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Hi, ask:

1) when I put (in my new st-70) my finger on the tube i can feel very little vibration. (similar to that of any large transformer)
this vibration in all chassis.
This is normal ?

2) I can hear a little hum when I turn on the amp on the baffles. (with the volume 0) this is normal ?

this hum , may be due to low quality tubes ? (jj)

The vibration is probaby from the power transformer and is present to some degree in most amps with a steel (magnetic) chassis.
I have single ended amps with separate filament transformers for the DHTs whos' magnetic field causes a lot of vibration (noise) in the nearby steel chassis. It took me a while to track it down and figure out how to damp it out.
Every stock ST70 I ever had also had a soft hum that was audible when you put your ear to speakers. It shouldn't be noticable from your normal listening chair though. What current are you idling through your power tubes? Dropping each one down 5 or 10 ma might also reduce the hum.
The 1.5H choke is marginal IMHO but there is really no room for anything much bigger. If it is entirely stock with the 4 section filter cap you might gain from soldering in a 47uf 500 volt cap in parallel with the second filter cap section (the one after the choke).

mesherm wrote:The vibration is probaby from the power transformer and is present to some degree in most amps with a steel (magnetic) chassis.
I have single ended amps with separate filament transformers for the DHTs whos' magnetic field causes a lot of vibration (noise) in the nearby steel chassis. It took me a while to track it down and figure out how to damp it out.
Every stock ST70 I ever had also had a soft hum that was audible when you put your ear to speakers. It shouldn't be noticable from your normal listening chair though. What current are you idling through your power tubes? Dropping each one down 5 or 10 ma might also reduce the hum.
The 1.5H choke is marginal IMHO but there is really no room for anything much bigger. If it is entirely stock with the 4 section filter cap you might gain from soldering in a 47uf 500 volt cap in parallel with the second filter cap section (the one after the choke).

Thank you Mesherm !

Solved the noise problem ! It was the cable amplifier, i have I have moved and now without hum
(very close with a pre cable power)

Vibration: i have think rubber washers ? (between chassis and transformer)? maybe desappear
(simulate engine blocks rubber)

What I have found works well are the washers normally used in bathroom faucets. They usually come with a hole in them they are just about the right hardness to hold up under the heat and weight of power transformers.

Those washers are great. I liked them so much, I used them instead of standoffs to mount the circuit board to the underside of the chassis. I'm using four 00 flat faucet washers over a 1" #8 machine screw. The faucet washers were $1.50 for a box of ten. You can see the 1/2" standoff on the far right edge of the photo for reference.

and o`rings ?
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Ty_Bower wrote:Those washers are great. I liked them so much, I used them instead of standoffs to mount the circuit board to the underside of the chassis. I'm using four 00 flat faucet washers over a 1" #8 machine screw. The faucet washers were $1.50 for a box of ten. You can see the 1/2" standoff on the far right edge of the photo for reference.

Good !
ask: is is appreciable a difference in sound ?

That's a great idea! Is that a Tube Lab "Simple SE" board? Looks a lot like one...

I've been wanting to try one out sometime...

/ed B

hi, im thinking about more orings bewteen 4 screws-nuts in power transf.

what you think ?

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