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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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25th Mar 2017, 1:16 pm | #1 |
Heptode
Join Date: Jun 2009
Location: St Helens, Lancashire, UK.
Posts: 641
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HP Neon replacement?
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
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25th Mar 2017, 4:40 pm | #2 |
Moderator
Join Date: Mar 2012
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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
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25th Mar 2017, 4:48 pm | #3 |
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Location: Exeter, Devon and Poole, Dorset UK.
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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
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25th Mar 2017, 5:11 pm | #4 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,395
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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.
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25th Mar 2017, 6:01 pm | #5 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,395
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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 |
Heptode
Join Date: Jun 2009
Location: St Helens, Lancashire, UK.
Posts: 641
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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
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2nd Apr 2017, 7:37 pm | #7 |
Heptode
Join Date: Jun 2009
Location: St Helens, Lancashire, UK.
Posts: 641
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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
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