Strange looking Fluke 845AB - Page 1
Forum section: electronics / general

author: 70bytes
author_rank: Contributor
timestamp: August 08, 2025, 03:56:41 pm
content: Hi,I received my new ebay score today. Its a Fluke 845AB.The item i received is different than the item pictured in the ebay ad.Has anybody seen this version of a fluke 845AB? It has an extra sensitivity potentiometer and the input terminals are on the right side.Looks like a very early model to me. I think the later models had different knobs.

author: TheDefpom
author_rank: Frequent Contributor
timestamp: August 08, 2025, 08:28:13 pm
content: That is interesting.I did a couple of videos on my unit, in case you want to compare the inside.🔴 Fluke 845AB Repair Part 1 - No.1142https://youtu.be/hW56Td8k1Iw🔴 Fluke 845AB Battery Replacement and Testing - No.1211https://youtu.be/cQc0AYtGqRg

author: TimFox
author_rank: Super Contributor
timestamp: August 08, 2025, 09:02:22 pm
content: Sheer vandalism to put a glued paper label over a glass meter face.

author: Stray Electron
author_rank: Super Contributor
timestamp: August 08, 2025, 10:30:00 pm
content: Quote from: TimFox on August 08, 2025, 09:02:22 pmWelcome to the world of surplus electronics!

author: 70bytes
author_rank: Contributor
timestamp: August 08, 2025, 10:49:58 pm
content: I opened the meter to have a look inside.Looks the same as in your youtube video's.I found a datecode of 1973 on a transistor.Batteries where also inside. Empty. Some have signs of (green) corrosion.After charging the batteries, i tried to power it on. Needle went to the far right off scale.After same checkups i found the cause : there are 2 transistors missing. Q113 (GA2875) and Q114 (GA2877). Both germanium.Does anyone know same replacements for these?Ratings are 25V C-B and 25V E-B , 300mA max.

author: TimFox
author_rank: Super Contributor
timestamp: August 08, 2025, 10:52:06 pm
content: Note that the E-B ratings of the germanium transistors are much higher than for silicon transistors of the same size.

author: TheDefpom
author_rank: Frequent Contributor
timestamp: August 08, 2025, 11:00:14 pm
content: Well Q113 and Q114 don't appear to be that critical as they are just driving the transformer T203, you might be able to substitute a modern part OK, you may need to adjust the values of R155 and R156 to ensure that they are working nicely together as they are working as a push pull with an AC signal on their bases.

author: TimFox
author_rank: Super Contributor
timestamp: August 08, 2025, 11:02:57 pm
content: Quote from: TheDefpom on August 08, 2025, 11:00:14 pmI haven't studied the circuit here, but I remember from learning about multivibrators back in the late 1960s that germanium transistors could withstand the full collector swing applied to the base, but silicon transistors would break down at 5 to 7 V.

author: 70bytes
author_rank: Contributor
timestamp: August 08, 2025, 11:11:47 pm
content: I found a replacement for the GA2877 in the Fluke 871A differential voltmeter manual.2n1303 or 2N3906 or 2N3638.Time for me to go to bed know. Its 1:00 AM. Will continue tomorrow.

author: TimFox
author_rank: Super Contributor
timestamp: August 08, 2025, 11:17:32 pm
content: The 2N1303 is germanium.The 2N3906 and 2N3638 are silicon.The 2N3638 is hard to find, but the 2N3906 is readily available in a TO-92 version.If it matters.