Bottlehead Forum
Bottlehead Kits => Kaiju Stereo 300B amp => Topic started by: thunderfrenchie on November 02, 2018, 05:13:18 AM
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Hi, total noob here. I assembled my Kaiju with zero problems, every test checked along the way. It worked perfectly at first. I was able to adjust the hum pots and the amp was 'quiet' at idle with no music. I left it on for 72 hours in a row to burn it in. It then developed a low level hum in the left/black channel. The pot is now out of whack. Turning it all the way to the left reduces the noise but meter still reads .123.
Some measurements.
Right (OK side):
53U: 57.6
IA: 504
OA: 297
32U: 174.2
Left:
65U: 23.1 [this seems a problem]
IA: 504
OA: 298
46U 174.0
Thoughts?
Thanks,
John
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Can you post some photos of your build?
Is the 100uF axial capacitor oriented correctly on that side? Are any of the legs of the hum pot touching the chassis?
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Also swap the 300Bs and see if the hum follows the tube and/or if you get different voltage readings
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Your pictures are teeny tiny, I can't see anything in there. If the forum is bugging you about file size, you can put a couple on a post, then post the rest separately.
The hum pot is the 10 ohm one with the 22 ohm resistors attached to it.
-PB
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OK, larger...
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10U doesn't look to be soldered.
What is the AC voltage between A1 and A4 with a 300B in the socket and the amp running? (A pair of clip leads would be helpful to measure this)
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On the affected side (actually B1 and B4) I'm getting 330v dc
On the unaffected side (A1/A4) I'm getting around 280.
Black lead was on the 1.
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Also desoldered 10U and 14-23U
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That's REsoldered
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Sorry, I meant to ask what the AC voltage is between B1 and B4, not A1 and A4.
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AC I get 0
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Be sure your meter is set to a very low range. You can compare your values between B1/B4 and C1/C4. I suspect you will find a difference between sides.
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In case it matters also notice I get a little transformer hum from PT9. All measurements with no speakers attached btw
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C1/C4 yields 4.92 V AC
Now getting about .003 v AC on B1/B4
My meter, Sperry DM-6250 is qutorange. Happy to buy whatever meter you recommend.
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B1/B4 now stabilizing around .007 v AC
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Could I have a bad 5670?
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Also in case it matters, when I first discovered the problems, I noticed that the affected side's OT was much hotter than the other.
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B1/B4 now stabilizing around .007 v AC
What AC voltage do you between terminals 5 and 7?
Could I have a bad 5670?
This is incredibly unlikely. You don't have heater voltage at your 300B.
I noticed that the affected side's OT was much hotter than the other.
The output transformer is on the bottom of the chassis and the plate choke is up top. The plate chokes will get warm during operation, but the output transformers tend not to. Can you confirm which was presenting a temperature difference?
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42U does not look soldered.
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The OT on the side that was humming. Even after the other side had cooled down the OT was quite warm. At full power it was definitely hotter than the other.
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OK, resoldered 42U. I found that one half of the 7 resistor was not soldered. Did that and the reading between 5 and 7 is .047v ac. Retested 1 & 4 and that is now 2.73.
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Also, in the short time I was checking the voltages, the OT on the affected side is warm where as the other side is cold.
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Sorry, just reread your post. It is the choke that is getting hot.
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OK, resoldered 42U. I found that one half of the 7 resistor was not soldered. Did that and the reading between 5 and 7 is .047v ac. Retested 1 & 4 and that is now 2.73.
Is that B1 and B4 shows 2.73V AC between them but 5 and 7 show 0.047V AC between them? (This is almost impossible BTW)
Sorry, just reread your post. It is the choke that is getting hot.
If the voltage at 14 isn't considerably lower than it should be, then this isn't a concern.
I would recommend performing the power transformer test found on page 34 of the manual. Specifically, you have no AC voltage between 5 and 7. There should be 6V AC there. You'll want to measure the AC voltage between power transformer terminals 12 and 13. If there is 6.3V there, then there is a break in the green twisted pair of wires between those terminals and terminals 5 and 7. If there is no AC voltage there, then power off the amp and disconnect each green wire on those power transformer terminals and retest.
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Thanks Paul. I just retested the PT as on pg 34 and everything checked out perfectly. I'll do your green wire test in the morning.
Sorry about the confusion on the last set of measurements. Just redid and I have:
B1/B4: 350v DC, 0v AC
B5/B7: .3mV DC, .041v AC
C1/C4: 4.97v AC
Will let you know how it f=goes and THANK YOU for all the help thus far.
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Paul, I just realized when you've been referencing 5 & 7 voltages, you mean that of the terminal strips, NOT positions 5 & 7 on the 5670 socket.
On the affected side, which is actually 20 and 22, I am getting the full 6.3v AC, all good there. C1 & C4 hold steady at 4.95v AC. The unit is wired for 4ohm spur taps.
Anything else I should try/inspect?
Thanks!
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ALSO, just realized I had been measuring B1 and B5 values. The correct B1/B4 reading is 80.5v AC.
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OK, let's go backwards a little bit. Can you also give me these AC voltages:
Between 4 and 7?
Between B1 and B4?
If you have OV AC between B1 and B4, that is your affected side, you will get no music out of that channel. If this is counter to what you have observed so far, perhaps a 300B swap caused the issue to change sides?
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ALSO, just realized I had been measuring B1 and B5 values. The correct B1/B4 reading is 80.5v AC.
There is no B5.
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OK, I'm officially an idiot. Where I have been writing "B" I meant "D", the 5670 socket, which is not at all what you have been asking for. OK, once more with feeling... measurements coming...
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I think one of the 22 ohm 5W resistors on the affected side was not all the way soldered or properly connected.