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Tube Toner Hum


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i just got a second hand tube toner from ebay. Don't know it's age nor if the valves have been replaced, but i'd swear no.

It develops a hum noise when i turn the lead channels. The preamp is the same preamp as in the screamer combo i had, and the combo doesn't have the noise.

On the other hand, the hum reacts to the tone stack, could that be a bad tube, or something with the input?

thanx for the help


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engl e-430 tube toner:

operator's manual

harmony central review

engl screamer schematic

it is just the preamp section of a screamer in pedal format. sounds great, but i want that noise away. i´ll try to record some samples of the hum to see if that helps identify the kind of problem it is. Howevery i'm using it connected to the desk, haven't tried to the poweramp yet. it should be working right in this setup anyways.

any help welcome. thanks!

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Hi, i've read some comments on a french site (helped by google translator XD) saying that there is a pot between the valves to adjust the symetry because the tubes are ac powered.

Could this be the source of the noise?? i've noticed that the screamer has something called tr2 (i dunno what the sign stands for) in the bottom right side of the schematic.

any help please??

my tech is on holiday, so i cannot ask him till a week or so, i´d love to see some feedback.

even with the hum i love the sound it has god :D

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TR2 is a trimpot that is your filament hum balance. By creating a variable (artificial) filament winding, you can adjust for the minimum filament hum. If you can't adjust that to remove the hum, I wouldn't recommend servicing it by yourself, unless you're very fammiliar with tube gear. Take it to a tech.

what would the process be to do it??


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if i knock on the pedal i can hear the knock on the amplifier. Not knocking it with a hummer, just mi fingers. Could it be a microphonic tube or is just normal. i can hear with the gain and volume set high, the same spot where i get hum.

any idea??

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ok, after the exam i had on the evening i went the where i play and plug the thing, i used a plastic thing to hit slowly both tubes and one of them reproduced on the amp the noise.

microphonic tube i guess. ggggggg. it was the most probable thing.

ok, time to replace it, what do you suggest me????

i could go with an engl replacement, but it is the most expensive 23 € plain, 33 € first quality. lol i don't think i could afford both with those prices.

tad, mesa, sovtek?? thank you very much

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