SOON!

for Dynaco Mark II/III/IV and DIY PP monoblocks

Postby Ty_Bower » Sun Mar 29, 2009 7:15 pm

Cracked radiators are a drag. You can only stick so many eggs in them before you need to finally install a new one. Sump pumps are a pain too. Zoellers are expensive, but mine's been running strong. I ought to upload the video of it running. Four thousand gallons an hour is a lot of water...

Even three volts across the 10 ohm cathode resistor is nearly one watt of power dissipated in that resistor. Seven volts would be 5 watts. Are you sure you've got your meter on the right scale? Those 10 ohm cathode resistors should (must!) be rated for 1/4 watt to protect against exactly this kind of over current situation. You want those resistors to burn out if the power tubes are pulling massively way too much current.

Before I install any tubes at all, I power up the amp and check voltages at F, G, and H. If you have a digital meter, attach the negative (black) probe of your meter to ground. Probe F, G, and H with the red probe. You've already indicated you see -73 volts at H which is a good thing. You should be able to get the same voltage at F and G as well. If you don't, stop here and figure out what is wrong before you install any tubes.

No voltage at pin 1 of V1 and V2 is odd. It suggests you poof'd something somewhere along the power supply. I'll assume pin 6 of V2 is in the same condition, as it should be at the same voltage as pin 1. I could believe the rectifier gave up, rolled over, and died. That would explain the lack of voltage on the driver tubes but then why is there voltage still present at the 6550s?
"It's a different experience; the noise occlusion, crisp, clear sound, and defined powerful bass. Strong bass does not corrupt the higher frequencies, giving a very different overall feel of the sound, one that is, in my opinion, quite unique."
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Postby JW34 » Tue Mar 31, 2009 4:29 pm

So I've been scratching my head and found a major problem, although new ones have formed.

I used 100 ohm rsistors instead of 10 ohm to ground the cathodes of the output tubes. I also went out and bought a new multimeter and now I'm seeing 420-440mv on the outputs before biasing.

Voltages with output tubes and rectifier and no pre's

V1:
1...483
3...?
4...6.83
9...6.83

V2
1...544
3...?
4...6.85
5...6.85
6...541
9...6.85

V3 & V4
1...427 & 448 mv
2...6.85
3...559
4...560
5...-70.4
6...-70.4
7...6.85
8...427 & 448 mv

V5
2...566
4...444
6...444
8...566
Power supply:

Sec 1- 570V
Sec 2- 564V
Sec 3- 489V!!!
Sec 4- 543V!!!

D: 6.84V
E: 6.84
F: -70.4
G: -70.4
H: -74
J: 489
K: 451

I"m guessing that R6 and R16 are fried (though they don't look fried) since the voltages are to high? What else would cause so much voltage on J and K? Is it because V1 and V2 aren't plugged in?

Thanks,

Jay
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Postby Ty_Bower » Tue Mar 31, 2009 4:57 pm

JW34 wrote:I used 100 ohm resistors instead of 10 ohm to ground the cathodes of the output tubes.


Ooops. That'll throw off your bias readings a little bit. Almost kinda funny, actually. No harm done there, though. Honestly, you could probably even leave them at 100 ohms. You'll get a little bit of "cathode bias" from them, which shouldn't matter much. Just remember to divide your millivolt readings by 100 instead of 10.

JW34 wrote:I"m guessing that R6 and R16 are fried (though they don't look fried) since the voltages are to high? What else would cause so much voltage on J and K? Is it because V1 and V2 aren't plugged in?


That is exactly why. The voltage at the plate pin will be very high with no tube installed in the socket. Resistors don't fry because of too much voltage, they fry because of too much power (current times voltage). Measure R6 and R16 with your ohmmeter. If they match what it says on the schematic, then they are still OK.

I just went through all your voltage readings. Your AC voltages are all 8.5% higher than spec, which is almost certainly due to higher than average line voltage. The high line voltage is resulting in higher DC readings across the board. Other than that, everything looks perfect (keeping in mind that V1 and V2 aren't installed). At this points I'd be inclined to stick the driver tubes back in and go for it.
"It's a different experience; the noise occlusion, crisp, clear sound, and defined powerful bass. Strong bass does not corrupt the higher frequencies, giving a very different overall feel of the sound, one that is, in my opinion, quite unique."
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Postby JW34 » Tue Mar 31, 2009 6:46 pm

So....I plugged in V1 and V2, as soon as the delay turned on I saw 52V instaed of 219V at V2 and then smelled something funny, looked and saw that the 680 ohm resistor on the 16 ohm tap fried.

Could you take a look at page 1 at how I ran the 680 resistor and let me know if it is right?

