Hello all,
Just finished my Guitar amp build based on the Ampeg B15N schematic...a 6L6 PP based output and a pair of 6SL7 input tubes doing the amplification and phase splitting...but I have a question...
Using PP Tubecad on my output I see that the 3rd and 5th Harmonic Distortion numbers quite high on the EL34, a fair bit better 6L6GC, and surprisingly rather low on KT88 - around 1/4th of the EL34...
Now I have listened to all three and have made my choice of what pleases me the most...
But question is the Odd Order harmonics - is it "good" to keep them low on a guitar amp? Is it nothing more than a myth that the high Odd Order Harmonics are what makes the "Marshal" sound and the dominant Even Order Harmonics make the "Fender" sound?
I don't know if it is just a coincidence that the EL34 have the highest Odd Order and the Marshals (I know of) run EL34 output tubes...
Again, it really doesn't matter in the end as I know which one I most like, but just asking in general...
BTW - great sounding amp - I rebuilt this thing at last three times before I realized the secret to removing all the Hum was just elevating the heaters...duh.
Just finished my Guitar amp build based on the Ampeg B15N schematic...a 6L6 PP based output and a pair of 6SL7 input tubes doing the amplification and phase splitting...but I have a question...
Using PP Tubecad on my output I see that the 3rd and 5th Harmonic Distortion numbers quite high on the EL34, a fair bit better 6L6GC, and surprisingly rather low on KT88 - around 1/4th of the EL34...
Now I have listened to all three and have made my choice of what pleases me the most...
But question is the Odd Order harmonics - is it "good" to keep them low on a guitar amp? Is it nothing more than a myth that the high Odd Order Harmonics are what makes the "Marshal" sound and the dominant Even Order Harmonics make the "Fender" sound?
I don't know if it is just a coincidence that the EL34 have the highest Odd Order and the Marshals (I know of) run EL34 output tubes...
Again, it really doesn't matter in the end as I know which one I most like, but just asking in general...
BTW - great sounding amp - I rebuilt this thing at last three times before I realized the secret to removing all the Hum was just elevating the heaters...duh.
TCJ = TubeCad Journal, afaik, the PP Calculator only models triodes and triode-connected pentodes/beam tetrodes. So the distortion profiles do not really tell you much when those tubes are used in guitar amps...
Which sounds best? The 6L6 - the GE metal can 6L6...not Sovtek 6L6GC or other 6L6GC I have (yup, I know the dissipation difference between the two)...crazy, but me likes! And they are dirt cheap too...just found a pair in my stash and decided to try them...
But in general, Odd Order Harmonics are to be avoided in design, or is it a myth...
But in general, Odd Order Harmonics are to be avoided in design, or is it a myth...
Odd order above the 3rd harmonic are not "musical," IE they don't fall close to a standard note that would be used in the same scale as the fundamental, and tus may sound dissonant in the presence of the fundamental and other notes of the same scale.
This applies to HiFi amps, especially those used to listen to complex music where many notes are sounded simultaneously.
A screaming lead guitar is usually a single note, or a power chord (one chosen such that the IMD products are not terribly dissonant). The "proper" distortion profile is the one that the user likes.
I must have blown up 50 or so metal 6L6's in my high school days. At the time they weren't cheap, they were FREE!!! Several hundred brand new RCA's were donated to our high school electronics class by the local US Air Force base. They did sound awesome as the paint was peeling from the can!
I was given a box full of old metal tubes at a hamfest. There were a pair of metal 6L6's, and EIGHT metal 6V6's along with some other metal tubes suitable for preamp duty......time for an all metal amp?????
The TCJ simulator does only do triode connected tubes, and no simulator on earth can accurately model a guitar amp overdriven by a pedal board set on KILL!
And there we have it!
I also found a few Metal 6v6 too (Sylvania?)...they definitely cannot take the punishment that the glass JJ 6v6 can...
But no paint peeling off the 6L6 yet, but I did manage to raise the 250 ohm cathode resistor to over 325 - 375 to slow the 'burn"... they sound pretty sweet...
Now if I can just find a pair of metal 6SL7 (yeah, not gonna happen, right?), I, too, could have an all metal guitar amp...
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6L7 is the same tube, only better, and often supplied in metal. AND has a grid-cap, kewl! But you probably want 6J7.....
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I don't think that they were ever made......but all is not lost.
The 6SC7 is a twin triode Mu of 70 similar to the 6SL7, except its cathodes are tied together......still good for a PI, and some gain stages. The 6N7 is similar to the 6SN7 but it's cathodes are also tied together.
