Hi-Fi tube amp kit from China - Printable Version
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RE: Hi-Fi tube amp kit from China - TV MAN - 12-18-2016
I did an initial power up to make sure I had the power transformer connected properly, and to be sure it was labeled correctly. I didn't want to get everything together to find the 600v was across a filament or something like that. Also to make sure voltage was passing through the choke and output transformers. I did an AC test with all the tubes out, brought up on the variac slowly. I checked the B+, and all of the filament voltages and connections. Next, I plugged in the 5Z4 to check for raw B+. Finally, I plugged in all of the tubes. I have one meter on the B+ coming from the choke, one on the plate of a 6L6, and one on the filament of a 6SN7.
So far, things look good
RE: Hi-Fi tube amp kit from China - morzh - 12-18-2016
Well it shows no load
RE: Hi-Fi tube amp kit from China - TV MAN - 12-20-2016
Well, no smoke anyway
RE: Hi-Fi tube amp kit from China - morzh - 12-20-2016
No load - no smoke. Maybe we should keep it that way!
RE: Hi-Fi tube amp kit from China - TV MAN - 01-16-2017
With all the lousy weather, and some sleep, I found some time to advance on the kit. I worked on the "signal wiring" part. I had a PC board to mount the level control on, then had to figure out the combination. I thought I had it documented fairly well, but still had to make some corrections. Took a couple try's to get all the wires pointed in the correct direction, and make everything line up. I think I finally succeeded. This resembled a Chinese jigsaw puzzle
Here is the rest of the signal wiring. This part was very straightforward and went smoothly. Looks like this circuit uses several different feedback loops. I didn't have enough shielded cable to go from the level control board to the tube terminal. But, according to the pic I have, they just ran a single wire to each tube, so that's what I did.
RE: Hi-Fi tube amp kit from China - morzh - 01-17-2017
Tim
You are better off soldering as you go, as if you then start soldering it all you might forget a tack or two and then you will be looking where those scratchy sounds come from.
RE: Hi-Fi tube amp kit from China - TV MAN - 01-17-2017
Gotta agree with you on that one Mike. Besides possibly missing a connection, if all the parts are in place before soldering, it makes it much harder to get a soldering iron in there, along with the solder without burning something. I have been attempting to document when to solder, and when not to. I don't want to have to add another wire from something and already have the hole soldered shut. Wouldn't be too big of deal with this kit tho, since it has pretty big solder lugs on everything.
RE: Hi-Fi tube amp kit from China - TV MAN - 01-17-2017
I found an idea in an old Heath assembly manual to help organize and layout parts for installation. So, I utilized the idea.
I started in building the power supply. I found that separating the sections - that is, caps in one section, then resistors, etc - well, that didn't prove out, so I had to revamp. I made a lot of notes and changed the order of the steps to aid in assembly.
One thing I did was replace their supplied 47mfd 450v cap with a big burly 47mfd axial cap that fit better. This was is the input filter cap, so I figure the bigger the better. I think the rest on down will be ok. I tried to lay things out in such a way that it will be fairly easy to replace when the time comes.
RE: Hi-Fi tube amp kit from China - TV MAN - 01-18-2017
Well I advanced a little more. I got the components put in the left channel. I had to "re-order" almost all of my steps in this section. Here are a few pics of how things turned out:
I started on the right channel. This one was a little more interesting due to a few minor parts routing issues. It took some thinking and trial and error, but I think it is turning out. It's kind of funny to be writing my "instructions" while I build the kit, but I bet that's what Heath and Knight did when setting up their kits. It has been challenging.
RE: Hi-Fi tube amp kit from China - morzh - 01-19-2017
Looking good so far, Tim. Good assembly.
RE: Hi-Fi tube amp kit from China - PhilcoMike - 01-19-2017
Great work. May want to consider using some RTV to bond the large electrolytics in the power supply to the chassis. If the were axial like the old days then they would be hung between two terminal strips for support.
A lot of weight to bounce and vibration around I would think.
Thanks,
Mike
RE: Hi-Fi tube amp kit from China - TV MAN - 01-20-2017
Thanks guys! I did stick the big cap with some hot glue, but probably should stick the other bigger ones before I close it up. I took some time and did some resistance checks from each tube to chassis ground and documented my readings. I didn't see anything unusual. I double checked all my component and wiring hook up. Checked ok.
Below is a picture of the completed chassis at this point.
Alwright ... smoke test #2. Lets fire this baby up and see what she's got!
Naturally, I wanted to flip the switch and see what happened.
Ok, maybe 30 years ago, but I followed my instincts, and brought it up slowly on the variac. I had meters plugged into that thing about everywhere. When I got her up to 120v, all the voltages looked right. They had some key voltages on the schematic taken at line voltage of 110v. They checked dead on. No signs of overheating, no funny smells. No fireworks.I took the time to document all the voltages for each tube. Thought that may help for future troubleshooting.
Now the big question, does it work?
Well ... while testing and prodding, I intentionally probed some of the small signal junctions. I got a nice hum and clicks. So, I connected a portable CD player, hit play and "IT WORKS!" Yeee hawww!Now the bad. It has a nice 60cycle buzz. Ugh! Not a hum, but more of a buzz on both channels. So, I double checked my inputs and grounds. Moved some wires and components around. Then I kicked into troubleshooting mode. First I killed the grid on the 6SN7 input. No change. Next I killed the grid on the 6L6. That quit the buzz, so I knew it was around the 6SN7. I probed some with the signal tracer and found it pretty much all over the tube, exc the input was clean. Sooo, I dug around and found a used 6SN7 and stuck it in there. Uh-huh. There was most of the problem. So I found another and stuck it into the other channel. That eliminated about 90% of my hum. Must have been defective tubes. Likely HK leakage.
I still get a little bit of very low 60 cycle hum/buzz when I turn the level control. Seems to be a sweet spot about 1/3 of the way up where it almost disappears. Gonna do more testing and fine tuning.
RE: Hi-Fi tube amp kit from China - morzh - 01-20-2017
Tim
You could possibly try a battery powered heater on the suspect tubes. There should be no buzz.
RE: Hi-Fi tube amp kit from China - TV MAN - 01-20-2017
I may try that. The 6SN7 heaters are run from a separate filament winding than the 6L6s. The China tubes really buzzed, but I subbed a couple I had on hand and it quieted a lot. Still trying to track the hum down. I may even have to set up the heaters on these as filtered DC. I have a dc power supply I may try to see if it helps. It really isn't bad, but with the filtering on this amp, I feel it shouldn't have any hum at all. Going to do some more checking.
RE: Hi-Fi tube amp kit from China - TV MAN - 01-20-2017
I got to prodding around when checking voltages around the tubes. I found on the filament terminals to chassis ground on ac I get about 150v on my Fluke. Same on all except the 5Z4. I get 5v to ground. Don't know if I have something connected wrong or what to make of that. It is very low current. I can use the VTVM and I get about 40v. I have a non-described green wire with yellow tracer on the PT - I assumed it was a ground, so I grounded it. I couldn't find any continuity to anything when I tested it, including the mounting bolts. Could be some leakage?