Thanks,

Dummy here
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Postby Ty_Bower » Tue Mar 31, 2009 7:53 pm

How is the 0 ohm tap of the output transformer's secondary tied to ground? I don't see it in your wiring diagram.
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Postby JW34 » Wed Apr 01, 2009 4:41 am

Common - connected directly to speaker binding post
4 ohm- capped off
8 ohm- speaker binding post
16ohm- to nfb with a 680ohm resistor tied to ground

I was under the impression that I didn't have to tie the Common to ground, just the binding post.
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Postby Ty_Bower » Wed Apr 01, 2009 5:03 am

The feedback circuit won't work unless the output transformer's common is tied to ground. Check the Poseidon manual on page 3.
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Postby TomMcNally » Wed Apr 01, 2009 8:45 am

You really need to put a junk speaker across the output and
make sure the amp isn't oscillating - be prepared to kill the
power fast and fix it. If the feedback loop is connected
wrong, you get a big oscillator !

Don't use good speakers - just something you can hear
with ... you could even bridge a speaker across your
dummy load temporarily.
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Postby JW34 » Wed Apr 01, 2009 5:28 pm

So now it is gounded but I only have 79V going to Pins 1 and 6 of the 12AU7/12BH7 and 400mV to Pins 3 & 8. J and K's voltages now look good and the 680 ohm resistor is not burning up.

I'm guessing that U1 is dead since R10 and R11 look fine. Is this a good assumtion?

As far as the speaker goes, I have to try to find a crappy one.
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Postby Ty_Bower » Thu Apr 02, 2009 3:05 pm

Are you sure you put a 10 ohm resistor at R9? Can you verify the value of R10 and R11 (should be 68K ohm)?

With such a low voltage (400 mV) on the grid of V2, there should be a lot of current running through it. The low voltage at the plate (79V) supports this theory. High current through this tube for prolonged periods of time won't be good for its life. I would not operate the amplifier too long in this condition.

Having said that, can you (carefully!) measure the voltage drop across R10? Or better yet, just tell me what voltage you saw a point K?

Here's a little math...

If you've got 430 volts at K, and 79 volts at the plate of V2, that's 351 volts dropped across R10. If R10 is 68k ohms, that's 5.2 mA current per side of V2. The 12AU7 is rated for 2.75 watts per side, or 5.5 total for the whole tube. 5.2 mA times 351 volts equals 1.8 watts per side, or 3.6 watts total. The tube should not be in any danger. Is it really a 12AU7?

If R9 is out of spec, that could cause problems. A precision metal film resistor is really needed here, I think. If R9 is 6.4 ohms instead of 10 ohms, you should get ~10.5 mA total current for V2. Or maybe something bad did happen to U1...?
"It's a different experience; the noise occlusion, crisp, clear sound, and defined powerful bass. Strong bass does not corrupt the higher frequencies, giving a very different overall feel of the sound, one that is, in my opinion, quite unique."
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Postby JW34 » Fri Apr 03, 2009 2:22 pm

Ty,

Wow! That is crazy drainage! I just looked at that video and it is insane! Why do you have so much drainage? Ever looked into a battery backup system for that. If you lose power you're screwed! Do you live in a valley? My God!

On another note, I'll be taking voltage readings soon.

Jay
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Postby JW34 » Fri Apr 03, 2009 3:01 pm

Voltages,

K - 436V
Across R10 - 336V

I also took a measurement across R9 and it read 6.4 Ohms on the board (like you said). I replaced it with a 10 Ohm from my other board (that still read 10 Ohms while connected to the board), took a reading it and it gave me 6.4 Ohms again. U1 is obviously toast right?

Thanks,

Jay
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Postby Ty_Bower » Fri Apr 03, 2009 4:39 pm

JW34 wrote:Wow! That is crazy drainage! I just looked at that video and it is insane! Why do you have so much drainage? Ever looked into a battery backup system for that. If you lose power you're screwed! Do you live in a valley?


Yes, it is crazy. The water comes right up from under the slab. A battery backup would be useless - ever see a battery backup that can handle 4000 gallons an hour? The pump in the video ran flat out for a couple hours. It never shut off. Yes, a power outage would be very bad. The soil here as all clay, and when the builder constructed the place he dug a big hole for the basement. The lot is on the side of the hill, so all the runoff from the uphill side flows through the loose packed soil around the foundation, fills up the clay bowl, and tries to find a way into my basement.

It's gotten a lot better since the earth has settled around the house, and the uphill neighbors have grown some grass on their yards. I'm still waiting for "the big one", and keeping my fingers crossed it doesn't happen.

That Zoeller is a darn good pump, though.
"It's a different experience; the noise occlusion, crisp, clear sound, and defined powerful bass. Strong bass does not corrupt the higher frequencies, giving a very different overall feel of the sound, one that is, in my opinion, quite unique."
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Postby JW34 » Fri Apr 03, 2009 6:14 pm

I wish I would have known about zoeller sooner. Maybe I'll pick one up this summer as a replacement the "El Cheapo" I just bought. Seems like the Zoeller has gotten great reviews.

Don't you have any spare capacitors you can use as back up power? :))
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Postby Ty_Bower » Wed May 06, 2009 7:09 pm

Jay,

How's your Poseidons doing these days?
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