Tube swap

TheBones

New member
Hey guys, just picked up a Kustom Defender 5h. For the price, a pretty decent little amp. I really like the clean tones I'm getting from it but when you really start to crank it up I find the drive to be rather harsh. I decided to swap out the preamp tube, first I tried a different 12ax7 and found little to no difference as far as clean headroom or tone. I decided to try a 12at7 and, to me, it was a vast improvement. More clean headroom. However, when the amp starts to break up, I still find the tone a little harsh for my liking. Should I try swapping power tubes next? I've thought about taking it to my local repair guy for some mods (master volume, tone knob). But if I can swap the pt myself and tone down the harshies to save a few dollars I figure that should be my first route. This is my first tube amp so I really have little to no experience when it comes to this stuff. Any suggestion? I'm not going to use the amp for much distortion, but when I crank it i don't want so much harshness. Thanks guys!
 

miroslav

Cosmic Cowboy
The 12AT7 has less gain (about 60% of a 12AX7)...so of course, it will provide more clean headroom.
Maybe it's the actual brand of tubes you tried...some of the Sovtek 12AX7 tubes are harsh, and many of the Chinese are too.
What tubes were they?
Is there just a single preamp tube, or are there more?

Also...it may be just the amp that has that tone quality, and you can swap tubes all day but never fully remove the harshness.
 

TheBones

New member
The tubes that came in the amp are Chinese. I swapped it out the a Russian groove tubes 12ax7 and then ended up liking the same brands 12at7. I realize it just might be the tone of the amp but I wanna do anything I can to tone it down a bit. Don't think switch the power tubes will help?
 

miroslav

Cosmic Cowboy
Well...tube swaps are about the easiest thing one can do to fine tune an amp or change up the tone flavor a bit, so by all means, try out some different tubes....though you have to buy a bunch so you can really see which work best for you. Just swapping out between two tubes may not have much difference.

What is the complete tube layout of that amp....from pre to power?
 

TheBones

New member
It has one pre amp tube and one power tube. It is a "single ended" (whatever that means) tube amp. It has only one knob "volume". Down for clean and up for dirty. Does that help?
 

Greg_L

Banned
Man if you have to do all this to a new amp, you got the wrong amp.

Nevertheless, maybe try an EQ pedal in front. By the time you spend money to mod that little thing and buy enough tubes to get the sound acceptable, you could have just bought an EQ pedal. I'm sure you can find one used for cheap.

By the way, love the avatar. Misfits are one of my all-time favorites.
 

TheBones

New member
El84. Haha yeah Greg I'm really digging the cleans I'm getting from it and that's the primary function of the amp for me anyway. I'm just trying to smooth out the rasp a bit. I expected to do some trial and error. Long time player, but never really got into gear too much. I've got a lot to learn so I figure I'll pick all the brains I can on here.
 

ranjam

New member
Me being the eternal tinkerer;
Kustom_Defender-5H_RevB.png

-Remove R15, R16, and C14.
-Don't add a Master or a tone control. If you have to have a tone control, replace R17 with a 100K linear taper pot.
-If you want some more low end, replace C1 with a .022uF/630VDC capacitor.
_Try different speakers.

That should give you enough to go and have some fun without spending much more cash than you already have.
 

TheBones

New member
Me being the eternal tinkerer;
View attachment 75731

-Remove R15, R16, and C14.
-Don't add a Master or a tone control. If you have to have a tone control, replace R17 with a 100K linear taper pot.
-If you want some more low end, replace C1 with a .022uF/630VDC capacitor.
_Try different speakers.

That should give you enough to go and have some fun without spending much more cash than you already have.

holy crap. i've never really tinkered with anything as far as removing r15, r16, and c14 etc. What exactly does that mean? should i take it to a shop and ask them to do that stuff for me or is it a noob DIY sort of task? i really appreciate that you have this information as i'm sure it's helpful in any case.
 

