"hf fuse" for sg output protection - UK Vintage Radio Repair and Restoration Discussion Forum

SM6FBY1 · 10th Apr 2011, 10:26 am

Hello, I am looking for the external N-plug with a built in fuse that HP and Marconi used at the output of their signalgenerators for attenuator protection. Does anybody know where the plugs and fuses can be bought today?
73 de SM6FBY Bengt

Stockden · 10th Apr 2011, 1:51 pm

Well, the plug assemblies sometimes appear on eBay, which is where I bought mine from. Sadly the cartridge fuses to go inside seem to be unobtainable.

neon indicator · 10th Apr 2011, 2:17 pm

That would be nice on my 8555 18GHz spectrum Analyser plugin on HP141T.

Though would the fuse blow faster than the mixer on the 1mW range

?

CambridgeWorks · 12th Apr 2011, 9:03 pm

Hello, an easier/more reliable alternative may be a 20dB or 30dB 1GHz (or suitable freq) power attenuator, rated at say 25W. May be worth considering?
I used to use a 20dB 25W (N type) attenuator permanently attached to my sig gen output. It was accurate (in dB) and many times paid for itself in protecting the sig gen. In fact, testing 25W VHF transceivers, I would often repeatably toggle between tx and rx whilst looking for intermittant antenna relay faults!
Like a previous post, the fuses (Littlefuse?) were hard to find.
73, Robin

Stockden · 13th Apr 2011, 5:53 pm

Actually, these seem easier to find than I thought. There's an example of the N connector version (TM5753) on eBay UK at the moment and there's examples of both the BNC connector version (TM9884) and an HP N connector equivalent (all with spare fuses!) here.

The fuses are 1/16A (62.5mA) produced by littelfuse, though my bit of paper with the type number on seems to have been mislaid. However short, fat fuses (1"-ish long but same diameter as 1.25" fuses iirc) rated at 62.5mA, as Robin says, aren't easy to find!

Having said that, I also agree with robin's point about using an attenuator.

Hugh

Herald1360 · 13th Apr 2011, 6:01 pm

Aren't 20mm 63mA fuses readily sourced? A simple adaptor (or just a bit of spring) should take care of the fitting........

Stockden · 14th Apr 2011, 5:57 pm

Indeed they are, thank you for reminding me.

Unfortunately, because of the way the fuse is mounted, replacing the 25x6.3mm original with a 20x5mm fuse needs a little bit more than a spring as the fuse "ends" need to be increased in both length and girth. The photos below illustrate what I mean.

Still, it's clearly not impossible and I've been toying with the idea of drilling a 5mm hole through the middle of an old (metal) pot spindle. One day I might actually get round to doing something about it!

10th Apr 2011, 10:26 am	#1
SM6FBY1 Retired Dormant Member Join Date: Apr 2011 Location: Molndal Sweden Posts: 1	"hf fuse" for sg output protection Hello, I am looking for the external N-plug with a built in fuse that HP and Marconi used at the output of their signalgenerators for attenuator protection. Does anybody know where the plugs and fuses can be bought today? 73 de SM6FBY Bengt

10th Apr 2011, 1:51 pm	#2
Stockden Heptode Join Date: Mar 2008 Location: Forest of Dean, Gloucestershire, UK. Posts: 648	Re: "hf fuse" for sg output protection Well, the plug assemblies sometimes appear on eBay, which is where I bought mine from. Sadly the cartridge fuses to go inside seem to be unobtainable.

10th Apr 2011, 2:17 pm	#3
neon indicator Retired Dormant Member Join Date: Jun 2010 Location: Co. Limerick, Ireland. Posts: 1,183	Re: "hf fuse" for sg output protection That would be nice on my 8555 18GHz spectrum Analyser plugin on HP141T. Though would the fuse blow faster than the mixer on the 1mW range ?

12th Apr 2011, 9:03 pm	#4
CambridgeWorks Nonode Join Date: Jun 2010 Location: Spalding, Peterborough, Cambridgeshire, UK. Posts: 2,858	Re: "hf fuse" for sg output protection Hello, an easier/more reliable alternative may be a 20dB or 30dB 1GHz (or suitable freq) power attenuator, rated at say 25W. May be worth considering? I used to use a 20dB 25W (N type) attenuator permanently attached to my sig gen output. It was accurate (in dB) and many times paid for itself in protecting the sig gen. In fact, testing 25W VHF transceivers, I would often repeatably toggle between tx and rx whilst looking for intermittant antenna relay faults! Like a previous post, the fuses (Littlefuse?) were hard to find. 73, Robin

13th Apr 2011, 5:53 pm	#5
Stockden Heptode Join Date: Mar 2008 Location: Forest of Dean, Gloucestershire, UK. Posts: 648	Re: "hf fuse" for sg output protection Actually, these seem easier to find than I thought. There's an example of the N connector version (TM5753) on eBay UK at the moment and there's examples of both the BNC connector version (TM9884) and an HP N connector equivalent (all with spare fuses!) here. The fuses are 1/16A (62.5mA) produced by littelfuse, though my bit of paper with the type number on seems to have been mislaid. However short, fat fuses (1"-ish long but same diameter as 1.25" fuses iirc) rated at 62.5mA, as Robin says, aren't easy to find! Having said that, I also agree with robin's point about using an attenuator. Hugh Last edited by Stockden; 13th Apr 2011 at 5:55 pm. Reason: Incompetence!

13th Apr 2011, 6:01 pm	#6
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: "hf fuse" for sg output protection Aren't 20mm 63mA fuses readily sourced? A simple adaptor (or just a bit of spring) should take care of the fitting........ __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

14th Apr 2011, 5:57 pm	#7
Stockden Heptode Join Date: Mar 2008 Location: Forest of Dean, Gloucestershire, UK. Posts: 648	Re: "hf fuse" for sg output protection Indeed they are, thank you for reminding me. Unfortunately, because of the way the fuse is mounted, replacing the 25x6.3mm original with a 20x5mm fuse needs a little bit more than a spring as the fuse "ends" need to be increased in both length and girth. The photos below illustrate what I mean. Still, it's clearly not impossible and I've been toying with the idea of drilling a 5mm hole through the middle of an old (metal) pot spindle. One day I might actually get round to doing something about it! Attached Thumbnails