Help Please: No Voltage on Terminal 9 and B6 / Resistance funky on terminal 12

[jbeard]

Just finished building my Crack and after checking resistance, the tubes would no glow after being plugged in.

Here are my resistance mearurements:
1   10M and falling
2   3.3M and falling
3   .1
4   2.15M and falling
5   2.6 K and climbing
6   2.489K
7   2.94K
8   .2
9   3.023K
10  2.492K
12  .3
13  starts at 6M and falls down to about 30 K over a few minutes
14  .3
20  .3
22  .3

B3  2.94K
B6  3.023K

RCA ground .5
RCA center pin 95K

Voltages were as follows:
1   93.5
2   223.7
3   0
4   223
5   25.44
6   .003
7   25.42
8   0
9   0
10  0
11  0
12  0
13  223
14  0
15  227
20  0
21  232

A1   25.41
A2   0
A3   1.42
A4   0
A5   0
A6   93
A7   0
A8   1.554
A9   0

B1  93
B2  226
B3  25.42
B4  25.47
B5  226
B6  0
B7  0
B8  0

After reading another post, I checked the heater voltage between B7 & B8, A4/5 & A9 and across transformer terminals 4 & 5 and all read 6.3V. 

The only other clue is that the LED between A3 and the cetner pin is not lit.

Please help!

Thanks!

[jbeard]

I forgot to mention in my previous post that I have checked checked and rechecked all of my connections by going back through the directions.

I have also re-wet all of my connections twice now without any changes in the measurements above.  I feel very confident that my solder joints are OK.

[Paul Joppa]

The voltages suggest that B3 is shorted to B4.

[jbeard]

Thanks Paul!

I will check B3 and B4 when I get home. 

I really do not recall seeing those two terminals being shorted together and I feel certain I would have seen that in my checks. 

Is it possible the tube is shorting those two together or it is being shorted somewhere up or downstream?

Would that also account for my strange resistance reading on terminal 13 and the fact that the LED from A3 to the center pin is not burning? 

I guess I am wondering if I need to request a few replacement LED's?

[Paul Joppa]

You can measure the resistance to see if they are shorted. Pull the tube to see if the tube's pins are shorted. The short can be anywhere - just follow the wires if the foregoing does not answer the question.

[jbeard]

I assume I would test for a short by placing one probe from my multimeter on terminal B4 and the other on B3 to measure the resistance?

I did so with the tube in and measured .6 ohms

Without the tube, I measured anywhere from 26K to 6M ohms.  It seems to fluctuate drastically up and down.

Does this indicate a short in the tube meaning I need to request a new 6080?

Thanks again.  I really appreciate all the help!

[Paul Joppa]

Sure sounds like it. Test the resistance between the tube pins themselves to be absolutely sure it's a tube problem and not a socket problem - but I'll be pretty surprised if that test fails.

[jbeard]

Testing the pins of the tube by placing one probe of the multimeter on the pin associated with terminal 4 and the other probe to the pin associated with terminal 3 results in the same resistance measure of .6 ohms obtained before when the tube was in the socket.

Thanks Paul!  I will request another 6080 from bottlehead tomorrow.

Do you think there is any chance that LED is bad?  I would hate not to order a few only to find out it is also faulty.  Shipping from bottlehead takes at least a week to get to me.

[Laudanum]

6080's / 6AS7's can be had for pretty cheap.  You'll get a replacement from Bottlehead but do youself a favor and pick up a spare or two from a reputable ebay seller or one of the tube sellers (cheaper on ebay).  Same goes for the 12AU7.  The cheaper types of these tubes may not sound the best but they'll get you up and running if you have a tube go south.  Always good to have a couple spares on hand.
I cant speak for sure for the gang at Bottlehead headquarters, but I would doubt that they would have any problem issuing you an extra LED just in case.

Are you near Florida or the southern east coast?  I MAY have an RCA ST shape 6AS7 (6080 equivalent) that I could send you.  It tests a little bit weak but is still a usable tube, it's been tested in circuit as well as by tube tester.  I'd have to check for sure if I still have it.  But if I do and you are close to me, it may save you a couple of days if you are anxious to get the Crack up and running before Bottlehead can get you out a tube (and LED).  I also have a spare led I could send with it.  PM me with your name and address info if interested, I'll send them out to you, gratis, if you will just pick up the few bucks for shipping.

[jbeard]

Thanks for the offer Laudanum; that is very gracious of you.

Bottlehead is putting a 6080 and a few LED's in the mail today.  I am going to take your advice and get a few extra tubes which will be a good excuse to get some upgrade tubes and use the stocks as backup.

I cannot thank everyone enough on this forum for being such a great help in troubleshooting this issue.

I now anxiously await my new tube and cannot wait to hear the Crack for the first time!

[Laudanum]

No problem jbeard.  Sounds like you'll be up and running in a few days.