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50L6 guitar amp
50L6 guitar amp
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Old 18th March 2019, 03:10 AM   #91
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by Tubelab_com View Post
Yes, you can put a switch on the cathode bypass cap. There may be a thump when the switch is flipped as the cap gets charged.
George didn't mention it, but simply putting a large resistor in parallel with the switch will get you thump-free switching. The resistor lets the cap charge up to the right DC voltage in advance, but the big resistor doesn't let it bypass the cathode until the switch is flipped.

The exact value of the resistor is not important. It needs to be much bigger than the actual cathode bias resistor (470 ohms in your schematic.) And it needs to be small enough to supply whatever small leakage current the 100uF cap needs, so don't use an enormous value such as 1 meg. I picked 22k for the schematic, but anything from 10k to 100k should work just fine.

The picture shows what I mean. (Please ignore the weird pentode model name and pin numbering - I just grabbed the first pentode symbol I found in Kicad, to stand in for your 50L6.)

-Gnobuddy
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Old 18th March 2019, 01:22 PM   #92
hex69 is offline hex69  Canada
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Originally Posted by Tubelab_com View Post
Yes, you can put a switch on the cathode bypass cap. There may be a thump when the switch is flipped as the cap gets charged. You can also experiment with different resistors in series with the cap.
That's what I'm gonna do.. I wonder why any commercial amplifier is having that switching option?

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Originally Posted by Tubelab_com View Post
Feel free to steal any of the switch ideas I used.
Had a look at your schematic.. will try some of them next time I jump on the breadboard!

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Originally Posted by Gnobuddy View Post
The inescapable conclusion from the first two videos is that a good guitarist, who knows what he's doing, can sound fantastic with a $100 guitar and $200 tube amp.
Indeed, the habit doesn't make the monk! A friend of mine was playing on a little 'home stereo', we were young and poor but he was (and still is) a very good guitarist, nowaday he's working to make musical tracks for 'Cirque du Soleil'.

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Originally Posted by Gnobuddy View Post
but simply putting a large resistor in parallel with the switch will get you thump-free switching. The resistor lets the cap charge up to the right DC voltage in advance, but the big resistor doesn't let it bypass the cathode until the switch is flipped.
I see.. I didn't experienced any thump while I tested on the breadboard but it's very good to know, I will use it anyway to stay on the safe side.

Many thanks gentlemen for the switching ideas and little drawing, picture is worth a thousand words!
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Old 18th March 2019, 01:40 PM   #93
Tubelab_com is online now Tubelab_com  United States
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I wonder why any commercial amplifier is having that switching option
Because switches are expensive.

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A friend of mine was playing on a little 'home stereo'
My first "guitar amp" was a hacked Magnavox mono HiFi from the 50's. It actually sounded pretty good for the surf music that I played in the 60's, except for the lack of reverb.
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Old 18th March 2019, 02:57 PM   #94
hex69 is offline hex69  Canada
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Originally Posted by Tubelab_com View Post
Because switches are expensive.
Long life to the DIYers!! We save money (just like they do) without any comprimise!

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Originally Posted by Tubelab_com View Post
My first "guitar amp" was a hacked Magnavox mono HiFi from the 50's. It actually sounded pretty good for the surf music that I played in the 60's, except for the lack of reverb.
As my memory goes my first ever guitar amp was a Lloyd home stereo with the big 8 track on it, I can't remember the hack I did to plug the guitar into it but for the music I was (trying) to play at this time, it was in the 80s and I was looking for a distorted sound to play rock and all that I have was a broken Boss DS-1 which I had to hook in reverse in order to make it work Good old time!

About one year later I came across such a deal, it was Fender Super Reverb that a guy was using to listen the music, no cabinet only the chassis sat on the table.. I asked how much he wants for it.. He said, give me 20$ so I can get some beer and it's yours. A couple of month later I came across a Marshall JTM50 1969 (blonde face) and the girl was asking 200$, it was like new.

I don't have these amplifiers anymore today, wish I knew about their values at this time
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Old 18th March 2019, 07:23 PM   #95
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by hex69 View Post
...the habit doesn't make the monk!
I like that saying! I've never come across it before. It says a lot in a few words.

Now the big question is, does the monk build guitar amps?


-Gnobuddy
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Old 19th March 2019, 03:00 PM   #96
hex69 is offline hex69  Canada
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Originally Posted by Gnobuddy View Post
I like that saying! I've never come across it before. It says a lot in a few words.

Now the big question is, does the monk build guitar amps?


-Gnobuddy
I think it's a french proverb, hope I didn't say something bad by translating word for word, it was meant to say that you can't judge a book by its cover, or clothes don't make the man.

Can you picture this -> Made (deep) in the Himalayan Mountains using ancient methods to infuse all amplifiers with spiritual energies! Warning: Do not play for more than an hour, danger of levitation!
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Old 19th March 2019, 06:43 PM   #97
Gnobuddy is offline Gnobuddy  Canada
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hope I didn't say something bad by translating word for word
No, not at all, I understood exactly what it meant. Somehow the message seems clearer to me than other proverbs with the same message. Particularly now, when peoples lives are filled with so much shallow nonsense coming from every direction, that hardly anyone can even tell what is shallow, and what is deep, any longer.

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Warning: Do not play for more than an hour, danger of levitation!
Yes, I can totally see that...it's no worse than mpingo discs: The Magic of Mpingo


-Gnobuddy
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Old 19th March 2019, 10:10 PM   #98
hex69 is offline hex69  Canada
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Yes, I can totally see that...it's no worse than mpingo discs: The Magic of Mpingo-Gnobuddy
Makes me think of walnut bracelet.. since the beginning of human society some would do (and say) anything to make money, all is relative they say but personnaly I don't believe in such concepts. If it's good for someone I'm okay however. For sure, some high quality (and expensive) gear are nice too, I think it's a matter of 'priorities'.. If I would do something professionnaly or in a serious way and I have the money.. why not! On the other hand, by comparing oranges with oranges, seems that all low quality gears holding a big brand name will be some kind of over-priced.
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