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03/04/26 at 18:10:05

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Tubes, It's Complicated 😡😡 (Read 67 times)

HockessinKid

Seasoned Member

Posts: 1330

Tubes, It's Complicated 😡😡
03/01/26 at 18:56:19

So after installing my new subwoofer, I noticed some tube rush in my left channel of my ZMA. Shortly after this, my left inside bias meter dropped to zero and output in the left channel dropped off considerably. No problem, a new pair of replaced tubes for the left channel and everything is AOK.

Next day still some tube rush in the left channel...huh?? After swapping left to right input tubes it turns out one of my 6N5P was the culprit. So two bad tubes in two days. Thankfully I've got a stash of 5 nice 6NP5 tubes😉

Moralels to the story - sometimes it's two tubes causing problems and always have some back up tubes. Cheers.

HK

Nottingham Interspace TT > MWI PH 9.0XT phono pre or MWI modded Cambridge CNX V2 > CSP3-25th preamp > STL STR-1002 Super > ZMA-25th amplifier > PI Audio UberBUSS > Caintuck Lii15 Magnum speakers > Rythmik F12G subwoofer > SA AUVA's > Snake River & ZenWave cables

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CAJames

Seasoned Member

"I've run every
red light on memory
lane."

Posts: 3121

Re: Tubes, It's Complicated 😡😡
Reply #1 - 03/01/26 at 20:12:37

Agree tubes can be complicated. Do you still have the old power tubes? It is possible the only problem was the input tube all along and it just was behaving better temporarily after you turned the amp off to replace the other tubes.

Regardless, good on you for having backups. Being able to swap tubes takes a lot of the frustration out of tube amp ownership.

[Volumio | Jay's CDT2 MRK3] -> Denafrips Terminator 2 + Gaia
Sumiko Pearwood -> Mapleknoll Athena -> Luxman SUT -> Mapletree Phono 3E
STR-1002 -> Woo WA22 -> 2x UFO25s, balanced monos
Omega SAM , Hifiman Arya, Audeze LCD-XC

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HockessinKid Seasoned Member Posts: 1330	Re: Tubes, It's Complicated 😡😡 Reply #2 - 03/01/26 at 23:05:59 CAJames, I changed out the input tubes on the left side of the amp first. The bias meter stayed zeroed out, so the power tube was definitely shot. All is well now, played the amp this afternoon for 3 hours with no hiccups. HK
Back to top	Nottingham Interspace TT > MWI PH 9.0XT phono pre or MWI modded Cambridge CNX V2 > CSP3-25th preamp > STL STR-1002 Super > ZMA-25th amplifier > PI Audio UberBUSS > Caintuck Lii15 Magnum speakers > Rythmik F12G subwoofer > SA AUVA's > Snake River & ZenWave cables IP Logged

__Jon__ Verified Member Posts: 37	Re: Tubes, It's Complicated 😡😡 Reply #3 - Today at 16:19:44 HK, Was wondering, are you using 6PN5 tubes for all four driver tubes on your ZMA or in combo with something else? I found some with a boxed anode from the 60's that I thought were nice. They show up periodically on eBay if you haven't tried them. Jon
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HockessinKid Seasoned Member Posts: 1330	Re: Tubes, It's Complicated 😡😡 Reply #4 - Today at 17:42:54 I'm using 6NP5'S in all four of the ZMA inputs. I prefer them to the 6NP1 tubes in my system. HK
Back to top	Nottingham Interspace TT > MWI PH 9.0XT phono pre or MWI modded Cambridge CNX V2 > CSP3-25th preamp > STL STR-1002 Super > ZMA-25th amplifier > PI Audio UberBUSS > Caintuck Lii15 Magnum speakers > Rythmik F12G subwoofer > SA AUVA's > Snake River & ZenWave cables IP Logged

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