Bristol Posse

Okey Dokey
I once got my hands on some NOS vintage Mullard tubes at a garage sale for a pretty reasonable price. I was so excited, couldn't wait to get home and drop them into my amps and just bathe in the glory of vintage goodness that would now blast out of my amps.

Guess what... the difference was really, really subtle my vox AC 4 setup still sounded like a vox AC4, My fender Blues Jr still sounded like a Fender blues JR etc etc etc. there was perhaps a 0.01% improvement in "smoothness" or whatever. no radical change in the character of the sound the amp made.
So now I just buy groove tubes cos they're tubes, the quality is pretty consistent and they work. If I ever run into another garage sales when I can pick up some vintage tubes for the same price as modern ones I'll grab em but I'm not interested in paying anymore than current production

I'm with Greg on this one. If after you buy an amp you have to drop another hundred bucks on tubes to swap in and out and then another hundred on a speaker swap and then more still on different cabs and so on, and then tear it open and start clipping out components and replacing caps and pots (possibly electrocuting yourself in the process) then you bought the wrong amp! (especially when it's an amp that retails for around $100)

Either go to ebay and spend $30 on an EQ pedal or return the amp and add in the $200 you would have spent on "upgrades" to make the amp acceptable and use it all to buy the right amp

as always YMMV
 
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ranjam

New member
C14 is part of a treble peaking circuit. Just removing that, or R16, removes the peaking circuit. The gain will go up a little (but more in the bottom end), and removing R15 makes the gain go up a little more. To compensate for this, if too much gain is an issue, you can try a 12AY7 tube, or remove C5. But know 'full volume' effectively removes the peaking circuit. Think of it as an advanced 'Brite' cap like on your guitar volume, or a Fender 'Brite' switch; they're only effective at lower volumes.
'Remove them' means just take them out, and put nothing in their place. If you can solder in a pickup inside your guitar, you can do it here with a small circuit board. Use a solder removing tool ('Soldapullt' or something similar), some wick, and away you go.
Maybe I am too stupid to be scared, but since way back when tube amplifiers just seemed easy and fun to mess with. You get to a point where you can guess what will happen if you raise/lower/remove any resistor or capacitor. And that's all your amplifier is; resistors and capacitors. And bumping up C1 you know allows more low end through. Kustom uses a .01uF here, where every Fender/Marshall uses a .022uF for coupling. C5 is a Cathode bypass capacitor,; removing it reduces the gain quite a bit. Right now it's 10uF, and a 22uF cap would give more low end gain as well. There's 101 ways to increase/decrease the gain, but for simplicity I'm only saying ways that are just removing parts, and not radically changing values. Well, other than bumping up C1, but .01uF seems small.
What else? Oh, C15 and R17 are a quasi-Vox treble 'cut' circuit, but preset, as the schematic even states. You could make R17 a potentiometer, and have variable treble cutting.
Wanna try something really simple? Take some small side-cutters and just snip out either R16 or C14 close to the board. You can do this without even removing the circuit board. Just pop the chasis out, look for that resistor, and snip it close the body. It will be colored orange-orange-yellow. I've done this to the Marshall 'Brite' cap enough times to know it won't give you a 6dB increase, but maybe a 1dB or 2dB increase from maybe 200Hz or 300Hz down. And again, that's at less than '10' on the volume control.
 

miroslav

Cosmic Cowboy
I once got my hands on some NOS Mullards at a garage sale for cheap. I was so excited, couldn't wait to get home and drop them into my amps and just bathe in the glory of vintage goodness that would now blast out of my amps.

Guess what... the difference was really, really subtle...


Well tube swaps ain't going to change an amp dramatically into a different one...so yeah, if it's a Blues Jr, it will still sound like a Blues Jr as you say....but different tubes can make a difference and can help fine-tune the overall sound quality to your liking. Also, some amps don't "change" as dramatically with tube swaps as others can. It's all about experimenting.

