Guess what?

CoyotesGator said:
Brother, others may tell you different but if I were you, I would build a light bulb limiter for initial startup.
Click to expand...
I did consider building one when you mentioned it upthread, but forgive my ignorance for a moment, if you will:
Should I be worried about other components exploding when I give em juice?
I'm not a tech, just a dude trying to fix his broken amp lol
 
mcblink said:
I did consider building one when you mentioned it upthread, but forgive my ignorance for a moment, if you will:
Should I be worried about other components exploding when I give em juice?
I'm not a tech, just a dude trying to fix his broken amp lol
Click to expand...
I never start an amplifier build or rebuild without one.

They are cheap insurance and easy to build.
 
mcblink said:
I did consider building one when you mentioned it upthread, but forgive my ignorance for a moment, if you will:
Should I be worried about other components exploding when I give em juice?
I'm not a tech, just a dude trying to fix his broken amp lol
Click to expand...
Parts have already died.

Anything in the fault current path might be suspect.
 
mcblink said:
R6, 1w, 1ohm.....I think?

View attachment 63688
View attachment 63687
Click to expand...
OK R6 is a fuse in case the tube draws too much current it's supposed to blow.
(it's a current limiting resistor)
You can replace that with 1 watt 1 ohm resistor and it doesn't matter which type.
Precision resistor is OK no problem.
It does not need to be a matching type resistor, any type resistor will work.

Note: do not change this resistor to a larger rating. It will prevent the resistor from blowing.
If the tube draws too much current the resistor is supposed to blow.

The bias failed, which caused the tube to red plate and draw too much current....
then the resistor is supposed to fail. This saves the output transformer etc.

The bias fails because:
The bias pot stops working (very bad design), then the tube red plates.

What makes the bias pot fail?
The B+ voltage is leaking into the B- voltage. This is what happened before you put the new board in.
This happens when the insulation of the old circuit board fails.

But now that the old circuit board is replaced,
the insulation should be good again. (that's what you test before you put the new tubes in).

So change the bias pots.
Change the 1 ohm cathode resistor R6.
Test the screen resistors. Test the grid resistors.

Then proceed with checking the bias voltages (I'll show you how to do that) on all the output sockets pin 5.
This is done with the high voltage turned OFF, and no tubes installed.
 
Amp Mad Scientist said:
OK R6 is a fuse in case the tube draws too much current it's supposed to blow.
(it's a current limiting resistor)
You can replace that with 1 watt 1 ohm resistor and it doesn't matter which type.
Precision resistor is OK no problem.
It does not need to be a matching type resistor, any type resistor will work.

Note: do not change this resistor to a larger rating. It will prevent the resistor from blowing.
If the tube draws too much current the resistor is supposed to blow.

The bias failed, which caused the tube to red plate and draw too much current....
then the resistor is supposed to fail. This saves the output transformer etc.

The bias fails because:
The bias pot stops working (very bad design), then the tube red plates.

What makes the bias pot fail?
The B+ voltage is leaking into the B- voltage. This is what happened before you put the new board in.
This happens when the insulation of the old circuit board fails.

But now that the old circuit board is replaced,
the insulation should be good again. (that's what you test before you put the new tubes in).

So change the bias pots.
Change the 1 ohm cathode resistor R6.
Test the screen resistors. Test the grid resistors.

Then proceed with checking the bias voltages (I'll show you how to do that) on all the output sockets pin 5.
This is done with the high voltage turned OFF, and no tubes installed.
Click to expand...

Wow, like a surgeon!
 
Looks like the box full of precision resistors kicking around here are all 1/4 watt, so I guess I'll be waiting for a few more days for the ones I ordered to arrive anyway.

I can still solder in some new pots and reattach the test pins on the bias board though. After that, there's no more I can do until those resistors arrive.

Looks like I'll get a few more Game of Thrones episodes watched lol
 
Here it is sitting under my DSL in the jamroom

Did you want a view of something in particular? It's dismantled in my RV but I could go grab a clear shot of whatever if you want

20200705_235725_resized.jpg
 

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