HP power button neon - Page 1
Forum section: electronics / repair

author: veedub565
author_rank: Frequent Contributor
timestamp: January 04, 2025, 03:36:23 pm
content: Hi, does anybody know a source of replacement neon's for the older HP illuminated power buttons (see picture)I tried goggling thr HP part number but haven't come up with much.And an image search just throws up lots of hits for miniature bulbs, which it's isn't it's definitely a neon (95v in this case)

author: DLJ
author_rank: Contributor
timestamp: January 04, 2025, 03:59:37 pm
content: I googled "T1 neon" and found thishttps://www.ebay.co.uk/itm/293178384132No idea if this seller is any good, or even if this part would work for you.It might just be the entrance to a very deep rabbit hole.Happy hunting.Dave

author: veedub565
author_rank: Frequent Contributor
timestamp: January 04, 2025, 04:03:39 pm
content: Ah perfect, thanks. I didn't even know it was called a T1 neon, or sub midget flange

author: schmitt trigger
author_rank: Super Contributor
timestamp: January 04, 2025, 04:05:34 pm
content: You may receive suggestions to replace the neon with an LED, by adding a diode and changing the limiting resistor.Unless you absolutely cannot find a suitable replacement neon, I would not recommend it. I may be prejudiced, but I positively love the soft neon glow. And you would keep your vintage device, well, vintage.

author: factory
author_rank: Super Contributor
timestamp: January 04, 2025, 05:30:52 pm
content: They are usually an A1H neon, the one linked in reply #1 is too small.David

author: Dave Wise
author_rank: Regular Contributor
timestamp: January 04, 2025, 05:50:37 pm
content: Edit prompted by "factory". I misspoke in my original post.My HP 740B DC Voltage Standard/Differential Voltmeter was made with two type A1G neon lamps. The envelope size is called T2, and the base is Midget Flange. One is powered by mains AC, the other by DC. I bought a pack of new-old-stock A1H lamps off eBay. (A1H is easier to get cheap than A1G.) The new lamp in the AC-powered spot is reasonable brightness even running at A1G current. It is still going strong, but the DC-powered one darkened after a few months due to metal sputtering onto the glass. This is a known failure mode, neon lamps prefer AC. I replaced that one with a Dialight LED lamp. With no circuit changes, the existing resistor gave the right brightness and it will probably outlive me. Part number 586-1101-005F 24V and tip negative, 586-1101-105F 24V and tip positive. I have two 740B's, and one is positive and the other negative.Just like cheap Christmas lights, if you run a LED off AC it will flicker unless you add a reservoir cap.HTH,Dave Wise

author: factory
author_rank: Super Contributor
timestamp: January 04, 2025, 06:12:13 pm
content: The 740B should have a A1G according to the manual, this is a lower brightness part, if it's getting burned out quickly, the supply voltage is either too high, or the series resistor value too low.The lampsizeof both A1H & A1G isT2, have a read of the GE glow lamp manual if you don't believe me.Additional info: The number codes used for the lamp/bulb diameter are in eights of an inch (⅛"), for some unknown reason the more modern A1H & A1G are sold as T1¾.David

author: veedub565
author_rank: Frequent Contributor
timestamp: January 04, 2025, 08:07:07 pm
content: Looks like there could be a lot of different permutations depending on which HP instrument it's fitted to.in this case it's for an 8447F and the HP part number is 2140-0244, mfr part number is listed as A1HSo an A1H T2 midget flanged neon is what I need byt hte looks.