can an OT generate HUM??? (5E3)

[richon]

hi,

after testing everything "and i mean everything"... on the circuito of my 5E3 and test:

changing filtering... screen resistors... ..changing tubes... matching tubes... changing bias...

y found that: When i turn ON the amp a little noise floor is present (like in every amp)...

but when i turn the VOLUME up (in bright or normal channel) the noise (like a 100hz) appear...

well i don't know where more to test...

if y take V1: 12AY7 the noise doesn't apper even if i turn the volume up..

so the last thing to test is... could a OT generate the noise??? (maybe i'm justo askeing nonsense.. but i don't know what to do)

[Manoteal]

Hi,
It looks like your amp is picking up hum somewhere in the preamp section, that is why when you pull the 12AY7 it goes away. How close is this tube to the power transformer? It isn't the output transformer if you make it go away by pulling the AY7. Have you tried chopsticking the heater leads in case they are running too close to sensitive circuitry? The fact that it increases with the volume up means it is not in the power supply.
M

[richon]

so... you say :

it should be the Heaters wires ???

all of this because the hum increase with the volume?

[Strat]

Does the PT have a centre-tapped heater secondary?

Have you wired the heaters as an original 5e3 where the hot side of the secondary goes to one side of the tubes and each tubes heaters are grounded next to it, or are you using the usual centre-tapped parallel string? If parallel, have you tried tieing the centre-tap to the cathode connection of the 6V6's to elevate the heaters?

[richon]

the secondary of the PT is: 3.15-0-3.15 , so i have the CT to the ground and each "3.15" to each heaters connection.

i will have to make some modifications to the lead dress maybe...

[Strat]

If you disconnect the heater centre-tap from it's ground point and reconnect at the junction of the 6V6's cathodes and the bias resistor/bypass cap. I don't think it will totally cure the problem but it should help some.