Narrow it down.
Do any other controls affect the noise?
If so, then the issue is before that control.
An audio probe would help immensely.

Thank you sir and I am on the same page.

This board is a major PITA to test given its orientation. I guess I could mark all the test points with a sharpie and then put it back on.  Is that what you all do?

Or do you test the board outside and run any applicable grounds?

Do any of you use a listening amp for tracing on preamp boards?

The ground symbols are not conventional on this amp which makes it that much more difficult

Lastly, and based on what I am describing i.e. full power/all preamp functions work/burnt C7 (which I cannot even find on the schem), does anything look like suspect?

Follow the noise backwards from the Master control.

Well....you knew I was gonna do it 

Amp in playing mode
You cannot view this attachment.

You cannot view this attachment.

Amp on standby

You cannot view this attachment.

You cannot view this attachment.

 

Hi all! 1st post and happy to be onboard. Thank you.

I am a tube tech for many years, know my way around a scope and sig gen but am just starting to further my knowledge into SS.

I have read many articles/educational topics on general Transistor theory, amp design etc but far from an expertise level of tube topology/design.

I was given a BT350 that was "dead".  There were several things going on and I will list them here just to give some back drop.

1- Both low voltage power supply fuses were blown
2- 22 ohm fusible resistor was blown on the preamp board C7
3- IC1 was found to be inop
4- Several diodes on the preamp board were bad
5- Of course...very little signal would pass

I have resolved all the above and even replaced IC2 given I had more than one 5532.  I have a  clean/strong output to the speaker jack and this can be seen both on scope and practical playing a bass thru it. 

However, it has a lot of static noise/some crackle pops and some hum that increases via the Master Level with or without an input plugged in

I have bridged the Effects jacks. No change. 

I have tested the signal at J3 pin 2 on the power amp and can see (scope) static/noise.  I have also sent the Effects out to another amp and get a clean signal BUT the same noise albeit less than what I see/hear at the speaker jack.

I have tested both power rails at every TP and they are solid at +/- 70 ish volts and +/- 16 ish volts with "ish" = tenths of volts and negligible I think

With no speaker load, I am getting -0.2 vdc at the speaker jack with Master at 0 and wild jumps from -36mvdc to 16vdc RMS via my meter when I turn up the Master Level.  In other words, voltage is bouncing after the master pot leaves ground

With an 8 0hm dummy load, it is the same +/- mvdc bounce

Any suggestions would be greatly appreciated and thanks in advance!

I don't see a way to post a schem file here.  But I have them

If there's a valve rectifier (especially indirectly heated like here 5AR4), I suggest to just ignore or eliminate standby; none of the typical arrangements are downside free or are anywhere near evenly balanced (in regard of technical downsides and benefits).

Holy cow 🐄🐮

Seeing the difference between LED and incandescent bulbs

  

Ok nm I didn't realize there were different models 

You cannot view this attachment.

Instructions for the one I have

You cannot view this attachment.

Working in single phase mode

You cannot view this attachment.

 

Finally got around to trying this thing

I splurged a few bucks on a manual

You cannot view this attachment.

You cannot view this attachment.

I hooked it to a box fan 

You cannot view this attachment.

So it has life but I couldn't get any response from the single phase mode aside from a small reverse movement I did reverse polarity to try it to no avail

I don't see any fuses anywhere on the unit or in the manual nor a power cord 

I need to calculate approximate watts of a dollar store box fan 

Thanks
I guess it would help if I looked it up and determined what actually happens circuit wise with a standby switch  like it shorts out the flux capacitor 

You cannot view this attachment.