Weird resistance readings - New build

[Rublyow]

Hi everyone,

Whew! I just finished the preliminary build of the Eros, and I have some weird resistance values that I was hoping I might get some advice on.  I haven't tried plugging it in yet and so I don't have any voltage readings.

First off, most of the resistances are high, but they consistently high.  That is, all of the 39k readings are coming in at 46k; the 60k are all at 75k; and the 71k are all at 85k.  All of the zero terminals give a reading of zero (or close to it), and all of the 47k terminals give the correct value of 47k.

Secondly, terminal C4 is not giving a reading of infinity as is stated.  Instead it is giving a value of 610 ohms.  This same reading is showing at terminals A4 and B4, as opposed to fluctuating readings (i.e., a * reading).  

I've checked and rechecked the wiring at C4, and I can't seem to find any issues.

Any thoughts?

Thanks for the help!

Dan

[Grainger49]

I have the manual open and can't find terminal 10 or 11 in the text.  I'm going to label the terminals on the schematic I have printed out and get back to you. 

For me, if I don't have the circuit and terminals locked down I can't figure out why the reading is wrong.

I promise to get back.

[Rublyow]

Thanks for taking a look into it.

I found this post http://www.bottlehead.com/smf/index.php/topic,1322.0.html which sounds pretty much like an identical problem to mine, and (assuming I'm reading it right), my readings seem to be OK.

That being said, it'd be great if I could verify this before plugging everything in.

[Grainger49]

Edit:  I pulled out my manual.  It was marked 75k at all the 60k specified points.  And the 39k points all came in at 46k.  That sounds familiar.  BTW, my manual didn't have any points called out to be 71k.

But... I did not get an odd reading from tube pin 4 on any tube.  I'm now betting the 10uF 16V Tantalum cap needs to get the solder joints rewet.  And maybe I didn't check that for resistance since the heater voltage checked out earlier in the manual.  I am confident that I wired the heaters as they should be.  I might have skipped it.

Once you do that go on to the voltage readings.  The voltages are the proof of the pudding.

[Rublyow]

Thanks Grainger --- after rewettting the joints on the two 10uF Tantalum caps and rechecking everything, I plugged it in and checked voltages.

The only voltage readings that are a bit off are the readings at the OA terminals on each of the C4S boards.  These OA terminals are specified at 170vdc in the manual, and I get a reading of 147 volts for both of them. All of the other voltage readings are pretty much spot on (within 3 or 4 volts).

Also, while the two center tube filaments are glowing, the two outside EF86 tubes have no visible glowing filaments, though they do get slightly warm.  I just wasn't sure if this is normal (as you can probably already tell, I know quite little about this).

[Grainger49]

OA is the output of the A side of the board.  I would expect the voltage to be what is expected. That is within +/-15% of expected so you ought to be OK.

I don't remember if the EF86 has a visible glow.  Did the tube get warm?  If so you have heaters.

Now go listen!  (I was out of town till this afternoon, I expect you have been listening!)

[Doc B.]

You can't see the glow of an EF86. It has a shield around the internal structure. Seems like this gets asked every week. You can tell if it's working by touching the envelope. If it is warm the heater is working.