HP Neon replacement? - UK Vintage Radio Repair and Restoration Discussion Forum

PETERg0rsq · 25th Mar 2017, 1:16 pm

I am repairing the IF section of a HP 141 spectrum analyser.

One of the Neon regulators VR1 (I think that is its function) on the vertical deflection board A7 has failed.

it is a Signalite Z103R2 (1940-0021).

Could this be replaced with a "normal" optical neon?

If not what could it be replaced with? I am thinking a Zenner, but what value should it be?

Thanks

Peter

Radio Wrangler · 25th Mar 2017, 4:40 pm

A zener is a possibility, maybe 47 or 56v

Be sure to pick a diode spec'd at 5mA. The current in it is even lower than this, but the neon has a soft corner anyway

David

Cobaltblue · 25th Mar 2017, 4:48 pm

According to Radio Museum it has a regulated voltage of 103V

Current 0.2 to 2 mA

http://www.radiomuseum.org/tubes/tube_z103r2.html

Cheers

Mike T

turretslug · 25th Mar 2017, 5:11 pm

Something rings a faint bell about a piece of Philips gear of similar vintage with a neon reference problem being discussed here at one point, there being a Philips official fix consisting of a ring-of-two and reference diode that soldered in place.

turretslug · 25th Mar 2017, 6:01 pm

Gottit- nice quick forum search, acknowledgements to WME bill for finding it and posting in the first place. Not in fact a ring-of-two circuit but a simple voltage drop multiplier- I imagine that the 7.5V zener was used to match the transistors' Vbe temperature coefficient. Philips generally seemed to know what they were doing (even if what they did sometimes seemed a little odd....), so I trust them here. I know from my own experimentation that high-voltage Zeners have lousily horrible temperature coefficients, so multiplying the voltage across one in the 4.7- 8.2V "happy" region seems to be the way to go. ISTR that 5.6- 6.2V types offer minimal change with temperature and going slightly either side offers predictable compensation. Obviously, anything proffering a CRT trace needs stable supplies to stop it shifting around with warm-up.

http://www.vintage-radio.net/forum/s...d.php?t=110814

PETERg0rsq · 25th Mar 2017, 9:24 pm

Many thanks for your suggestions.

Will see what Zeners i have to hand and give the suggestions a try.

Thanks again

Peter

PETERg0rsq · 2nd Apr 2017, 7:37 pm

Just an update to let you know the results.

I had a 60V zenner in my parts box, so gave this a try. Unfortunately it did not work, so I ordered a pack of 100V zenner diodes.

When they arrived i fitted one, and on powering up heard a "crack" as something let go!

I made some checks, only to discover I had installed the zenner (and the previous 60V one) backwards

Fitted a new one, the correct way round

voltages looked OK, but still no trace.

Some diagnostics later found Q5 blown. Replaced it with an equivalent, and now all working as should do.

Thanks again for the help and advice.

peter

25th Mar 2017, 4:40 pm	#2
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,867	Re: HP Neon replacement? A zener is a possibility, maybe 47 or 56v Be sure to pick a diode spec'd at 5mA. The current in it is even lower than this, but the neon has a soft corner anyway David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

25th Mar 2017, 4:48 pm	#3
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,864	Re: HP Neon replacement? According to Radio Museum it has a regulated voltage of 103V Current 0.2 to 2 mA http://www.radiomuseum.org/tubes/tube_z103r2.html Cheers Mike T __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk

25th Mar 2017, 5:11 pm	#4
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,394	Re: HP Neon replacement? Something rings a faint bell about a piece of Philips gear of similar vintage with a neon reference problem being discussed here at one point, there being a Philips official fix consisting of a ring-of-two and reference diode that soldered in place.

25th Mar 2017, 6:01 pm	#5
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,394	Re: HP Neon replacement? Gottit- nice quick forum search, acknowledgements to WME bill for finding it and posting in the first place. Not in fact a ring-of-two circuit but a simple voltage drop multiplier- I imagine that the 7.5V zener was used to match the transistors' Vbe temperature coefficient. Philips generally seemed to know what they were doing (even if what they did sometimes seemed a little odd....), so I trust them here. I know from my own experimentation that high-voltage Zeners have lousily horrible temperature coefficients, so multiplying the voltage across one in the 4.7- 8.2V "happy" region seems to be the way to go. ISTR that 5.6- 6.2V types offer minimal change with temperature and going slightly either side offers predictable compensation. Obviously, anything proffering a CRT trace needs stable supplies to stop it shifting around with warm-up. http://www.vintage-radio.net/forum/s...d.php?t=110814

25th Mar 2017, 9:24 pm	#6
PETERg0rsq Heptode Join Date: Jun 2009 Location: St Helens, Lancashire, UK. Posts: 641	Re: HP Neon replacement? Many thanks for your suggestions. Will see what Zeners i have to hand and give the suggestions a try. Thanks again Peter __________________ SPECIALIST.....Knows everything about nothing EXPERT..........Knows nothing about everything

2nd Apr 2017, 7:37 pm	#7
PETERg0rsq Heptode Join Date: Jun 2009 Location: St Helens, Lancashire, UK. Posts: 641	Re: HP Neon replacement? Just an update to let you know the results. I had a 60V zenner in my parts box, so gave this a try. Unfortunately it did not work, so I ordered a pack of 100V zenner diodes. When they arrived i fitted one, and on powering up heard a "crack" as something let go! I made some checks, only to discover I had installed the zenner (and the previous 60V one) backwards Fitted a new one, the correct way round voltages looked OK, but still no trace. Some diagnostics later found Q5 blown. Replaced it with an equivalent, and now all working as should do. Thanks again for the help and advice. peter __________________ SPECIALIST.....Knows everything about nothing EXPERT..........Knows nothing about everything