Advice needed. Terminal 46 over limit for resistance check.

[CuriousMister]

All other resistance readings are good. This is the only one out of range. I checked connections and reflowed a couple joints to see if it’d make a difference. Do I need to add more solder to the binding post areas?  I know my soldering skills aren’t great.  Before I do any harm, I’d like to seek your advice. Am i missing something?

 

[Paul Birkeland]

46 gets its ground reference from the solder lug on the chassis, does this show proper resistance if you test it?  If it doesn't, there may be some reason that your ground wires up front aren't contacting the chassis, so this is definitely something to get sorted out before turning on the amp for the first time.

 

[CuriousMister]

Yes, the solder lug on the chassis reads correctly at near zero.  That’s what led me to reflow some more.  It worked.  46 is back on track.  Appreciate the help Paul!  I appeciate it!

 

[CuriousMister]

Man. I hit another snag during DC measurements. Terminal 30 ranges from 111-118 (should be 398) and terminal 17 ranges from 15-19 (should be 0). Reflowing doesn’t seem to be working. Attached a few more photos. I’m sure I’m missing something again. So close!

 

[Paul Birkeland]

A 2A3 has two fat pins and two skinny pins.  The fat pins go into the fat holes on the socket, which have the 3W resistors soldered to them.  If you are off on how you plug the tube in, you'll get results like this and you can damage your amplifier.

 

[CuriousMister]

So I swore I had 2A3 tubes dropped in correctly. I checked and did. Even swapped the tubes to see if it made a difference. It didn’t. The fat pins connected to the 3w resistors are receiving the fatter pins. I took another couple photos to illustrated it. What else do you think may be happening? I wish it was as easy as you suggested?

 

[Paul Birkeland]

Those voltages are actually on opposite sides of the amp.  What DC resistance do you get between 16 and 13?

The 100V or so at terminal 30 should come with smoking hot 130 ohm resistors as well.  If that isn't happening, then it's more probable that there's a solder joint problem on the resistor between 30 and 44.

 

[CuriousMister]

13=0
14=153
15=65
16=0.1

I’m giving up for the evening and will try again tomorrow night.  I wicked and soldered at lot between 30 and 44 to no avail.  17 hops around a lot when reading too.  I noticed terminal 27 is off as well.  Maybe the joint between the transistor at 27 and 30 is a problem now. That’s where I plan to to start again.

Thank you for your continued patience and help trouble shooting.  I really appreciate it.

 

[Paul Birkeland]

I would start by trying to measure the resistance of each 130 ohm resistor with the amp off to see if one has opened up. I think if you do accidentally plug in a 2A3 the wrong way, one of those 130 ohm resistors will open up pretty quickly. 

 

[CuriousMister]

Great idea! Am I correct the only way to measure resistance on these is to detach them from the amp?

 

[Paul Birkeland]

You should be able to measure them with your meter while they are installed, just be sure the amp is off and you get 0V DC at each of the 450V rated capacitors.

 

[CuriousMister]

Here’s what I got for DC readings at the 450v capacitors.
Between 41/42: 0.8 probe, 0.8 alligator
Between 44/45: -0.7 probe, -0.7 alligator
Between 26/27: 61.3 probe, -3.0 alligator
Between 29/30: 35.8 probe, -29 alligator
Between 31/32: -27.3 probe, -13.6 alligator
Between 34/35: -28.7 probe, -14 alligator

31/32 and 34/35 readings seem to move together.

Now, I’m super confused. I measured resistance at the 130ohm resistors just to see what I got. Only the one connected at 31/34 read correctly. Not sure if this is meaningful.

 

[Paul Birkeland]

I am strongly suspicious that a 2A3 or two got plugged in the wrong way.  You'll have to remove the 130 ohm resistors that aren't measuring properly in circuit, then double check them out of the circuit (you can just disconnect one end to double check them), then replace any that aren't working properly. 

 

[Thermioniclife]

It appears that your four pin sockets are oriented 90 degrees off. It looks like the large pin holes are facing toward the center of the amp and not the back as they should. If that is the case your filiment connections will go pin 1 and pin 2 which is the plate,  this is a bad situation. Just one man's opinion.

 

[Paul Birkeland]

It appears that your four pin sockets are oriented 90 degrees off.

The photos are just taken looking from the side.  Thankfully the sockets weren't improperly manufactured, that would be a fun one to chase down!

 

[CuriousMister]

You’re right about the 130ohm resistors.  Only one could be read while attached - the only good one.  3 are toast.  Based on what’s online, does it matter what wattage rating I replace them with?  This may have been my problem from the beginning.  I’ll replace them and report back when installed.

I really do appreciate your advice.

 

[Paul Birkeland]

That issue will happen either from the 2A3 insertion as I mentioned, or from backwards 100uF/450V caps, which act like a short when installed backwards and destroy the 130 ohm resistors.

If you use 1/2W resistors, they will probably last a few days/maybe a week.  A 1W resistor around a year or two maybe, and a 2W resistor indefinitely (other than failure from fault conditions of course).

 

[CuriousMister]

Another request for advice after installing three new 130ohm resistors.  The good news, my initial problem is fixed.  I think.  A new one sprung up though.  At both terminals 4 and 17 I get fluctuating DC readings (trending up over time).  Measurements ranged from 8 to low 30s after a second reading.  29 is also not zero.  It is -1.  Do you have any ideas or thoughts? 

Once again, thank you for helping me get this one over the finish line!

Tom

 

[Paul Birkeland]

Another request for advice after installing three new 130ohm resistors.  The good news, my initial problem is fixed.  I think.  A new one sprung up though.  At both terminals 4 and 17 I get fluctuating DC readings (trending up over time).  Measurements ranged from 8 to low 30s after a second reading. 

What are the units on this reading?  Is that 8 to 30 mV, 8 to 30V, etc?

29 is also not zero.  It is -1.  Do you have any ideas or thoughts? 

29 connects to all sorts of terminals via the buss of black ground wires.  If it doesn't measure exactly the same as any of the terminals its wired to, then there's a bad solder joint along that string of black wires.

 

[CuriousMister]

The readings at 4 and 17 were both in mV.  I’ll do some joint management on the black wires connected to 29 like you suggested later tonight.