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NAD Bummed!

DFWGuitarMan

Member
Messages
146
NAD and I am Bummed! Getting a bad bad pre amp hum from Jet City JCA50h head that came today.

I also have an Orange TH30 head that I have been using and its quiet. Got the JCA plugged into the same power in the same room---the hum is so loud its almost as loud as playing.

Its not the pedal chain, not the guitar...its definitely the amp. And its most noticeable when the Overdrive Channel preamp is dialed up. And to get into gain land on that channel where I want to go its up around 6-7-8 and its awful.

Wondering if its bad amp? Bad tubes? Or if this is "just the way" this amp performs.

but in all my research hadn't heard or seen any complaints about it

Ideas? Suggestions?
 

ledzep618

Member
Messages
4,751
Try rolling some new pre amps tubes into it. It's so common for tubes to get knocked around in shipping, especially if they are left in the sockets.
 

DFWGuitarMan

Member
Messages
146
ok thanks for the tips. Never replaced tubes before. Not worried about how, worried about which ones/brand do I buy? I definitely don't want to put any in that bring the gain down.
 

MRscratch

Member
Messages
7,408
just try anything right now. Try the first one closest to the input of the amp. most likely it is V1 or "valve one" as the Brits say.
One at a time. It will be fine dude. mark them all 1 to 4 or 5 so you know where they were. try taking one from each spot and putting it in the spot in front of it. pay attention to the last of the pre amp tubes as this will most likely be a phase inverter tube, and it may be different. Soldano usually uses sovtek LP. The last one will probably say sovtek 12ax7 LPS on it. you should try to keep that one in place.
 

lang.murphy

Member
Messages
3,582
Try reseating the tubes. Every one. Just push down firmly but slowly and evenly.

If that doesn't help, you can try moving the pre-amp tubes around. Figure out which pre drives the channel that is noisy and swap with another position. The manual should disclose which tubes drive which channels. You can google it and look it up. If the manual doesn't disclose which tube drives which channel, see if they, Jet City, have a phone number you can call and ask them which tube drives which channel. If there are three pre-amp tubes, V1 should be farthest from the power tubes, V2 the next closest, and V3 closest and V3 is the phase inverter position. (In an amp with 3 pre's.)

I'd start by switching V1 and V2. If the noise moves to the other channel, you've just identified the bad tube. If the channel remains noisy, then, yep, might be the amp. But I'd try swapping either V1 or V2 with V3, just to see what happens.

To pull a tube, grab it firmly and wiggle it side to side in the tiniest increment possible while pulling up. When inserting, ensure the pins line up with the socket holes and ever so slowly push straight down. If you feel any resistance, stop and try realigning the pins with the socket holes again. Also... can't hurt to look at the pins and make sure they are all straight. After you've done it a couple of times, it becomes less of a magic trick... it's pretty simple stuff, actually.

Good luck!
 

Winnie Thomas

Gold Supporting Member
Messages
650
NAD and I am Bummed! Getting a bad bad pre amp hum from Jet City JCA50h head that came today.

I also have an Orange TH30 head that I have been using and its quiet. Got the JCA plugged into the same power in the same room---the hum is so loud its almost as loud as playing.

Its not the pedal chain, not the guitar...its definitely the amp. And its most noticeable when the Overdrive Channel preamp is dialed up. And to get into gain land on that channel where I want to go its up around 6-7-8 and its awful.

Wondering if its bad amp? Bad tubes? Or if this is "just the way" this amp performs.

but in all my research hadn't heard or seen any complaints about it

Ideas? Suggestions?
If you just got it and it was new, take it back and don't f*ck with it.

Winnie
 

DFWGuitarMan

Member
Messages
146
Try reseating the tubes. Every one. Just push down firmly but slowly and evenly.

If that doesn't help, you can try moving the pre-amp tubes around. Figure out which pre drives the channel that is noisy and swap with another position. The manual should disclose which tubes drive which channels. You can google it and look it up. If the manual doesn't disclose which tube drives which channel, see if they, Jet City, have a phone number you can call and ask them which tube drives which channel. If there are three pre-amp tubes, V1 should be farthest from the power tubes, V2 the next closest, and V3 closest and V3 is the phase inverter position. (In an amp with 3 pre's.)

I'd start by switching V1 and V2. If the noise moves to the other channel, you've just identified the bad tube. If the channel remains noisy, then, yep, might be the amp. But I'd try swapping either V1 or V2 with V3, just to see what happens.

To pull a tube, grab it firmly and wiggle it side to side in the tiniest increment possible while pulling up. When inserting, ensure the pins line up with the socket holes and ever so slowly push straight down. If you feel any resistance, stop and try realigning the pins with the socket holes again. Also... can't hurt to look at the pins and make sure they are all straight. After you've done it a couple of times, it becomes less of a magic trick... it's pretty simple stuff, actually.

Good luck!
Thanks! I did all of the swapping this am. Numbered the pre amp tubes (there are 5) and started by moving #1 to 2 and 2 up one slot etc right down the line. After each swap, turned on the Overdrive channel and still the bad hum.

When I did gently push down on the tube/socket for 4 (which was original tube 1) it made the most noise/popping/hum etc. So I am thinking it either IS tube #1 that is bad, or that socket for #4 is bad.

So now I have all the tubes back in the original slots. I will google the mannual and see which tubes drive the OD channel.

frustrating to have a new amp and not be able to play it! lol
 

LPMojoGL

Music Room Superstar
Silver Supporting Member
Messages
9,097
Sounds like #4 tube socket could be bad. They shouldn't make noise when you're messing with the tubes. So either the socket or that tube is shot. I'm off Monday and Tuesday, could take a look at it and bring some new preamp tubes if you wanna.
 

Roodboy

Member
Messages
1,478
Take the preamp tubes from the orange and put them in the jca that should rule out preamp tubes.
 

lang.murphy

Member
Messages
3,582
Yeah... the JCA50h page on the Jet City web site has a link to a manual, but it's for the 100w head, not the 50... and it doesn't detail which pre's do what.
 

DFWGuitarMan

Member
Messages
146
Thanks again for the help. Did the tap test on the all the tubes and it was clear that #1 was bad. Just changed it for a Groove Tube 12AX7-R that they had the local shop here. That definitley helped out alot. I will play it today and see if that did the trick

If not, I'll be PM'ing you LPMojoGL. Thanks alot for the offer. Of course I am on this forum so now I am wondering, hmmmm maybe I should change a couple more tubes out and see what she sounds like! lol
 




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