Help! The little bear valve stage

[mad-moon]

Arrived safely Andy...many thanks...put it together..but got a terrible hum....any suggestions...anyone ta...

http://i236.photobucket.com/albums/ff281/spooneymoon/little%20bear%20complete_zpspwojx5ti.jpg (http://s236.photobucket.com/user/spooneymoon/media/little%20bear%20complete_zpspwojx5ti.jpg.html)

[struth]

is it working other than the hum and is the volume about right etc if it is Alan.. are all the tubes lighting up?

[walpurgis]

Check all earths and earth the mains transformer metalwork (attach a wire under one of the mounting bolts and take it to earth). Assuming all signal negatives are common to earth, check those too.

[struth]

Ive got the circuit for that somewhere

[mad-moon]

Yes all working...can get exceptionally good volume...all valves are lit...at low volume it's not too bad...but the louder you take it....it gets quite bad...
is it working other than the hum and is the volume about right etc if it is Alan.. are all the tubes lighting up?

[mad-moon]

I'll give that a go tomorrow...thanks Geoff...with the hum gone...this could be a lovely little stage...
Check all earths and earth the mains transformer metalwork (attach a wire under one of the mounting bolts and take it to earth). Assuming all signal negatives are common to earth, check those too.

[struth]

Probably shielding problems. They had a reputation for having shield probs. Dont think they have an earth point but may be wrong. running an earth from tx may help Alan. I did hear the some folk were using foil to act as a shield but dunno. any difference if you move the cables? also improved valves may help, as the Chinese ones are supposedly crappy. found the diagram if anyone wants it...its in 2 halves though lol

http://imagizer.imageshack.us/v2/xq90/631/Yidc5G.jpg

http://imagizer.imageshack.us/v2/xq90/910/lTUqaw.jpg

[walpurgis]

Dont think they have an earth point

That could be the case. Earthing being via the signal negative. In which case if there's anything that should be earthed, it should likely be commoned to the negs.

[mad-moon]

I'll check it out tomorrow..there is an earth point...I hope it fettles it....cheerz chaps....I'm good with adobe mind you...:-

http://i236.photobucket.com/albums/ff281/spooneymoon/lil%20bear%20sceme_zpsty7wovsd.jpg (http://s236.photobucket.com/user/spooneymoon/media/lil%20bear%20sceme_zpsty7wovsd.jpg.html)



Probably shielding problems. They had a reputation for having shield probs. Dont think they have an earth point but may be wrong. running an earth from tx may help Alan. I did hear the some folk were using foil to act as a shield but dunno. any difference if you move the cables? also improved valves may help, as the Chinese ones are supposedly crappy. found the diagram if anyone wants it...its in 2 halves though lol

http://imagizer.imageshack.us/v2/xq90/631/Yidc5G.jpg

http://imagizer.imageshack.us/v2/xq90/910/lTUqaw.jpg

[walpurgis]

Sorry. You're good with a dopey what? :scratch: :)

[struth]

Nicely done that man.:) Maybe earthing everything will help then...good ho

[mad-moon]

Nope...pulling out what is left of my hair...ho-hum...literally..

[Desmo]

Have you googled this problem? There are loads of people reporting hum issues with this Little Bear amp and there are lots of suggested solutions....

[helma]

Also have you tried repositioning the unit further away from other stuff (or turning it around) to find out if the hum is picked up intereference from transformers etc?

[mad-moon]

yep..been there...I've wrapped the input tube in aluminium...which has cut down the hum quite a bit..I'm now ordering some aluminium sheet to make a new base..which will further shield the components...allegedly...
Have you googled this problem? There are loads of people reporting hum issues with this Little Bear amp and there are lots of suggested solutions....

[mad-moon]

yeah..doesn't matter where I put it...
Also have you tried repositioning the unit further away from other stuff (or turning it around) to find out if the hum is picked up intereference from transformers etc?

[Arkless Electronics]

With the transformer where it is I'd be surprised if it didn't hum....

[Ali Tait]

My thought also. Solder some wires on the transformer leads so you can move it away from the board.

[mad-moon]

Yep..I'll do that the morra...Think I'll get rid of those green chocolate block thingies on the board and solder the transformer tails straight to the board also
My thought also. Solder some wires on the transformer leads so you can move it away from the board.

[mad-moon]

Thanks Jez...how far from the board do you think will be far enough...should I house the transformer in another box??
With the transformer where it is I'd be surprised if it didn't hum....

[struth]

Start with a couple of feet, and if quite then move it in and about to see how close you can get it. if not too close then as you say house it seperately

[Ali Tait]

It might suffice just turning it 90 degrees.

[spm]

Alan

did you ever solve this, if so what do you think of it? While the kids are pouring over the Argos catalogue looking for Christmas presents was thinking I ought to tip off the wife on what I might want soon before she buys me something I don't want. I see some on ebay have added an EMI filter between the transformer and board which they say solves (reduces?) the hum.

Sean

[Wakefield Turntables]

Im glad that this has been resurrected. I'm getting one of these delivered in next few days. I hope I dont get the same problem.