Old Variac stiffening up - UK Vintage Radio Repair and Restoration Discussion Forum

Tractorfan · 6th Jun 2017, 8:52 pm

Hi,
I have a very old Variac that uses a thin walled Bakelite tube to carry the moving contact while insulating it from the frame & handle. The tube is a snug fit through the brass top plate and, after a time, becomes tight due to the tube 'swelling' a tiny amount due to Bakelite being slightly absorbent.
Now, if I enlarge the hole in the top plate a bit to allow free motion once again, will the tube continue to expand and become tight once more, or will it finally reach a 'limit'?
Cheers, Pete.

The Philpott · 6th Jun 2017, 10:58 pm

I think it will stabilise, but will defer to anyone who has more gen on this subject.

6th Jun 2017, 8:52 pm	#1
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,182	Old Variac stiffening up Hi, I have a very old Variac that uses a thin walled Bakelite tube to carry the moving contact while insulating it from the frame & handle. The tube is a snug fit through the brass top plate and, after a time, becomes tight due to the tube 'swelling' a tiny amount due to Bakelite being slightly absorbent. Now, if I enlarge the hole in the top plate a bit to allow free motion once again, will the tube continue to expand and become tight once more, or will it finally reach a 'limit'? Cheers, Pete. __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

6th Jun 2017, 10:58 pm	#2
The Philpott Dekatron Join Date: Aug 2016 Location: Colchester, Essex, UK. Posts: 4,106	Re: Old Variac stiffening up I think it will stabilise, but will defer to anyone who has more gen on this subject.