tube failure

[lesouthern]

Hi

These are the stock 2A3 tubes on my Stereomour I bought in 2021, order 28291

In this picture, I tried switching tubes- the ones on the right work if I switch them to the  left, and conversely the ones on the left disable the right channel if I switch them to that side.

So from my switching, the right tubes work, the left do not.

From what I see in the forum, it's strange these tubes didn't last much longer. Please advise.

thanks,

Larry

[Doc B.]

Sounds like you swapped 12AT7s and 2A3s at the same time. Try swapping just the 2A3s so you can better narrow down which tube (12AT7 or 2A3) has the issue.

[lesouthern]

Yes you are right.

Switching the 2A3 tubes is the issue.

As is the 2A3 on the right is making the right channel work, and the left is disabled.

I'm getting a deep loud buzzing noise on the right channel when I switch the 2A3 from the right to the left, and the left channel is disabled

[lesouthern]

from above....I mean the right channel is disabled, and the left is buzzing when I switch the 2A3 tubes...

[Doc B.]

Left is buzzing when you put the good tube from the right in it? That would indicate there is something in the left side circuit that is awry, not just the tube from the left side. You may have in issue in the wiring that has taken out the tube. Let's not run the good tube on the bad side anymore until we know a little bit more about what is going on.

Start by measuring resistance across the two big pins of the bad tube. Those are the filament pins and there should read very low resistance between them. If it reads open the tube is toast.
Next redo all of your resistance measurements per the manual and note any discrepancies. There may be a bad connection around the four pin socket or hum balance pot on the bad side.

[Paul Birkeland]

I'm getting a deep loud buzzing noise on the right channel when I switch the 2A3 from the right to the left, and the left channel is disabled

It is possible to force a 2A3 into the socket with the fat two pins in one or both of the skinny holes.  If the fat pins connect pins 1 and 2 of the 4 pin socket by accident, you'll get no sound and some disturbing noise through your speakers.

[lesouthern]

Here are the results of my resistance and voltage check of my build. Basically voltage on 15, 36, 37, 39, 40 are wrong

Excuse the basic question- what do the knobs behind the tubes do? Can the tubes or build be harmed if they are twisted with the unit on? I had some children over recently and might have been messing with it :-(

thanks

Larry

resistance
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 0
2 0
3 .6
4 248.5k
5 .7
6 1.196k
7 13.4
8 .8
9 n/a
10 13
11 13.9
12 n/a
13 0
14 0
15 1.19k
16 0
17 248.4k
18 .3
19 *
20 *
21 1.39k
22 1.2k
23 .6
24 1.2k
25 1.19k
26 .8
27 *
28 .6
29 0
30 *
31 *
32 .6
33 1
34 *
35 0
36 1.19k
37 1.2k
38 .5
39 1.2k
40 1.4k
41 .7
42 *
43 .8
44 *
45 *
46 .8
47 *
48 *


voltage check
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 375
2 404
3 0
4 0
5 0
6 64.3
7 237
8 0
9 n/a
10 0
11 0
12 n/a
13 0
14 180
15 0 <~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ should be 58
16 0
17 0
18 0
19 418.4
20 417.4
21 64
22 65
23 0
24 65
25 64
26 0
27 403
28 0
29 0
30 411
31 418
32 *
33 *
34 417
35 0
36 0 <--------------------------------should be 58
37 0 <---------------------------------should be 58
38 0
39 0 <----------------------------------should be 58
40 0 <-----------------------------------should be 58
41 0
42 0
43 0
44 419
45 209

[Paul Birkeland]

The knobs behind the tubes are hum pots and cannot damage the tubes if they are twisted while the amp is running.

On the 2A3 that's causing you problems, can you still see it glowing on the inside while the amp is running? 

[lesouthern]

The 2A3 that is giving me issues is not glowing as you can see from this image

I assume this is a bad tube? Is there anything from my resistance or voltage results that could have caused this?

Trying to understand what happened that made a perfectly working system not, as these tubes should last longer...

[Paul Birkeland]

I assume this is a bad tube? Is there anything from my resistance or voltage results that could have caused this?

It's possible that there's a loose joint in the tube socket base.  When I have run into this, I will use a beefy 100W iron to get the fat pins as hot as possible and add some solder into each hole at the tip of the socket pins to encourage the connection to reestablish.  What you have isn't what is expected for a tube that has been run into the ground and is dead, it's more that the filament is no longer connected internally.

It is also possible that the tube could have been inserted improperly with the fat pins not in the fat holes, and that can certainly cause its fair share of issues, but your tube failure would have happened immediately after pulling the tubes out and putting them back in, not just from random use. 

[Doc B.]

Did you measure the resistance across the big pins with the tube removed from the socket? That will tell you for sure if the filament is open. Supposed to read just a few ohms.

[Thermioniclife]

I have had poor connection on heater pin on a Chinese el34 that required an a** load of heat on the pin plus real 60/40 solder that fixed the problem, it worked but I switched to kt88's anyway. If you look at the 4 pin sockets the their are semi circular dimples in the ceramic that denote the position of the filament positions.

[lesouthern]

Hi Doc et al..

The tube on the bad side is showing resistance, same readings as the one on the good.  Great I can assume it's still functional..

I'll proceed on investigating the connections on the left.

[Paul Birkeland]

What's the resistance reading you're getting on each tube?  If the correct resistance is there, the tube should be able to glow.

[lesouthern]

The resistance is 1.2 on the tube, on the side that does not work. I'ts .5 on the side that does

So am trying to understand, I need to put solder on the bottom of the tube pins?

Inside the connector base where the tube pin contacts?

Want to double check before I start putting solder everywhere.