PSU11/Phono11 - voltage drop

[Black Stuart]

Hi all,
finally finished re-building Phono11 using the new PCB, completely forgetting to do the RIAA mod (tonto).

Decided it was as easy to test voltages 'in situ'. After changing R6 in PSU11 to 18K as I previously had around 265V being delivered to the phono stage, I plugged in. Strange I'm only getting around 145-150V at the Cliffcon socket in Phono11 so, I need to check out PSU11.

As you will see from the voltage check I'm getting near perfect readings under no load and also from T/P 1/2/4 under load. In brackets desired voltages:

No Load Under Load
Test point 1/ 364 (363) 338 (338)
2/ 355 (353) 323 (327)
3/ 354 (345) 143 (250)
4/ 110 (110) 108 (106)
5/ 44 (44) 142 (41)
5/ 44 (44) 142 (41)
6/ 58 (56) 153 (50.5)
7/ 50 (50.3) 148 (47.3)
7/ 50 (50.3) 148 (47.3)
8/ 45 (44.6) 142 (41.6)
9/ 46 (45.2) 142 (42.2)

I changed R6 back to the original 15K - no difference. Measuring leg nearest to T/P 1 all is well - the second leg is where it all goes wrong. I also changed connection lead to Phono11 - no difference.

All in all very weird. I suppose it must be component failure but where?

I hope you can interpret the figures for some reason they have all been lumped together which is not how I set it out.

Black Stuart

[Greg.]

Hi Stuart,

I don't understand the recording of your readings. You might want to be a bit more specific. You seem to be publishing two readings for every test point when each test point is specific to an individual channel. You seem to have bad readings on test points 3(L),5(R),6(R),7(L),8(L),9(L). I think that if you can sort out this confusion, we (or the 'Wiseones') will be able to sort it. Other than that, check over all your joints and run the iron over the joints if you're not sure about the quality of your connections. Pay particular attention to board through connections. You have a later PC board. have the instructions changed? Can you download the latest version from the WAD site? Just some suggestions.........I also suggest you get this sorted before you convert Pre II to CF, otherwise you will totally lose direction.

Best wishes,

Greg

[Black Stuart]

Hi Greg,
I simply do not understand how when I actually posted my figures, they were all lumped together - can someone explain?

They do however still make complete sense if you look closely.

The header line shows 2 categories - No Load and Under Load. I also explain that all figures in (brackets) are the 'desired voltages' as set out in the PSU11 instructions

There are 9 Test Points each followed by a slash - there are 4 sets of figures, obviously the first two sets refer to No Load and the other two to Under load.

If you look in the instructions you will see there are two sets of T/P 5 and two for T/P 7 - as per the instructions.

If this is clear (which it should be) then you will see that the first set of figures ie. No Load show that the test figures are near perfect.

Looking at the second set of figures Under Load - you will see that T/Ps 1,2, and 4 are near perfect as well, after that all the T/P readings are 300-400% out.

I can't understand your comments about Right & Left channels Greg - this post is all about PSU11 not transferring enough volts to Phono11 that is why there are (2) sets of Test Point 5 & 7 in PSU11 instructions - one set goes to Phono11 Cliffcon and the other to Pre11 Cliffcon.

Until I dismantled the old Phono11 PCB, PSU11 was working but as I have e-mailed you it was transferring too many volts, around 267V to Phono11 - hence changing R6 (PSU11) from 15K to 18K. As I have stated in my initial post I took a reading at the Phono11 Cliffcon which is all wrong ie. 145-150V. Incidentally all 3 Phono11 valves are functioning so it would seem there are no bad joints in Phono11.

I have also put the s/iron to R6 (PSU11) above and below PCB and the reading has risen slightly from 145-150V to 157V but then I have used the 18K 5W resistor. I noted that the original 15K resistor body looked a bit discoloured but I measured it at 15.32K.

I hope that is all clear, if not I will repost the figures in single columns but that really should'nt be nec.

I state again, what I find so crazy is the near perfect figures for no load, surely if a cap,diode or resistor has gone it would show up in these figures.

Black Stuart

[buddam]

Hi Stuart

this may be a fooliosh Q, but weren't you doing the Cath Foll mod? If so, what do these test points refer to?

Adrian

[NickG]

What I can't undersand is from your description of the numbers, some of the voltages are higher under load than no load, is the what you are seeing?

