signal stability super reverb ab763

[pbiagi]

Sorry my previous post was long and covering different subjects.

Since then, improvements.

The one side of the PI plate sine...

[pbiagi]

Update - sorry for the long post!

For a single probe, see my post May 17.
This is still the case - using a single probe on the PI after...

[pbiagi]

Quick update - I tried another tube yet the exact same wobbliness from the same PI plate is displayed.
The trace from the PI plate's grid is fairly...

[pbiagi]

Thanks for the advice.

Correct, the previous photo was 2 channels showing out of phase relationship of PI plates.
Swapping the probes...

[pbiagi]

While researching why the amp tone was raspy - I believe its a speaker which I'll change out tomorrow -
I fed a ~400Hz sine wave and noticed that...

[pbiagi]

Thanks Chuck for the responses.

The primary concern was safety and not ruining something.
I would like get close to the Harvard sound,...

[pbiagi]

Answered my question - with tubes:
B+ 375V - 373V - 299V - 175V, going down stream.

Since the heater voltage is 6.3V, I'm thinking of adding...

[pbiagi]

Just completed, I think, a Harvard build, bringing it online the voltage maybe normal, but want to double-check with the experts here.

The...

[pbiagi]

To close -
Changing out the output transistors worked.
Resistors tested fine, and we checked a sine wave before hooking up a speaker.
...

[pbiagi]

Thanks for the info.
I ordered a couple MJ15015, which I believe is the replacement transistor. I got the NPN version.
Question - do I need...

[pbiagi]

Thank you Jazz Bass.
It is the '78 design - what you sent is perfect. (Seems Peavey has a '78 and a '90's model).

Stupid question -...

[pbiagi]

Hello,

Could use some guidance in restoring a Peavy bass amp. I could be wrong but believe there are two versions of the TKO 80, and this...

[pbiagi]

My signal generator is fairly old, I'm guessing 70's, but seems to be working fine..
It actually has a "Fine" attenuator similar that you...

[pbiagi]

Thanks for this point.
My sine wave generator has 3 signal outputs, 0db, -20db and -40db. I was blindly using -20db.
I just measured the output...

[pbiagi]

Hello,

Trying to learn what an oscilloscope can do, is showing.
By making measurements I learned that my 5E3 output transformer blue/brown...

[pbiagi]

To let readers know how this all ended..

The rectifier socket change out obviously helped hold the tube but did nothing for the raspy sound,...

[pbiagi]

Some results -


That appears correct - after removing the two 2M resistors in parallel, the original resistor now measures 115K ohms (which...

[pbiagi]

Thanks for the advice Steve!

Making progress.. but new challenges..

The normal channel treble cap was a original ceramic, 250p....

[pbiagi]

Ok, got back to this amp.
- disabled the heaters artificial center tap (since the green-yellow wire was grounded already)
- removed the death...

[pbiagi]

Wow, thanks Steve. I've got plenty to digest now.. It'll be a couple weeks before I get started and I think I'll be pouring over your every word.

[pbiagi]

Initially I didn't like the thread being hijacked by what I regarded as a distraction however I think it had to be.
One more point - this is a great...