Site Links
Howdy, Stranger!
It looks like you're new here. If you want to get involved, click one of these buttons!
Quick Links
Categories
In this Discussion
Cheap nobsound tube preamp
Picked up a little tube pre amp to go with the recent tube amp purchase. I popped the bottom of the case off to see what was inside the preamp . I noticed there was no AC ground to chassis strap, unless Im missing something ? If that is the case should I be worried ?
Best Answer
-
Atleast the connection without heatshrink draped over it should be the neutral sinse it is not the one going through the fuse. So that is something I guess.
If that ground pin is unconnected then there is no reliable safety ground. Simple as that
I'd say, if there is nothing else electrically connecting to the chassis then it should be ok to connect a ground strap from the pin to chassis yourself. With the unit off. Check the resistance form all the connections compared to the chassis. Anything with less than a large resistance has some sort of contact with the chassis.
[Edit] Did a little digging and found a report of someone connecting earth ground to the chassis (might not be your identical version but probably close).. It is down in the amazon reviews, so not the most reliable info, but atleast they have photo evidence they did it:
https://www.amazon.com/Nobsound-Preamplifier-Shigeru-Circuit-Assembled/dp/B07F3FDX7CIf the signal is somehow grounding to the chassis then often you will see a "ground lift" switch added to break this connection when needed (if you get ground loop hum), allowing the safety ground to still be connected to the chassis.
As a side note.. It seems many designes of these chinese units with tube rectifiers have way too large of capacitors directly connected to the rectifiers with no resistance between. From what I've researched this puts a ton of stress on those rectifier tubes from inrush current. They already have the hardest job, so this will likely kill them quickly. Something to check.
Answers
Where are those green wires on the transformer going?
Steve, they are terminated to the rectifier tube socket.
The yellow and green might be a ground. Considering the ground pin is not connected, one heat shrink tube is not shrunk and the other ac wire is missing heat shrink I would assume there is little to no QC.
You will need to be the QC.
Sigh , well , I guess Ill see you guys on the other side!
Thanks for the info Drew. The preamp in your link is pretty damn close to what I have. Mine is using a single 6Z5 rectifier tube vs the dual 6Z4 in your link. I think I will take the bottom off tonight and see if I cant do something similar to what was in that review. Thanks for the link.
Took some time to terminate the ground to the chassis . Used 16 true copper stranded wire . Also took care of the heat shrink on some of the terminals in the chassis. Got it plugged in looking for smoke.
