Voltage on heater circuit [resolved]

[xavk]

HI Guys,

First time posting about the first ever soldering / electronics project I have started.

I've fully assembled my Crack and it was all proceeding really nicely.  Resistance checks are all in line and when power is connected, both tubes glow.  However, when working through the voltage checks, I seem to have 4v flowing through the heater circuit which shouldn't be there.  I get a reading of 4v at A4, A5, A9, B7 and B8 and I am at a loss to explain it. 

A visual check suggests all is in the right place and i cannot see any obvious short.  I left the connection at 22L rather than moving to 14U to keep things simpler first time around (starting to get a bit cramped over by 14).

As I'm not confident that the voltages are correct, I am yet to connect a source or headphones.

Any suggestions or recommended next steps most welcomed.  Can post pics if it will help.

Xav

[Doc B.]

At what terminals are you putting the two test leads for those measurements? That may have some influence on your readings.

[xavk]

Terminal 12 with a black clip lead and then touching the others (A4, A5, A9, B7 and B8) with a red pointed lead

[fullheadofnothing]

Are these AC or DC measurements? Are all of the other voltages in spec?

[xavk]

Below is the output of my last voltage check.

Target       Actual
1     75-90    74
2     170   153
3     0   0
4     170   154
5     75-90    79
6     0   0
7     100   97
8     0   0
9     100   98
10   0   0
11   0   0
12   0   0
13   170   154
14   0   0
15   185   174
17   ?   0
18   ?   69
19   ?   69
20   0   0
21   206   192
A1   90   76
A2   0   0
A3   ?   1.55
A4   0   3.2
A5   0   3.4
A6   90   76
A7   0   0
A8   ?   1.5
A9   0   3.3
B1   90   76
B2   170   157
B3   100   98
B4   90   78
B5   170   157
B6   100   100
B7   0   3
B8   0   3

Oddly I get pretty much the same reading (3.1-3.4v) on both DC and AC settings on the multimeter. 

[Doc B.]

I'll suggest going over the heater wiring. Your other numbers look pretty good, like the tubes are getting enough voltage. The reading you are getting kind of indicates that there may be a problem with the grounding of the heater supply. That is the wire you mentioned in your first post, from power trans terminal 4 to T22. You might measure AC volts with the red test probe on power trans terminal 4 and the black one touching the chassis panel. You should see zero or very close to zero volts AC. If you see more like 3 or more volts there may be a bad solder joint or some other kind of open connection between power trans terminal 4 and the chassis.

[xavk]

 Doc,

Thanks for the pointers - as always you nailed it.

So first I rewired and cleaned up every connection in the heater supply (new cabling, removed all existing solder as best i could) but upon rerunning the tests, the problem was still the same.  Decided to move from 22L to 14U and went the long way around (entering via the outside as the inside is covered by the resistor).  Once that was done, the tests all came back as expected (0v on the heater circuit, other values went up slightly but well within tolerances).  Decided to take the plunge and connect it up and I'm pleased to say, all now working very nicely 

Thanks again!  Now to go read up on Speedball....

Xav