ALL TUBES ALL THE TIME

ozover50 · Post by **ozover50** » Fri Jun 10, 2005 4:56 pm

I got lost when they started talking about halves! All I ever knew (and probably need to know now) is that my 60s Goldentone 40 amp had EL34s in it!

Carry on, chaps!!

brammy · Post by **brammy** » Fri Jun 10, 2005 6:20 pm

>>>Try putting one of the Groove Tubes 12ax7M's in place of the JJ's one at a time and see if the hum lessons.

Yipes!!!!... and that leads us back to the beginning. Perhaps the amp tech DID know what he was doing and was doing just that.

ok... its off to the gig and I'll report back tomorrow. The saga of the AC-15 aint over as I will be trying the EI's at minimum and possibly the more expensive stuff.

soundmasterg · Post by **soundmasterg** » Fri Jun 10, 2005 11:04 pm

Hi Kent. The GT 12ax7M's are a relatively recent offering from GT. They're made in China and are supposed to be a copy of the old Mullard 12ax7. They're a good quality and good sounding tube, but a little overpriced. Your previous tech isn't all bad because he had these in there....but he also put in a 12at7 and a 12au7 if I remember your first post, so he was wrong there. You can run into hum problems with any tube that has a lot of gain, because more gain equals more hum. I have a NOS Sylvania that is very powerful and hums a lot. The JJ ECC83 has a reputation for lots of gain, so it isn't surprising that it might hum a bit more. The new JJ ECC803 is a long plate type 12ax7 that they just came out with and it sounds much more like an EI, or an old Telefunken, and it isn't quite as high gain either, so it would probably be quieter. If you remember back when I first replied on this post, I recommended that you just keep the GT 12ax7M's as they should be fine. Its ok that you got some others...because you learn by doing, and by trying out the new JJ's, you can see they hum a bit more. Now try subbing the GT's back one at a time and see if it changes. And when you get other brands like EI or NOS stuff, sub them in. You'll see that tubes are pretty individual and can sound quite different due to manufacturing tolerances and materials used. I use different brands of tubes depending on where they are going in my amp, and what amp they're going in. Familiarity with the tubes and their sounds help me to decide which one I want to use where.

Paul, thanks for the compliments. Tubes and tube amps are an obsession for me and I've been reading all I can get and experimenting for about 6 years or so, and that leads to me getting smarter as I go thankfully! Maybe one day I'll design and market my own amp but I'm not to that point yet!

revolver · Post by **revolver** » Sat Jun 11, 2005 7:06 am

Hey Greg,

Is it essential to have your amp recapped? Are there any signs that the caps might be going? I have a 1972 Hiwatt Custom 50 which I purchased from the original owner. I'm pretty sure it's never been done. Is this an expensive procedure?

rictified · Post by **rictified** » Sat Jun 11, 2005 8:13 am

Does it hum? Do the cans get hot when it has been running for a while? Hum is a sure sign, heat, maybe. Can be expensive, $100-$150. Or more depending on how bad the tech rips you off.
Be careful a lot of the younger techs know nothing about tube amps.

revolver · Post by **revolver** » Sat Jun 11, 2005 8:32 am

No hum, it runs hot, but it's always run hot. I've had the amp for ten years. It's only ever required regular maintenance twice. Just read somewhere about a recap and wondered how urgent this would be to do.

brammy · Post by **brammy** » Sat Jun 11, 2005 12:43 pm

Last night the amp sounded great. At the gig, the hum/buzz that I heard in my living room was almost non-existant. The only explanation I can think of is that I've finally found some confirmation of my theory that my neighbor is a space alien who is beaming his evil thoughts in my direction.... (these voices in my head aren't bothering you are they?)

But seriously, I think the AC-15 is in pretty good shape. My next step (I think) is to purchase a set of EI preamp and power tubes and see how that goes. That way I'll have the JJ's as backups. It'll be interesting to see the difference a change in brand can make.

soundmasterg · Post by **soundmasterg** » Sat Jun 11, 2005 2:26 pm

Dave, the filter caps are almost always an electrolytic capacitor. These type of caps have a limited lifespan, with the chemicals inside drying up after age, or due to non-use. They fail in different ways too.

I'll be recapping a 1958 Gibson GA20T for my uncle soon. In this one the caps physically look ok, but if you play the amp you get a loud buzz. The end result is that the caps are completely dried up and can not filter out the 60 cycle AC ripple, which is basically hum that is not getting into the amplification circuit and geting amplified out throught the speakers.

