Author Topic: sorado hummm  (Read 2807 times)

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Offline max headrrom

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sorado hummm
« on: March 29, 2006, 09:45:54 am »
has anybody changed a stock plug for a 3prong and reduced humm? how 'bout werber's adding dc bias to the fillament center tap aprox 40 v? split it from the b+ off of the first filter cap?

sorado played with bass thorugh original 2x15
 any help? tone is perfect;  hum is irritating

Offline loudthud

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sorado hummm
« Reply #1 on: March 29, 2006, 05:25:10 pm »
Does the hum change when you change the ground switch ?
Does the hum change when you turn down the volume and tone controls ?

Offline JoeArthur

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sorado hummm
« Reply #2 on: March 29, 2006, 05:52:48 pm »
Quote from: loudthud
Does the hum change when you change the ground switch ?
Does the hum change when you turn down the volume and tone controls ?


Hmmm.... (no pun intended).

I see where you are going with the first question.  A three prong plug conversion will not decrease hum beyond the correct setting of the ground (or polarity) switch.

The second question.  Could be a variety of different causes.  If it does, then I would assume hum pickup through the pickups (say that fast three times!!).  

If it doesn't... well, my suspect would be the power supply caps probably need replacing.

I didn't know Weber (or Werber if you prefer) was associated with a practice done to hi-fi amps back at least as early as the 1940s (if not before). Imposing a positive voltage on the heaters could cut down on some hum - assuming the heater supply is the source and the primary pickup of that hum source is the cathode of the tubes.  

This would be my last and final step - well, not exactly since I would have  converted the heater supply to DC operation long before this.  But before that last and final step... I would have re-twisted the heater supply lines to the tubes, which would 99.9 % have taken care of that problem.

AS I said before... it's more likely that your power supply caps are the culprits.

Offline max headrrom

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sorado hummm
« Reply #3 on: March 29, 2006, 06:59:54 pm »
hummm only changes as volume goes past 6 if trbl and bass are on 10.
(hey thas my tone)
polarity can add noised, but not this hum.

thanks for the filter cap tip they might be a bit crispy rated at only  500v
and b+ is stable at 535v

have you had to (re) twist the filament supply on sunn's often?

am I asking to much to be dead silent? my Heathkit UA1 is  and so is my Dynaco st -70.

MAXHeadroom

Offline loudthud

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sorado hummm
« Reply #4 on: March 30, 2006, 01:26:12 pm »
Elevated heater supply bias will remove some of the 60Hz component of the hum. Any buzz won't be changed. To be really silent, some changes need to be made how things are grounded and that four section can cap has got to go.

One problem old Sunn amps have is bad ground connections at those terminal strips that are riveted to the chassis. If you have access to a really big soldering iron, solder them to the chassis. Check for corrosion between the input jacks and the chassis and make sure the nuts are tight.

Offline max headrrom

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sorado hummm
« Reply #5 on: March 31, 2006, 08:01:40 am »
great scoop thanks

MAXHeadroom

Offline Soundmasterg

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« Reply #6 on: March 31, 2006, 04:28:56 pm »
I totally rewired my 200S with a true ground buss, and isolated all grounds from the chassis, except for where they ground at the one point through a ground lift switch. I also used the elevated filaments, and got rid of the can cap and used series connected caps to get a 700v rating in the first two sections. It is VERY quiet now, but of course there was a ton of work to do this and since I did it myself the labor wasn't too bad. If you were going to pay someone to do it for you it wouldn't be worth the cost. But it does make a MUCH quieter amp.

Greg

Offline max headrrom

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sorado hummm
« Reply #7 on: April 04, 2006, 12:19:20 am »
who can afford labor it's me myself & I.

caps gotta go ok ok ok I know your right

thanks so much
All I can hear is flatwound thump and tone

ASATBASS