Bottlehead Forum
Bottlehead Kits => Stereomour II => Topic started by: hbonilla on October 17, 2015, 06:02:34 PM
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This is my first DIY amp.
I checked all the OHMs and everything seems ok. However, when I put voltage only the small bulbs light up and my measurements are exactly half the voltage in the manual. Any ideas?
Thanks
Hector
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Were your power transformer secondary voltages (p.31-32) correct?
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I agree with Josh. Sounds like you have the primary of the power transformer set for 220 but feeding it with 110. That would give you roughly half the voltage on the secondary.
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:) Thanks. I checked my wiring on pages 28 and 29 and found a mistake. I had connected 2 to 48U rather than 3 to 48U. Connection is correct now but my readings are still exactly half of what they should be.
My input voltage is 122.5
I reviewed my notes and the Power Transformer Secondary test was on target +- 10%
Any other thoughts?
Thanks again
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Look at the high-voltage rectifier connections (and orientation).
If you don't see anything there, somebody will get more meticulous once the work week begins. <eanwhile, it never hurts to re-flow all the solder connections, and that fixes more than half the problems...
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What is the AC voltage between terminals A1 and A4? (Put one probe on each terminal to measure)
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AC Voltage between a1 and a4 is 2.0V
Does this make any sense?
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What's your line voltage?
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122.5 V AC
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Can you post a photo of your mains wiring?
122V on 120V mains should give more than 2V. I suppose it's also possible that your meter can't resolve the next digit, so if you had 2.4V, it might just say 2V.
-PB
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Hi, sorry for my late reply. Here are the picture please let me know if you see something.
Thanks
Hector
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That all looks correct. How about a photo of the terminal strip with the UF4007 diodes and pair of caps.
-PB
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Thanks
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What AC voltage do you have between terminals 19 and 20 on the power transformer?
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It is 161.7.
Thanks
Update Sunday Morning.
Yesterday I tracked back all my steps. I resoldered a few connections that I thought might be better and, voila, my numbers improved a lot. My only real problem now is number 7 which throws 407v rather than 170-230. I resoldered but to no avail.
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OK, well, this is a good indication.
What DC voltage do you see on terminal 44 with no tubes installed?
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Hi, thanks for the help. DC V terminal 44 is 464 without bulbs
Maybe you already saw this but here is an image of my last check. I am very off on terminal 7 with AC V 408 rather than 170-230
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OK, I seemed to remember you saying that all the voltage measurements were about half, but it looks like only 1 of the measurements is about half of what it should be. This is a big difference.
408V at 7 can have many causes, one of which is the 12AT7 not getting heated (is it glowing?), a missing ground jumper to the middle of the adjacent 9 pin socket, an incorrect resistor value installed between the center post and pin 8 of that 9 pin socket, etc.
Can you post a photo of that region of your amplifier?
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Yes, everything was half when I started this process, it is only 7 that is off now.
Here are the pictures of 12AT7. Yes the bulb is glowing and heating.
Thanks
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Try reheating the center leg of the MJE5731 feeding those terminals. Something is not conducting properly.
-PB
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I reheated both MJE5731. I also made a continuity test between the center of MJE5731 and terminal 7 and there is good connection, please see image.
DC V at terminal seven still 407.
Thanks
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Measure the voltage at pin 8 on the 9 pin socket of the offending side, then swap tubes and remeasure.
-PB
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Paul, I am back from my trip.
DC V on pin 8 is 12.2V
Thanks
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Paul, I am back from my trip.
DC V on pin 8 is 12.2V, how does that sound?
Thanks
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Do you get that voltage with both 12AT7's on the offending side?
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I just checked with both12A7's and voltage is the same. However the voltage is now 440 rather than the 407 that I was getting a couple days ago. I have done nothing to the amp.
Thanks
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Measure the resistance of pin 8 on the offending 9 pin socket.
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Resistance of pin 8 (against the center pin) is 366. Thanks
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12V over 366 Ohms is 32mA, which is way off target.
Can you carefully check the DC voltage on pin 7 of the offending socket?
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I have zero voltage, please see image
Was I correct in measuring resistance of pin 8 against the center pin? Or should I have done it against something else?
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Paul, thanks for all your help. I am leaving on a three week long work trip, I will reach out as soon as I come back..
Hector
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The red wire in that photo that you posted is not connected to the correct terminals.
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Hi Paul,
I am back from a ver long trip and ready to tackle this. You say the red wire is not in the correct terminal, can you tell me which of the two red wires ypu are talking about? A or B? Again thanks for all your help.
I checked A and as per page 48 should be connected to 7L and B6, which is as it is.
I also checked B and as per page 41 shpuld be attached to "lug closest to the chassis plate in the center of the volume potentiometer" and the other side to 10L, which is where they are now.
Are you talking about a different red wire?
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Sorry, it's been about a month since I posted that, and I don't see any errors. There is something pretty wonky going on here, you have 12V at the cathode of the offending side, the correct resistor in place, and 440V on the plate. This doesn't jive with the curves for a 12AT7.
This leaves us at flaky solder joints, which is very likely your issue. You can also swap the connections at OA and OB, and if the offending voltage stays put, then you know the C4S board is working.
-PB
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We received this amplifier in today, and a solder joint on the center lug of one of the 9 pin sockets was not flowed all the way. Upon resoldering this connection, the amplifier works properly.
-PB