you'll get it going in no-time.

drew*

[kidjan]

Ah, okay. I'm retarded. In my rush to get things running before I had to get some work-work done (since, strangely enough, this is FUN for me. Heh.) I accidentally wired up the inputs to J1 wrong.


Anyways, redid them after I saw the mistake I made, fired it up, and it runs absolutly like a charm. Even running on my crap speakers (old infinities) using my laptop as a "preamp", it was clearly about a billion times better than my old amp (sony POS). Tommorow I'm going to hook the sucker up to my Rotel preamp, marantz cd player, and some vandersteens (don't think I'll have enough juice to "drive" them since they're pretty inefficient speakers, but certainly enough to get an idea of the amp quality) and see how it sounds.

Thanks much, shannon! And, of course, the obligitory pics:





The plexiglass top works real nice in a dark room. Still need to clean a few things up on the case, but...8)

[kidjan]

Oy. Okay, it *easily* goes head to head with my Rotel amp (at this point in time, I think the Rotel is about to get ebay'd). The 35 is definetly much smoother and less harsh--the rotel is solid state, and brutally accurate with high frequencies, almost to the point of being overdone. The 35 isn't muddled in the slightest, or blurry, but just smoother. The vocals also blow the doors off of the Rotel.

Surprisingly, the 35 will also drive the Vandersteen 2Ce's with relative ease, which are by no means efficient ( http://www.vandersteen.com/pages/2Celit2.html - around 86 db, 7 ohms nominal 4 ohms minimum) and fairly power hungry (reccomended minimum of 40 watts@8 ohms).

The only recording that really brought the amp to its knees was a pipe organ recording with extremely low frequencies (around 16hz or so, not even technically "audible" anymore) which caused noticable distortion of the rest of the range of frequencies. I also managed to get very slight (almost indiscernable) distortion with Crystal Method (techno stuff, very good recording though--extremely demanding highs + lows, and very clean so any distortion is pretty obvious). Other than that, it punished pretty much everything I threw at it, which I think is amazing since supposedly I'm working with 17.5 watts....


Don't even get me started on Sinatra. Whew!!



On a side note, I noticed that when I measure AC voltage on the power transformer (PA774) to ground, I pick up about 4.5 volts AC--this is measuring the transformer on the outside. Is this normal, or is my power transformer not grounded properly? Just curious. Other than that, it's working spectacularly.

[Shannon Parks]

On a side note, I noticed that when I measure AC voltage on the power transformer (PA774) to ground, I pick up about 4.5 volts AC--this is measuring the transformer on the outside. Is this normal, or is my power transformer not grounded properly? Just curious. Other than that, it's working spectacularly.

Kidjan,
First off - very cool work! I was visiting one of the other members here yesterday, Thermion, and we were having a brew listening to his Dynaco ST-70 with his custom-made driver board using all dual triodes (sounded very nice, btw). Anyhow, he starts talking to me about the plexiglass amp on diytube and I was confused - what plexiglass amp? I had been messing on a prototype that morning to show Therm. So he logs on and shows me your pics - fantastic!!! I imagine the reflections in a dark room are quite a light show. Great news on the listening reports - glad to here this little guy can keep inefficient speakers happy. I will be doing research over the next year in seeing how much bass we can tweak out of those EL84 tubes. May even play with a fixed bias circuit!

OK - to your problem. I would attribute this to the plexiglass contruction. I would recommend three short ground jumpers - one from each of your trannies - to the PCB ground (eg you could connect to J2-3, J6-6 & J5-3). Maybe the surest way to get a good ground connection is to mount the wire on the top-side tranny mount flange along with a star washer, then thread it through the grommet down to the PCB. BTW, this is all UL safety related (in case one of your trannies shorts internally). Good luck!

Shannon

[Martin]

Wowww it looks great. I love it. BTW, could you please direct me to where I can get that plexiglass?
Thanks,
martin

[kidjan]

I got the plexi at home depot.



You can get a sheet about two foot square for five bucks or something like that. Really cheap, for the most part. If you are going to do the plexi, I reccomend quarter inch, and don't forget you'll also have to buy longer mounting hardware to account for the depth change. I'd also make sure you have access to a good drill press and clamps, since working with plexi can be a bit tricky--and be sure to leave the protective covering on the plexiglass until you're all finished.

[kidjan]

Shannon-
That's what I thought. Next time I go to adjust the bias on the tubes, I'll be sure to run some ground wires.....other than that, much thanks, and my old man is itchin' to see the monoblocks.....:D

[kidjan]

One more thing: I'd use a 7/8" drill bit for the tube sockets, even though you could technically get away with 13/16". Because of the depth of the plexi, it's hard to get the tubes in unless you were brutally accurate drilling--that, and the tube may be against the plexi, which I wasn't real comfortable with...



Anyways, I'll stop rambling.

[dhuebert]

What a pleasure it is to see all the different ideas for construction. As soon as the snow flies here in Winnipeg I'll be getting back to my project with some great new possibilities for my amp. I dunno, I'm thinking retro myself.

[Shannon Parks]

What a pleasure it is to see all the different ideas for construction. As soon as the snow flies here in Winnipeg I'll be getting back to my project with some great new possibilities for my amp. I dunno, I'm thinking retro myself.

Don,
I just did a retro prototype using light blue Hammertone paint and the Hammond cage. Looks straight out of the 1950's!! I'll be using the pix shortly for adverts so you can see it.

Shannon