No output

[C Moore]

Since we haven't seen pictures of what you did, I'll just share some comments about YOUR comments about using the AA864 NFB.

To follow up on xtian's post:

As someone who has done the hybrid AA864/AB165 conversion on two AB165 circuits, and converted a Pro Reverb to a "Bassman Combo" using the same hybrid circuit and a real '66 Bassman OT, I can tell you that when using an AB165 OT and converting (fully or partially) to the earlier AA864-style output stage, you need to swap the OT SECONDARY leads - meaning, the lead that was grounded at the output jack should now be hot and vice verse.

The AB165 OT secondary phase is the opposite of an AA864 circuit (don't ask why they did that... no one knows...).

You may have known that already, but in case you didn't, make the change.

Good Heavens....
I would not, in a Million years, have ever thought that swapping the secondary would matter. I have it wired per the color of the AB165 layout. I will try swapping the leads and see if that helps.
But would that account for the power tube B+ dropping 90 volts when they are installed.?
What I did:
1. Normal channel per the AB165 schem.
2. NFB per the AA864 schem.
3. Last gain stage before PI mixes both channels per the AB165 schem.
4. Bass Channel:
a. Deep switch is a cathode switch between 2 values of cap/resistor options.
b. 150k plate resistor
c. 51k slope resistor
d. Cathode follower before the tone stack.
e. Tone stack is typical Fender with some value changes to the components.
So there is no un-used triode in this amp. It was gobbled up by the Cathode follower.
I cannot help thinking that my noise/hum problem is tied into the fact that the pwer tube sockets drop 90 VDC when I install the tubes. I have tried other power tubes. I must have caused this problem somehow, but I am at my limits of ability in trying to figure out what I did wrong.
One thing I have not seen before. With the DMM set to read VDC....when I touch Pin 2 of the PI, the amp makes a real funny Oingo-Boingo kind of a sound. A real strange spongy, squishy type of sound that I do not ever recall hearing before.
The OT primary is just temporary. I will tighten/shorten those up before I am done.
Christ....sorry for another long post.
Thank You

[martin manning]

How about some voltages on the tube pins and power supply nodes?

[Firestorm]

The grid wires to the output tubes are frighteningly long. They should be maybe 50% shorter (as as close as you can). Why did you route the wires down to Pin 1 instead of straight to Pin 3? Fender only did that because they wanted to mount the grid stopper there. No magic to it.

Lead dress of the various B+ leads is dodgy. (You've got the screen supply right against a coupling cap). These wires could all be shorter and routed more "Pre-CBS" style.

Still squinting at these trying to spot something that could cause the 90V drop.

[C Moore]

The grid wires to the output tubes are frighteningly long. They should be maybe 50% shorter (as as close as you can). Why did you route the wires down to Pin 1 instead of straight to Pin 3? Fender only did that because they wanted to mount the grid stopper there. No magic to it.

Lead dress of the various B+ leads is dodgy. (You've got the screen supply right against a coupling cap). These wires could all be shorter and routed more "Pre-CBS" style.

Still squinting at these trying to spot something that could cause the 90V drop.

Thanks.....
I think I had the heater wires over at Pin 3 earlier. Not connected to Pin 3, but not up in the air like they are now. So I was trying to keep the grid wires away from the heaters. I will take them straight to Pin 3, though I am not sure how much shorter that will make them.
I was checking under the board where that screen wire is, so I moved it away from that screw. I can shorten it up a bit and get it back away from that .022 cap.
Not sure now much shorter I can make the B+ leads. I barely got the plate supply to its eyelet. I can twist them up a bit and try to do what you suggest. I realize everything adds up, but it seems like they come out of that grommet and head for their destination. I will make them as tight and short as I can.
Thanks Again

[C Moore]

How about some voltages on the tube pins and power supply nodes?

Yeah.....sorry.
I will get those numbers before I correct some of the problems that firestorm pointed out. Be back soon with that info.
Thank You

[C Moore]

OK....shit, I forgot the B+ nodes....sorry.
V1 is a cat follower.
With no power tubes:
V1
1-164
2-0
3-1.05
6-355
7-164
8-166

V2
1-186
2-0
3-1.3
6-184
7-0
8-1.4

V3
1-238
2-0
3-1.7
6-182
7-0
8-1.4

V4
1-214
2-50
3-92
6-214
7-53
8-82

V5
3-390
4-387
5- Neg 30
6-386

V6
3-389
4-387
5- Neg 30
6-387

With power tubes
V1
1-126
2-0
3-0.8
6-275
7-125
8-128

V2
1-144
2-0
3-1.1
6-142
7-0
8-1.1

V3
1-185
2-0
3-1.3
6-142
7-0
8-1.1

V4
1-169
2-37
3-62
6-169
7-40
8-61

V5
3-301
4-300
5- Neg 30
6-302
8-30mA

V6
3-302
4-300
5- Neg 30
6-302
8-30mA

[solderstain]

Good Heavens....
I would not, in a Million years, have ever thought that swapping the secondary would matter. I have it wired per the color of the AB165 layout. I will try swapping the leads and see if that helps.

