Cornford 60 cycle hum

Gear
#1

Coming from the Cornford at about -50db when recorded. I find it noticeable, especially on the clean channel. And I feel like it gets marginally louder the longer the amp is on, but I might be imagining that. Don’t know when it started, but I noticed this about a week ago.

No hum with the JCM 800 we have, even with the preamp maxed or a Tubescreamer in front of it. So I’m guessing it may be something with the Cornford itself. I can replace a preamp tube, but if it’s power tube or transformer related it’s over my pay grade.

What do you think?

#2

How many preamp tubes does it have? Do you have one spare tube you can replace each one at a time just to see if there’s a rogue guy in there?

#3

No spares on hand, but we should probably have some on hand. I’ll pick some up.

#4

Hmmmmm. Usually hum from the preamp section will go up and down with the volume control.

Hum that stays the same regardless of volume usually isn’t in the preamp section of the amp… But could be several things. Try the tube thing though, I guess…

You can look to see if the filter caps are swelling or leaking any liquid. It could be the power trans, output trans,. A ground somewhere… Call Cornford? :thinking:

#5

Are you using the effects loop per chance?

#6

They ceased operation 4 years ago unfortunately.

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#7

Martin Kidd, who worked at Cornford, now owns Victory Amps. It would be worth a shot.

#8

Nope! It’s there whether the loop is active or not.

#9

Excellent point. Gets louder with master volume.

#10

Picked up two 12AX7s from Giutar Center.

Me: On the top shelf the little boxes that say Tung-Sol on them.

Sales guy: What’s that?

Me: It’s a tube it goes in an amp.

Sales guy: Ok cool.

Me: I’ll take two of those.

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#11

He didn’t understand because his iPad running BIAS doesn’t need any of those light bulb things.

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#12

It’s in the preamp section then. Probably a preamp tube!!!

:kiss::kiss:

#13

So many variances in those things. Hopefully it doesn’t change your tone. If it solves the hum problem, but your gain staging or tone changes, you might have to research and find tubes closer spec to what was in it. I don’t think all 12ax7s are created equal. Keep your fingers crossed. :scream:

#14

If I A/B closely with recordings I’ll hear the difference and I might care about it, so I try not to do that too much. The amp is mostly in the same ballpark no matter what I put in it.

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#15

There’s big demand for “new old stock” 12ax7s now. I think the newly produced stuff is made in just a couple of factories in Russia and China, and tone chasers obsess over not only the different specs produced under various brand names, but testing the properties of the individual tubes.

I think the kids with the ipads are on the right track.

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#16

That’s the funniest thing I’ve read in a year.

3 Likes
#17

Yeah, you are right. I hear they all come from the same factories. They get QC, branded, and packaged by the “brands” selling them.

That kid at guitar center was pushing the tubes like a touchscreen. Wondering why they didn’t light up.

:bear::bulb:

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#18

No dice on the preamp tube replacement. Swapped all of them out with a set from another amp and still buzzing.

However I now notice that it appears tied to the reverb knob. It gets worse when that knob is cranked, whether or not the tank is even connected. i.e. You can loop back the tank cable to its own return jack and it still hums.

Barring other suggestions I’ll find a local shop and take it in.

#19

Tried contact cleaner on the cables and jacks that the reverb tank uses?

#20

Are there separate tubes to drive/recover the reverb?