• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

midification to srpp preamplifier input voltage

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hello and happy new year to everybody

a friend gave me a srpp circuit that uses two 6n11 tubes (I have some vintage e88cc to use ) input voltage is 135v and 6v , but asa I'm in Italy it wouls be much easyer to have a 220v input so not need for a transformer,maybe just changing the value of a couple or resistors would be enought ?
anyone has the knowlwedge to exactly advice what to chenge ?
How can I put the circuit diagram following the message (please excuse but it' s the first image i try to put here on the forum) ?

Many thanks
Peace
 
Thomas is VERY right on this. Never rectify DC directly from AC mains. Ever.

If you need 135 volts DC then you will need an isolating step-down transformer, and you will need to do some calculations.

Duncan amp's PSU designer II is a free application that is good to use when starting out.

If you are new to electronics then PLEASE read the sticky thread on safety practices!

Ian
 
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:cop: Discussion of direct mains connection without a transformer is forbidden.

note two from the rules

While most projects on this site deal with electricity and construction which inherently involve some risk, particularly dangerous topics and procedures should include a warning in the thread that adequately explains these risks. Certain inherently dangerous topics are not allowed. At this time they include but are not limited to: discussing power supplies directly fed by mains current without a transformer, and mucking about in CRT video monitors. Posts and projects are those of individual members of diyAudio. The forum itself is not in the business of vetting projects or posts for safety, accuracy, performance, reliability, function, or fitness for use. If you attempt to make something and it blows up, or turns expensive parts into charcoal, or just doesn't work the way you were hoping, that's between you and the person posting the project or idea. The forum is merely a bulletin board which allows anyone to post ideas, criticisms, or discussions. It is up to the individual to make the final determination of how appropriate a project is for them to attempt, based on their own experience.
Thomas and Ian are 100% correct. Do not try this, and do not discuss it further. You are welcome to continue the thread if you discuss ways of solving your problem with a proper mains isolation transformer. :cop:
 
Hello and thanks for your wise advice

I'll definitely use an isolating step down transformer so 'll just stick to the project stamped on the circuit board , I just wanted to make the circuit simpler with direct rectification of 220 but semms thet' not a better option so . . . everything solved

the final (coupling?) caps rating is not adviced on circuit board so . . . 3,3 uf wima mkp ? would be good (if I find them at reasonable price maybe aurucaps) or smaller ?

Many thanks peace
 
Thomas is VERY right on this. Never rectify DC directly from AC mains. Ever.
Well, I guess you weren't around in the late 50's to build a few Knight kits that rectified directly off the AC line. Some had U shaped chassis so you could stick you fingers into the side of a hot chassis. Ah, the good old days. :D Oh, I know they used a resistor/capacitor scheme to ground the chassis but if the non-polarized AC plug was turned you still got a shock if you touched the chassis and something else. My favorite was the Ocean Hopper I built that the headphone jack came right off the 50C5 plate through a capacitor. You learned not to plug or unplug the headphones with the set on.
 
Any link to good toroidal step down transformer ? 220v in 135 + 6 double out

many thanks
peace

Hi Matt

It might be worth noting that Mouser carries Hammond transformers and will deliver by UPS for free if the order is something like $100 or so.. (even to europe). Hammonds are not torroidal but are ok for DIY when starting out.

Also, simulate the circuit in PSU designer II before you buy the transformer. Make sure you have a good idea of how many mA's you need to draw. Each triode of an ecc88 can draw ~10 mA (post the circuit and we can easily calc how much), which will drop your B+

If you are starting out then you will probably do silicon bridge rectification and CRC networking... This is of course the cheapest way to do it. But even a 5 Hy choke will make a big difference in the sound quality. You can also order Hammond chokes from Mouser. If you go for a choke then get one that can easily cover your mA's.

Ian
 
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Most people who are old enough to remember transformerless sets are also old enough to know they were dangerous. . ..

Many vintage vacuum tube table radios used mains direct rectification so they could be used on AC or DC, I have a 1950's vintage GE model. I recently restored a 1950's mono phonograph that used direct mains rectification retrofitting it with a stereo cartridge. Still mono but can now play stereo LP's without tearing up the groves. I did add an isolation transformer because in order to keep the hum low the pickup arm and turntable need to be grounded. That's just too much of a chance even with a new three prong AC plug. Also added a fuse it never had. Amplifier uses push-pull 50C5's, I added a second 12AX7 for the magnetic stereo pickup pre-amp. Speaking of old, would you believe that in 1970 when I started working for CBS radio in Chicago I went to the Palmer House for a news conference in the Grand Ballroom and discovered they still had working 110VDC outlets. I said "your kidding", no they weren't.
 

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