Just out of curiosity, was that the only time you ever tried something else in you amp beside the current "Groove Tubes" stuff, which is mostly Chinese or Russian current production tubes...?
Not everything that has a famous brand name is going to have an outstanding effect, but yeah, like you said, you did notice some improvement with smoothness.
Also, unless you can test the tubes before even putting them in your amp...you have no way of knowing how good the tube is.

I don't think people need to loose their minds over tubes, but sometimes the stock tubes do suck and can make an amp harsh/fizzy sounding, so you don't really need to buy a different amp, you just need different tubes. :)

For the large amount of tube gear that I have between a bunch of guitar amps, rack gear and mics....I acquired a decent amount of tubes over the years. Lots of NOS stuff back before people started going insane with their prices.
I also have a decent tube tester to check and grade the tubes.
When I decide to try out some different tubes in an amp, I'll spend maybe a couple of hours experimenting with various combinations in the pre, rect, tone and power sections of a given amp, and sometimes it's exactly like you say, very subtle from one tube to another, but then there are some combinations that are quite noticeable (either in a good or bad way).
It's actually fun to experiment, though you need a good amount of spare tubes on hand, otherwise you can't get a sense of what a tube swap can do to a given amp from just a couple of tubes.
Oh...and I actually do also use current production tubes in some of my gear, so I'm not snobby about "NOS" tubes....I just like tubes, so I keep a good stash for now and future use. :cool:
 

Bristol Posse

Okey Dokey
Just out of curiosity, was that the only time you ever tried something else in you amp beside the current "Groove Tubes" stuff, which is mostly Chinese or Russian current production tubes...?
Not everything that has a famous brand name is going to have an outstanding effect, but yeah, like you said, you did notice some improvement with smoothness.
Also, unless you can test the tubes before even putting them in your amp...you have no way of knowing how good the tube is.

I used to be into hunting around for that kind of stuff, I also have a friend who owns a public storage place and does a lot of those auctions of the contents and he keeps an eye out for tubes for me and a couple of other friends. He also has access to a tube tester so we can see if they are still good,

In the past I've used Groove Tubes, Sovtecks & Tung Sol and I think Electro Harmonix as well as vintage Mullards, GE and RCA etc. I stick with GT for now because that's what my local music store carries and I like to support my local economy and be able to wander in and grab some when I need them. If they switch brands I guess I'll switch brands. My vox setup now has GTs in it, I still have NOS Mullards in the Blues Jr. That amp runs pretty hot and the Mullards are a little tougher than current production stuff and seem to stand up to it a little better but when I run out it's going to get whatever the local store has.

I'd say that If you find a great amp that you really like then a couple of little mods like a tube or speaker swap to push it over the top are certainly in order but I'd never try an fix an amp that I just can't get on with by spending three times the value of the amp on modifications, I'd just save my pennies and buy an amp that does work for me

As always YMMV
 

miroslav

Cosmic Cowboy
... spending three times the value of the amp on modifications...


Oh I agree.

I've seen guys do it...spend crazy money on mods, and then sometimes they end up selling the amp on eBay, saying how it's the best sounding amp with all the mods.....
...but I have to ask myslef, "WTF is he selling it for if it's so great with all the mods"? :D


Sometimes people just get all caught up chasing their elusive tone to die for......
 

TheBones

New member
Me being the eternal tinkerer;
View attachment 75731

-Remove R15, R16, and C14.
-Don't add a Master or a tone control. If you have to have a tone control, replace R17 with a 100K linear taper pot.
-If you want some more low end, replace C1 with a .022uF/630VDC capacitor.
_Try different speakers.

That should give you enough to go and have some fun without spending much more cash than you already have.

so ranjam, if i take these steps what should i expect as far as changes? i guess what exactly does this stuff do to the tone etc.? i like the cleans i'm getting and i don't wanna sacrifice the cleans i'm getting just to smooth out the distortion because i bought it as primarily a clean amp…
 

Greg_L

Banned
Man, listen, I'm sure ranjam gave you some good advice and DIY mods are always cool, but don't go snipping bits and pieces in your new amp if you're not 100% comfy with doing so..
 
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