So this picture is not from the Randall?
http://s18.photobucket.com/user/Jskrapper/media/P1120828.jpg.html

Quote from: BrianS on August 21, 2014, 04:45:44 PM
g1, can you tell me a little more about the heating elements?  I may have a couple different sources for something like that.  Was it luck that they ohmed out correctly, or lucky that you found them?

I was lucky to find them for free, and lucky they were 8 ohms.  I'm not 100% sure they were base board heaters, but was told they were.  I believe they were industrial as they came out of a college. 
  They are about 2 feet long, with ceramic squares stacked and a single thick wire spiraling along the length.  Any modern elements I see pics of are the finned type, which would not allow changing impedance.
  I will try to post a pic, maybe someone will recognize the type.
Meanwhile, thinking about this has made me wonder about stove-top electric elements.  Anybody try these or know if they would be a viable load?

  The ZD3 zener may have just failed.  They usually short when they fail which explains the low resistance reading.
  To be sure there are no other faults on that -15V line, check resistance across the points where the zener used to be.
  A low resistance reading there will mean there are other faults.

  Big power resistors are about the only option.  Most load boxes have them wired up in multiples to get the power rating, and in different combinations with switching for choice of load impedance.  Also fan cooling when dealing with so much power.
  I lucked out with a couple old heating elements from baseboard heaters.  The are wirewound, about 8 ohms each, and good for at least 1KW each.  Because they are wirewound, you can tap off at any point for lower impedances (but lower power handling).

  A couple more things you could try even before you open it, just to make sure:
you mentioned trying other speakers, you need to also try other speaker cables.
Also, try going straight into the aux input with something that puts out a fairly hot signal (some kind of preamp out) to see if the problem still occurs.

  Make sure it has the correct polarity at the connector.  This is critical as the wrong polarity will damage the amplifier.

  For a pair of modern 6L6 or EL34, running around 450V B+, around 40W at the onset of clipping is pretty normal.  Push it into clipping just a little and the power goes up.  I think most of the big manufacturers spec their power at 5% distortion.
Do your power calculations with a meter measuring RMS rather than using the scope numbers and you will see how the power jumps at clipping.

  From the looks of the schematic, this should be around a 40W amp?
Yes 1 watt is loud, but probably not to be confused with 40W  .
When I run into problems like this, (if there is not gross lack of B+ or very odd waveform on scope), I start looking at what I may have done wrong, or what could be wrong with my test setup.
  For starters I would throw another amp on the bench and verify the test rig.

JM:  that thread about the TA-16 was by BrianS, (not the OP of this thread) so he already fixed the amp in that thread  .
http://www.ssguitar.com/index.php?topic=3511.0

  The point marked +9 goes to ground.  The points marked with ground symbol go to your negative supply voltage.  The TL071 should be able to handle up to 36V difference between pins 4 and 7 so you should be fine.
As you see, pin7 will still end up being "positive" in relation to pin 4.
Pin3 still ends up being at half the supply voltage (due to R1/R2 voltage divider).

Quote from: galaxiex on July 29, 2014, 02:29:17 PM
3 wire cord is in the plans but I was unsure how that works with the Pos voltage on the chassis?

There is no voltage on the chassis.  It is positive ground.  The supply is negative instead of positive.  Many old cars used to be positive ground.
  Voltage and ground can be tough to wrap your head around, all voltage is relative to something, we usually use ground as that reference, but it is not necessarily so.
  In this case, everything is in reference to the positive, so we call that ground, and you will be connecting that point to the chassis.

Ok. the 12DW explains the PI imbalance, as you proved by trying the 12AX and finding it was balanced. 
Yes, you can plug 6L6's right in with this circuit.  Just have to be good enough to handle the high plate voltage.
Of the old tubes, not likely they are all bad, try them one at a time, probably the one or two that redplate are pulling down the bias for the others.

Triple check that both side heaters are lit.
Remove PI tube, power off.  Measure resistance from pin 8 (at the socket not at the board) to ground.
Now measure resistance from socket pin 6 to point D of power supply resistors.

  Sorry to nitpick, but standard "safe" wiring of fuseholder is for incoming power to go to back end of fuseholder first, then out the side.  This is so as soon as the fusecap is disconnected the hot can no longer touch anything.  With the hot on the side terminal like you have it, as the fuse is being pulled out it can contact the "hot" side terminal.
Of course we assume the unit will be unplugged before the fuse is removed, but mistakes happen.

Quote from: ilyaa on July 03, 2014, 04:49:28 PM
if i just pull v4 out and play without a tube in that socket, will the amp be mad?

Should be fine, preamp supply voltage will probably come up a little.