#1
So I recently retubed my Jet City 100HDM, which came stock with 4 6L6WGBs in the power section and 5 12AX7s in the preamp. 

I swapped in some JJ 6L6GCs, and for the preamp I added one 5751 in V1 and four EGC83S for V2-V5, with the last EGC83S being balanced for the phase inverter.

However, after plugging my guitar in and playing, there is excessive feedback, even when on the clean channel. This was not the case before. Are the tubes seated wrong? Should I tap them gently to see what's up?
 
Any help is appreciated  
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#2
pencil test the preamp tubes. probably a microphonic tube.
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#3
Quote by trashedlostfdup
pencil test the preamp tubes. probably a microphonic tube.

Yeah, that would be my guess too.  Most likely the phase inverter or one of the power tubes if it's happening on both channels.
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#4
for some reason I was thinking v1. it seems like jj 5751's aren't as robust as the 12AX7's.
WTLT 2014 GG&A

Quote by andersondb7
alright "king of the guitar forum"


Quote by trashedlostfdup
nope i am "GOD of the guitar forum" i think that fits me better.


Quote by andersondb7
youre just being a jerk man.



****** NEW NEW NEW!
2017-07-07 2017-07-07 Update and a Chat On Noise Constraints *** NEW FRIDAY 7/7
2017-04-13 RUN AWAY from COMPUTERS!!! TCE? RANT ALERT!!!
2017-03-02 - Guitar Philosophy 1001- Be Prepared For the Situation (Thursday 2017-03-02)
2017-02-21 How to Hot-Rod the Hell of your Stratocaster for $50! (Tuesday 2017-2-21)
Resentments and Rambling from a Guitar Junkie
---> http://trashedengineering.blogspot.com/
#5
trashedlostfdup i ment to say robust inbterms of lifetime and durability
WTLT 2014 GG&A

Quote by andersondb7
alright "king of the guitar forum"


Quote by trashedlostfdup
nope i am "GOD of the guitar forum" i think that fits me better.


Quote by andersondb7
youre just being a jerk man.



****** NEW NEW NEW!
2017-07-07 2017-07-07 Update and a Chat On Noise Constraints *** NEW FRIDAY 7/7
2017-04-13 RUN AWAY from COMPUTERS!!! TCE? RANT ALERT!!!
2017-03-02 - Guitar Philosophy 1001- Be Prepared For the Situation (Thursday 2017-03-02)
2017-02-21 How to Hot-Rod the Hell of your Stratocaster for $50! (Tuesday 2017-2-21)
Resentments and Rambling from a Guitar Junkie
---> http://trashedengineering.blogspot.com/
#6
replace the small tubes  one at a time with one of your old tubes , play between each tube change to determine which position has the bad tube ..... or try removing and reinstalling one at a time see if one tube didn't seat into the socket correctly
#7
Did you clean the tube sockets with electrical contact cleaner like DeOxit when you changed the tubes?
Guitars:
Ibanez RG1570 Prestige
Jackson Kelly KE3 - MIJ (Distortion/Jazz)
Jackson DKMGT Dinky (EMG 81/85)
ESP E-II Eclipse Custom (JB/'59)
ESP LTD EC-1001FR (EMG 81/60)
Fender MIM Strat

Amps:
Mesa/Boogie Dual Rectifier Roadster 212
Laney IronHeart IRT-Studio
Peavey Vypyr 30
Peavey ReValver Amp Sims
TOOOO many T.C. Electronic Pedals. . .
#8
Quote by Fumble fingers
replace the small tubes  one at a time with one of your old tubes , play between each tube change to determine which position has the bad tube ..... or try removing and reinstalling one at a time see if one tube didn't seat into the socket correctly

Definitely gonna try this. 
Quote by metalmingee
Did you clean the tube sockets with electrical contact cleaner like DeOxit when you changed the tubes?

