to much hum jcm800

[giordydiver]

beautiful amp.

The v1 heater wire is still less than perfect. I don't know how easily hum can be induced into the plate wire, but one of the plate wires spends some time parallel to a single heater wire, that's the kind of thing you want to avoid. For the moment you could bend the blue wire such that it wasn't running alongside the red heater wire to rule it out.

Where are the speaker jacks grounded? I think I see the common, but where is the ground reference for the speakers?

A great article on grounding. I'm not suggesting changing everything as suggested in this article, but it might give you some ideas as to the source of your hum.

http://www.aikenamps.com/index.php/grounding

Hum is caused from AC ,maybe the plate wires can be influenced the hum but not in this way. I move the Ot from other side of chassis, cut the induced loop unter PT and now work so good

[Haze13]

Buss wire on the back f the pots - remove it. Chassis is grounded, metal parts of the pots are touching that chassis , making them grounded too. Than you add a buss wire to the backs of the pots, and ground it one more time and creating many ground loops. Look closely at the pics that Neikeel posted here and you will see that in these layouts buss wire is not touching backs of the pots.
Had same issue and I wrote about it. Then don't forget place a sheet of metal in you box and to mount your chassis on it.

[giordydiver]

Buss wire on the back f the pots - remove it. Chassis is grounded, metal parts of the pots are touching that chassis , making them grounded too. Than you add a buss wire to the backs of the pots, and ground it one more time and creating many ground loops. Look closely at the pics that Neikeel posted here and you will see that in these layouts buss wire is not touching backs of the pots.
Had same issue and I wrote about it. Then don't forget place a sheet of metal in you box and to mount your chassis on it.

The chassis has a big paint coating, is not a good ground for me, now the buss wire il ground to chassis, i divided in nodes my schematic with isolated ground for node, new preamp valve, and OT is moved from other side of chassis. No hum with master to 8 and no hiss with gain to 10.
Also I have mod my 34 and now I have the perfect amp for me, the amp I ever dream. Never try an amp like this.
Now I left my town for work,when came back I made a post with new foto, semples and my mods

Thank for yours helps

[Doug H]

Hum is caused from AC ,maybe the plate wires can be influenced the hum but not in this way. I move the Ot from other side of chassis, cut the induced loop unter PT and now work so good

I understand the AC current in heater wires can cause hum which is why we twist them to cancel the field. I wasn't sure if this was an issue for the plate wire, but it does carry a signal even though it isn't a grid wire.

Good stuff you got it sorted out.

[herbvis]

I move the Ot from other side of chassis, cut the induced loop unter PT and now work so good

Can you clarify what you mean. Did you rotate the pt?

[giordydiver]

I move the Ot from other side of chassis, cut the induced loop unter PT and now work so good

Can you clarify what you mean. Did you rotate the pt?

i have removed it and installed ot at bigger distante from pt. hum .

[neikeel]

Very strange

I could understand it on a 12 series where the OT and PT are close and the OT is in 'wrong' orientation, but on yours the filter caps are between and they are quite a distance apart, it is not usually an issue .

Me-thinks it was another issue........................but I doubt that you will be dissuaded from the confident posts you have made before

[giordydiver]

Very strange

I could understand it on a 12 series where the OT and PT are close and the OT is in 'wrong' orientation, but on yours the filter caps are between and they are quite a distance apart, it is not usually an issue .

Me-thinks it was another issue........................but I doubt that you will be dissuaded from the confident posts you have made before

So i think like you...jcm800 stock has a lot of hum after 5 master, but mine is a lot with 1 master .I change preamp tubes with china nos with low noise, probably the tubes were the first problem because when i built amp I had a problem and on v1 v2 v3 and the plate voltage was 430v( two resisto failed) . But also tubes I have done what my fried told me about tranformers. Transformers has a electromagnetic camps and when they are closed like jcm this camps add each other and the hum (50hz) are present. He told me that the first mod to do to reduce hum is cut induced current from chassi and move the OT or PT, infact the hum reduce is proportional to quadrate distance. If you see new marshall( also Afd100) or modern amp with no hum problem( blackstar one series , soldano slo ecc) you can see the ot and pt have a lot of distance. Other mod isolated ground for nodes like sdm layout. Now all pot to 10 and no hum or hiss.

Jcm800 was a war machine but why not make it better not only for the sound?

Now I am out for work, when I came back post a topic with all my mod, semples and photo.