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Old 15th April 2006, 04:30 PM   #11
Giaime is offline Giaime  Italy
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You know what?

Those photos were taken yesterday night at a friend's house, we were willing to try my preamp with his wonderful audio chain.

As soon as I flipped on the power switch, smoke come out of the power tranny

This morning I replaced the PT, it was a poorly done solder joint that shorted the B+ on the chassis

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Old 15th April 2006, 05:32 PM   #12
poobah is offline poobah  United States
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Giaime,

Get some paper and tape... and then paint those capacitors!


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Old 15th April 2006, 05:39 PM   #13
Giaime is offline Giaime  Italy
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No no no I like them, they're pricey Nichicon!!!
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Old 15th April 2006, 08:48 PM   #14
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Quote:
Originally posted by Giaime

As soon as I flipped on the power switch, smoke come out of the power tranny

This morning I replaced the PT, it was a poorly done solder joint that shorted the B+ on the chassis

Have you heard of something call'd fuse?

But serious, thats a very nice pre!

Still waiting for my funds to make mine. My SE amp with 6l6 ended up with a much simpler powersupply becouse I ran out of money.
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Old 15th April 2006, 11:23 PM   #15
Giaime is offline Giaime  Italy
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Fuse, amazingly, didn't blow. But I'm starting to think that 1A is a bit overrated

You're right, funds is the thing that block me. I have to study at the university...

if not, my preamp would have been:

- all octal
- all tube regulated
- 2 chassis (power supply and signal path)
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Old 16th April 2006, 10:07 AM   #16
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Hi Giaime,

Ah, you are also in the student group... Well, at least your a little higer up in the system. Its a couple years left before I'm going to the univeristy.

Forgot to mention a thing that I also do to protect my circuit and transformers. In preamplifiers and other equpitment that don't use much power or have large resistans in the powertransfomer, I usally put a small value resistor in series with the ht winding, if its center tap'd, one from each side from the tap, if not, one on each side of the winding. The value usally is from 4.7ohm-10ohm. low value for more power full transformer, 1watt metall reistors are fine. That trick saved me once. Only the reistors burn'd. But, of course, you need to solder clean and solid before the resistors...
Oh, sorry, that was mean, couldn't resist. Please forgive me.

Have a nice day!

Best regards,

Magnus Kofoed

Ps, 1 amp is way to much! I have a 250ma fuse in my power amplifer! I live were it is 230v. Double it if your living in a country with 110v.
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Old 16th April 2006, 01:44 PM   #17
Giaime is offline Giaime  Italy
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Thank you very much Magnus Kofoed for you reply.

I do live in a 220V country, and I must admit that 250mA fuse blows, but I'm using fast ones. I'll get some retarded ones and try. You're right, obviously. On more "expensive" project I'll fuse everything on the back panel (both mains and HV, and if it's an amp I'll fuse EACH output tube).

Money is not too much... I'm now listening to a 1.6W triode connected EL84SE. Sound is good, but frequency measurements show a not-so-hi-fi response...
Attached Images
File Type: gif frequency response.gif (7.5 KB, 349 views)
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Old 16th April 2006, 09:59 PM   #18
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Hi,

Haha! I must admit that your freq. response once and for all says that it is the ear that make the final desition. I always trust my ears.

My 6L6 amp has around 1-2w ouput, it is becouse of the opt. I wound them my self. But they are very good. Freq response was almost flat from about 35-23khz. Very little ringing too. But they are very, very ugly. I have no idea how much dist. my amp has, but for me it sounds good.
If you like I can always send you a pic and schematic.

Yes, that 250ma fuse must be slo-blo if it has solidstate rectifier. In my 6l6 that has a toob rectifier I use 250ma fast.

Maybe we should make our one: "We demand a free world!" club?

Best regards,

Magnus
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Old 16th April 2006, 10:31 PM   #19
Giaime is offline Giaime  Italy
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I've been told that if the annoying buzz of my preamp suddenly disappears when disconnecting the power cord, it doesn't depend on wiring / grounding issues. So it's pickup from the transformers... I have to better decouple them from the chassis, at least mechanically.
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Old 17th May 2006, 07:36 PM   #20
Giaime is offline Giaime  Italy
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Hello there, sorry for forgotting about this thread.

I've since resolved all humming problems, they were caused by bad grounding.

I've made a page on my site to suggest some possible Plate Follower tube candidates, since I recived some feedback from some people who built the PF as a standalone linestage, with very good results.

Here it is, please feel free to make suggestions!
http://www.giaime.altervista.org/plate_follower.html
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