Another failure mode is that the caps will not look ok physically, but may still work to where you don't notice a problem. This happened on my brother's Silvertone 1484 Twin Twelve head. The positive end of the caps were bubbling. They used Planet brand caps in these which were very cheap (******) caps when made, and on the outside of the caps, it says "guaranteed for one year"!...hehe. The amp still worked with them in there, and it sounded fine, but the caps were well on their way to exploding. After replacing the caps, his amp now sounds a LOT better, with a tighter bass response, and overall, just a lot better sound. Less mushy and less indistinct/more articulation would be a good description of how it sounds now. The plate votlage of the amp also went up with the new caps. This tells me that the old ones were leaking current to ground when they shouldn't have been.

Good quality electrolytic caps nowadays generally have an expected lifespan of 10 years before you notice any problems or performance degrading. Older electrolytic caps were greatly inferior to modern stuff, and even though they appear to last longer with amps being original and still working from 50 years ago, if you speced out the amp, you would see the signs that the odler caps need to be replaced for the amp to perform as it should.

Now having said all of that, replacing old filter cap swith new ones WILL change the sound of the amp. It will put it back to how it sounded when new. This can be a good thing or a bad thing depending on what you like about the sound of that amp. From a strictly technical perspective, YES the caps should be replaced, just because of their age. BUT, if the amp still works ok, and if you physically look at the caps and don't see any bubbling on the positive ends, then you're fine and can leave it. If the caps are can caps, it can be hard to tell if there is any bubbling. If they are axial type caps, it is easy to see. Keep in mind, that if you elect to not replace the caps, they cna fail at any time, usually with an explosion that sounds like a firecracker....which can cause a fire, and also leaves highly corrosive chemicals inside your amp all over the other parts. In addition, depending on where the cap is in the circuit, if it blows, it can take your tubes and transformers with it when it goes. Depending on how many caps are in your amp, and how they are installed, it can be cheap, or expensive. The caps themselves range from a couple bucks apiece to twenty dollars apiece or more..just depending on what type of caps they are. The labor time involved can be lots or little, again depending on how the caps are installed in the amp.

Kent, I'm glad to hear the amp sounds good! When you do decide to get the EI's, try to buy from someone who screens the preamp tubes for microphonics, or you could have problems with that. You can get their EL84's anywhere because they don't really have that problem..its just their 12ax7 types that do sometimes. And don't be afraid to mix and match brands with the preamp tubes. You may like the sound options it gives you.

soundmasterg · Post by **soundmasterg** » Sat Jun 11, 2005 2:28 pm

I'll be recapping a 1958 Gibson GA20T for my uncle soon. In this one the caps physically look Have a correctino to make to that last post so no one gets confused!! What I said follows....

ok, but if you play the amp you get a loud buzz. The end result is that the caps are completely dried up and can not filter out the 60 cycle AC ripple, which is basically hum that is not getting into the amplification circuit and geting amplified out throught the speakers.

What I meant to say was....

I'll be recapping a 1958 Gibson GA20T for my uncle soon. In this one the caps physically look ok, but if you play the amp you get a loud buzz. The end result is that the caps are completely dried up and can not filter out the 60 cycle AC ripple, which is basically hum that is NOW getting into the amplification circuit and GETTING amplified out throught the speakers.

Sorry for the mistakes...my editor is on strike!

brammy · Post by **brammy** » Sat Jun 11, 2005 3:14 pm

>>>>When you do decide to get the EI's, try to buy from someone who screens the preamp tubes for microphonics, or you could have problems with that.

otay, will do. When I ordered from tubesandmore.com the sales guy said that they dont do that for preamp tubes. I'll need to find another vendor.

http://store.triodestore.com ?

soundmasterg · Post by **soundmasterg** » Sat Jun 11, 2005 4:10 pm

Ned at Triode electronics is a good guy, but I'm not sure if he screens preamp tubes or not. I think he had more older NOS stuff than new stuff last time I checked but I could be mistaken. You may post that question at ampage or the webervst amp boards and see what the opinion is.

revolver · Post by **revolver** » Mon Jun 13, 2005 5:43 am

Greg, thanks for the post, it was very informative. I'm going to have someone in town check out my Hiwatt and go from there.