Bottlehead Forum
Bottlehead Kits => Stereomour II => Topic started by: lesouthern on January 07, 2023, 07:27:11 AM
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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
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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.
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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
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from above....I mean the right channel is disabled, and the left is buzzing when I switch the 2A3 tubes...
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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.
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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.
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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
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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?
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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...
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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.
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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.
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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.
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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.
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What's the resistance reading you're getting on each tube? If the correct resistance is there, the tube should be able to glow.
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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.
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Apply your iron to the tip of each fat pin and hold it there for a while with the tube upside-down. Eventually, you'll see the solder start moving inside the tube pin, and you can feed a little extra through the hole in the tip of each of those pins. Do not add any solder to the outer portion of the tube pins where they slide into the socket.
I've attached a picture of what a 4 pin base looks like before it's installed on a tube. You can see that the ends of the pins are hollow and that's where the solder goes in. The EH bases aren't all the way hollow on the ends, but there's still a hole where solder can be fed in. For the tube in question, it's possible that one of the filament leads wasn't perfectly soldered and it has just moved away from touching whatever was allowing it to conduct.
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I have added solder to the tops of the large pins of the offending tube twice now, installed the tube, and am getting the same erroneous voltage readings I list above in this post. The resistance of the offending tube remains the same, about 1.2au. Wonder if I'm doing something wrong, or if something else is causing this failure.
1. This is my soldering iron->
https://www.amazon.com/gp/product/B07RZV2DW8
I'm turning up this to 8- the highest it will go.
Is that hot enough to do the work you are advising me to do?
If so, how long should I have the tip on the pin for this to work?
Is it just the tip of the pin I should be heating, or other parts of the pin?
And just the large pins I need to do this on, not the small ones?
I'm noticing once the iron is hot it takes about a minute for the top solder to melt.
2. Given the erroneous readings of 0V on the terminals I listed above, could this be any other issue other than the tube one you are advising me?
3. I have three other Bottlehead projects- Crack, Reduction, and Moreplay. As far as I know, the tubes on these are fine. Are the 2A3 tubes more susceptible to have this happen?
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I suspect you will need to have the tip held against the base pins for 1-2 minutes to get the solder to flow out as desired.
I have never run into this issue on any tubes other than new production 2A3 and 300Bs.
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After about five tries the big pins on my bad tube stopped accepting additional solder
I have plugged the tubes in, and am getting a small glow from the sides of the bad tube, but the top is still not glowing. It is getting slightly warm, but not hot like the good one
In comparing the bad tube to the good one, note that the solder in the small pins is recessed. Do I need to add solder to the small pins here as well?
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At the end of they day it's certainly possible you got a short lived dud of a tube, and just buying a replacement for that one tube would be the best way to go. Though I would expect most new 2A3s to last 5-10 years, there will be a few here and there that die early.
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Ok- I'd like to avoid buying another dud, as you know these aren't cheap.
With tubes- do you get what you pay for? Are there more reliable 2A3 I can get? Not looking for anything fancy.
Do you have a recommended vendor or site?
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Doc B. and Eileen can speak to the number of tube failures we experience early in life from New Sensor production, but in general I would expect it to be well under 1%. Yes, you can buy a pair of EML 2A3s for $700+ and they will offer you a nice warranty, or you can buy a quad of Psvane 2A3s off eBay for $250 and have some spares that you're unlikely to need. The EH 2A3s have shot up so much in price that the one you have could probably sell for $100+ on its own as a good used tube to offset the cost of whatever you decide to do.
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Yes, the Sovtek 2A3s from New Sensor are generally quite reliable. That is always a major consideration when we choose a tube.
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Is it possible that you have somewhere locally that can test both of your valves? Guitar shop?