So for preamp what we really want is a metal 12AX7, right......like you said....ain't gonna happen, but there ARE single triodes with a Mu of 100. The 6SQ7 is a common old radio tube available in metal and glass, just ignore the diode plates. The 6SF5 is another Mu 100 triode, also available in metal or glass, but not quite as common. The 6C5 is half of a 6SN7 Mu of 20.
The 6SJ7 is a pentode that makes a nice voltage amp, or can be triode wired. My first DIY guitar amp was built in the 60's using a Fender Champ 5C1 schematic. It used a 6SJ7, a 6V6 and a 5Y3.
There are some metal rectifiers, but I can't recall the numbers right now. There is a metal gas rectifier that doesn't need a heater winding it's the 0Z4, common in 40's and 50's car radios.
I was in a destructive mood this morning...so I put in a pair of old Tung Sol 6Y6 (I found these in a dumpster at work - they used to have them running the control system at the Oil Refinery I work at) in place of the 6L6... Now the Ampeg B15N I built has Cathode bias with a single 250 ohm resistor, followed by a 250 ohm pot (I put this pot in - not part of original design)... with the 6L6GC, I have the pot at 0, and with the 6L6 I have the pot at maybe 50 - 100 ohms (its a metal can and cannot see the plates glowing - so far so good)...anyway, I had the pot at full 250 ohm and the plates did not glow, so I plugged in and played the guitar. It actually sounds nice...breaks up nearly the whole time. Sounds really aggressive when I jump on it, and quite sweet when I turn it back. I turned the pot down a bit but looked like the tube was having a little difficulty...I called it ORP (Onset Red Plating), so I put the pot back...I'm thinkin' this may even sound better than the 6L6...I should have around 350v on plates...This tube should not be able to survive this kind of abuse!!
The 6Y6 is a 12 watt tube, like a 6V6?
I am gonna have to pull out those metal 6V6 again...
And this is the tube got me laughed at years ago when I mentioned it here!!!
Ha!
The 6Y6 is a 12 watt tube, like a 6V6?
I am gonna have to pull out those metal 6V6 again...
And this is the tube got me laughed at years ago when I mentioned it here!!!
Ha!
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Shhhh. Laughs or not, I have squeezed 40 watts out of a pair of 6Y6's WITHOUT GLOW!!!! The secret, abuse the plate voltage all you want. I have been to 400 volts without issue, just keep the screen grids down around 125 volts and nothing bad will happen. The red glow of death starts at around 400 volts into a 3300 ohm OPT. By then you are over 40 watts output.
My tubes are the 6Y6GA, they have a bit more room to radiate heat than the smaller 6Y6GT, but even the little guys can eat 350 volts........the 6W6 types can eat this abuse as well, just keep the screen voltage down.
Note: Except for heater voltage the 6W6 = 12W6, 25W6, 12L6, 25L6, and 50L6. The 6L6 and 35L6 are different and not related to each other. The 6GC6 is a 6W6 in a fat 9 pin bottle. These can all eat lots of plate voltage if G2 is kept around 125 to 135 volts, and they ROCK doing it.
I stuffed 4 of the metal 6V6's into a HiFi amp that I am designing and turned pots until I got some nice sound and about 30 watts per channel. I began to wonder if a nuclear meltdown was going on inside that metal can. I popped the metal tubes out and stuffed some 40's vintage glass 6V6GT's in the amp and nothing was cooking. I did decide to save the 6V6's for a guitar amp.
I'm really thinking about the all metal amp......the 6V6's would look cool with an aluminum finned heat sink on them! I have plenty of small tubes for driver and gain stages.....I just have to find some more of those Mu = 100 triodes. I only have one. They used to be common in the old radios I cannibalized as a kid making guitar amps.
My tubes are the 6Y6GA, they have a bit more room to radiate heat than the smaller 6Y6GT, but even the little guys can eat 350 volts........the 6W6 types can eat this abuse as well, just keep the screen voltage down.
Note: Except for heater voltage the 6W6 = 12W6, 25W6, 12L6, 25L6, and 50L6. The 6L6 and 35L6 are different and not related to each other. The 6GC6 is a 6W6 in a fat 9 pin bottle. These can all eat lots of plate voltage if G2 is kept around 125 to 135 volts, and they ROCK doing it.
