Humming devilles

[CosmoK]

Hi!

I bought a hot rod deville for dirt cheap. Didn’t noticed any hum when I pick it up from the seller. But back home I hear a hum from the power transformer. I have taken it apart and been thinking of switch the power transformer(original part) but they seem to not be available at any online stores. There is one from hammond(290vex, I’m in Europe) that’s supposed to fit but that one only has 9 hookup wires while the original part has 13(or 12, don’t remember exactly now)hookup wires.
Some of the hum translates to the speakers even when standby is off and with no tubes connected. When I lay my ear on the transformer with no speaker connected it’s no doubt that the transformer is the main problem. Filter caps needs to be switched though but that does not seems to be the main problem here.
Then I came over a cheap hot rod deville(ML edition from 2016) for cheap so I couldn’t resist buying that as well to use while the other amp is under repair.(I might use the first one I bought as cab only if I decide took keep both). When I came home and plug in the ML, I hear a slight hum from the power transformer as well, less than the hot rod I first bought but still slight hum but not audible trough the speakers. Now the strange thing is, no other amp hums from the power transformer in my apartment, I’ve tried my old hot rod delux, dead silent power transformer. My deluxe reverb, dead silent power transformer.
I’ve still not tried to plug the amps in at my rehearsal space so not sure how different power from the wall outlet will effect the hum or not.

(It hums with no speaker or tubes connected so no need to address that as a potential problem. It is coming straight from the power transformer)

As suggested in other threads and forums I’ve tried the following:
Different power outlet(different house).
Moved the transformer 90 and 180 degrees.
Changed the voltage to 240v and then back to 230v.
Tighten the screws on the transformer.
So far nothing has helped. What happened is that two screws on the transformer broke right of, I more or less just touched them with no force.

Anyway, with the newer amped mic’d up for recording the hum from the power transformer wasn’t audible trough the speakers/headphones if the amp was normally loud for recording and the mic preamp gain low. When lowering the volume on the amp and increased the gain for the mic preamp the hum started to get audible through the recording.
All in all. The newer deville will stay as is I think. The older one needs a new power transformer and new filter caps.
(How can both the devilles has humming power transformers but not the hot rod deluxe which is more or less the same amp? I know they have different transformers though given the more wattage on the deville)

Anyone have any idea what’s up with my devilles?
Giddi up
/C

[bepone]

first to understand better, remove the output tubes and start the amp. if it humms then all is from power transformer.. if not, it is not from power transformer.
like this you can leave only output tubes, and rwmove PI.
if it humms now, and not with the PT, then is coming from output tubes. you need matched to stop humm ..etc.. like this tube by tube you will arrive to the preamp and will be detected from where it is

[Stevem]

Most of the times PTs hum when they where not potted correctly during manufacturing, or they have been due to circuit or tube issues running hot.

The heat up and cool down cycles ( expansion and contraction) can brake down the potting over time with the result of vibrating coils.

On vintage amps with issues like this with PTs that can't be had, or would have to go out for a rewind, I get a tube of high heat automotive silicone gasket maker, remove the PT from the amp, remove the end bells one at a time and pack until overflow with the silicone and then slap the bells back on and let it all set up for 3 days.

If you do this be very very careful with where the wires come out of the insulation wrap since the PT wires down in there are super fragile!

I like to first dribble epoxy on them and down in the gaps these wires exit from before I pack the thing up with silicone

[CosmoK]

first to understand better, remove the output tubes and start the amp. if it humms then all is from power transformer.. if not, it is not from power transformer.
like this you can leave only output tubes, and rwmove PI.
if it humms now, and not with the PT, then is coming from output tubes. you need matched to stop humm ..etc.. like this tube by tube you will arrive to the preamp and will be detected from where it is

It hums without the tubes inserted.

[CosmoK]

Most of the times PTs hum when they where not potted correctly during manufacturing, or they have been due to circuit or tube issues running hot.

The heat up and cool down cycles ( expansion and contraction) can brake down the potting over time with the result of vibrating coils.