I did not, as the sockets were fairly clean. Should I have regardless? (first time changing tubes btw so please forgive me if it's a rookie mistake)
I NEED TO CHANGE MY USERNAME


  • Agile AL-3XXX Custom Tobacco Sunburst w/ EMG 57/66
  • ESP LTD EC-1000T CTM Black w/ Seymour Duncan Blackouts
  • Jet City JCA100HDM w/ Avatar Contemporary 2x12 Cab
  • Seymour Duncan 805 Overdrive
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  • MXR Smartgate
#9
I always have.  The way I learned it is that the tube pins form a fingerprint into the socket.  Using the contact cleaner strips away the fingerprint in the socket and allows for a clean, smooth connection.  I spray the tube pins and then insert the tube into the socket a few times - you can feel the physical resistance give up when all that small crud comes loose and allows the tube to seat easily.  
Guitars:
Ibanez RG1570 Prestige
Jackson Kelly KE3 - MIJ (Distortion/Jazz)
Jackson DKMGT Dinky (EMG 81/85)
ESP E-II Eclipse Custom (JB/'59)
ESP LTD EC-1001FR (EMG 81/60)
Fender MIM Strat

Amps:
Mesa/Boogie Dual Rectifier Roadster 212
Laney IronHeart IRT-Studio
Peavey Vypyr 30
Peavey ReValver Amp Sims
TOOOO many T.C. Electronic Pedals. . .
#10
Quote by metalmingee
I always have.  The way I learned it is that the tube pins form a fingerprint into the socket.  Using the contact cleaner strips away the fingerprint in the socket and allows for a clean, smooth connection.  I spray the tube pins and then insert the tube into the socket a few times - you can feel the physical resistance give up when all that small crud comes loose and allows the tube to seat easily.  

Got it. I'll definitely make note of that going forward when I retube in the future. I actually did buy some DeOxit yesterday as well.

Update: So last night I decided to give my amp another go before conducting the aforementioned things above,  just to get a measure of what was up. When I turned it on and plugged in, the issue was gone - clean channel was fine, and the overdrive channel was back to normal as well. 

I'm still gonna keep an eye out in case the excessive feedback comes back, and go from there. Thanks everyone for the help
I NEED TO CHANGE MY USERNAME


  • Agile AL-3XXX Custom Tobacco Sunburst w/ EMG 57/66
  • ESP LTD EC-1000T CTM Black w/ Seymour Duncan Blackouts
  • Jet City JCA100HDM w/ Avatar Contemporary 2x12 Cab
  • Seymour Duncan 805 Overdrive
  • Dunlop OG Crybaby Wah
  • MXR Smartgate
#11
Out of curiousity, did you pull the head out of the shell for the retube? That will make it much more susceptible to interence from other electronics and things like radio waves, lighting, etc.
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#12
Quote by dementiacaptain
Out of curiousity, did you pull the head out of the shell for the retube?  That will make it much more susceptible to interence from other electronics and things like radio waves, lighting, etc.

Only to clean the amp and install the tubes. I put the shell back on afterwards. 
I NEED TO CHANGE MY USERNAME


  • Agile AL-3XXX Custom Tobacco Sunburst w/ EMG 57/66
  • ESP LTD EC-1000T CTM Black w/ Seymour Duncan Blackouts
  • Jet City JCA100HDM w/ Avatar Contemporary 2x12 Cab
  • Seymour Duncan 805 Overdrive
  • Dunlop OG Crybaby Wah
  • MXR Smartgate
#13
If you didn't play it while out of shell then shouldn't have madr a difference
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#14
Is it possible it's just a 'noisier' tube? A local amp tech claims that most 5751s are not suitable to guitar amps due to excessive feedback (Lucas Miles @TubeAudio.com.au - source). He does like the JJ 5751 if that's what you have, though. I have never heard of EGC83. If it's not those, then as has been said, a power tube might be the problem.
The above post is in terms of 'YMMV' and 'IMO', etc...

