Heeeeelp with huuuuum

[isaac_teller]

https://www.facebook.com/reel/851160736847855


Working on a Fender Super clone(not built by me) with an incessant hum issue that rises and falls with the turning of the reverb knob. Here's what I've done so far:
1)Put isolated jack on reverb send
2)shielded cable from reverb return to reverb return stage
3)replaced reverb tank and cables
4)moved all wires from tube sockets and volume pots with chopstick
5)switched tubes
6)when I remove tube V4(recovery and gain stage) 90% of the hum disappears
Any suggestions?

[Latole]

1- I can't see photos. it do not work.

2- Wich Fender Super is this clone ?
3- Show us the schematic
4 -Has it ever worked well and without hum ? Or always hum ?

[isaac_teller]

It's a Mojotone clone. The layout is exactly the same as the original Fender. It always hummed. The owner bought it used from someone who had it for several years. He's only had it for a few months.
I'll post the video of the hum later.

[Esquirefreak]

If it's an AB763 SR clone, the v4 reverb recovery stage is probably the most sensitive stage in the whole amp. Look for wires crossing/near proximity around the tube socket. Make sure that the RV tank orientation is correct (the most sensitive transducer should be furthest away from the PT.

/Max

[Latole]

If it's an AB763 SR clone, the v4 reverb recovery stage is probably the most sensitive stage in the whole amp. Look for wires crossing/near proximity around the tube socket. Make sure that the RV tank orientation is correct (the most sensitive transducer should be furthest away from the PT.

/Max

You are right ; Mojotone only Fender Super is SR ; https://www.mojotone.com/amp-kit-resources

Super Reverb AB763 it is not what I call Fender Super .
 

Esquirefreak must provide more information and should be more precise.
To hear hum is not usefull.

Most of hand built amp have some mistake or defective part.
They are the most difficult amp to fix.

[isaac_teller]

Here's the hum.


https://drive.google.com/file/d/1CK1gIFk9AfSgmy05n8IzAb3KqBWKilKp/view?fbclid=IwZXh0bgNhZW0CMTAAAR1_w8Kl6TCi80XGfkI2RsMcUlP8lEQFGeuabF05ILOsDLoj8PVIChYB7Rk_aem_AXZXtFMN4tbH-RuExxnLIQ0p37aMlHSt9FDgYkFmdDb4FBqA1_jwjODfH7DDxXuq3mbm2m1ZL6Lzy6J_KDWVZyyI

[Latole]

As I said before, we need more good pictures of the amp than hum sound .

What are these capacitors ? Amp is not build as Mojo layout !

And wiring dress is poor.

[Latole]

Mojotone layout

[isaac_teller]

They are added to the first 2 nodes of the power supply. I have no idea why the original builder did that. Should I just remove them? All of the other e-caps are on top of the chassis(in a doghouse). There is one ground point for all the ground leads and the 4 input jacks are grounded to the chassis.

[Latole]

They are added to the first 2 nodes of the power supply. I have no idea why the original builder did that. Should I just remove them? All of the other e-caps are on top of the chassis(in a doghouse). There is one ground point for all the ground leads and the 4 input jacks are grounded to the chassis.

You have to look at the amp as a whole.

 Compare it to the original schematic and you'll know (if you have the knowledge) what they're for and whether or not they're necessary.
At the moment, your information doesn't allow you to know.

This amp probably has several flaws to correct.

[isaac_teller]

Also, the hum was still present when I disconnected the tank and the cables. Here are some more pics.


https://drive.google.com/drive/folders/198VMoN7nd1VnaNMzD_eRaXIjGWrB-Q96?fbclid=IwZXh0bgNhZW0CMTAAAR1L1ilkD6E4x4mD6hukbTKEShCWgkjoXSqo1-f_A5N-VGK-9Q4UMWpD1-c_aem_AWklSLwAh8Tb7SzP8-jvEbjL77B4Bv6A31sZ-Op6MN_5Gw3_8m7B7JH4C4AsgsmgZS5YQYp3GI9_6eYEPRyRFTFl


https://drive.google.com/drive/folders/198VMoN7nd1VnaNMzD_eRaXIjGWrB-Q96?fbclid=IwZXh0bgNhZW0CMTAAAR1L1ilkD6E4x4mD6hukbTKEShCWgkjoXSqo1-f_A5N-VGK-9Q4UMWpD1-c_aem_AWklSLwAh8Tb7SzP8-jvEbjL77B4Bv6A31sZ-Op6MN_5Gw3_8m7B7JH4C4AsgsmgZS5YQYp3GI9_6eYEPRyRFTFl

[Latole]

Thank's for the good pictures.

