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Guitar amp, and PP Tubecad Calculator
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Old 30th January 2018, 10:01 PM   #11
john65b is online now john65b  United States
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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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Old 31st January 2018, 12:46 AM   #12
PRR is offline PRR  United States
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Originally Posted by john65b View Post
...if I can just find a pair of metal 6SL7 (yeah, not gonna happen, right?)...
6L7 is the same tube, only better, and often supplied in metal. AND has a grid-cap, kewl! But you probably want 6J7.....

Last edited by PRR; 31st January 2018 at 12:49 AM.
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Old 31st January 2018, 01:57 AM   #13
john65b is online now john65b  United States
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But they are not dual triods, correct...pentode / heptode...

I have many 6J7...
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Old 31st January 2018, 01:07 PM   #14
Tubelab_com is offline Tubelab_com  United States
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I can just find a pair of metal 6SL7 (yeah, not gonna happen, right?)
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.
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Old 3rd February 2018, 07:32 PM   #15
john65b is online now john65b  United States
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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!
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Old 3rd February 2018, 09:57 PM   #16
Tubelab_com is offline Tubelab_com  United States
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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.

Quote:
I am gonna have to pull out those metal 6V6 again...
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.
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Old 4th February 2018, 12:05 AM   #17
john65b is online now john65b  United States
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just keep the screen grids down around 125 volts and nothing bad will happen
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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Old 4th February 2018, 01:36 AM   #18
Tubelab_com is offline Tubelab_com  United States
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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.

Quote:
great trannies and can be had for under $40...unreal deal...
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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