Hi-Fi tube amp kit from China - Printable Version
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RE: Hi-Fi tube amp kit from China - Mondial - 01-20-2017
The filament windings of the amplifier tubes should not be floating with respect to ground.
In the case of the yellow wires winding supplying the 6SN7 tubes, there should be a winding center tap connected to ground, so there should be continuity to the chassis and no DC voltage present.
As to the black wired filament winding for the 6L6's, there is no center tap so one side should be grounded.
The 5V rectifier winding should be floating as it has B+ voltage on it.
RE: Hi-Fi tube amp kit from China - TV MAN - 01-21-2017
That may be it. I was studying the only picture of the chassis I had, and on closer examination it looks like the CT of the filament for the 6SN7 tubes is indeed grounded. I didn't do that, I left it unhooked. Going to try to ground the CT and one side of the 6L6 filament. Didn't show it in the schematic, so I didn't do it.
RE: Hi-Fi tube amp kit from China - morzh - 01-21-2017
Yes if you left it unhooked that might just be it. CT on the filament windings are specifically made to be grounded.
RE: Hi-Fi tube amp kit from China - TV MAN - 01-22-2017
You guys were spot on with this one!
I clipped a jumper on the CT and the hum all but went away, so I clipped another on one of the filament terminals on a 6L6 and now she is quiet as a church mouse! I had a 6L6 that had a mechanical buzz or ringing, and when I connected that terminal to ground, it even quieted down. I originally thought that was the rectifier and wasn't concerned. I'll get those soldered and can start burning this thing in. I am eager to try some better speakers and preamp and see how it really sounds. Thanks Guys!
RE: Hi-Fi tube amp kit from China - Arran - 01-23-2017
This is rather interesting, although with the number of things you had to add to this "Kit" to bring it up to a decent standard, it's almost worth just buying the parts and going with your own design. Mid air solder joints is a crappy way to construct a point to point wired chassis, I can't believe that they didn't include at least a 1/2 dozen terminal strips with it. Some British radio manufacturers did that and they looked like a boar's nest, and unlike in Soviet radios they were not spot welded.
With regard to line capacitors it may or may not need them, some transformers have an electrostatic shield built in, like in RCA radios, and others like Philcos do not and need line caps. MOVs will work for surge protection, though they do have a service life and should be replaced about every five years, look up power bar fires if you want to find out why.
Regards
Arran
RE: Hi-Fi tube amp kit from China - Mondial - 01-23-2017
I believe that the power transformer does in fact have an interwinding shield. Tim mentioned a green/yellow wire with no seeming connection to the other leads which he connected to chassis ground.
I would remove the line caps as they really don't serve much purpose in this case as an RF bypass for interference suppression. As to MOV protection, A tube amp is pretty much immune to line spikes considering tubes are very rugged and can sustain peak voltages of thousands of volts without any damage.
RE: Hi-Fi tube amp kit from China - TV MAN - 01-26-2017
I have been playing around with this some. I tried a set of Denon speakers that sounded pretty good, but about 10 minutes later I started hearing scratching and distortion. Oh boy - wassagoinon?
Thought maybe I failed an output tube or something. Well ... after checking some things I found the foam on the woofers went to pieces! Whew! So, I grabbed a set of 8"Yamaha speakers and connected. I was surprised! So far that little amp rocks! I have it connected to a cheapie portable CD player, and had to add an EQ. She's flat without some kind of tone control. Has plenty of volume, more than I need anyway 
Not the best preamp setup, but something to test it with. Next I'm going to try it with my old Sanyo (please don't laugh, these babys sound great!) 12" speakers and may power up my Dyna preamp and see what I get. I have (had) some nicer speakers, but the foam disease has gotten all of them, including my favorite Cerwin Vegas. So, I will use what I have.More to come...
RE: Hi-Fi tube amp kit from China - Eliot Ness - 01-27-2017
Nice job Tim
If one of us ever takes the plunge and buys one of those amps your notes and instructions will be invaluable.
RE: Hi-Fi tube amp kit from China - Ron Ramirez - 01-27-2017
You can't buy that kit from the seller which TV Man purchased his from anymore.
However, you can still purchase the kit:
http://philcoradio.com/phorum/showthread.php?tid=16146
RE: Hi-Fi tube amp kit from China - Ron Ramirez - 01-27-2017
Oh, Tim -
I have never heard Cerwin-Vega speakers, but I can tell you that both of my sets of Bozaks (E-300 and Urban) sound best with the bass and treble set to flat. They are the only speakers I have ever owned where I didn't have to turn up the treble, or the bass, or both, for them to sound good. Very lifelike. The best speakers I've ever owned.
RE: Hi-Fi tube amp kit from China - morzh - 01-27-2017
Same can be said of Klipsch Cornwalls. I keep it flat most of the time. Every once in a while I might add base just a little. No treble.
RE: Hi-Fi tube amp kit from China - TV MAN - 01-29-2017
Ok, here is the real test. How does this little amp really sound?
I decided against connecting the Dyna preamp since I haven't had it powered on for at least 10 years, and I am sure it is due for a recap. So, I stuck with the EQ and CD player.I dragged down the Sanyo 12" speakers that I have had since tech school. Pretty much filled up my small radio room!
I used these since I know how they sounded with the Fisher and Dyna setup, so I had something to kinda compare to. I grabbed a few 'pet' CDs and powered up. I must say, I was surprised
, and in a good way! I started bringing it up and that little amp stayed right with it! I kept thinking the next 'click' on the level control would start clipping, but it just came up another notch and kept on. It will definitely thump. Way more than I really expected. It's clean across the board. Now, I didn't get out the scope and audio generator to see just how good or not it is, but my ears say it is strong for a "one lunger". It seems to have plenty of reserve. I didn't know how well those China 6L6 tubes would do, but they seem strong. I had a stash of USA tubes if I needed to try, but after the test, I didn't bother. I wish I had a nicer set of speakers to try, but all my better speakers have rotten foam edges. So, I use what I have. More to come...
RE: Hi-Fi tube amp kit from China - TV MAN - 01-29-2017
Just for grins, here is a pic of the way it is factory built in China:
Here's the way I did it:
RE: Hi-Fi tube amp kit from China - morzh - 01-29-2017
I say it looks good.
Glad it is workng well. It is a Class A, right?
Class A has its perks, like no crossover distortion.
And in all honesty, you only need so many watts to get it to be really loud.
Wait till you get no-compression old style speaker. They are about tens of times more sensitive.
RE: Hi-Fi tube amp kit from China - TV MAN - 02-04-2017
Well, so far so good. I have the amp connected to some test speakers and a portable CD/FM player and have been letting her run. I have been trying to find some speakers on Ebay for the last week or so. Had a real nice set with 0 bids, set my sniper and waited. All my instincts told me to enter a bid manually, but I resisted. The bid went in and went to pay only to find it wasn't my bid!
Stinkin' sniper hiccupped and didn't fire my bid! I sat for awhile in disbelief. Snipers aren't 100%. So, I got my eyes on a couple other sets. 
Need something fairly small, yet good sounding and efficient. I don't have room for anything too big. So far the amp is plugging away real nice. I need to finish the notes and update my drawings, put it into PDF and make it available. It is a class A.