My comments are based on assuming that you've configured your ENTIRE output stage, from the PI input forward, to the AA864 configuration. Is that what you did? If not, what DID you do with the NFB? If you moved it from one side of the PI to the other (more common) side, then yes, you must reverse the secondary side of the OT. No big deal - swap the wires at the output jack.

Will that account for the voltage drop? I have no idea - I've never done the AA864 power section conversion WITHOUT swapping the OT secondary, so I have no idea what the impact is. But since the primary and the secondary of the transformer are not directly coupled, I doubt that will solve the voltage drop problem. But it will put at least THAT portion of the amp electrically correct.

[C Moore]

Input to the PI is AB165, because both channels mix at the last gain stage, per the 165 schem.
The NFB is AA864.
So I am just curious about the theory behind swapping the OT secondary. Would that only affect an amp with a NFB circuit.?
Thank You

[Firestorm]

You've got the AA864 PI, with the OT secondaries connected correctly for that implementation. The AB165 swaps the black and green secondaries because the NFB comes in on the other side. If you had the secondaries reversed, you wouldn't be able to hear the hum over the squeal.

[C Moore]

You've got the AA864 PI, with the OT secondaries connected correctly for that implementation. The AB165 swaps the black and green secondaries because the NFB comes in on the other side. If you had the secondaries reversed, you wouldn't be able to hear the hum over the squeal.

I do not mean to be dense, but what you are talking about (OT secondary), would that be any different than swapping the OT primary or swapping the gird wires in a amp that uses NFB.? Do all 3 of those actions have the same effect.?
Thanks

[Firestorm]

Yes, all three actions the same. Looking at one of the larger pics, I see you've got the brown and blue (primary) wires swapped from all the Fender layouts. Since it doesn't squeal, that means you've also got your grid wires swapped from the layouts (I can't make that out from the pics). It would be better for those to be different colors so you can be sure you've got them going to the right tubes.

[solderstain]

From what I've read now in further posts (haven't looked at your pictures), it sounds like you've taken other actions that accomplish the same thing as swapping the polarity of the OT secondary. So you've got the right stuff done, you've just taken the complicated way to get there.

When I've done the AA864 configuration to an AB165, I've chosen to leave all the polarity, and hence color coding of wires, etc, the same on the tube sockets and circuit board, and just swap the two wires at the output jack. Quick and sweet. But since you accomplished it another way, it's all good.

[C Moore]

OK....
So now I am up to date on the whole "swap the Brown and Blue wire" scenario. I can do it from 3 locations if there is NFB involved.
Back to my real troubles.....
I still cannot figure out what is causing this 90 VDC drop.
As far as the humming is concerned.....
when I move that group of B+ wires toward the circuit board and away from the front panel, the hum just about disappears. I used a ground buss for the preamp grounds (input jacks all the way up to, and including the PI) is it possible that is coupling with the B+ leads for PI, Screens, and Plates?
I do not know of any other way to find out, except to take the 14 AWG buss wire down, and ground it like Fender did with that brass plate.....or something similar.
Maybe I will move the location of the output B+ grounds over towards the power tubes and see if that helps. That would be an easier first thing to try. If that does not work, I guess I will take the buss wire down and see what happens.
Thank You

[Firestorm]

I don't think it's the ground that's the problem; it's the proximity of "hummy" wires to sensitive leads and components. Still don't know about the 90V tho.

[C Moore]

I don't think it's the ground that's the problem; it's the proximity of "hummy" wires to sensitive leads and components. Still don't know about the 90V tho.

Not sure how well my pictures show it, but I don't think my layout is so different than most Fenders of this time line. I have rebuilt quite a few SF and BF Fenders and I have never had this problem. And this is the only one I have used a ground bus on. I realize that does not mean the bus is the problem, I could easily have something wrong somewhere else....just a thought.
I hate to burn up the bandwidth of the whole forum.....but I am just going to let you see my filter caps. Maybe I did something stupid. I can take it....just want to finish my friends head.
Thank You
actually....I have the filter cap for the screens sharing the ground with the PI and preamp tubes. Should that cap get grounded with the plates, screens, and HT center tap.?