Pearl Two

ra7 · 2011-12-07 5:18 pm

You are not alone in leaving the jumper open. I spent quite a bit of time before trying to troubleshoot what's wrong before I realized the jumper was open

6L6 · 2011-12-08 2:58 pm

6L6 said:
Here are the abnormal readings on Rich's 'left' board.

Q3 1.2v base/ .49 collector/ .46 emitter
R24 (or the source of Q9) .1v
R13 1.33v
Q2 +21.0v gate/ +23.9v drain/ +20.45 drain (Look! It's positive!)

There is some DC fluctuation across the output. The input is open, not shorted.

Any ideas?

Do you think there are some inoperative transistors or something else?

richluvsound · 2011-12-08 3:15 pm

Right Board .

I'm tempted to pull ZVP and use the 2.2k to see if everything settles . P1 is acting the idiot and not doing what we want . I got it to 6 VDC and it swung to
-24.39 VDC and no amount of adjustment will move it ?

All the other voltages are pretty much the same as the first test we ran .

At least the aluminium is here so I can crack on with the cases

R

nar · 2011-12-08 5:25 pm

6L6 said:
Q3 1.2v base/ .49 collector/ .46 emitter

Clearly it doesn't work as intended.
Q3 is the cascode for 4 paralleled Jfets.

6L6 said:
R24 (or the source of Q9) .1v

Way too much current

From those last two points, I would say one to four of the jfets are defective / Q3 is maybe also culprit here

6L6 said:
R13 1.33v

I dunno if the gate should rather be close to Ground potential ???

6L6 said:
Q2 +21.0v gate/ +23.9v drain/ +20.45 drain (Look! It's positive!)

Drain should be aroud 0V too

6L6 said:
There is some DC fluctuation across the output. The input is open, not shorted.

Try to short inputs and re-read the measure points ...
if still fluctuation at output, then maybe the thing just oscilates. Make sure C7 is out, and C9 in place.

6L6 said:
The + and - rails are good
The voltages on the input stage capacitance multiplier is good (R9 20.0v)
All the readings on the output stage current sources are good.

Makes me think in relation to diff. pair gate voltage that maybe those are not working properly. Then issue finds its way at the output.

All I can say for now. is it possible to trace a small input signal and see where it goes out, or finds itself at the output ?

nAr

richluvsound · 2011-12-08 5:50 pm

thanks nAr and 6 ,

i just received all new actives from a friend in California

New Jfets and Regs . I have all new caps if needed .

Perhaps you guys can come up with a way to sort this out between you.
I'm not going to look at it till a plan is made and orders issued

I'm OK with it now , I have learned there is no short cut with this stuff and now I feel more confident reading a schematic its easier to take direction.

I really do appreciated all the help and patience . Having done some teaching myself I do understand it can be a bit frustrating ,but ultimately rewarding .

Rich

wayne · 2011-12-08 10:26 pm

Placing the 2.2K Ohm resistor is just as a test to look for about 10 mA of current flow in the ZTX450. To look closer at the front end try using just one of the four FETS at a time and looking at Q3 voltages.

6L6 · 2011-12-08 10:53 pm

I thought we were talking about the 2.2K resistor in place of the ZVP3310 (Q2) ??

Should the 2.2k be used instead of Q3?

wayne · 2011-12-08 11:22 pm

Yes for the 3310. I was just including two things.

6L6 · 2011-12-08 11:35 pm

Ok, that makes sense.

gagnou · 2011-12-09 10:20 am

wayne said:
Corrected voltages on the schematic. 6L6 pointed out I had a negative voltage exceeding the supply.

Isn't the CE voltage of Q3 too low?

Regards,
George

richluvsound · 2011-12-09 10:32 am

Hi Gents ,

I have replaced Q3 and inserted 2.2k on the left board .....no change for the better .

Is there someone with more knowledge than me that could me some more voltages around Q3 - I have 2 VDC and need 10 VDC . R 9 is good at 19.99 VDC
and should be 20.2 VDC .

Rich

nar · 2011-12-09 1:37 pm

richluvsound said:
Hi Gents ,

I have replaced Q3 and inserted 2.2k on the left board .....no change for the better .

Is there someone with more knowledge than me that could me some more voltages around Q3 - I have 2 VDC and need 10 VDC . R 9 is good at 19.99 VDC
and should be 20.2 VDC .

Rich

Q1 is additional filtering for the power supply. From the schematic if you got correct voltage after Q1 then Q3 should work.
Have you double checked resistor values / and / or if they are still good, not open ? I mean R8, R9, R10. I would then check joints arond those / continuity test; and use a new Q3 ZTX450 with only one K170BL on below. You should get 4 times less current approx, but it should work even if lower gain. Can you try this and report if success, and values you get on Jfet drain ?

R11/ R12 values correct ? 6K81 and 909 ohm Check anty shorts to ground plane in that area too

Best,

nAr

richluvsound · 2011-12-09 2:31 pm

18 V drop across R9 ? fried ?

nar · 2011-12-09 2:38 pm

richluvsound said:
18 V drop across R9 ? fried ?

Probably not, otherwise it wouldn't do such a V drop. A short is maybe after, R8/R10 or R11, or the K170BL has too much current draw for another reason

short @ drain or R source maybe ? Or totally open ? Sounds so, seen the V drop you have on R24 (or simili ), you stated 0,1V ; on 10 ohms it does 10 mA ... that is a little high, which is the IDSS of the Jfet you use ???

Best,

nAr

richluvsound · 2011-12-09 2:44 pm

7.43 mA to 7.29mA Q6-Q9

nar · 2011-12-09 2:52 pm

Can you precise if you mounted one or four jfets, and which V drop you get on source(s) resistor(s) plus tension on the drain(s). Sorry not to see through things

Best,

nAr

6L6 · 2011-12-09 5:04 pm

Nar - (and everybody else...)

Just finished another conversation with Rich.
The output stage is disabled, all the transistors have been removed.
The input stage has only one K170BL installed.

There are no shorts that can be found, and the resistors appear to be all correct.

Voltages --

R9 20.3v
Q3 17.6v collector/ 10.4v base/ 9.4 emitter
Q6 9.3 drain/ .05 source

nar · 2011-12-09 5:16 pm

6L6 said:
Nar - (and everybody else...)

Just finished another conversation with Rich.
The output stage is disabled, all the transistors have been removed.
The input stage has only one K170BL installed.

There are no shorts that can be found, and the resistors appear to be all correct.

Voltages --

R9 20.3v
Q3 17.6v collector/ 10.4v base/ 9.4 emitter
Q6 9.3 drain/ .05 source

Thanks 6K6

Rich, those voltages look fine to me.

Next, use 4 BLs and see how it turns. If readings still fine, then yo ! 2nd stage

Best,

nAr

6L6 · 2011-12-09 5:24 pm

What about the 17v on the collector of Q3? Will that become better when the rest of the input chain is installed? Or when the output stage is connected?

nar · 2011-12-09 5:33 pm

6L6 said:
What about the 17v on the collector of Q3? Will that become better when the rest of the input chain is installed? Or when the output stage is connected?

Dunno. Rich should now try with 4 BLs and post read values.
Mostly 17V, I expect R11 and R12 not to be short to gnd plane.
I can't do any measure on mine for now

Got to get ready to go

Best,

nAr

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