Hum when turning amp on

guitarpicker_ma · February 22nd, 2004, 05:58 PM

I had my 1966 Ampeg Gemini I retubed a couple of weeks ago, and ever since it came back from the shop as soon as I turn it on there is a dull hum that grows for about 5 seconds and then takes about 4-5 seconds to trail off and go away. Once the hum ceases the amp sounds great!

Has anyone had this experience? Is there a problem?

Thanks,
jesse

Brendan · November 24th, 2006, 04:33 AM

Wow, talk about resurrecting a thread! My little Champ 12 has done this since I bought it. It was cheap, so I never worried about it much. Tonight I noticed it seems to have another problem. It sometimes crackles when I hit the strings. I thought it was the guitar, so I switched to another and the same thing is happening.
Any thoughts on what could be causing either problem?

Wally · November 24th, 2006, 01:43 PM

Quote:

Originally Posted by guitarpicker_ma

I had my 1966 Ampeg Gemini I retubed a couple of weeks ago, and ever since it came back from the shop as soon as I turn it on there is a dull hum that grows for about 5 seconds and then takes about 4-5 seconds to trail off and go away. Once the hum ceases the amp sounds great!

Has anyone had this experience? Is there a problem?

Thanks,
jesse

There is no standby switch on this amp, correct? Two questions....
1) Does the hum begin when the power switch is switched on or when the tubes have warmed up enough to conduct signal?
2)Turn all controls pots to zero. Does the hum still occur?

Brendan · November 25th, 2006, 02:26 AM

Thanks, Wally.
There is no standby switch on my amp. The hum starts shortly after the switch is turned on and stops abruptly after about 5 seconds. Then it's fine....except for that new crackle issue... ;-(

Pepi · November 25th, 2006, 11:37 AM

Quote:

Originally Posted by Brendan

Thanks, Wally.
There is no standby switch on my amp. The hum starts shortly after the switch is turned on and stops abruptly after about 5 seconds. Then it's fine....except for that new crackle issue... ;-(

As Wally asked. Does it still hum with all the pots down? If so, sounds like you getting AC into the DC voltage. Filter capacitor maybe going south. Sometimes preamp tubes can do this too. Once they warm up they quit.

Brendan · November 26th, 2006, 02:19 PM

Quote:

Originally Posted by Pepi

As Wally asked. Does it still hum with all the pots down? If so, sounds like you getting AC into the DC voltage. Filter capacitor maybe going south. Sometimes preamp tubes can do this too. Once they warm up they quit.

Thanks, Pepi. It doesn't hum when all the knobs are down.

Wally · November 26th, 2006, 05:21 PM

Brendan, that hum is likely to be related to the heater filaments in one of your tubes. Tube by tube substitution will probably lead you to the problem.

Pepi · November 26th, 2006, 08:40 PM

Quote:

Originally Posted by Brendan

Thanks, Pepi. It doesn't hum when all the knobs are down.

Yep, probably a preamp tube causing it.

February 22nd, 2004, 05:58 PM	#1 (permalink)
guitarpicker_ma TDPRI Member Join Date: Nov 2003 Location: tax-a-chusetts Posts: 44	Hum when turning amp on I had my 1966 Ampeg Gemini I retubed a couple of weeks ago, and ever since it came back from the shop as soon as I turn it on there is a dull hum that grows for about 5 seconds and then takes about 4-5 seconds to trail off and go away. Once the hum ceases the amp sounds great! Has anyone had this experience? Is there a problem? Thanks, jesse

November 24th, 2006, 04:33 AM	#2 (permalink)
Brendan Tele-Meister Join Date: Feb 2004 Posts: 324	Wow, talk about resurrecting a thread! My little Champ 12 has done this since I bought it. It was cheap, so I never worried about it much. Tonight I noticed it seems to have another problem. It sometimes crackles when I hit the strings. I thought it was the guitar, so I switched to another and the same thing is happening. Any thoughts on what could be causing either problem?

November 25th, 2006, 02:26 AM	#4 (permalink)
Brendan Tele-Meister Join Date: Feb 2004 Posts: 324	Thanks, Wally. There is no standby switch on my amp. The hum starts shortly after the switch is turned on and stops abruptly after about 5 seconds. Then it's fine....except for that new crackle issue... ;-(

November 26th, 2006, 05:21 PM	#7 (permalink)
Wally Friend of Leo's Join Date: Mar 2003 Location: Lubbock, TX Posts: 4,212	Brendan, that hum is likely to be related to the heater filaments in one of your tubes. Tube by tube substitution will probably lead you to the problem.