N1ESE said:
I've got 2 tested 12AT7s to send to you Monday, I almost shipped them without testing them today since I bought the as "tested". 2 of the first 5 I tested had bad sections so that would have been a disaster.
Baring that I'm sure we can figure something out about getting you over here to try the amp on another set of speakers. I'm not sure my eyes will do you much good though, I've built lots of stuff, with a lot of help from other folks.
Do you have a scope, or access to one to trace the ac signal through the amp?
Since the Simple SE is only a two stage amplifier, there are not a lot of places that the signal can get lost.
If you have the signal and common leads transposed on the input, this can lead to very low output. Your OPT's looked to be wired correctly, it's unlikely that you have two each bad (triode sections, coupling caps, etc.) of the other bits that can cause you to have no output. I would look to your input connections and see if something is amiss before the board, or at the point of connection to the board.
Good luck,
Win W5JAG
Since the Simple SE is only a two stage amplifier, there are not a lot of places that the signal can get lost.
If you have the signal and common leads transposed on the input, this can lead to very low output. Your OPT's looked to be wired correctly, it's unlikely that you have two each bad (triode sections, coupling caps, etc.) of the other bits that can cause you to have no output. I would look to your input connections and see if something is amiss before the board, or at the point of connection to the board.
Good luck,
Win W5JAG
w5jag said:
That's along the lines of what I've been thinking. The grid voltages on the KT88 agree with what he is seeing across the speaker terminals, so I have every reason to believe the output stage is wired correctly. The plate and cathode voltages of the 12AT7 are within reason too. At the very least, the close matching on their cathodes suggest the tube is healthy. Although I'd like to blame all problems on a dud driver tube, I'm not yet convinced that's it.
The only thing I forgot to ask him to check is the AC voltage input to the 12AT7 driver tube. So, what's the AC voltage on R22 with a full signal input to the amp? It should be ~1 volt. If you see something like 6 mV, we might be onto something...
w5jag said:
Negative on the scope. One of the first things we did was to eliminate the volume pot. Since then, the input has been wired directly to my output source. The outer pads are the signal pads with the three inner pads the commons.
Ty_Bower said:
I don't have a stable reading, it bounces around with a high of around 285 mV.
N1ESE said:
You won't have a steady reading unless you've got a signal generator handy. Music is going to bounce around all the time.
Remember the 12AT7 in this circuit has a gain of about 50. If you see 285 mV to its grid, then you should be getting over 14 volts to the KT88. You reported a while back that you got about 315 mV. Something is wrong around that first stage...
Nate,
Here is a good overall shot at high-resoulution that covers just about everything. Some comments about what's going on here:
For grounding the board and commons on the input, I am using the extra ground pad that's in the middle of the two input terminals. From the pot, the middle pins go to the outer most pads on the board (signal in) and the right pins go to the inner most pads (common). The center common pad is wired to ground. Left pins on the pot goes to the Left (Tip) and Right (Ring) on an 1/8" jack. Shield is wired to the earth ground. If I completely remove the input jack and pot and hard wire the terminals directly to my source, performance is the same. When I do this, I wire the tip to the left outer most terminal and the ring to the right. Shield is then wired to both inner most terminals. I have also tried floating the shield with no difference.
As you can see, oil cap is not wired at this time.. just the choke.
Outputs currently wired for UL mode. Amp behaves roughly the same when wired for Triode mode.
Everything is star grounded to the earth ground on the power cord. The second link shows the ground lug.
Speaker wiring: 8-ohm is yellow, white is common, the black goes to earth ground as shown on George's wiring diagrams.
Pics:
http://img529.imageshack.us/img529/6535/overallqf5.jpg
http://img529.imageshack.us/img529/3858/groundnr4.jpg
Here is a good overall shot at high-resoulution that covers just about everything. Some comments about what's going on here:
For grounding the board and commons on the input, I am using the extra ground pad that's in the middle of the two input terminals. From the pot, the middle pins go to the outer most pads on the board (signal in) and the right pins go to the inner most pads (common). The center common pad is wired to ground. Left pins on the pot goes to the Left (Tip) and Right (Ring) on an 1/8" jack. Shield is wired to the earth ground. If I completely remove the input jack and pot and hard wire the terminals directly to my source, performance is the same. When I do this, I wire the tip to the left outer most terminal and the ring to the right. Shield is then wired to both inner most terminals. I have also tried floating the shield with no difference.
As you can see, oil cap is not wired at this time.. just the choke.
Outputs currently wired for UL mode. Amp behaves roughly the same when wired for Triode mode.
Everything is star grounded to the earth ground on the power cord. The second link shows the ground lug.
Speaker wiring: 8-ohm is yellow, white is common, the black goes to earth ground as shown on George's wiring diagrams.
Pics:
http://img529.imageshack.us/img529/6535/overallqf5.jpg
http://img529.imageshack.us/img529/3858/groundnr4.jpg
n_maher said:Well, not that it makes you feel any better but I don't see anything jumping out at me that looks incorrectly wired. I'm useless to you.
Yeah, I'm stumpified. The wiring is pretty basic, I've been building amateur radio gear for years so I generally can wire stuff up properly and have a good grasp of basic electronics. I pretty much followed George's wiring drawings to the letter.
You're not useless if you are sending me a couple input tubes to try. I appreciate it.
It could very well be the input tube still. I dunno.Ty_Bower said:
Actually he does have a signal generator handy. If it's driven from a computer, just look on the net for a freeware signal generator, or even find some tone samples. All you need is something in the range of a couple hundred Hz to a couple kHz. Measure the AC output from the sound card on your Multimeter, then check AC levels all along the signal path, i.e., input grid, input plate, output plate, speaker output. Note that as long as you are using a single test frequency, you don't even need a true RMS meter. If your meter can't handle the DC offset voltages, use an inline cap - something like 0.1uF will do fine.
Sheldon
You will find it very instructive. BTW, do keep your output transformers loaded. You can use the speakers if the level is not too high, but that can be annoying. Tip em over onto carpeting. But keep the level below loud listening levels or you could toast the drivers. Or, safer, use a load resistor. An 8R power resistor is ideal, but you can use significantly higher or somewhat lower values too. Parallel up some resistors if you don't have one big one.
Sheldon
Sheldon
I'd suggest either of these pieces of software...
http://www.fesb.hr/~mateljan/arta/download.htm
http://www.zeitnitz.de/Christian/Scope/Scope_en.html
http://www.fesb.hr/~mateljan/arta/download.htm
http://www.zeitnitz.de/Christian/Scope/Scope_en.html
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