One ( of many ? issue) are the poor wiring dress.
Look at the Monotone layout.

Wires must be short as you can.

The wires must also run along the metal frame and not be in the air, as they will act as an antenna to pick up any noise = hum.
Furthermore, the wires should ideally cross each other at 90°, but above all not be parallel to each other.
The reverb circuit is very sensitive to this. I'd start there.

Look at Mojo's layout. The amp is far from that

[Esquirefreak]

I've never seen a Fender amp where the wires cross at 90°. And those have worked fine for 60-70 years.

I was precise enough about what I mentioned before, Latole. Based my answer on the fact that the reverb pot hade a big effect on the hum.

Compare the whole amp to the layout. The devil is often in the details; lead dress, routing and grounding. If done exactly like the layout (and knowing that the components work) all should work well.

/Max

[tdvt]

Thank's for the good pictures.

One ( of many ? issue) are the poor wiring dress.
Look at the Monotone layout.

Wires must be short as you can.

The wires must also run along the metal frame and not be in the air, as they will act as an antenna to pick up any noise = hum.
Furthermore, the wires should ideally cross each other at 90°, but above all not be parallel to each other.
The reverb circuit is very sensitive to this. I'd start there.

Look at Mojo's layout. The amp is far from that

I would have to strongly agree. Trying my best not to offend, but honestly, that amp is real mess & I don't see how you can remedy the issue(s) without a good foundation.

If I were faced with that, I think I would break it out & clean-up/shorten/re-dress in sections; control wiring, tube socket wiring & grounds.

Then you should be able to see what you are dealing with.

You know the design is proven, as are the parts. The wild-card is the implementation.

[Latole]

I've never seen a Fender amp where the wires cross at 90°. And those have worked fine for 60-70 years.

I was precise enough about what I mentioned before, Latole. Based my answer on the fact that the reverb pot hade a big effect on the hum.

Compare the whole amp to the layout. The devil is often in the details; lead dress, routing and grounding. If done exactly like the layout (and knowing that the components work) all should work well.

/Max

90 degrees is ideal; anything closer is acceptable, and this generally applies to ( some ) signal-carrying wires.
What should be avoided are ( some ) signal wires in the air or in parallel and very close together.

This can be seen very clearly in this photo of an AB763, whose wiring has nothing to do with your amp.

If all this is impossible, you need to take certain measures, as CBS did in the mid '70s and beyond

[Latole]

If I were you, what I'd do would be to go through the whole assembly again, checking all the connections and wiring from the input sockets to the output transformers to detect any assembly errors, because I'm sure there are some.

By the way, you need to know why 2 electrolytic converters have been added at the first 2 nodes as you say.
Are there any other "modifications" that would be undesirable?

[HotBluePlates]

Working on a Fender Super clone(not built by me) with an incessant hum issue that rises and falls with the turning of the reverb knob. Here's what I've done so far:
1)Put isolated jack on reverb send
2)shielded cable from reverb return to reverb return stage
3)replaced reverb tank and cables
4)moved all wires from tube sockets and volume pots with chopstick
5)switched tubes
6)when I remove tube V4(recovery and gain stage) 90% of the hum disappears
Any suggestions?

You posted about this amp on another forum, where I pointed out certain wires were bundled that shouldn't be bundled & could be contributing to your hum.

You posted that you'd made all changes recommended.  However, your photo today shows the same bundled wires:




You should simply have all wiring re-done in this amp to build it the way it was originally made by Fender.  The original amps don't hum, and they're not assembled the way this amp is assembled.

[Latole]

I re -edit

What I read HotBluePlates :  he doesn't trust us

[isaac_teller]

This was posted on another forum by the the amps owner, not me. He later requested my help. I'll probably end up rewiring everything. In the amps current situation which would be better- adding a ground buss or using the chassis for ground(all the input jacks are grounded to chassis).

