73 Fender Silverface Twin Reverb Noise New Findings & Questions

[gtrplayr1976]

I'll have to check the voltages again g-one. I have replaced nearly every resistor also. I will swap the .047 ,and the 250pf ,and see what happens. I get the noise through the volume, but the tone controls seem to amplify the noise. I have thought about gutting it ,and building a new board .

[g1]

Don't think about a new board yet, there is little left that could be causing your ch.2 noise. You said the noise is affected by the tone controls so it must be before them. As far as the DC on the pots, it wasn't clear if it was there all the time or just when turning the controls so I'll ignore that for now, and list remaining items that could be issues.
-the .047 and 250pf caps mentioned in last post
- the 1500ohm resistor and 25uf cap at pin 3 of V2A (you said you replaced the 100K at pin1)
-the 100K resistor between the .1 and the 250pf
-a bad tube socket for V2 (or solder at the pins)
-loose or corroded pots or jacks (they ground through their lockwashers and can become oxidized where they meet the chassis)
-dirty/oxidized jacks (especially the grounding switch at unused ch.2 jack)
-resistors at the input jacks.
That's about all I can think of. Poking, heating, or cooling these items may help identify the problem or locate a bad solder connection.
Now is not the time to lose hope!

[gtrplayr1976]

Thanks g-one ! The process has already begun ...I had talked with Doug Hoffman at Hoffman Amps ,and he had told me that he had replaced many of these type circuit boards that were prone to issues. I just thought I would totally eliminate that possibility ,and try to make the wiring more clean. It isn't that big of a cost. It just takes some time. I should have the board soon ,and I can start putting that together. In the mean time I can check all the other parts. I just need a good schematic ,and /or layout to go by since none really seemed to match what was there.

[Tom Phillips]

If you are replacing the whole parts board are you planning to rebuild it as a 1973 Twin or a Blackface style circuit?
If you go with BF there are AB763 Schematics , layouts and photos readily available.

[gtrplayr1976]

If it were mine I would BF it ,but it belongs to a friend. Seems they are similar except for the MVS ?
Why are the wires from the dog house wrapped with another wire ,and grounded at both ends ? Shield ?

[überfuzz]

I say ease down a bit. What if you replace the board and it turns out to be something else...

If I were you I'd start all over again. Swap V1 and V2, chop-stick around, check grounds, etc. Then after you triple checked everything bring the shotgun, or Howitzer.

[überfuzz]

Edit, double post...

[gtrplayr1976]

I've swapped every V in there ,used the chopsticks more than the Chinese use them to eat , grounded ,and ungrounded.....Boat anchor ?

[Tom Phillips]

...Boat anchor ? ...

I say no. It's just a frustrating job. Sometimes there is more than one problem causing the same symptoms so swapping things doesn't always give a definitive answer.
Based on what I have read in the two threads (and don't take this wrong) you just need more detailed troubleshooting to isolate the problem(s) and less shotgun replacement of parts that "could" be causing the problem. I realize that is easier said than done and it requires more experience but in the end it works out best.

I believe the wrapped wires were a lame attempt at shielding. The wiring dress in those models is quite a mess. For those who want to spend the time to clean it up you can create quite a little pile of leftover wire when you are done.

Have you actually ordered a replacement board?

Cheers,
Tom

[gtrplayr1976]

I agree Tom I need more experience ,and yes I have a board on the way, but it isn't the fiber type. I intend on cleaning up some of the wiring also. Maybe run some under the board.

What would you do with the wrapped wires from the dog house ?

[Tom Phillips]

...What would you do with the wrapped wires from the dog house ?

I'd just leave them in place. I don't think they hurt anything.

Is the board on they way populated with parts? Is it advertized as a SF replacement or a BF replacement (There isn't much difference, if any, for your amp) or as a universal replacement?

Since you mentioned that the physical amp does not match any schematic or layout that you have found so far, what do you intend to use for a schematic going forward?

Cheers,
Tom

[Enzo]

Are you talking about the grouped wires with another wire wrapped around them? That other wire should be grounded, and it is actually a shield. Don't eliminate it.

[gtrplayr1976]

I'd just leave them in place. I don't think they hurt anything.

Is the board on they way populated with parts? Is it advertized as a SF replacement or a BF replacement (There isn't much difference, if any, for your amp) or as a universal replacement?

Since you mentioned that the physical amp does not match any schematic or layout that you have found so far, what do you intend to use for a schematic going forward?

Cheers,
Tom

I received the board yesterday from Hoffman amps. it`s a different layout ,but made for the Twin. No components. Only problem is that it is longer ,and overlaps the rectifier board. I will ever have to make some mods ,have a custom one made ,or make my own. Some of the schematics I have are pretty close. The BF is as close as any with the exception of the MVS.

[gtrplayr1976]

Are you talking about the grouped wires with another wire wrapped around them? That other wire should be grounded, and it is actually a shield. Don't eliminate it.

Yep Enzo I figured that`s what it may be. It is grounded on both ends.

[Tom Phillips]

I received the board yesterday from Hoffman amps. it`s a different layout ,but made for the Twin. No components. Only problem is that it is longer ,and overlaps the rectifier board. I will ever have to make some mods ,have a custom one made ,or make my own...

Well, this is how small projects can turn into big ones. As the amp stand's now is the only remaining issue the noise in Ch 2?