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Old 21st October 2005, 03:06 PM   #1
Trout is offline Trout  United States
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Default Guitar Amp Hum Question

Hi Guys,
Ok I am back at it on another project, But I have a couple questions about what to expect.
Primarily, I am building a Deluxe 5E3

I have everything punched mounted and partially wired up. Heres my question. I have the entire Output & Power sections completely done. up to the volume Control. I plan on using a slightly different Pre-amp section so I connected Pin 2 of the 12AX7 to the wiper(center) on what will be the master volume pot.

1 (left)outer pin of pot to ground, Other (right)outer Pin of pot will be my input.
I Decided to power up the unit at this point to confirm functionality of the work to this point.

So as it sits, I have a 12AX7 Driving a pair of 6V6's into a 8 ohm cab.
Should I expect hum without a sources connected?
The Amp does respond as expected when the input pin of the volume pot is touched.

BUT, I thought If the pot was rotated it should kill the open input hum?
Gene
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Old 21st October 2005, 03:45 PM   #2
dhaen is offline dhaen  Europe
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You're right, with the grid grounded, there should be no hum. Hum could be caused by supply ripple, a bad grounding scheme, or even induced directly into the output transformer.

Assuming no wiring mistakes:
Quick check list:
Is there hum without the 12AX7?
If yes, check for ripple, and check transformer orientation.
If no, does the hum change with the pot setting?
If worse at low volume setting, check grounding.

Are the heaters floating? They should reference to ground some way.
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Old 21st October 2005, 05:37 PM   #3
Trout is offline Trout  United States
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Whew, Got it.

Da olde guy had a brain glitch, I had a sheilded lead from pin 2 (grid) to the pot, The outer shield to outside connection on pot, Inner to wiper. BUT, forgot the ground!!! and therefore the shield only contributed to the problem. Attached ground, Problem solved!

Sometimes I wonder why I just didnt stick to RC Aerobatics, At least I was a national champion at that as well as a top designer. But NOOoo I got bored and switched to this stuff

Eh, either way, I am having loads of fun learning. Your response got me looking at the grounds and bingo!
gene

BTW Grid shorted = Dead silent
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Old 21st October 2005, 05:54 PM   #4
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RC Aerobatics, bet thats expensive when things don't work right. My buddy flew the RC pylon races. Grown men cry when things go wrong there. He gave that up too, lots of broken parts.
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Old 21st October 2005, 07:03 PM   #5
Trout is offline Trout  United States
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Quote:
RC Aerobatics, bet thats expensive when things don't work right. My buddy flew the RC pylon races. Grown men cry when things go wrong there. He gave that up too, lots of broken parts

Honestly, In my particular position it wasn't bad. I had a sponsor on the radio equipment during my last 5 years. I flew my own design 5 of those years, And since I owned the kit manufacturing co, It was fairly easy to keep actually costs at a minimum. And of course all trips to competitions were advertising expenses.
In 11 years of competition, I lost 2 Models, Both valued just over $2500.00 each if you had to buy them. But actual cost was about 1/10th.

Really besides regional contests lacking any serious competition, The primary reason I got out was basically age (old eyes). Though I could literally close my eyes and know the orientation of the model it had become an issue due to long term exposure to the sun starring at the sky 2-6 hrs a day " Nearly EVERY Day". Even Now, 5 years later, there is no such thing as a bright enough work area. Had I not used the best protection of the times, No doubt I would be legally blind. I just had my first restriction put on my DL this past May, At age 51??

gene
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Old 21st October 2005, 07:54 PM   #6
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After 53 years of life in the Florida sun, I have similar problems especially at night. Not to mention skin cancer.
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Old 11th August 2013, 09:42 AM   #7
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Have you gentlemen tried wearing an Optivisor when working on projects?

I began wearing one (gift from my dad) when building fishing rods.

Now, whenever I can I put them on for working on circuitry and building guitars, etc.

They are fantastic for doing the fine finishing work on the guitars!

John
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Old 11th August 2013, 01:19 PM   #8
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Quote:
Originally Posted by headstack View Post
Have you gentlemen tried wearing an Optivisor when working on projects?

I began wearing one (gift from my dad) when building fishing rods.

Now, whenever I can I put them on for working on circuitry and building guitars, etc.

They are fantastic for doing the fine finishing work on the guitars!

John
I really need a pair. I have reading glasses for near field viewing but for doing electronics in cramped spaces, with a single thread of stranded wire going its own way...

I keep saying no more ship in the bottle builds, but then I have a project and no larger chassis made up, guess what goes in the little one? My RC experience had been, build - crash - fix - fly - fix - fly - fix... Got into car building after that. All the fixing done me well with the acoustic guitar I am building now though.
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Old 11th August 2013, 01:32 PM   #9
kevinkr is offline kevinkr  United States
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Long dead thread moved to I&A per forum policy since it is guitar amp related. Might consider starting a new thread rather than dredging up 8yr dead ones. Thanks..
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Old 11th August 2013, 04:29 PM   #10
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Originally Posted by kevinkr View Post
Long dead thread moved to I&A per forum policy since it is guitar amp related. Might consider starting a new thread rather than dredging up 8yr dead ones. Thanks..
I should have looked at the date, found it funny Trout was asking the question. Oops.
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