Question for those who might know

P Thought

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I didn't want to barge in on @Midgetje94's thread, about tubes, because my question is not exactly related to his, but it's sort of close.

I have a Peavey Delta Blues 1 x 15, an older one I think, that I bought a year or two ago. Everything works, and it sounds good while I'm playing it. That I like. But when it's idle there's a noise floor, kind of like the hiss you get on your radio when it's between stations, and it's pretty loud even when the guitar volume is turned all the way down (I keep the amp volume up a ways and use the guitar's volume control so it sounds good at home volume.)

My question is: would a new set of tubes be likely to fix this? Do I need to drag the amp and my ignorant butt down to the shop (I don't know much about the qualifications of the local tech, either way) and hope I don't get hosed; can I replace the tubes myself; or should I just leave it alone and learn to like it?

Delta Blues and Simple.jpg
 

northernguitar

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I think you need to adjust bias on output tubes. Or, some tube vendors might select tubes that work well with the factory setting. I’d buy a backup set and try them out. As long as the tubes aren’t redplating you’re likely alright. If not, I reckon a basic bench fee would cover the cost of a tech biasing it.
 

JL_LI

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Mesa Boogie sells low noise 12AX7 preamp tubes as SPAX7 tubes. They’re apparently selected for low noise. I replaced the five 12AX7 tubes in my Express 5:25 with them and hiss became significantly less noticeable. They were a few dollars more than other tubes but a good value because they did exactly what I bought them for.
 

Chiogtr4x

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I didn't want to barge in on @Midgetje94's thread, about tubes, because my question is not exactly related to his, but it's sort of close.

I have a Peavey Delta Blues 1 x 15, an older one I think, that I bought a year or two ago. Everything works, and it sounds good while I'm playing it. That I like. But when it's idle there's a noise floor, kind of like the hiss you get on your radio when it's between stations, and it's pretty loud even when the guitar volume is turned all the way down (I keep the amp volume up a ways and use the guitar's volume control so it sounds good at home volume.)

My question is: would a new set of tubes be likely to fix this? Do I need to drag the amp and my ignorant butt down to the shop (I don't know much about the qualifications of the local tech, either way) and hope I don't get hosed; can I replace the tubes myself; or should I just leave it alone and learn to like it?

View attachment 921285

I'm not as DIY adventurous' or really knowledgeable as many on TDPRI, but I do have the experience of many years playing tube amps...

(note: I'm actually gigging small SS amps now, and happy)

...to have learned one truth ( from my own trial and error):

A real tube amp tech ( if you don't know how amp stuff, like me!) is invaluable!

They may cost a few $$, but they are the ones that track down, noise/hums/ distortion, that may have nothing to do with tube replacement- and that can keep someone like me from throwing money at tubes, thinking that's the issue.
Sometimes tubes are the issue, but I
am more comfy with a pro making the call.
I know this is maybe a too cautious or conservative opinion, but I just know the fantastic work that the same MD tech has done for me, and about 8-9 of my guitar and bass buddies, and
the at-large DC-aea guitar community.
We all 'know the guy!'
 

bebopbrain

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There are easy tests.

You have already done one helpful test: turning the volume down to zero. This shows that V1A is not the (only) problem, since there is still hiss.

How about when you turn reverb to zero? Trem intensity and speed to zero?

V2 is only used when, I believe, boost is enabled (or is the channel selection?). Otherwise, V2 is bypassed by 12V relays. If you leave boost off, do you get the hiss? Leave boost off and swap V1 with V2. Still get the his? Then V1 and V2 are not the (only) problem. Go ahead and swap either with V3. Still have hiss? Your preamp tubes are not the issue.

I would try pulling two output tubes at a time. I wouldn't crank the amp for hours that way, but for a noise test it should be OK.

I doubt it is tubes.
 

dougstrum

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Simple thing to do would be clean the tube sockets with contact cleaner, and try a different 12ax7 in the first spot.
Either of those may help without opening the amp up.
Otherwise with your level of comfort working on an amp it's probably best to find a tech.
Always try the simple stuff first;)
 

Midgetje94

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Hey I got a shout out! And no issues here! I don’t mind tangent rabbit holes on my posts. But seems you got great information here!

AND it helps me! Haha. Installing tubes and adjusting them is something I’ll need too!

luckily I have a amp builder like 6 mins from my apartment. He makes the Crossfire amps. Mainly a lot of local guys. I’ve seen them online and various guitar centers. He was gracious enough to fix my Crate VC50 when I got it.
 

hepular

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it is likely time to replace the filter caps. which is probably a job for a qualified tech, given the peculiar construction of those amps. you wouldn't that to be your fist experience in diving into the interior of a tube amp . . .
 

mfguitar

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Telekarster

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Cleaning tube sockets sounds like something I might pull off. Will somebody run through the procedure real quick?

Giving your thread a bump here but also, FWIW, I'm the same as you. I can swap tubes out fine but outside of that, it's amp tech time ;) I wish I knew more about em though. When I was a kid my Dad would clean sockets with some sort of electronic cleaner stuff, pull the tube in and out a couple times, and call it good. This was on our floor model Zenith radio, or our TV set, stuff like that.... not guitar amps. My Dad was a music lover but not a musician. There's this stuff called deoxit that I see mentioned out here quite a bit. I suppose it's the modern version of the stuff my Dad used decades ago? Anyway, here's a link to the MFG that makes the stuff

https://caig.com/deoxit-d-series/

Hopefully some of the techies out here can further advise
 

King Fan

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You have new hiss? Old hiss? Tubes can hiss. You’re smart to see that tube swaps are a tech step you can do; they're a near-universal first test for new amp noise. The smart post by @bebopbrain may even save you buying all new 12AX7s — V1, often the most common suspect in a typical amp, is ruled out by the volume knob thing.

But folks who use tube amps need backup tubes. Even one new AX7 would be a big step in a smart direction — you can swap them out one at a time with the new tube. And we can hope those are more more suspect than the what, 4xEL84s?

Socket cleaning is a good plan too, tho IME sometimes sockets make more crackle than hiss. Are you comfortable opening the (unplugged) amp and discharging the caps?
 

darkwaters

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A 12ay7 always works for me. If you’re not into lower gain, a good NOS 7025 should certainly knock the noise floor way down. In V1 of course.
 




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