More tranny trouble? [solved]

[Karl5150]

     Ok, the shunt regulator install seemed to go without a hitch (although I didn't try it before starting the C4S install) LEDs and #s all good.
     The C4S however is different. The 2 LEDs on the A side of the B board don't light and the numbers are:
       2 - 77.3
     18 - 104.9
     26 - 105
     31 - 81.7

Time to replace the transistors on that side of the board..... or do those numbers point to something else?
Thanks for any help on this.
 

[Paul Birkeland]

How are the numbers from the voltage regulator?

Do the socket LED's light up?

What were the voltages at 18 and 26 before the upgrade?

Do all the socket LED's light?

[Karl5150]

I don't have the pre install #s on the Reduction, the original build #s were all good and it has functioned well since built (noticably lower output than digital sources).
The 4 socket LEDs light (brightest)
The regulator LEDs light (brighter than the C4S board LEDs) The MJ... transistors both read 103V and terminal 56 is 129V
The 6 LEDs that do light on the C4S are dimmer but steady.
Thanks as always

[Paul Birkeland]

LED's not lighting can be caused by not having the bA/bB jumper, or not having the Ib/Ia jumper, or potentially a cold joint on a resistor.

I'd also have a good look at those PCB solder joints, just to be sure you didn't miss one.

-PB

[Karl5150]

Thanks Paul,
The jumpers are there, but as always my soldering skills (or lack of) are always suspect. I will check before pulling and replaceing the transistor.

[Karl5150]

Apparently this time it wasn't my soldering as much as my ability to follow directions:
( ) Attach and solder the white wire
connected to 26U to OA.
It clearly reads 0A not IA.
Now all 16 LEDs light and it functions. I think must have at least screwed up one or both MJE350s cause 18, 26, and 31 all read 102-105V, the volume on that channel is 3-4 dB lower and has a scratchy (not the bad ground type) undercurrent to it.
Once again some guidance would be appreciated.

[Doc B.]

Did you try swapping tubes to see if the voltages follow?

[Karl5150]

Well Doc the voltage, volume and noise (worse) all follow the tube. Installing a SS phono stage clears channel variance issues. I guess my oops on the C4S board wasn't fatal to the board components.
Thanks, I'll start the tube search.

[Doc B.]

Try cooking the tubes in a for a few hours.

[Karl5150]

They were very quiet for the 3-4 months I've been using the Reduction prior to the upgrade. Would running them upside down for the multiple voltage checks cause something that is reversible?
(This is not an expression of doubt, it is just most of my very very limited knowledge is from lurking on the forum and any information helps)

[Paul Joppa]

It is possible that some junk inside the tube got into a critical area. But if the tube has always had low gain, then you probably need better matched tubes.

One of the disadvantages of zero-feedback designs is that the gain variations between active devices (tubes or transistors) are not equalized. IMHO the cure (feedback) is worse than the disease.

[Karl5150]

First, thanks everyone for responding.
  Originally the tubes were reasonably matched as far as I could tell, images were well centered. I have ordered a matched replacement set.
 For future reference: do preamp tubes need signal flowing through them for break-in?
Thanks again for the help.
 

[Doc B.]

Yes, it seems that all components need signal in order to break in in the most expedient manner. There is of course some very tiny noise floor present whenever the circuit is on, but it seems to  take much much longer for that to have any effect than a music signal at normal levels

[Karl5150]

The new tubes arrived today and all the LEDs light and the C4S voltages check out (69-70V)
I listened for a couple of hours with only the usual ("that sounds a little off" then a little later "no, its ok") new tube issues. Considerably more gain than before the upgrade.
Then the dreaded scratchy, volume dependent, intermittent noise from only the right channel (not the side I originally miss-wired, post #6)
I swapped tubes, still in the right side. (maybe I wasn't careful handling them and mixed, post 3-28-14)
I swapped one end of the interconnects and it moved to the left, so it's not the amp.
Tried another set of cables, no change.
Swapped the TT interconnects, no change.
Back to the bench, all LEDs light (the 2 on the A side of the right channel board definitely take a little longer to light and subjectively seem not quite as bright) and the voltages are the same.
Looked at the ground solders and one looked a little less shiny so I reflowed both ends of the jumper.
Back inside- no change, after a brief warm-up the right side is still troublesome.
Tried the original tubes, except for volume mismatch, still always the right channel.
I hope this is enough for the bigger brains to point me in the right direction, thanks in advance.
Karl
 
 

[Doc B.]

So did the noise not follow the original tubes as you posted earlier? Reading back thru the posts I can't get a grasp on whether the noise follows a tube and/or whether it is in the channel that had the wiring error, or if it is showing up in different channels at different times. Can you now verify that

A) the noise is not associated with a certain tube

B) the noise stays in one channel and that channel is or is not the one that had a wiring error and

C) give us a new set of voltage measurements with the new set of tubes.

I would guess that there may be a damaged transistor after all, but some of the previous info posted was indicating otherwise.