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Old 26th April 2014, 03:50 AM   #3211
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You're measurements make no sense at all. You cannot have a different reading across C5 and R27. Your technique is flawed or you are not matching your measurements to the schematic correctly. You are showing 30 mA base current in the cascodes and 1.5 mA collector current. You also have 10x the current in the cascode base stoppers as there is in the voltage divider. These readings defy physics.

Try this way: attach the black lead of your meter to ground and LEAVE IT THERE! Now move just the red lead to the various points and record the readings. Don't worry about the voltage across components, we vs easily calculate that from the voltages at each end. I'm wondering if it is working fine it's just your measurement technique is totally FUBAR.
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Old 27th April 2014, 02:08 AM   #3212
dazed2 is offline dazed2  Canada
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Bob,
Yep you're right, I made some measurement mistakes. Here are the new measurements. attached black to ground and move the red around.

However, the measurements at Jfet is stil the same. 0.6V on K170 and 0,54V on J74.

BTW.... I was careless... and touched the probe across two resistors.... and let the smoke out.... scare the daylights out of me ! iIn fact blown two or three resistors So whatever BJT and jfets that was there, there are most likely blown now .

This is what I got before the magic smoke left.
Sooo anyone have a few jfets and bjt's lying around.....
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File Type: jpg schematic F5TV3 voltage2.jpg (364.4 KB, 229 views)
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Old 27th April 2014, 06:17 AM   #3213
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Something is seriously amiss with your cascodes. The voltage divider seems to do its job, giving you ~+/-16V but there is a huge voltage across R29 and R30. Double check their values. The cascode transistors are the next suspect. They shouldn't draw much base current (little to no voltage across R29/30 is normal)

What was your rail voltage before your accident? What are the part numbers on your BJTs? Read them off the part, and verify that they are in the proper place.

Last edited by BobEllis; 27th April 2014 at 06:19 AM.
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Old 28th April 2014, 03:08 AM   #3214
dazed2 is offline dazed2  Canada
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Yes the BJT's should be in the right place. I have pics of them here #3193

However. I think I figured out the issue. And it only took a burned up board for this
I took out all the components from the board to transplant the good ones to another board I have (had to buy extra set due to the double secondaries)
R29 and R30 are 475Kohm resistors, not 475ohm resistors
somehow I ordered the wrong ones

Oh well I guess that solves that now..

I haven't gotten around testing the bjt and the jfets to see if they are blown. but I suspect I need new ones....

anyone sell me a set?
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Old 28th April 2014, 08:06 AM   #3215
Zen Mod is offline Zen Mod  Serbia
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both Jfets and bjts are probably alive

well - you paid your price ....... hope from now you'll check all components trice , before placing them on pcb .....
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Old 28th April 2014, 10:39 AM   #3216
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Glad you got it sorted. Enjoy your amp as you finish it.
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Old 28th April 2014, 12:09 PM   #3217
BigE is offline BigE  Canada
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Quote:
Originally Posted by Zen Mod View Post
both Jfets and bjts are probably alive

well - you paid your price ....... hope from now you'll check all components trice , before placing them on pcb .....
That is great advice....I've done the same but with less disastrous consequences.
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Old 28th April 2014, 05:08 PM   #3218
dazed2 is offline dazed2  Canada
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Quote:
Originally Posted by Zen Mod View Post
both Jfets and bjts are probably alive

well - you paid your price ....... hope from now you'll check all components trice , before placing them on pcb .....

Yes, and pay attention to that itty bitty little symbol at the bottom of the DMM that tells you the order of magnitude the number is .
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Old 28th April 2014, 07:51 PM   #3219
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Originally Posted by dazed2 View Post
Yes, and pay attention to that itty bitty little symbol at the bottom of the DMM that tells you the order of magnitude the number is .
Get an auto ranging multimeter.
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Old 28th April 2014, 08:11 PM   #3220
dazed2 is offline dazed2  Canada
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Quote:
Originally Posted by nashbap View Post
Get an auto ranging multimeter.
Actually it is because it is autoranging that I didn't realize the "Mohm" instead of ohm. If I had to physically dial the range I probably would have caught it
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