A thread in which Dave haz a sad [solved]

[davechen]

I finished assembling my BeePre yesterday.  I checked all the resistances, and they seemed ok.  So naturally I plugged it in and fired it up. 

The two 6BQ5's glowed as did one of the 300B's, but the other one didn't.  That was the one on the left when the tubes are up, i.e. the B socket.  Also the front two LEDs (closer to the power switch & knobs) of the C4S board above the B socket didn't glow.

Here are my resistances with the tubes in

1: 3.4
2: 0L
3: 0
4: 5.3
5: 0
6: 143K
7: 455K
8: 0
9: 0
10: 0L

11: 144K
12: 457K
13: 0
14: 0
15: 0L
16: 3.9
17: 0L
18: 0
19: 5.0

20: 0
21: 0
22: 140K
23: 0
24: 0
25: 117K
26: 0
27: 0
28: 0

33: 0
34: 0
37: 0
38: 0
39: 0

40: 176K
41: 0
42: 0
43: 161K
44: 0
45: 0
46: 151K
47: 430K

49: 601
50: 0
51: 601

A1: 4
A2: 0-47K
A3: 0L
A4: 5.3

B1: 5.1
B2: 0-46.1K
B3: 0L
B4: 4.0

C2, D2: 214, 214
C3, D3: 0L, 0L
C4, D4: 72K, 70K    Are these too low?
C5, D5: 78K, 72K

C7, D7: 144K, 144K
C8, D8: 144K, 144K

And my voltages:

1: 6.5
2: 130

4: 12.5

7: 186

10: 0L
11: 0L
15: 0L
16: 7.7
17: 0L

19: 12.9

22: 297

25: 297

29: 9.34

30: 9.34
31: 189

34: 194
35: 9.7
36: 9.7
37: .63

40: 301

44: 302

47: 302

A3: 138

B3: 262

C3, D3: 5.5, .15

C7, D7: 205, 268

C9, D9: 204, 266

I left off the 0 volt ones that corresponding with the manual.

Clearly my voltages are off.  I didn't see anything obviously wrong in the wiring, although I'll go over everything again and re-heat the joints.  That's what eventually fixed my first Bottlehead kit, a Foreplay 2 I built many moons ago.

I swore that my resistances were good before I plugged it in.  But when I remeasured after plugging in, C4, D4, C5 and D5 seem to be low.

I guess I'm kind of bummed because my last kit, a S.E.X. worked without a hitch.  Anyways, anything particular I should be looking at?

Thanks.

[davechen]

Also, I'm a little worried about plugging it back in.  The bottom of the 300B that didn't light up is a bit white, like it might have burned out.  Do you think I nuked that tube?

[Doc B.]

If the tube has a kind of milky white coating inside where you would normally see the shiny metallic getter flash, yeah, unfortunately the tube has a leaky envelope and has gotten some air inside. If the tube is forced into the socket the wrong way or twisted in the socket it can create a small crack in the envelope down inside the base where the wires come out for the pins. So you can't necessarily see where the leak is. Did you happen to notice that white part before you put it in the amp?

[davechen]

Unfortunately I don't recall what the tube looked like before I put it in.  I am sure I didn't force it in though.  I've attached a picture of the tubes.  I think the one on the left is toast.

[Grainger49]

Yup, butter it now, it is toast.

[mcandmar]

That's such a shame    If it were me i'd set it on my mantelpiece as an ornament.

[Doc B.]

Yes, that tube is dead. Send it back to us so we can get a credit from the distributor and we will send you a brand new one.

[davechen]

So I sent the bad 300B back, and USPS says I should get a new one today.

My concern is, if I messed up my wiring am I going to blow another 300B?  Do you think it was more likely bad wiring or a bad tube?

I've double checked my wiring against the manual, and everything seems OK to me.  Also I reheated the joints on that side of the pre-amp including all the ones related to the 300B and the power transformer.

Any other ideas?  Or should I just plug in the new tube and pray?

[Paul Birkeland]

Your tube was physically damaged, which means physical trauma or a leak around one of the pins allowed air to enter the tube and ruin it.

An issue with how the circuit was built will not cause this kind of issue, so I don't believe you have anything to worry about.

-PB

[Doc B.]

Yeah there was a hole in the glass inside the tube in a spot where I can't imagine an impact would have caused it. Looks more like it simply had a weak spot in the glass that gave out when the tube warmed up.

[davechen]

Well, I've made a step forward, but not all the way there yet.  Got the new tube, put it in, and powered the BeePree up.  Joy!  Glowing tubes!

So I put the pre-amp into my stereo.  I get sound out of one channel, the B side, but not the other, A side.  I tried swapping tubes and changing inputs and the sound stayed on that left side.  When I swapped the outputs the sound did switch to the right speaker.

So now I've got to figure out what's wrong with the right side of the BeePre.  I'll re-heat joints and measure voltages (when I get a new battery for my meter).

But for now, the one channel sounds very nice.

[Doc B.]

Please do remeasure your voltages before you go too much further. Though it looked like a bad tube, let's make sure that the first tube died of natural causes and not something inflicted by the circuit.

[davechen]

Will do.  The bad tube was on the side that works now.  But I will check the voltages tomorrow.

I've attached a pic of the tubes glowing.

[davechen]

I just checked all the voltages and they came out good.

Maybe I'll check/reheat the joints that go to the output on the right side.

[davechen]

So I'm back.  Been trying to figure out why my BeePre isn't working properly.  Right now the left channel sounds weak and hollow.  The bass is pretty good, but voices sound distant.  The left channel doesn't make any sound at all.

In checking the resistances, the following measurements were a bit funny:

25 & 40: 1M ohm and falling
43 & 46: rising to 120K ohm and continuing up
C3, D3, C4 and D4:  slowly rising to 5K ohm and up

That last is lower than what the manual says.  Is that a problem?

The measurements were made without any tubes in.