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SOHA II Builders Thread - Page 88

post #1306 of 1687
Thread Starter 
Yes, I agree, the only possible failure here is Q1/Q2. Are you sure that these are BC560 and not BC550?

Also, pin 7 of the opamps should be at 15V. Then you have pin 4 at -15V,15V. This is probably a typo. If not, pin 4 should be at -15V on both opamps. But pin 7 not at +15v indicates a problem.

Before you do anything else remove C1 from both channels. Let's decouple the AC just to remove this as a possible transient startup problem.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #1307 of 1687
Quote:
Originally Posted by runeight View Post
One problem would be that you are running 12v tubes at 6V. Try setting the heater for 12v and see what happens.

Edit: Never mind. I see that you say 6.3V but are actually running at 12V. Off to look at the schematics.
Aren't 5963 tubes supposed to work at both heather voltages?

Anyhow I see what you mean, Instead of the jumpers I'm using this switch: Farnell Export, could it be the cause?
post #1308 of 1687
Thread Starter 
No, a switch is ok and the voltage readings at your sockets say 12.6V. 5963 can only work at both heater voltages through connecting the interal triode heaters in series or parallel modes. In the SOHA II all 12V tubes that have this feature are wired in series mode and hence they all must run at 12V.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #1309 of 1687
Quote:
Originally Posted by runeight View Post
You're welcome.

Here's an alternate way to wire the LEDs that might be preferable because it keeps the LED current out of the ground flow. RLED is calculated using 24V instead of 12V.



Edit: I've changed the drawing slightly to be consistent with common representations of dual LEDs. And, of course, one can always use individual LEDS.

I've also changed one resistor value. It's not important, but it does serve to equalize the base currents for the alternate version.
Is this diagram out of date? Why does it refer to 12V rails when the current design is 15v rails. Did I miss an update somewhere?

Thanks
post #1310 of 1687
Quote:
Originally Posted by runeight View Post
Yes, I agree, the only possible failure here is Q1/Q2. Are you sure that these are BC560 and not BC550?
Yes, they are BC560, and they where purchased in a differente place and long ago, so it's unlikely that they are faulty too.

Quote:
Originally Posted by runeight View Post
Also, pin 7 of the opamps should be at 15V. Then you have pin 4 at -15V,15V. This is probably a typo. If not, pin 4 should be at -15V on both opamps. But pin 7 not at +15v indicates a problem.
Mmmm, I made a mistake numbering the pins when passing the measurements to the post , this is actually what I'm reading (top view of the opamp):


Quote:
Originally Posted by runeight View Post
Before you do anything else remove C1 from both channels. Let's decouple the AC just to remove this as a possible transient startup problem.
Argh!!! Don't know if I could be able to do it now, my girlfriend is claiming some time for herself . I'll try to be quick, luckily I'll be finished before she finishes to dry her hair .
post #1311 of 1687
Thread Starter 
OK. Opamps are correct. Good luck.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #1312 of 1687
Ok, I've removed C1 from both channels, but still 230 mv of voltage drop between TPL and TB+L.

I have to go now (if I want to keep my masculinity intact jejejeje). Tomorrow I will spend a few ours more with the amp.

Many thanks for your help runeight!!!
post #1313 of 1687
Thread Starter 
Try another tube, like 6922 running at 6.3V heaters. Just in case these tubes are bad.

There are only two ways you can have this problem.

1. The current mirror Q1/Q2 is not working
2. The right hand triode is not conducting
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #1314 of 1687
Thread Starter 
Quote:
Originally Posted by stringgz301 View Post
Is this diagram out of date? Why does it refer to 12V rails when the current design is 15v rails. Did I miss an update somewhere?

Thanks
Diagram is out of date because there is a simpler solution. The 12v rails come from the 12V regulators that step down the 15V rails to get the correct voltage for the e12 relay.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #1315 of 1687
Quote:
Originally Posted by runeight View Post
Try another tube, like 6922 running at 6.3V heaters. Just in case these tubes are bad.

There are only two ways you can have this problem.

1. The current mirror Q1/Q2 is not working
2. The right hand triode is not conducting
Ok, good news

I've replaced the tubes with a pair of new Electro Harmonix 6922 and with the heather selector set to 6,3 V I get white smoke coming from R3P resistor. I've replaced it with a new one and, again, white smoke.

The removed resistor still measures 8,2 Ohms, so I believe it's not really fried. Should I get a new resistor with more wattage?

Is this a new sympton of what's happening or is it unrelated and does not give us any information?
post #1316 of 1687
Quote:
Originally Posted by runeight View Post
Diagram is out of date because there is a simpler solution. The 12v rails come from the 12V regulators that step down the 15V rails to get the correct voltage for the e12 relay.
Ummm. Ok. Can I ask what the simpler solution is? Pretty please!
post #1317 of 1687
Thread Starter 
Quote:
Originally Posted by Alcaudon View Post
Ok, good news

I've replaced the tubes with a pair of new Electro Harmonix 6922 and with the heather selector set to 6,3 V I get white smoke coming from R3P resistor. I've replaced it with a new one and, again, white smoke.

The removed resistor still measures 8,2 Ohms, so I believe it's not really fried. Should I get a new resistor with more wattage?

Is this a new sympton of what's happening or is it unrelated and does not give us any information?
My guess is that your heater switch is wired incorrectly. Please check the jumpering information on the PS schematic on the website. I bet you have wired as though the jumpers are crosswise instead of lengthwise.

If not, then there is another more serious problem.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #1318 of 1687
Quote:
Originally Posted by runeight View Post
My guess is that your heater switch is wired incorrectly. Please check the jumpering information on the PS schematic on the website. I bet you have wired as though the jumpers are crosswise instead of lengthwise.

If not, then there is another more serious problem.
Actually, there's no wiring, it's an ultra-miniature switch (this one:http://www.farnell.com/datasheets/32938.pdf) soldered directly to the board.

As per the datasheet, it should be ok. The connection diagram is like this:



Hope that I'm wrong and it's just the switch

EDIT: Nevermind, the switch seems to be faulty , I've checked and there's continuity between pins that shouldn't be connected.

I will replace it for a couple of jumpers and report back, hopefully the problem is just that
post #1319 of 1687
I've replaced the switch for a couple of jumpers. No smoke now with 6,3 V heather selected and 6922 tubes in (though R3P gets pretty hot).

Unfortunately TPL is still almost the same as TB+L (about 220 mV of difference). Should I try with another set of new BC560?
post #1320 of 1687
Thread Starter 
Yes, this is your only choice now, but before you put new transistors in do diode checks on the junctions and make sure that they are really pnp and that they are working.

R3P will get hot so that your heater regulator doesn't.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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