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Post by Mr Trev on Dec 4, 2017 23:51:35 GMT
I ordered an adapter to use the 5670 tube in my Little Bear P1
So I plugged it in and nothing exploded - good thing, but I couldn't get any bias voltage reading - bad thing. A bit of exploration with a multimeter and I found neither of the internal shield pins are connected. Is this still workable? Where else could I use for that - I use grabber probes on the socket legs to get my voltages at the moment
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Post by Mr Trev on Dec 5, 2017 3:55:04 GMT
Did some experimenting. Since I couldn't get any reading directly off the socket for some reason, I went hunting for a place to measure bias on the bottom of the PCB. Using the + side of the output cap and the RCA shield for ground I can get the 13v for one side, both the other is stuck at 20v regardless of how the bias pot is dialled in. Does this seem like the adapter is bad, the tube just won't work in my sad little amp, or gross human error caused by measuring the wrong thing
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solderdude
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Post by solderdude on Dec 5, 2017 7:20:03 GMT
possibly the converter is not wired properly inside or the tube itself is not O.K. or simply the adjustment range is too small for this tube.
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Post by Mr Trev on Dec 5, 2017 17:25:53 GMT
Poked at the adapter last night, and the pins seem to be going to the correct place going off the data sheets I found - L/R may have been switched or I could just have mirror images confused. The only possible issue I found was that pin 5 (internal shield) on the 5670 side and pin 9 (heater mid-tap) on the 6922 side aren't connected to anything.
I found it odd that I can adjust bias on the one side between 9-17v but the other side is 20v no matter where the pot is sitting
With the 5670 being a .350a tube, is it a case of the amp not having the output to handle it. I assumed that the .05a different wouldn't be enough to cause an issue but maybe that is the reason these amp are so cheap
Is it possible to test the tube without any fancy equipment?
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solderdude
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Post by solderdude on Dec 5, 2017 21:01:00 GMT
Does the heater light up ?
You can measure the DC resistance of the heater (a few Ohm) of the tube itself and you can check the DC resistance of the tube in the socket.
Check if you can measure the heater resistance on the tube socket pins between: 4 & 5 4 & 9 5 & 9
When the heater is measured between 4 and 5 then the heater should work fine.
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Post by Mr Trev on Dec 5, 2017 23:56:44 GMT
The tube lights up as expected - quite brightly. if nothing else I have a good mood light Which tube socket should I be measuring (pcb, 5670 side adapter, 6922 side adapter). Nice thing about the adapter is since its a socket saver type there is enough room to fit grabber hooks between the adapter and the pcb socket. For the time being I put the ecc189 back into my main amp - to confirm the amp is still working correctly (it is) I stuck the adaptered 5670 into my 2nd P1 (the unmodded unit) and have the same issues, except the permanently maxed bias is ~18v instead of ~20 and only the one side 5670 Pinout6922 pinout Here's some pics of the pinouts Lobalwarming sent to me. I found the same datasheet last night and the only "problem" I found is that pin 5 of the 5670 isn't connected to anything whereas the spec sheet mentioned it should be connected to ground
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solderdude
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Post by solderdude on Dec 6, 2017 0:48:28 GMT
When it lights up no need to test for heater issues. Pin 5 can be left open in this case/ A screen is only needed when used in RF applications.
Just check if cathodes, grids and anodes go to their respective tube halves. When they do most likely the tube is faulty on one side or the amp does not have the required adjustment range.
1 6922 to 4 C8J 2 6922 to 3 C8J 3 6922 to 2 C8J 4 6922 to 1 C8J 5 6922 to 9 C8J 6 6922 to 6 C8J 7 6922 to 7 C8J 8 6922 to 8 C8J 9 6922 open 5 C8J open
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Post by Mr Trev on Dec 6, 2017 2:02:25 GMT
Your cross reference confirms what I measured last night, so the adapter is wired correctly.
If you were a betting man what would you say is the problem if I can get an adjustment range of 7-18v on one side and a range of only 17.9-18.1v on the other: tube or amp? (I'd probably guess the amp, but shouldn't both sides have the same limited range).
Thanks for your help, by the way
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solderdude
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Post by solderdude on Dec 6, 2017 10:02:03 GMT
Either one tube half is faulty or the adjustment range of the amp is too small. It is why G1217 amps have a different way of biassing tubes. To allow for a bigger usable range of tubes.
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Post by Mr Trev on Dec 6, 2017 17:16:13 GMT
I did message the seller about the possibility of a bad tube, but I'm more likely to believe the problem is with the amp. I guess I'll need to hold out for a proper amp - maybe I should've opted for the Big Bear Thanks again. ps: if any forum members have been listening in and have a cheap g1217 or Vali 2 they want to get rid of, shoot me a PM
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