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In the Forum: Melquiades Amplifier
In the Thread: Planning my DSET
Post Subject: Keep looking, I was there....:-)Posted by Romy the Cat on: 5/21/2019
 anthony wrote:
I did finally manage to get a day and a half to make the second DSET operational but it refuses to bias correctly.  I've traced the circuit a dozen times, checked component values, tried to find shorts, checked cap polarities, swapped tubes...no result.  The gas regulators both sit on 148v-149v with 15ma of current.  With the input shorted I am able to roughly bias the 6e5p/6e6p but a couple of channels only bias to -1.2V (Channel A & C), one to -2.2V (Channel B) and the rest are fine at -4V.  When I unshort the input I have 4.5V, yes volts, of DC offset, and the low bias tubes (A & C) actually swing into positive bias, which is strange.  Something is not right but I just cannot find it...a day and a half last weekend looking for it and I did not even turn on the soldering iron.  Very frustrating.  The fault will be found, I just need to be smarter about how I look for it...
So Romy, if you are able to offer any insight into how to find this fault I would be much appreciative.  I do understand that you will have much better things to do that hold my hand on this.
 Anthony, unfortunately I have no time now to look into it deeper and I assure you that unit I will you will find the fix on your own. There is something that you did wrong of one of you component is faulty. The best way to fine it is to roll the complexity back, to isolate the channels and to test them independently. Take the circuit and write the voltages that should there before and after of each element in the channel, then measure the actual voltages. You will very soon find the location where the inconstancy took place.

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