Where the **** is the hum-balance on a Hammond?

[The Red Bladder]

I was servicing our A100 yesterday and I realised that it was getting a bit hummy lately, so I got the Oscar out to do a simple hum balance. I have done this hundreds of times in years gone by, when I was Captain Repair-Man and I have even done it to our A100. The only thing is, I haven't done it for a while, but I was expecting to see the hum-balance pot somewhere on the output amp, but no. Nothing. Not a sausage.

I know the thing is there somewhere, but where? Anyone? Hugh?

[Hugh Robjohns]

R22 Hum balance control is a recessed screwdriver trimmer accessed through a hole on the AO39 power amp's top plate between the small output transformer and the output tubes:



hugh

[The Red Bladder]

Sound effect of penny dropping!

Many thanks, Hugh! Right now, we have a band in there all month, so my chances of getting in to do the hum-balance are remote. It'll have to wait, but at least I now know where the thing is. I thought I was going mad!

Now I have to swap out a defective patch-bay strip, but that only takes a couple of minutes.

As Basil Fawlty said, "This place would run all right, if customers wouldn't keep barging in and out all the time!"

[Hugh Robjohns]

we have a band in there all month, so my chances of getting in to do the hum-balance are remote.

Tiz but the work of mere moments! Whip the back off, short the amp inputs to ground, tweak for minimmum hum, remove the short, put the back on again. Job done in under five minutes.

hugh

[The Red Bladder]

If nothing else decides to break and she-who-must-be-obeyed doesn't need me to be somewhere, then there is that golden two or three hours in the morning, before the producer and his engineer are still recovering from their various hangovers. I'll do it then.

Ta!

[Folderol]

we have a band in there all month, so my chances of getting in to do the hum-balance are remote.

Tiz but the work of mere moments! Whip the back off, short the amp inputs to ground, tweak for minimmum hum, remove the short, put the back on again. Job done in under five minutes.

hugh

Tempting providence aren't we?
I would always recommend allowing several hours for a five minute job - especially on old valve kit. I can just see it now...

Pot has not been touched for years and is partially frozen, so you give the screwdriver a bit of a shove and it suddenly frees and hits the end-stop. Pot now makes a disconcerting clicking noise when you turn it, and there is a dead spot exactly where you want the wiper to be - and I mean dead, as there is a bit of gunge stuck to the track which lifts the wiper away resulting in both valves cutting off (no bias current). You have indeed found the minimum hum spot!

[Hugh Robjohns]

It would be an unusually stable (or criminally underused) Hammond if the pot hasn't been touched in years!

H

[zenguitar]

And, more importantly, HAPPY BIRTHDAY Folderol

Andy

[Folderol]

Awwww. Thanks Andy

[Hugh Robjohns]

Oh yeah! Happy Birthday!

hugh

[Folderol]

Ta Muchly

P.S.
The B3 I had in mind was indeed criminally under-used. It was also stored long-term in an unheated room on the side of a village hall

[Hugh Robjohns]

It was also stored long-term in an unheated room on the side of a village hall

As long as the village hall was dry, it probably better that than sat unused in an overheated lounge with the generator oil evaporating to leave a nasty sticky sludge!

H

[Matt_Moose]

It was also stored long-term in an unheated room on the side of a village hall

As long as the village hall was dry, it probably better that than sat unused in an overheated lounge with the generator oil evaporating to leave a nasty sticky sludge!

H

Don't! Just ordered some more oil for mine - first time oiling and although it's in a warm lounge it does get used couple times a week. The run motor just seemed to sound/spin up a bit sluggish today.