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Old 15th April 2003, 11:37 PM   #11
mig-ru is offline mig-ru  Russian Federation
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Skippy,

Thanks for the compliment! Also, those all are ceramic sockets, never used anything but ceramic. As for patience, I have very little to none, but I have found out that I (so far, knock on wood) solder 100% correctly, hopefully it stays this way.

Morse,

Although I do not have an oscilloscope, I do know what you are talking about with moving the wires around, and as you can see the PS and the audio section are somewhat spaced out and on opposite sides of the chassis. I will have to find some time to dig through the insides again soon.

Thanks for all the input!!!
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Old 15th April 2003, 11:59 PM   #12
Morse is offline Morse  United States
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Default A little clarification....

Hi Dmitry;

No offence was intended about your layout - it looks fine to me!

What I was referring to primarily was the placement of the 6.3V heater wires. If you're using AC heating (as I do), you might find that a shift of as little as 1/4" to 1/2" will drop your hum level. That was exactly my experience - the heater wires were just a LITTLE too close to the signal leads at the socket of the right 6SL7 on mine.

In my case, I just (CAREFULLY) bent the tabs on the underside of the sockets a trifle to keep the 6.3V wires a little further away from the signal leads to the 6SL7's. Also I shifted the signal leads just a little further away - since I can't see your wiring, I don't know if you already did this.

Also, I found that a shift of 3/4" in the position of the secondary from the HT trafo to the B+ switch had about a 1mV effect on hum level. It was just a little too close to the PS choke in it's former position (even though it was almost 3" away at it's nearest approach to start with!).

All the best,
Morse
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Old 16th April 2003, 12:05 AM   #13
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Default Hum.

Hi,

Mig,

If you experience less hum with the 2A3s than with the 6A3/6B4Gs than layout may be an issue.

If not, it may be caused by inductive coupling between xformer windings amongst other things.

Just a thought,
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Old 16th April 2003, 01:50 AM   #14
mig-ru is offline mig-ru  Russian Federation
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Morse, I didnt take offense, and sorry if it seemed that way, I was just sayign I planned the layout to avoid hum and all that nasty stuff. I decided to go and try your suggestions, sadly did not help much, so I guess I'll get a bigger choke and see how that fares.

Fdegrove, haven't tested it with 2A3's, and I dont know about inductive coupling, after all the PT is 90 degrees in relationship to the OPT's, or am I missing something?

Anyway while I was in there I took a pic, here you go.
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Old 16th April 2003, 02:09 AM   #15
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Mig...first of all your amp looks very nice!!...Job well done....If I could give you hints on why you "MAY" be getting noise is that your wiring and placement of components needs to be straightened up....you have too many wires all over the place and its just an invitation for noise.......maybe some perf board and tie wraps would do the cure and you would be set!!!


Cheers!!The DIRT®
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Old 16th April 2003, 02:17 AM   #16
Morse is offline Morse  United States
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Hi Dmitry;

No problem; I was afraid I'd been a little cavalier with my comment about wiring. I remember how long I agonised over the layouts of my 2A3.....

Sorry to read that the 'hum monster' is still with you. Yep, sounds like you've got a good plan there. FWIW I'm using a 10H Hammond 193M in mine.

Those PS filters look really familiar!! I'm using Sprague Atoms, too! You might add some .1uF 800V bypass caps (series pairs of .22uF 400V film and foil caps) in parallel to the main filter caps - I did and was really happy with the results.

One other "little tweak" that worked wonders to make a smooth sound even smoother and more pleasing was the fitting of an "X rated" safety cap to the mains in; I've standardised on .1uF 250VAC Panasonic brand class X2 interference filter caps in that role and am very pleased at the results of a 90 cent capacitor!

One word of warning for anyone reading this: under no circumstances should a non "X" rated AC safety cap be used in that role; some of the things that make an "X" cap what it is are a built in tendency to fail open as well as fire retardent potting. Any other type of cap is a fire hazard as an AC mains filter!

Anyway, good luck on your amp! It looks like a winner!
Morse
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Old 16th April 2003, 02:21 AM   #17
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sorry Mig...Dmitry already commented on what I said....for some reason posts are taking along time to show up for me


Cheers!!The DIRT®
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Old 16th April 2003, 06:25 AM   #18
SHiFTY is offline SHiFTY  New Zealand
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You may want to try DC on the filaments, it really got rid of the hum on my 6B4s.

BTW what are your output transformers? They look neat!
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Old 16th April 2003, 04:21 PM   #19
cdeveza is offline cdeveza  United States
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Suggestions that may help, based on my experience building
SE amps, they are very susceptible to hum coming from insufficient
filter. I see you use 20uf and such, try using 220uf/450v after the
choke and see if it would help.

Alex
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Old 16th April 2003, 04:24 PM   #20
Joel is offline Joel  United States
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Quote:
Originally posted by cdeveza
...try using 220uf/450v after the choke and see if it would help.
Yuck! 220uF is 180uF too much, IMO.
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