25 ohm dummy loads - UK Vintage Radio Repair and Restoration Discussion Forum

Julesomega · 13th Dec 2020, 10:19 pm

Haven't been on the forum for a few days, been working 12 hour shifts plumbing since the hot water cylinder sprung a leak. I know a very experienced plumber but he's on house-husband duties while his wife is having Carpal Tunnel surgery so I had to do it myself. We had a national contractor replace the cylinder only 2 or 3 years ago, fitting a new stainless cylinder with all the new bonded insulation. New immersion heater too, but access is so difficult I can't just unscrew the heater and fit a new one. My local friend knew the problem before he even came to look: when the stainless cylinders were first introduced it wasn't realised that the traditional copper tube which houses the long thermostat body would corrode in the presence of the stainless steel. So I've now ditched the cylinder and fitted a new one with side access to the immerser, which will be Incoloy.

Turns out the old immerser measures 25Ω (Chinese component analyser doesn't indicate any inductance) so a couple in series would make a good dummy load at RF, or for AF in ||el. Rating would be 5kW in water (or oil) and there's no shortage of the

things if you ask any plumber

Anyone want a 140 litre stainless cylinder?

G3PIJpeter · 13th Dec 2020, 10:42 pm

Quote:

Originally Posted by Julesomega

Turns out the old immerser measures 25Ω (Chinese component analyser doesn't indicate any inductance) so a couple in series would make a good dummy load at RF, or for AF

Interesting thought. The element is resistance wire embedded in an insulator such as magnesium oxide inside an earthed sheath - effectively an open length of lossy coax. Connect two in series and earth the far end, feed RF into the open end and test with an SWR meter, which will tell you if there is any appreciable reactance or whether the load is essentially resistive.

I am tempted to include a photo of my ex-hot water cylinder cut open that shows it literally half full of lumps of limescale - but that would be deemed off-topic, so I shalln't.

Peter G3PIJ

G6Tanuki · 14th Dec 2020, 2:49 pm

I did wonder about keeping one of the spiral-element boiling-rings when I was scrapping my old Tricity Viscount cooker some years back, and seeing if that would work as a HF dummy-load.

But someone wanted the cooker's rings to still work (so she could boil up mash for her chooks).... so I couldn't _completely_ gut it.

13th Dec 2020, 10:19 pm	#1
Julesomega Nonode Join Date: Dec 2012 Location: Stockport, Greater Manchester, UK. Posts: 2,106	25 ohm dummy loads Haven't been on the forum for a few days, been working 12 hour shifts plumbing since the hot water cylinder sprung a leak. I know a very experienced plumber but he's on house-husband duties while his wife is having Carpal Tunnel surgery so I had to do it myself. We had a national contractor replace the cylinder only 2 or 3 years ago, fitting a new stainless cylinder with all the new bonded insulation. New immersion heater too, but access is so difficult I can't just unscrew the heater and fit a new one. My local friend knew the problem before he even came to look: when the stainless cylinders were first introduced it wasn't realised that the traditional copper tube which houses the long thermostat body would corrode in the presence of the stainless steel. So I've now ditched the cylinder and fitted a new one with side access to the immerser, which will be Incoloy. Turns out the old immerser measures 25Ω (Chinese component analyser doesn't indicate any inductance) so a couple in series would make a good dummy load at RF, or for AF in \|\|el. Rating would be 5kW in water (or oil) and there's no shortage of the things if you ask any plumber Anyone want a 140 litre stainless cylinder? Attached Thumbnails __________________ - Julian It's good here

14th Dec 2020, 2:49 pm	#3
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: 25 ohm dummy loads I did wonder about keeping one of the spiral-element boiling-rings when I was scrapping my old Tricity Viscount cooker some years back, and seeing if that would work as a HF dummy-load. But someone wanted the cooker's rings to still work (so she could boil up mash for her chooks).... so I couldn't _completely_ gut it.