[mresistor]

The wiring from the board to the tube sockets should not cross OVER the filament wires as is shown in HBPs photo and elsewhere in this amp. The twisted-pair flament wiring should be in the air above all the other wires. 
Hum can also come from a faulty tube..  and swapping to known good tubes is a good practice to make sure one tube is not the source of hum.
If the bias is way off on one power tube as compared to the other this can cause hum. 


The filament transformer should be grounded very near the tube socket near it. I use one of the tube socket bolts sometimes.  There should be only one ground location for the preamp and pots and that is on the input jack. The power supply end should have it's own ground.
There is probably more.....

[mresistor]

What is the part # for the reverb transformer in this amp?   Is it the correct one?

[isaac_teller]

These are older photos. All filament wires have been routed away from signal wires and there is shielded cable from the reverb return to the grid of V4. Also swapped tubes. Didn't help.
The reverb tx number is 022921.
https://www.tubesandmore.com/products/transformer-reverb-driver-fender-amps-125a20b-replacement


https://drive.google.com/file/d/126rtaPz68MgWo4Mh84SZAFtTWsxoVONk/view?fbclid=IwZXh0bgNhZW0CMTAAAR2ORIKc-Y3drtWj8nP3tModB8syZdPirfwdnFc-l8oX9ukdthKrKuL_6Bk_aem_Aa1XrgB0EsWjnUmL7hr-wLCHQcYaCoksbPYqBp9YHk5fukObRpYGYejAOe_ayqbANvXA2-CIulQ6PW75QyP8CSjB

[separateness]

If unplugging the reverb return has no effect and the Reverb pot turns up the hum, the problem (which is probably compounded by other issues, given the lead dress) has to lie in that V4a triode circuit.  Does grounding the grid kill the hum (can be done with the footswitch)? How is the integrity of that 220k resistor? Is there any weirdness with the connection to the footswitch/jack? Extra care really has to be put into that short length of wire from the Reverb return jack to V4a grid; if your heaters are flying, the grid wire should hug the chassis down the wall and across the floor to reach the pin.

[stratomaster]

I also suggested troubleshooting steps on a Facebook group post about this same amp. (Since when did it become standard practice to shotgun all known amp forums with a problem?)

I was told my troubleshooting steps were tried, weren't a fix, and dismissed. 

I suggested strategic grounding of grids to zero in on the area of the problem.  Pulling V4 kills the signal in that whole channel and is a coarse investigative tool.

Since we're on the Hoffman forum I'll also suggest a listening amp.

I hope you follow through this time.

[tubeswell]

Consensus is bad lead dress and it sure looks bad. Also suspect poor/multiple grounding. Strip the wiring and grounds out and redo everything. Keep wire runs short, reduce parallel wires, lay unshielded signal wires close to the chassis etc

[isaac_teller]

 "(Since when did it become standard practice to shotgun all known amp forums with a problem?)"


As i mentioned above the amps owner posted on the other forum before he requested my help. Currently everything is grounded at one point(next to the vibrato channel input jacks) except for the input jacks which are in contact with the metal chassis(can be seen in the picture). What tubeswell recommended is what I'll probably end up doing.

[stratomaster]

"(Since when did it become standard practice to shotgun all known amp forums with a problem?)"


As i mentioned above the amps owner posted on the other forum before he requested my help.

Is this you?

We like to answer technical questions and solve puzzles.  It's why most of us are here.  We need to be open and honest with each other if we're going to make progress. 

It's ok to throw up your hands and ask for help.  No one is judging your technical skill or ability. But we do need to be able to trust that you're being straight with us. 

[isaac_teller]

I know that it doesn't look good that I posted on 2(leading) forums. Sorry about the bad vibes. The amps owner has delayed signing a rental contract with a studio here until his amp is in working order and he's kinda stressed about it. I hope that rewiring everything will solve the problem.

[Latole]

I know that it doesn't look good that I posted on 2(leading) forums. Sorry about the bad vibes. The amps owner has delayed signing a rental contract with a studio here until his amp is in working order and he's kinda stressed about it. I hope that rewiring everything will solve the problem.

 Without passing judgment on your skills, this amp should be seen by a competent technician if your customer is so stressed that he doesn't want it back for months.