Quote by Offworld92
This debate is exhausting to read.
The guitar world is drowned in fairy dust.
We need to start at the very beginning. What is tone.
#15
Quote by 2Crosser
Is it possible it's just a 'noisier' tube? A local amp tech claims that most 5751s are not suitable to guitar amps due to excessive feedback (Lucas Miles @TubeAudio.com.au - source). He does like the JJ 5751 if that's what you have, though. I have never heard of EGC83. If it's not those, then as has been said, a power tube might be the problem.



That's the first time I've ever heard of that...


But I agree, a 'new' tube doesn't always guarantee great tone or noise free.

Edit: i"ve heard of good things about the JJ 5751 but never tried one.
#16
311ZOSOVHJH Lucas doesn't like gold pin 12AX7s either, fwiw.
The above post is in terms of 'YMMV' and 'IMO', etc...

Quote by Offworld92
This debate is exhausting to read.
The guitar world is drowned in fairy dust.
We need to start at the very beginning. What is tone.
#17
2Crosser correct me if I'm wrong but I believe that ecg83 is just the British name for a 12ax7.  Also, it sounds to me like the tubes may have just needed to break in a bit?
#18
DeadHeart7 no it's ECC83, not egc. Perhaps OP made a typo. I wouldn't know how exactly a tube would need breaking in, since it's just a part that handles electric current. Perhaps my ears fail me
The above post is in terms of 'YMMV' and 'IMO', etc...

Quote by Offworld92
This debate is exhausting to read.
The guitar world is drowned in fairy dust.
We need to start at the very beginning. What is tone.
#19
^ ecc83 is the same as 12ax7, i think deadheart7 made a typo
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#20
Dave_Mc nah it was snake
The above post is in terms of 'YMMV' and 'IMO', etc...

Quote by Offworld92
This debate is exhausting to read.
The guitar world is drowned in fairy dust.
We need to start at the very beginning. What is tone.
#21
ah good point
I'm an idiot and I accidentally clicked the "Remove all subscriptions" button. If it seems like I'm ignoring you, I'm not, I'm just no longer subscribed to the thread. If you quote me or do the @user thing at me, hopefully it'll notify me through my notifications and I'll get back to you.
Quote by K33nbl4d3
I'll have to put the Classic T models on my to-try list. Shame the finish options there are Anachronism Gold, Nuclear Waste and Aged Clown, because in principle the plaintop is right up my alley.

Quote by K33nbl4d3
Presumably because the CCF (Combined Corksniffing Forces) of MLP and Gibson forums would rise up against them, plunging the land into war.

Quote by T00DEEPBLUE
Et tu, br00tz?
#22
Quote by Dave_Mc
^ ecc83 is the same as 12ax7, i think deadheart7 made a typo

Indeed I did! Ha, thanks for calling me on it.
#23
Was it worth it to change the tubes? I just bought a used Carmen Ghia from 1990. It sounds awesome! I do not plan to change the tubes...ever. 
#24
I didn't realize this thread was still kicking!
 
No noise since the day after, so all has been good lol. 
Quote by NostraHistoria
Was it worth it to change the tubes? I just bought a used Carmen Ghia from 1990. It sounds awesome! I do not plan to change the tubes...ever. 


For me, yes. The amp has slightly more headroom and sounds smoother than before. The differences aren't crazy dramatic, but to me I like it more. I'd say eventually you gotta change the tubes, especially if you're playing it a lot. 
I NEED TO CHANGE MY USERNAME


  • Agile AL-3XXX Custom Tobacco Sunburst w/ EMG 57/66
  • ESP LTD EC-1000T CTM Black w/ Seymour Duncan Blackouts
  • Jet City JCA100HDM w/ Avatar Contemporary 2x12 Cab
  • Seymour Duncan 805 Overdrive
  • Dunlop OG Crybaby Wah
  • MXR Smartgate
#25
Fumble fingers This! You'll find where the issue is.  Tube combinations can be tedious especially in high electrical environments (everywhere these days!)...small changes can make a big difference.  You may find that only one or two are causing the issue so replace them and save those for down the line.  
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