[dem626]

Hey guys,  I've decided to try out the vinyl thing and started out by building a Cornet2.  I don't have a turntable yet, figured I'd make that decision while building my phono pre (that's turning out to be a difficult decision).  Thanks to everyone who has posted, I got lots of help from reading it all.

Finally finished the Cornet2 build and I'm trying to see if it works.  All of the tubes light up and the voltages are fairly close to spec.  I can post them if it will help.  I had a few problems to resolve to get to this point, so I was really happy to get this far.

Since I don't have a TT, I've tried hooking my Ipod to the inputs and can't measure any voltage on the outputs with my dmm.  I actually put the cornet/ipod in my system (turned the volume down low to start) and get no music.  That didn't work so I tried my CDP, still nothing.  I assume there is a problem somewhere but don't know how to diagnosis it. 

If anyone knows how I can zero in on this, please let me know.  I'd really like to have the Cornet2 ready when I get a TT.

Thanks!

[dem626]

Measurements I took are as follows:

R107 (370V)
R219L (156V), R219R (152V)
R211L (338V), R211R (338V) high side
R211L (305V), R211R (305V) low side
R212L (149V), R212R (145V)
R204L (144V), R204R (145V)
Heater voltage is 5.76V

Edited voltages to include both sides of R211

[el34]

Try this basic test:
With your amp powered up, and the channel the cornet is connected to selected,
and the volume at a typical listening level, power up the cornet.  You
should hear a low-level 'thump' in the speakers as it powers up.

Another test:
With the cornet powered up , put your fingers near the first 12ax7 tube
(farthest from the transformer.)  It shouldn't be too hot.  You should get
a low hum in the speakers.

[dem626]

Thanks el34.  I'll try those suggestions out.  I understand your first tip, if the cornet is putting anything out it will cause the thump on power up. 

I've got the cornet back on the bench at the moment, trying to understand what parts of the circuit haven't been proven by the voltage points I checked.  Once I'm  done with that I'll hook her up an try your suggestions.  I'm hoping I find a problem before that though.

I'm trying to learn as I go, and obviously still have a way to go with all of this. 

[el34]

The 'thump' at turn on will show you have some signal from at least the
12au7 output.  The hum from a finger near the first 12ax7 will tell you you
have signal from that tube on.

The idea is to break the problem down into pieces to isolate where the fault is.

You can also try a meter probe on an input grid of one of the tubes, you
should get a little pop or scratchy sound.

You should see about 300v on one side of each R211 and 330v on the other.

When poking around in there with the cornet powered up, you have one hand
behind you back for safety, right?  Don't touch the chassis at the same time
as you probe the circuit.  Take your time.

Also good checks (with the cornet unplugged and capacitors discharged,
check with meter for near zero voltage at the high 330v check point)
do continuity or resistance checks throughout the circuit across solder points.

[dem626]

I'm not getting any voltage reading after the input caps (C203) or after the output caps (C208).  Both have voltage before them.  I checked continuity between the leads and the board (with power off) and I get the beep so I think they're soldered in ok. 

Does this mean they're bad?  It's the same on both channels.

[el34]

That's what you should see.  The caps block DC voltage, but pass the AC signal.
If you have a way to run a sine wave somewhere in the audio band through the
cornet, you should be able to measure an AC voltage at those caps.

I read back in your post with measurements, I wonder if the low heater voltage
is a problem (unless you're talking 5y3 heater which should be 5v) the heaters
should be within about a volt of 6.3v.

[dem626]

Thanks el34, really appreciate your help with this.

I saw that the heater voltage was low and read that I can bring it up a little by changing R223.  I'm using a 1.8R now that is measuring at 2.0R.  I guess that will be the next thing to try.

I hooked her up again this morning and realized that I am getting very faint (and very distorted) "music" out of both speakers.  Not sure how the Ipod signal compares to what the cornet is expecting.  The distortion was real bad.  I could tell it was music but that's about it.

Let me know if this provides any clues. 

About the only think I have left that I can check are some of the caps and all I can test is for bad solder joints (checking continuity between lead and pcb).  Have to get to the other side of the board to check them out.

[el34]

No problem, glad to be of help...

If you're getting some signal though with a line source, maybe your build is ok.
It might make sense to wait until you can hook up a turntable, and see if that works.

In the meantime, the continuity and resistance checks are good insurance, and
getting the heater voltage within a volt of 6.3 will help the sound.

[tubesforever]

I would trust your build.  Everything looks perfect.  The power coming from a MM cartridge will be between 1 and 10 millivolts.  I figure your other devices are creating phono overload of the circuit.

BTW, I had to use a smaller resistor for the H+.  I cannot remember off hand what it was but it was approximately 1/2 ohm less than JH specs in the build sheet.  This gave me 6 to 6.1 v with the Bendix 6106.  Buy this rectifier tube if you can.  I also had to modify the the first two B+ voltage resistors to 12k and 9k instead of two at 10k in order to hit the right mark.

This is easy stuff. 

My C2 sounds amazing and after two years I feel absolutely no need to rush out and find another phono section unless Jim is willing to release the Trumpet as a kit!

Cheers! 

[dem626]

Glad to hear it is possible that the build is ok, given the other factors. 

Think I'll order some resistors to bring up the H+ voltage and take a break while I shop for turntables.  If I still have troubles, I'll be ready to tackle them after a little break.

All in all the project has been educational and fun, although all of the recent taking apart and putting back together, soldering, unsoldering, head scratching, web searching, etc. was getting quite frustrating.  Should be very rewarding eventually.  Keeping my fingers crossed for now.

Doug