trinityamps.com

Hi there!

I bought a beautiful second hand green Trinity 18W TMB head a few years ago while in California, and then brought the amp back to France where I live. The amp is still in 110V, and I bought an external transformer so it can be run at 230V. However, as I was trying to connect the head to a cab, I realized that the impedance switch got loose. As I tried to tighten it, I then saw that the switch has 9 positions, even if there are only 3 options on the back plate (4, 8, 16 Ohm). My question is thus very simple: how can I know which ones of the 9 positions match 4, 8, and 16 Ohm?
I'm feeling quite sorry for my lack of knowledge in electronics, but I thought it would be safer to ask before trying anything stupid! Apologies if this a frequent question, I did a basic search and didn't find anything.

Best,

Matthias

Matthias, I would recommend going to the main Trinity site. Scroll to bottom of page and click on "Support". From there you should be able to download the 18W Build guide, schematic and layout. Be sure to get the layout for your particular version (there are numerous versions). You may have the white Lorlin switch in which case you'll need to find a build guide that has instructions on how to set it up for 3 positions (Tweed and Tramp guides come to mind). The 18W guide only shows a 3 position switch (black). Please post a picture of the switch, if you are able to.

_________________
"The only problem with being retired is you never get a day off"

Hi Hankules,
Thank you so much for your message and explanations, I really appreciate it! I opened up the amp and it is a white Lorlin UK switch indeed!
The Tramp build guide explains that a white 12 positions Lorlin switch can be adjusted to 3 positions by turning it fully anti-clockwise and then rotating the tang washer to adjust number of positions, 3 in this case.
What I can't understand is that although the tang washer on my switch is adjusted to 3 positions, I can still move it to 9 positions (probably because the switch has not been turned fully anticlockwise before adjusting the tang washer). What would happen if i leave it as it is? Should I set it right back?
Here are some pictures joined for some better clarity!
Best,
Matthias

The other 9 positions on the switch aren't wired so if it is a single-pole,12-position switch it will disconnect the speaker from the output transformer if the unused positions are selected. Running an output transformer with no load can burn it out.

It could also be a 4-pole, 3 position switch. In that case it will repeat the first three settings as you rotate it to the other nine. No harm done, but it can be confusing.

Either way the tang washer should be set properly. Remove the washer, rotate the switch fully anti-clockwise, then put the washer back so you can only rotate the shaft through three positions. The switch appears to be wired so 4 ohms is the fully anit-clockwise position, followed by 8 and 16.

Thanks Hankules and mitch m for your precious help! I adjusted the washer as you described, and the amp runs just fine. I can't wait to record it now.

Best,

Matthias