Nitro sounds like crap - FIXED!

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Hi guys - I excitedly plugged up my new (to me) Nitro KT88 today, sounds like shit. I've not owned a KT88 amp before, and I'm not sure how much they are the culprit or these an issue somewhere, but it's wooly and dull - no bite, all flub. Rather than replace them, was thinking I should go straight to EL34's.

Anyone done this? Presumably I can follow this thread backwards: https://www.rig-talk.com/forum/threads/kt88-bias-instructions-thanks-bubbastain.216792/

The amp seems to function fine, it's clean sounding, plenty of gain, no crackling, not weak on power so it doesn't really sound like there's an issue, other than it sounds shit.

Thoughts?
 
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Normally, KT88s are the opposite of flub. Also, they usually add sparkle, compared to EL34. Not dull at all. There may be another issue with the amp. Have you tried swapping preamp tubes ?
 
Hmm ok something's not right. All preamp tubes changed, same. Bias on KT88's looks fine. Something's up, will prod around for a bit and see where it leads me. Does anyone know if the attached schematic is accurate?
 

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I can't see the schematic from here but the Nitro should be anything but dull and wooly. I would also try preamp tubes and speaker cab/cable/ohms/etc. What plate voltage and bias reading did you get?
 
Does it have a loop and if so maybe try using another amp for the Return. That might tell you if it is the Pre or Power amp or possibly the loop/jacks.
 
What cab. are you using? Have you tested it with other cab/speaker options? My Nitro was anything but wooly and dull.
 
Ok so it was the KT88's - not sure what the actually problem was but a quad of KT77's did the trick. Kinda weird, but sounding good now.

Only issue is now cosmetic - idiot previous owner hit the front and back panels with brasso to 'shine them up'. What a muppet - the plastic laminate is now cloudy and worn though in places. I reached out to Scott but don't like my chances, he specifically states in his FAQ he won't supply faceplates. I hope he has a change of heart.

Thanks for your help guys.
 
Good to hear on the tubes - meaning it is nothing major. The SGR you have in there now should be geared for KT88s. Only asking in case you want to go EL34s/KT77 long term. I think it would just be a matter of swapping those out per your OP. I think the KT77s are closer variants to the EL34s. SpidarWars will probably know if he comes back.

Maybe if you send Scott a pic of your amp he might hook you up. He probably wrote that a long time ago as he is very protective of his brand.

Oh yeah, and tell Scott he's got a dedicated sub forum over here. I know he wont' post but yeah....
 
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Don't know what year, no serial - could have been polished off by the moron.

Nitro1.png
 
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KT-77's are EL-34 derivatives, KT-88' are 6550 Derivatives. did the previous owner do an experiment or was it set up as KT-88 amp at birth. You don't want to damage this thing I'd call Scott and get this all clarified.

KT-66 is bias like a 6L6

KT-77 bias an EL-34

KT-88 bias like 6550
I don't know what this will do to your amp as I've never owned a 6550 amp
 
Man have a closer look at the panel - that's not reflections, the panel is shiny in places and a cloudy matte in others. The rear is worse:
Nitro rear.png
 

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  • Nitro rear.png
    Nitro rear.png
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Yes, loop volume. And yes, I've changed the relevant resistor to allow for EL34/KT77's - it biased up well. My try KT88 down the track.

And yes I emailed Scott a few days back, no reply. Damn, the panels really do look awful.
 
Scott is basically a one man show right now so be patient he will respond, it's funny sometimes he'll respond in minutes , other times it takes a couple of days, so I guess what ever he's got right in front of him takes precedence.
I've been wondering if KT-77's would sound good with the Quick Rod circuit (SS, SR all basically the same).
I don't have any at the moment and I've got so many different types of EL-34 power tubes ready to go in and test but I like what I'm getting right now so ...... too lazy :)
 
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Man have a closer look at the panel - that's not reflections, the panel is shiny in places and a cloudy matte in others. The rear is worse:View attachment 69337
Click to expand...
Geez what a mess... man that's a bummer. Maybe there's something else you can do, solvent of some kind, might just make it worse. :(
 
Yeah bummer. There's no fixing it, replacement is the only option but isn't looking good - no response from Splawn.
 
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