Slight Hum vanishes when volume or tone cranked .

showbander · Post by **showbander** » Sat Apr 05, 2014 11:02 pm

Well i added that shielded wire after using a chopstick there & getting more hum appearing when touched or moved ...so i left it in !
I will try moving away from filaments more .

showbander · Post by **showbander** » Sat Apr 05, 2014 11:05 pm

seemed ok earlier when moving it about with choppy .

showbander · Post by **showbander** » Sat Apr 05, 2014 11:55 pm

Hey Martin ,i just noticed i didnt connect the ground buss to the 0.022uf cap that then goes to pin 7 of the ax7.....(Circled)

showbander · Post by **showbander** » Sat Apr 05, 2014 11:57 pm

Hey Martin ,i just noticed i didnt connect the ground buss to the 0.022uf cap that then goes to pin 7 of the ax7.....(Circled)

showbander · Post by **showbander** » Sat Apr 05, 2014 11:59 pm

my previous message wasnt suppose to sound snotty its our shitty English language here where we just sound angry all the time

I read it back and i sound like mr Angry ha.

martin manning · Post by **martin manning** » Sun Apr 06, 2014 12:46 am

Edit: Don't ground that cap.

showbander · Post by **showbander** » Sun Apr 06, 2014 12:50 am

thanks martin ,i will get on the case tomo ! cheers again for your help

Firestorm · Post by **Firestorm** » Sun Apr 06, 2014 3:22 am

showbander wrote:Hey Martin ,i just noticed i didnt connect the ground buss to the 0.022uf cap that then goes to pin 7 of the ax7.....(Circled)

Er, the one circled is a coupling cap. If you ground it there will be no sound. I'm sure Martin didn't mean to tie that one to the bus.

martin manning · Post by **martin manning** » Sun Apr 06, 2014 8:54 am

FIrestorm is correct! I had it right the first time, and it will be totally silent if you ground that cap. Sorry for the confusion, don't know what I was thinking!

Does the hum still come and go with the tone and volume control settings? How are the input jack and first cathode resistor grounds done now? Can you post a pic of that area?

Stevem · Post by **Stevem** » Sun Apr 06, 2014 12:15 pm

How much hum are we talking about here?
If you turn all the controls down and hook up a AC voltmeter across the speaker, how many millivolts do you read?

cbass · Post by **cbass** » Sun Apr 06, 2014 12:45 pm

How is your heater circuit grounded?CT? 100 ohm resistors?

showbander · Post by **showbander** » Sun Apr 06, 2014 1:30 pm

cbass , hmm not sure tbh it is grounded , so the 2 heater wires run from pilot light and just daisy chain to the last ax7 ....

cbass · Post by **cbass** » Sun Apr 06, 2014 1:35 pm

On the layout it looks like The Center tap of the heater winding is connected to the power tube catodes through a 100 ohm resistor.
Is this how you have yours wired?
If your PT doesnt have a CT you need to do the "artificial"one

showbander · Post by **showbander** » Sun Apr 06, 2014 1:39 pm

yes that resistor goes to pin 8

cbass · Post by **cbass** » Sun Apr 06, 2014 1:43 pm

some pictures would be helpful.
Double check that that resistor going to pin 8 is indeed 100ohm

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Slight Hum vanishes when volume or tone cranked .

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