Temporarily cranked bias to .50, see if it warms up.
After a few minutes.......well some minutes later, sink, nor devices are any warmer.
Going to start going through stuff to see if I have necessary outputs on hand.
Anyone have answer for "cool but plays with correct bias and offset? Quite cool on that side!
Stumped,
Russellc
After a few minutes.......well some minutes later, sink, nor devices are any warmer.
Going to start going through stuff to see if I have necessary outputs on hand.
Anyone have answer for "cool but plays with correct bias and offset? Quite cool on that side!
Stumped,
Russellc
This is where an oscilloscope, a dummy-load resistor and a simple signal generator come handy...
The voltage drops across all 3W resistors should be pretty much the same...
I am not sure if there was a case where the short-circuit, protection ("snubbing") transistor was playing up...
The voltage drops across all 3W resistors should be pretty much the same...
I am not sure if there was a case where the short-circuit, protection ("snubbing") transistor was playing up...
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Sorry... I was joking that I had done precisely the same thing and in addition was silly enough to also try to measure bias without having a set of leads hooked up to the DMM on another occasion. To everything turn, turn, turn.... with no result. That joke fell flat.
Anyway - so glad you've got it sorted. Enjoy!
You should have seen me trying to set my first BA3 while working under a ceiling fan! never mind a slight breath sends meters going wonky!
Half of mt AlephJ is nice and hot, half cool....despite bias and offset showing normal. Can hardly wait to see what boneheaded thing Im doing wrong. Amp was fine....but I just had to zero settings...Grrrrr. Oh well.
Russellc
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My biggest fear is that I may have damaged the jfets and the front end CCS. I have more Jfets stuck away, but I hate to think of cooked toshibas. Not hot on heatsink, but plays and measures offset and bias as normal. Outputs just not heating up...may have to wait for Zenmod to throw in. I know he will ask, this is the kit Jim offered when he did the build guide and the boards and circuit are the same as used in 6l6's build guide.
Rereading guide to see if someone else had a "cold" side...
Russellc
Rereading guide to see if someone else had a "cold" side...
Russellc
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That's a good question - particularly because the bias is measuring normally.
Check the screws for sure.
He's a Sea Ranch for the next few days. Supposedly going to make a 2000W per channel single-ended germanium Tonkin 7.1ch home theater amp from parts scrounged from Nelson's garage.
Or something.
Maybe...
You do know that Jim and 6L6 are, in fact, the same person...
Much like Bruce Wayne and Batman
I've been spending too much time on the 15 song album thread
Hmmmm, maybe my next suggestion will be songs that remind you of your first build... Sometimes It's a Bitch comes to mind...
Relevant to this thread and your current situation - I 2nd Dennis' recommendation.
Part of the "tuneup" I was doing was to tighten the outputs. I built this before zenmod suggested using lock washers on outputs, so occasionally check it. Then I decided to zero offset and recheck bias. Was just fine, but I had to fix it...... now the cold side. i'm measuring at the device.
Thanks for the thoughts,
Russellc
Yes. Slight variation, but all close. I will power it up and remeasure and post results. I mean if it didnt play or measure right I would understand, but oddly, it measures and plays. A cold heatsink is not AlephJ normal. I must have damaged something "fixing it"
Russellc
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Did you tighten the output MOSFETs?
If yes, carefully check that you did not short any drains to ground.
Also!!!!
If you were tightening the MOSFET's whilst they were soldered to the PCB (which is almost certainly the case), you may have created the cold joint between one of the MOSFET gates and their outlets on the PCB... you may have even cracked the pin altogether.
... worth checking, easily done with an ohmmeter.
... in general, you tighten the MOSFET's and that's it.... then you solder them.... and leave the combo alone. Any additional tightening will almost certainly move the MODEF't a bit, which will put the stress on the solder joints (in the best case)
If you were tightening the MOSFET's whilst they were soldered to the PCB (which is almost certainly the case), you may have created the cold joint between one of the MOSFET gates and their outlets on the PCB... you may have even cracked the pin altogether.
... worth checking, easily done with an ohmmeter.
... in general, you tighten the MOSFET's and that's it.... then you solder them.... and leave the combo alone. Any additional tightening will almost certainly move the MODEF't a bit, which will put the stress on the solder joints (in the best case)
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Actually, I guess from heating and cooling, they slowly loosen up. Tighting once and that's it will lead to insufficient contact and overheating resulting in failure.
The amount tightened is small, no further stress on joints. If completely undone, as in replacing the keratherms, I would reflow the joints.
While tightening could possibly have caused a short, would this still allow proper bias to be set, as well as offset as well?
Russellc