I stuffed 4 of the metal 6V6's into a HiFi amp that I am designing and turned pots until I got some nice sound and about 30 watts per channel. I began to wonder if a nuclear meltdown was going on inside that metal can. I popped the metal tubes out and stuffed some 40's vintage glass 6V6GT's in the amp and nothing was cooking. I did decide to save the 6V6's for a guitar amp.
I'm really thinking about the all metal amp......the 6V6's would look cool with an aluminum finned heat sink on them! I have plenty of small tubes for driver and gain stages.....I just have to find some more of those Mu = 100 triodes. I only have one. They used to be common in the old radios I cannibalized as a kid making guitar amps.
So Triode connected 6Y6 with high plate voltage not possible??
I found some more 6Y6GC - these have specs that go to 350V on the plates...I have to check the screen voltage, but with the 6L6, the screen voltage was just a tad under the plate (I only have 1k screen resistors)...I guess if I am seriously considering using the 6Y6GC, I need to up those screen resistors...
I remember seeing amp schematics that had the screen resistors on 6V6 based amps rather low, and screen voltage was high (compared to the 6L6) I guess not quite same on 6Y6GC...
My output transformer is from a 40wpc Fender Hot Rod Deluxe (Freakishly good amp, BTW) and around 4200 ohm. These are great trannies and can be had for under $40...unreal deal....The Power transformer for the Fender HRD is around $55. You can build a monster kick a$$ guitar amp with these two....
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Any time I have tried to stuff more than 150 volts into the screen grid of a 6Y6 or 6W6 type, bad things happened. I was not using cathode bias, so a big enough cathode resistor may help, but there is probably a limit somewhere.
I have fried a 6W6 trying to triode wire it. The datasheet shows 300 volts in triode for TV vertical amp service, A TV vertical amp is essentially a 60 Hz linear class A single ended amplifier, so I tried 300 volts for audio. It fried. Previous experiments running TV sweep tubes in triode have also ended with fried tubes. It took me a couple of years and several toasted tubes before I figured it out.
Every failure I had in an audio amp was when it was idling, just sitting there doing nothing. Idle is worse case dissipation in ANY class A amp since no power is coming out. It's all being burned up in the tube. A TV set doesn't have a volume control on the sweep. It runs at full output all the time. If it didn't the picture would shrink.
Back in the 90's I built a lot of guitar amps. I found a deal on some OPT's that were custom made for ADA right as their factory burned down, hence the transformers were on the surplus market. I bought 200 "80 watt 6600 ohm" P-P transformers for amp building. I still have a few left. They work as a 6600 to 0-4-8-16 ohm, or 3300 to 0-2-4-8 ohm OPT. I have stuck them in everything from guitar amps to high end HiFi amps. That's all I'll use until I run out of them. I tend to use Antek toroids for cheap power transformers.
Another deal is the 6K7VG from Allied Electronics. I was buying them in the 90's for $30 something. Now they are $50 something. They will power a KT88 amp to the 60+ watt level. 375-0-375 volts at 175 mA with 5 and 6.3 volt windings. It's essentially a Hammond 274BX for less money, made by Hammond.
I have fried a 6W6 trying to triode wire it. The datasheet shows 300 volts in triode for TV vertical amp service, A TV vertical amp is essentially a 60 Hz linear class A single ended amplifier, so I tried 300 volts for audio. It fried. Previous experiments running TV sweep tubes in triode have also ended with fried tubes. It took me a couple of years and several toasted tubes before I figured it out.
Every failure I had in an audio amp was when it was idling, just sitting there doing nothing. Idle is worse case dissipation in ANY class A amp since no power is coming out. It's all being burned up in the tube. A TV set doesn't have a volume control on the sweep. It runs at full output all the time. If it didn't the picture would shrink.
Back in the 90's I built a lot of guitar amps. I found a deal on some OPT's that were custom made for ADA right as their factory burned down, hence the transformers were on the surplus market. I bought 200 "80 watt 6600 ohm" P-P transformers for amp building. I still have a few left. They work as a 6600 to 0-4-8-16 ohm, or 3300 to 0-2-4-8 ohm OPT. I have stuck them in everything from guitar amps to high end HiFi amps. That's all I'll use until I run out of them. I tend to use Antek toroids for cheap power transformers.
Another deal is the 6K7VG from Allied Electronics. I was buying them in the 90's for $30 something. Now they are $50 something. They will power a KT88 amp to the 60+ watt level. 375-0-375 volts at 175 mA with 5 and 6.3 volt windings. It's essentially a Hammond 274BX for less money, made by Hammond.
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