Also, when you say "load" does that mean just the phono-II plugged in?

Remember that we haven't all a copy of the instructions, so the test point numbers don't mean that much (to me at least).

Stuart,
I'd guess that you tried to set out your figures using spaces? It is common that repeated spaces will be truncated to one when posting, and any at the beginning of a new line will be removed.
You may find it useful to use the '_' character instead. Using the fixed-width fonts like Courier or Lucida can help, and if you really want to go the extra mile you can make the underscores disappear with the use of a little 'color'.
I've had a go at formatting your figures:

_____________ No Load _ Under Load
Test point 1/ 364 (363) 338 (338)
__________ 2/ 355 (353) 323 (327)
__________ 3/ 354 (345) 143 (250)
__________ 4/ 110 (110) 108 (106)
__________ 5/ _44 (44) _142 (41)
__________ 5/ _44 (44) _142 (41)
__________ 6/ _58 (56) _153 (50)
__________ 7/ _50 (50) _148 (47)
__________ 7/ _50 (50) _148 (47)
__________ 8/ _45 (44) _142 (41)
__________ 9/ _46 (45) _142 (42)


Nick/All,
The circuits (including test points): PhonoII & PSUII

[Greg.]

Hi Stuart,

My apologies, I thought you were recording voltages on Phono II rather than PSU II. I must read more carefully before I reply in future. I was also hoping to kick start your thread so you get some help. I must admit, at present I'm a bit puzzled.

Best wishes,

Greg

[Greg.]

Hi Stuart,

Further thoughts are that as PSU II has correct voltages with no load, the fault will be in Phono II although it would be good to eliminate the umbilical, so measure voltages on the contacts of the Cliffcon plug that would be plugged into Phono II. These should correspond with your readings at test points 3 and 5 with the other two contacts measuring 0 vdc. If that is correct I suggest you connect and measure voltages in Phono II and report your findings back. This may indicate where the problem is.

Best wishes,

Greg

[Black Stuart]

Hi all,
yes Matt your layout of the figures is correct.

Nick this is the terminology used in WAD's instructions, so I did'nt want to confuse issues by introducing other descriptions.Yes under load many readings are what I stated 300-400% over. Yes as I am working on my KAT88s, I am using Angela's KEL34 which is an integrated amp, so I am not using any kind of pre at all and it is a passive anyway at the moment.

Yes Greg, I have measured at the Cliffcons. to begin with I had no reason to test voltages in PSU11, assuming that a simple change of 1 resistor from 15K to 18K would not upset PSU11. So I went straight to Test Points 3 & 6 in Phono11 to see if the required voltage drop to around 250V had been acheived when the readings were 145V or so I went straight to the Cliffcons and measured both PSU11 and Phono11.

I then checked all the heater wiring in Phono11 but as I said in my last post as there was current going to all 3 valves albeit far too little it would suggest that there is no problem with the solder joints.

I have re-used all the resistors that were used with the first PCB and changed only the caps but I don't see that they or the resistors can be at fault since the low reading is taken at the point of introduction to Phono11 ie. the Cliffcon and T/P 3 & 6.

Incidentally all the heater wiring is untouched at the Cliffcon from the first build of Phono11.

So for those that do not have either PSU11 or Phono11 the figures in brackets kindly re-arranged by Matt are the desired voltages and the no load figures which are near perfect are better than when I first built PSU11!

Perhaps someone can explain why R6 shows with either a 15K or 18K the leg nearest T/P 2 is identical to that reading of 323V but the second leg shows the problem of 157 approx. (initially 145-150V.

I carefully compared the two PCBs (of Phono11) against the light and the only differences were erroneous caps near the cathode resistors and another drop through point on an earth line which as I said I plugged with a pcb pin and soldered as to leave it untouched would have left the earth line broken.

I've just gone through to the lounge to check and double check what I have written above and to also look at PSU11 and I noticed that at the Cliffcon the wire from T/P 3,the 250V under load tab was touching the tab of the adjacent Ovdc - fingers crossed that this is the answer - I will test and get back - if it is the answer there will be an awful lot of self bollocking going on in Guadix tonight.

Black Stuart

[Black Stuart]

Hi all,
hopes dashed - still the same problem. I've got Phono11 on the bench but I still can't see how that is the problem.

Why does the voltage drop so much across R6 - this surely is the key to the problem.

Black Stuart