stereomour 2A3's not glowing

[azrockitman]

So I completed my kit last night, did a resistance check, everything looked super, so I bypassed the voltage check and went straight to moment of glory.  but no glory.  The little single 12AT7 sylvania tube began glowing promptly but the 2A3's did not.  So I waited a few minutes to make sure I didn't see or hear (or smell    )any other issues and then powered it down.

So I'm going to go back and do the voltage check but I"m curious about two things:

1)  Do those large tubes glow like the traditional tube? 
2)  Does the fact that the little single tube has power... point to any specific red flag that would help me zero in on something?

As I said, I'll complete the voltage check and make notes and see what that tells me but I thought I would see if this "smells" like one particular issue or not.  Thanks

 

[mpeg2]

The filaments on the 2A3s are really hard to see - especially in room light. If you turn off the lights & look directly down on the tube you'll see 3 (or 4) dimly glowing spots on top).

  Rich

 

[azrockitman]

Thanks MPEG2.....that made my morning!  I expected those puppies to glow like my s.e.x. kit tubes but was very discouraged to see nothing.  I"ll complete the check and then power it back up.  Thanks again.

 

[azrockitman]

I couldn't resist, so I reconnected a sound source and speakers but no sound.  I also didn't think to check earlier but the 2A3's aren't getting warm either so they aren't getting power.  So it's back to the voltage check. 

 

[Grainger49]

There is a frequent mistake.  Several Bottleheads have plugged the 2A3 tubes in wrong.  If you don't get the right voltage to the cathode/heater it won't work.  Check the orientation of the tubes.  Then check the orientation of the sockets. 

Post back.

 

[azrockitman]

First, Grainger;  I've got both sockets mounted with the larger holes in back next to the hum pots.  Tubes are mounted also with larger pins in the back.  Underside, wiring matches the instructions and finished photo, per my eyes, so I don't think I've messed that up but here are my voltages...they may prove otherwise:

1  411
2  0.810
3  0
4  0
5  0
6  0
7  0
8  0
9  0
10 0
11 0
12 0
13 0
14 203.7
15 410
16  won't settle
17 411
18 won't settle
19 411
20 won't settle

A1 won't settle
A2 410
A3 0
A4 0
C1 0
C2 412
C3 0
C4 0

IA 409
IB 411
OA  0.8
OB 203.8
KREG 2.8 A SIDE
KREG 2.5 B
-REG 0
-REG 0

Clearly some missing/wrong voltages.  FYI "won't settle"  my suspicion is that my meter it responding in the same way on these terminals as if I was just waiving the pin around in the air attached to nothing.  My meter does that as I'm moving into location with the pin.  Once connected to something, it settles and give me a voltage.  but in the case of the "wont settle" it just keeps behaving as if I never touched the red terminal pin to anything.

 

[jimiclow]

Set your voltmeter to AC and measure voltages across A1/A4, C1/C4 and see if the filaments are getting power.

 

[azrockitman]

I'm getting zero on the A's
2.36 on the C's.

 

[jimiclow]

The C side should warm up as it's getting power.
Re-trace the heater wires on A side, check the transformer taps if you have power. There's probably a cold solder on that side.

 

[Grainger49]

I expect the Stereomour transformer has only one 2.5V AC heater winding.  So if one channel has the voltage and the other doesn't there is an iffy solder joint between the two. 

Of course I could be wrong, and there might be two heater windings on the transformer.  In that case yo check from the transformer forward to the tube to see where the voltage disappears.

 

[Paul Joppa]

There are two 2.5v windings. It's necessary to allow the tubes to bias independently.

 

[Grainger49]

D'oh,  I forgot about the heaters being the cathodes.

 

[azrockitman]

So clearly I have a right channel (A side) power issue. But I noticed no warmth out of the left channel tube when I had the unit powered up for a few minutes.  Do these tubes not warm to the touch as much as other tubes.  Or are they slow to warm?

If so, that might explain no warmth out of that tube for the few minutes it was turned on. .  I also might see if either tube powers up on that side....maybe one of the tubes is bad...?

 

[Paul Birkeland]

Trace the red/black pair of wires back to the transformer that feed socket C.  I would bet on a loose connection at the power transformer.

In either case, neither of your 2A3's are drawing any current, but it would be nice to know that they are both heating.

You also have an issue in your driver stage, the OA pad is showing a short to ground, I'd double check that there are no miswires on or under the PC board, and that all the transistors are mounted consistently from side to side.

-PB

 

[azrockitman]

Paul, did you mean C or A?  (because I was getting 2.36 v out of the C's when I checked them previously...it was the A's with zero)

But that aside, You are talking about the connection from the power transformer terminals 12/red to C4 and 13/black to C1, correct?  If so, I have continuity from past both terminals on the power transformer (I'm touching the little "solder nubile" that sticks out on each terminal on both sides of the transformer) to also past the C1 and C4 terminals on the C socket.  In other words, I'm not touching any part of the actual wire, so to me that confirms a good solder since continuity is achieved outside of the wire or the solder itself.   

Now, on the other hand, I also checked the same on the A socket.....and while the black wire has continuity past both ends of the wire, the Red wire does not. I have continuity from the A1 socket terminal and all around that solder itself, but The red is dead on the terminal 11 on the power transformer side....I do not have continuity there. 

So that being the case, should I simply try to resolder that connection on 11 on the power transformer?

 

[Paul Birkeland]

Yes, either there is a break in the wire, or the solder joint is not complete.

-PB

 

[Grainger49]

With a bad connecting wire you never know if it is the from part of the wire not making connection or the to part of the wire.  Try touching up the destination first, 11.  Then try the interconnection.

 

[azrockitman]

well, I fixed the cold solder between the A socket and the power transformer.  I now have continuity between those two points.  It was just a bad solder and 4 or 5 seconds with some fresh solder on the soldering iron tip solved that.

So far, I can only find one thing amiss on the Active Load PC board...and it's the wire from GND on the Power Supply PC board to the -REG hole.  I had two problems....one, it was a bad solder.  I wiggled it and the solder popped right off.  So that's easy enough to fix. But here's the rub:  I couldn't install it in the correct hole...I accidentally filled that hole with solder, and I couldn't get the hole cleaned out....it was run-off from the top side black wire solder that comes from the bB side.  So, my GND from the power supply is/was soldered to the empty hole right above the "g" in the "-reg" section.  I do have continuity between those three holes:  a)the hole above the "-", b) the hole that resides above and between the "r" and "e" and c) the hole above the "g", where I have the GND wire soldered.  Is that ok?  (in fact, I have continuity between the 4 successive holes in that area the 4th one being the one closest to the "C" next to the "Cc" label.) 

If that's all ok, I can simply resolder that GND connection on the active PC board and hopefully have my problem fixed.  If it must be soldered to that 1st hole above the "-" then I'll have to figure out a way to remove the solder runoff filling that hole.

Thanks

 

[Paul Birkeland]

You can use one of the other holes that you found with your continutity test.

-PB

 

[azrockitman]

That will make it easier.  Thanks!