Coupling c amp?

[andresound]

Hi Guys, I am using this JTM45 type pre section in a bassman re-build. 2 ch (JTM and Dumble clean). Is the coupling cap circled in red, really necessary?
Thanks

73EC5C12-3454-4D88-929B-5DB20D593D3E.jpeg

[nworbetan]

Looks like a yes to me. Keeps DC from the bottom channel away from the tone control pots on the top channel.

Edit: A more conventional location for that coupling cap would be between pin 6 on the normal channel and the 220k mixer resistor.

[andresound]

Thank you. Makes sense. I was looking at the “JTM” stage in isolation. The Dumble channel on my build, does have a coupling cap after the plate. So then ... I do not need the coupling cap in the JTM channel?

[nworbetan]

You do need a coupling cap on the fourth triode in the JTM channel. There's already 3 of them in the tone stack though, so that's covered already without the circled .1uf cap.

[andresound]

My Dumble channel is based on #40 clean v1 only. So to be clear.. I dont need the cap circled .1? Sorry for the repeated question

[andresound]

Here is the other ch.

8383B1CE-407E-4BB3-AC97-6D0B48751721.png

[pompeiisneaks]

since you don't have a unified schematic, it's only a guess, but yes, since that channel in the dumble has a coupling cap, no DC could go onto the tone stack of the other channel.

~Phil

[chocopower]

Hi Guys, I am using this JTM45 type pre section in a bassman re-build. 2 ch (JTM and Dumble clean). Is the coupling cap circled in red, really necessary?
Thanks

That's funny... i "draw" that schematic maybe 10 years ago using Windows Paint.
I'm not a pro now, but back those days i barelly understand the whole thing...

As nworbetan and my ✴✴ note said, coupling cap could be in the other channel.

[andresound]

Wow, chocopower, Thanks for chipping in. I did notice the note next to the cap, but ~I don’t speak that language (French?). But thank you for that. I will post the build when finished. Here is a pic of the new board so far.

94D73109-45C3-46DC-AC9F-A75CF7B6FB0C.jpeg

[chocopower]

I don’t speak that language (French?).

Spanish!

that was an amp i modded for a friend of mine.
the unnused triode make it easy.

[andresound]

[andresound]

Amp is up and running. Sounds good, is quiet, but a little “hot” in both channels. Biased at 35ma for RCA black plate 6L6’s. Getting approx 36w clean into 8 ohm. Seems a bit low?

9882AC4E-5366-42C0-9397-F80F55549CC1.jpeg

Will do some tweaking next week.