5B6 build... no output

[zephyrblau]

the transformer was harvested from a Wurlitzer model 6144 (320 - 0 - 320) neither the layout nor schematic indicate output voltages of the OEM PT.
the board is a Hoffman 5F6 type modified as required. I've moved the 25R and 6K8 to the board. (next page) I'm working from the layout and don't know if there are any mismatch(s) between this and the schem.
after completion I put the unit on a Variac as a test to see if any of the smoke wanted to escape. so far so good ?
the voltage readings are not as expected. (next page)   

[zephyrblau]

more pix.


 

[zephyrblau]

voltages:
filters L to R;


layout says 400. I have 412
layout        320            411
                 300            383

[sluckey]

Is your speaker jack a Switchcraft 12A? If so, I believe the yellow wire is connected to the switch terminal. It should be connected to the tip terminal.

[zephyrblau]

here's where things really start to get wacky;
circled points L to R;
layout says 160. I have 370
layout         2.6             5.4                 
2.6              5.4

[zephyrblau]

Is your speaker jack a Switchcraft 12A? If so, I believe the yellow wire is connected to the switch terminal. It should be connected to the tip terminal.

it is. I'll double check. would that cause the wonky voltages I'm seeing ?

[sluckey]

I'll double check. would that cause the wonky voltages I'm seeing ?

No, but it will certainly cause you to have no output.

[PRR]

layout says 400. I have 412
layout        320            411
                 300            383

Small tubes are not sucking current. Are they wired right? Heaters too? Are they in their sockets?

-OR- your "10K" are really 1k.

[AlNewman]

What are your voltages at all socket pins?  Including AC/heater voltages?

[zephyrblau]

I'll double check. would that cause the wonky voltages I'm seeing ?

No, but it will certainly cause you to have no output.

output jack wiring corrected. thanks!
gosh my dummy load is warming up 

[zephyrblau]

layout says 400. I have 412
layout        320            411
                 300            383

your "10K" are really 1k.

yes... and no.
while I routinely check the comps to make sure they're in spec. I may have skipped that here. I may have taken it on faith when I ordered 10K that all were the correct value. the value striping on this modern stuff is pretty crappy. so... one is 10K the other is 1K.
back in a moment.

[AlNewman]

It looks like on your pictures you have 2 heater wires running from tube to tube.  If you're following the layout, there should only be one with a chassis return.

[zephyrblau]

proper 10K installed. PS outputs are now in spec.

[sluckey]

output jack wiring corrected. thanks!
gosh my dummy load is warming up 

That dummy load should not be warming up unless you have a signal (guitar, signal generator, etc.) connected to the input. If it is getting warm that means you have an oscillation going on. Better plug in a speaker to know for sure. An oscillation would most likely be caused by incorrect phase of the negative feedback. This can cause damage to the output transformer.

[zephyrblau]

new readings for these points are as follows;


circled points L to R;
layout says 160. I have 290
layout         2.6             4.7                       
                  2.6             4.1

[zephyrblau]

It looks like on your pictures you have 2 heater wires running from tube to tube.  If you're following the layout, there should only be one with a chassis return.

got it.
@ this point I there's some family chores I can't put off (any longer than I already have). I'll be back ASAP. again, my thanks to all.   

[zephyrblau]

output jack wiring corrected. thanks!
gosh my dummy load is warming up 

That dummy load should not be warming up unless you have a signal (guitar, signal generator, etc.) connected to the input. If it is getting warm that means you have an oscillation going on. Better plug in a speaker to know for sure. An oscillation would most likely be caused by incorrect phase of the negative feedback. This can cause damage to the output transformer.

yep... "hash" of some sort. definitely not 60 cycle hum. I need to double check the relocation of these two.

[sluckey]

Disconnect the 6.8K from the speaker jack. Any better?

[zephyrblau]

It looks like on your pictures you have 2 heater wires running from tube to tube.  If you're following the layout, there should only be one with a chassis return.

agreed.
...and originally I had the green 6.3V wire going to the ground side of the pilot light and the green-yellow wire going to the tip. I've since reversed this.
my thinking is that this is AC and polarity is not an issue. too simplistic ?
I also have short jumpers from each filament to ground for all sockets.    

[zephyrblau]

Disconnect the 6.8K from the speaker jack. Any better?

no change.

[AlNewman]

It looks like on your pictures you have 2 heater wires running from tube to tube.  If you're following the layout, there should only be one with a chassis return.

agreed.
...and originally I had the green 6.3V wire going to the ground side of the pilot light and the green-yellow wire going to the tip. I've since reversed this.
my thinking is that this is AC and polarity is not an issue. too simplistic ?
I also have short jumpers from each filament to ground for all sockets.   

