M100 - electrolytic caps kit

[bourniplus]

Hello everyone,
I bought the electrolytic caps kit from Tonewheel general and am not sure where everything is supposed to go. First, I can solder and understand the safety precautions. I have done this job on my A100 successfully but it was pretty straightforward as far I remember.
For example the old silver can has 4 tabs, while the new one has only 3. The tab that is absent from the new one goes to V3. It seems the missing cap would be 30 mfd, 25 volts, but I don't see anything close to that in the kit.
Secondly, the new black can has three tabs instead of two, with one marked in black. Is that a ground lug? (The old black can has ground lugs around.)
Any help would be greatly appreciated! thanks!
Martin

[bourniplus]

Hello again,
the schematics for the M100 say that C14 is 30 mfd, 25 vdc. In the kit there is a 3.3 uF, 50 V cap. Could this be it?? As far as I know, uf and mf are the same, are they not? I went to the store and got a 33 uF, 25 V to make sure I have the right one, but I still wonder about the one in the kit.

[Admin]

mF and uF both stand for microfarad. The "u" is actually an ISO approved substitution for the Greek character mu "μ" so to be perfectly correct it should be μF.

There's an order of magnitude of difference between 3.3 μF and 33 uF so you want to use the right value here. I've seen many cases where the decimal point is missing on schematics, so I'd double check with the supplier of the kit, or read the value off the capacitor you're replacing.

[bourniplus]

Thanks for the comment. The schematics clearly indicates 30/25, and so does the old can capacitor, so I'm very confident that 30 mfd is the required value.

[alpine]

Why don't you ask TWGH, where you got the kit from? They are helpful people.

[bourniplus]

I did send them an email about two weeks ago and haven't received an answer. This being said, I have always had great service from them and will order again, and I understand if they might not want to give specific instructions for these kinds of products. Actually on the site it says something to that effect. I get it that this is kind of an item for "techs" who will know what to do with it, and not for DIYers like myself who might hassle them with questions. Again, when I used their electrolytic caps kit to do the job on my A100, it was pretty simple and straightforward to tell what goes where. However for this one I find it's not that obvious. I will keep studying the schematics.

[muckelroy]

For example the old silver can has 4 tabs, while the new one has only 3. The tab that is absent from the new one goes to V3. It seems the missing cap would be 30 mfd, 25 volts, but I don't see anything close to that in the kit.

Please forgive me if this response sounds blunt, but your post makes it sound like no instructions were included. Did you receive a PDF document via email with your receipt, with instructions? I have bought this kit of theirs once when I was short on time and didn't have the cans I wanted. They included a PDF document with VERY detailed instructions, including very clear photos. I would defer to them for any / all questions about those instructions. There is a reason that there is a disclaimer near the top, which reads "This kit is designed for persons with vacuum tube circuit and point to point wiring experience."

Judging from your description of the capacitor, this was originally a 30uf 25V cap that was a part of the old silver can. The replacement in the TWGH kit I received was a 100uf 35V axial capacitor. Install it in a way that it attaches where the old 30uf 25V cap can wire did. This is outlined in the kit instructions, so I won't elaborate any further here. Suffice to say, it is an axial replacement for C14 on the schematic.

Secondly, the new black can has three tabs instead of two, with one marked in black. Is that a ground lug? (The old black can has ground lugs around.)
Any help would be greatly appreciated! thanks!
Martin

The black lug of the 50/50 can is the negative of both of those capacitors, but it should NOT touch the chassis. It should be connected to the power transformer HV center tap, as well as R101 (180 ohms), R103 (10k ohms). That point in the circuit is a negative voltage. The specifics of which wires to connect, again, is outlined in the instructions that TWGH should have provided you.

[bourniplus]

Muckelroy, thanks so much for this. I had completely missed the .pdf in the email. I just downloaded it and it's indeed very clear and detailed with good pictures, it all makes sense now.