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Old 26th September 2012, 11:24 PM   #1
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Default K12G Help

I'm a first time tube builder and very little electronics experience. I just finished building the S5 Electronics K12G kit and it did power on with no smoke or blown fuses....but it doesn't work right either.

Problem: I get either low sound and popping noises from the right channel with only background hiss from the left, or I get clear full volume sound from the left with only hiss and popping noises from the right channel. I have tried moving the tubes around in different orders and the above is the only result I can get. All the tubes light up, although one of them will light up brightly for a second before settling down to match the others; I thought this one might be bad, but it's position doesn't seem to make a difference.

I double checked to make sure everything was in the right place, all my solder connections are very clean, no burn marks anywhere, all of the pins from each socket has at least some resistance value when measured from the pin to the speaker black.

Any thoughts? I don't have any testing tools beyond a multimeter, keep that in mind in your replies please. I'd like to try and figure out what went wrong, but worst case, I'll package it up and send to S5 for repair.
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Old 27th September 2012, 07:42 AM   #2
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It would greatly help if you could give us some voltage readings for both channels.
This has to be done with the amp switched on - of course - so please be very careful. Use clip-leads on your multimeter and change clip-position only when the amp is turned off and caps have discharged.
Interesting values are the anode and cathode voltages and the B+ voltage.
This would be IIRC voltages on "upper" leg of R8 and R17, R1 and R3, R9 and R13 (cathode resistors), "lower" leg of R2 and R4, R10 and R12 (anode resistors), as well as C8 and C9 (power supply voltages).

If you could post a schematic that would also help because not everyone is familiar with the K12G design.
Is it this one? I based the part numbers on that schematic:
http://diyaudioprojects.com/Gallery/...ge.php?pid=368

I build a K512 amp (or what's it called?) from AES some years ago which is very similar in design. It is a simple design and I am confident we will find the error easily.

Best,
Martin

Last edited by bayermar; 27th September 2012 at 07:51 AM.
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Old 27th September 2012, 10:30 AM   #3
rock12 is offline rock12  United States
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I built the same amp and am very pleased though still working on a case. go over all you connections again because it is easy to reverse or screw up the numbering
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Old 27th September 2012, 08:05 PM   #4
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Quote:
or I get clear full volume sound from the left with only hiss and popping noises from the right channel.
Hi Soundwave steve,

Try reproducing this result in the left channel and see if you can turn the volume down as normal. If so you have a working channel with good valves. The other two valves can now be checked by swapping. Voltages in the good left channel can now be compared to the right channel.

I like to power up a new build for the first time without the valves. This gives convenient and usually safe access to the socket pins from above. Basic voltages can then be checked before insertion of the valves.

I have ecc83 valves that flash brightly on startup but is not a problem in my case, not sure about the 10gv8.

Checking voltages with respect to ground with your multimeter should be more than enough to trace your fault.


Good luck

Bill
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Old 28th September 2012, 03:51 AM   #5
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Bill - are you saying that I can probably run my amp with no tubes in and not harm it? I was thinking about testing all of my tubes in the left channel only to see if they were all good, but I was afraid I would harm something.
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Old 28th September 2012, 12:22 PM   #6
rock12 is offline rock12  United States
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It is easy to burn up db1 so check your voltagesDIY Audio Projects Forum • K-12G Tube Amp Kit Build Thoughts hope this link helps and works
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Old 28th September 2012, 01:57 PM   #7
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Quote:
Bill - are you saying that I can probably run my amp with no tubes in and not harm it?
Yes.

Bear in mind with all tubes out you are running the stereo amp under no load conditions. This will elevate the voltages by about 10% compared to what you might measure with all the tubes put back in.

A quick measure of the ac voltage across pins 4 and 5 of each socket should tell you if alls well with the heater supply.

Measuring pin 6 to ground of each socket will tell you if the B+ ( high dc voltage ! ) has arrived from the rectifier. Expect a variation of a few volts in measurement. Each output transformer may not be perfectly matched and centre taps in their primaries may not be perfectly centred.

Measuring pins 7 to ground should show no variation. It will have a lower voltage than the B+ due to the effect of dropping resistor R18.

Quote:
I was thinking about testing all of my tubes in the left channel only to see if they were all good, but I was afraid I would harm something.
Best to put all the tubes back in as this will load the power supplies properly. Reproduce the conditions where you have a loud clear channel. Unless you've marked the "good" tubes already with a felt tip pen then this might be a bit of pot luck. Check your volume pot is functioning properly as this might be the cause of your woes, not your tubes. Turn off and let your tubes cool down for about 10 minutes. Swap a good tube for an unknown one from the other channel. If good then label. Turn amp off and leave to cool then repeat the process for the last unknown tube.


HTH Bill
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Last edited by Soonerorlater; 28th September 2012 at 02:00 PM.
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Old 29th September 2012, 06:19 PM   #8
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I'll get back with you guys soon on my findings - I'll be out of town for the week and will check everything when I get back. Hopefully with your help I'll be enjoying my first tube amp soon!
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Old 14th October 2012, 04:45 AM   #9
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Hey guys! Just wanted to give an update on my K12G, I got it working! Bad soldering was the cause - I ended up resoldering about half of the board to make sure every connection clean and solid. When I powered it, everything worked great!

Thanks for everyone's support and willingness to help! Winter is coming in two months or so and it will be great time to start digging into the unit and begin modifications
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