On vintage amps with issues like this with PTs that can't be had, or would have to go out for a rewind, I get a tube of high heat automotive silicone gasket maker, remove the PT from the amp, remove the end bells one at a time and pack until overflow with the silicone and then slap the bells back on and let it all set up for 3 days.

If you do this be very very careful with where the wires come out of the insulation wrap since the PT wires down in there are super fragile!

I like to first dribble epoxy on them and down in the gaps these wires exit from before I pack the thing up with silicone

Thanks for your reply. The screws to the bell broke when I tried to remove them :/
If I’m getting those screws out and replace them I will try the silicone method.

[CosmoK]

Do you have any idea why the Hammond transformer have 9 wires and the original has 13 wires? I’m no electrician so I can’t figure out how to setup that transformer with only 9 wires to fit. I know how to solder and do tweaks in amps from instructions on what to remove or ad and pedals from tagbord layouts. How power transformers and complicated schematics works I harder to understand.

[bepone]

extra wires are for the primary voltage selection, if you are in Europe, you need only 240V/ that is what the Hammond transformer providing on primary

[bepone]

without the bolts for sure you will have some mechanical noise, you can buy from the local store.. i think M4 will be ok.. also plastic washer below the bolts will be good to reduce the losses in the core,humming will be less, but is difficult to find

m4.png

[CosmoK]

without the bolts for sure you will have some mechanical noise, you can buy from the local store.. i think M4 will be ok.. also plastic washer below the bolts will be good to reduce the losses in the core,humming will be less, but is difficult to find
m4.png

Yeah but the noise was there before the bolts snapped
And the noise is there when holding it with firm grip in my hands.
If I’ll try to restore the transformer there’s well sorted hardware store nearby that probably gonna have screws bolts that’ll fit. Not shure about the washers thought.

[CosmoK]

extra wires are for the primary voltage selection, if you are in Europe, you need only 240V/ that is what the Hammond transformer providing on primary

Okay, thanks! I think it’s beyond my knowledge to try to fix that and to figure out how to make it work in my amp.
I guess I’ll have to take it to a amp tech. I had a tiny bit of hope I could fix it myself. I’m used to fix stuff that normally most people will take to a tech to fix.
Problem is that amp techs doesn’t seem to want customers. They’ll rarely answer phone calls or calls back with simple questions like, -do you have time to take a job?

I think I’m gonna start to treat and think of my amps like smartphones to calm me down. They are expensive but no one complains when they are useless after 4-5 years. But still they cost as much as an decent tube amp that is supposed to work a lifetime if doing repairs.

[bepone]

if you want to make transformer change, and have no idea about electricity.. this is not good way
i dont want to say it is impossible, but will be very difficult to you.

actually it is simple, order proper transformer.. see the wire diagram.. locate the terminals on the pcb in the amp, they are marked..
remove previous one. install new one. connect according to the diagram. start the amp with long stick or broom from the other room, wait until explosion! if nothing happens, you can approach to the amp, still with stick in the hands - just in case!

check if the vibrations and humm is gone! if yes, suceeded!

[CosmoK]

if you want to make transformer change, and have no idea about electricity.. this is not good way
i dont want to say it is impossible, but will be very difficult to you.

actually it is simple, order proper transformer.. see the wire diagram.. locate the terminals on the pcb in the amp, they are marked..
remove previous one. install new one. connect according to the diagram. start the amp with long stick or broom from the other room, wait until explosion! if nothing happens, you can approach to the amp, still with stick in the hands - just in case!

check if the vibrations and humm is gone! if yes, suceeded!

It certainly won’t hum any more after the explosion
But yeah I know it’s dangerous to deal with high voltage. Always use one hand and drain the caps. That’s the mantra.

Thing is I already have an Hammond that I supposed to fit the deville replacement with 9 wires. I didn’t think of it much when ordering it. It was a surprise when I got it so I thought it was wrong so I may return it. But someone told I might work if you know what you’re doing, I don’t
In my mind I thought I just could replace it and connect the wires at the right positions if it where the same amount of wires. Now when it’s not and there seems to be a workaround to make it work I’m lost.