Sounds like you got er all figured out.

[zephyrblau]

It looks like on your pictures you have 2 heater wires running from tube to tube.  If you're following the layout, there should only be one with a chassis return.

agreed.
...and originally I had the green 6.3V wire going to the ground side of the pilot light and the green-yellow wire going to the tip. I've since reversed this.
my thinking is that this is AC and polarity is not an issue. too simplistic ?
I also have short jumpers from each filament to ground for all sockets.   

Sounds like you got er all figured out.

only the filament wiring unfortunately.

[zephyrblau]

it seems that someone who shall remain nameless got his hands crossed and installed a 6SL7 in V1 (S/B 6SC7) 

[zephyrblau]

it seems that someone who shall remain nameless got his hands crossed and installed a 6SL7 in V1 (S/B 6SC7)

the net result of the above is no change in the "hash" output.
I've checked the resistance of the primary side of the O/T and both sides measure 61R (+ / - .5ohm)
@ the moment I'm building a proper cap discharge "pen".

[sluckey]

Divide and conquer. Pull the 6SL7. Any better?

[zephyrblau]

Divide and conquer. Pull the 6SL7. Any better?

better but, not good.

[zephyrblau]

...and I should clarify something. the "hash" that I refer to above is indeed an oscillation. the owner supplied a few 6SL7s, all Ruskie. one of which, the first one I tried is especially noisy with some crackling added for good measure.
the other two don't have the crackle but the oscillation persists.
 

[sluckey]

Not much left... power tubes and power supply. Wiring error should be high on the list.

[zephyrblau]

it seems that someone forgot a ground connection.
 

[sluckey]

it seems that someone forgot a ground connection.

Is everything working now?

[zephyrblau]

it seems that someone forgot a ground connection.

Is everything working now?

not yet. better but not OK. I'll post updated info tomorrow (Fri.)

[tubeswell]

Time for another set of voltages?

[zephyrblau]

Time for another set of voltages?

yep!
per the attached layout I put the Fender values are listed first. mine are in brackets. numbered 1 through 9 from left to right. yellow was probably a better color to use, but...
1) 400 [490]
2) 320 [461]
3) 300 [433]
4) 160 [417]
5) 180 [140] note; this drops to 47 if I unplug the umbilical cord / control panel. adjusting the Vol or Tone settings has no bearing.
6) 390 [490]
7) 180 [135]
8) 320 [461]
9) 390 [490]

[Esquirefreak]

Cathode voltage on the power tubes would be good to know. Unusually high voltages usually indicate that something is not pulling its share of current.

/Max

[zephyrblau]

does 63V sound right ?

[Esquirefreak]

No, but it depends on what value the resistor is. Compare it to the schematic or layout.

Divide that voltage with the resistance of the cathode resistor to figure out how many milliamps the power tube are pulling.

/Max

[zephyrblau]

250 ohms ... pretty standard Fender stuff of the era (?)  25 ma ?

[Esquirefreak]

250 mA?

[shooter]

63vdc/250 ohms = 144mA
if it's shared then 144/2 mA

[AlNewman]

Have you actually tested the resistance on your 250R resistor?  Because with your described voltages, it's putting out like 15W of heat, which is fairly significant.  That, and your power tubes are running at 200% +

[Esquirefreak]

63 ÷ 250 = .252A on my calculator. Have I misunderstood something here?

Sorry.

/Max

[tubeswell]

Measure the 250 ohm resistor with your R-meter to get its actual resistance.

[zephyrblau]

somewhere along the line it's burned up. I didn't verify it prior to installing but I do recall it being hot at some point during testing... too hot to touch if that's relevant.
it was purchased as part of a pair and the other reads 247 ohms. I'll be swapping the other one in shortly.


 

[shooter]

   dyslexia  I keyed in 36/250 TWICE
sorry for the confusion

[Esquirefreak]

Haha, that happens to me every now and then too 

Hopefully voltages will come down when the bias is steady.

However, I'm at a loss with the test point where you noted the voltage dropping.

/Max

[shooter]

appears to be the PI input, whichever plate pin 5 is


EDIT:  looks like you remove G1's reference to ground through the Vol pot, sending into lala land??

[zephyrblau]

per entry #5 above where I note the voltage drop this is the only change of all listed when I pull the umbilical. all other testing is done with the control panel hooked up.
dropping resister changed out.
control panel and layout pix attached.
   

[sluckey]

Input jacks are wired wrong.

[zephyrblau]

better ?

[sluckey]

They are on the correct lug now but the soldering job looks terrible.