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Old 3rd January 2013, 07:16 AM   #1
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Default midification to srpp preamplifier input voltage

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
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Old 3rd January 2013, 07:52 AM   #2
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Hi!

Do you mean the circuit does not use a mains transformer? Such circuits are very dangerous and absolutely not recommended unless you know exactly what you are doing and everything is properly isolated including signal in- and outputs. Other wise such circuits can be lethal!

Best regards

Thomas
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Old 3rd January 2013, 08:04 AM   #3
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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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Old 3rd January 2013, 08:36 AM   #4
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Discussion of direct mains connection without a transformer is forbidden.

note two from the rules

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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.
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Old 3rd January 2013, 12:22 PM   #5
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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
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Old 3rd January 2013, 12:23 PM   #6
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Any link to good toroidal step down transformer ? 220v in 135 + 6 double out

many thanks
peace
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Old 3rd January 2013, 04:35 PM   #7
kevinkr is offline kevinkr  United States
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Bartolucci may be able to help you with a suitable transformer, also plenty of manufacturers of trasformatori in the EU..

HI (Link to Audiomarketing/Bartolucci)

For some strange reason I cannot find an Italian language page for them..
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Old 4th January 2013, 03:01 AM   #8
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Quote:
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. 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.
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Old 4th January 2013, 09:48 AM   #9
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Most people who are old enough to remember transformerless sets are also old enough to know they were dangerous, even at 110V. Younger folk might not recognise a hazard they have not seen before. 220V is likely to be more dangerous than 110V.
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Old 4th January 2013, 12:31 PM   #10
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Quote:
Originally Posted by MattWatt View Post
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

Last edited by soulmerchant; 4th January 2013 at 12:35 PM. Reason: typo
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