• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

The complete 6SN7 preamp

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#44
WIRING.

Hi,

That's a good idea John.

Here is the pin layout for the 12AY7A :

So if you use only section one on one channel you would use pins 1,2 and 3 and than 4+9 for the heaters.
The use section 2 of the twin triode using 6,7 and 8 and 5+9 for the heaters.

Cheers,😉
 

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#45
Joe,
a) Did you center-tap, and then ground, the filament wires? This will elimanate a lot of fil. hum related issues. Get a 100 ohm pot, wire it across the filament winding with the wiper to ground.

b) If you have a scope, or a meter with frequency on it, can you tell if it's 60Hz, or 120Hz hum? That helps a lot in a diagnosis.

c) Other than the extra work and money, why'd you use two 12AY7's?? :bigeyes: hehe

Joel
 
#46
Well, I wired up the heaters wrong on the 12AY7's. I had the AC going to pins 4&5. I corrected that and now you can see life inside them. LOL

The hum is still there but I just turned the volume up slightly and enjoyed the music.

Joel

Please diagram the pot circuit so I don't make anymore mistakes.
I just plain liked the looks of two 12AY7's instead of one sitting on the chassis.

Note: This is hard for a SS guy to say but this lineamp beats both of my class A preamps. I'm hearing things I haven't heard before.

Joe
 
#55
Frank

I tried my CD player and a FM tuner with the same amount of hum. I have also tried several poweramps (both SS) with the same result. I think its a power supply problem if I were to make a guess. Haven't shorted the input yet but do plan to see if my frequency counter will give me an idea what the frequency is. Checking with my digital meter I get about 6mv of DC offset on the output and about 3mv on the AC scale.

Joe
 
#58
Frank

I // pin 4 to 5 and wired to 4 & 9 for the heaters. I also pulled the CT of this winding and installed a 100ohm pot as suggested. I am assuming that the noise must now be grounding issues. Will check tonight after work and measure frequency of noise after amplification. There is no noise when using a SS preamp or my other tube(Hong Kong) preamp.

Joe
 
#59
I good tip for heaters, if it has not been already mentioned, is not to ground the centre-tap (or wiper of the hum balance pot) but instead to sit it on +40V; this was used in old RCA designs. It turns off the "diode" created by the cathode and heater winding.

Another important mod is to AC ground each heater pin AT THE VALVE SOCKET* using 10nF ceramic capacitors. This will prevent any RF reaching the cathode via the heaters.

Proabably best to use DC in preamps though!

7N7

* I have used capitals because I cannot make the underline facility work
 
#60
7N7 said:
* I have used capitals because I cannot make the underline facility work
Click to expand...
Paul, I find the software to do underlines italics etc awkward, so perhaps HTML or Markup would be easier. It's what I use, and I just type it in as I go.

HTML
{b}all this will be bold{/b}
{i}and this will be italicised{/i}
{u}and this will be underlined{/u}

To directly link to an image from another site
{img src=image URL}

NOTE: I have used {} brackets where in reality you would use <> for HTML, but if I did, it wouldn't show it as examples, but actually bold, underlined etc in the finished post.
You can also use HTML at audioasylum.


Markup:
Similar to HTML, but uses [] for brackets instead of <>. I'll use {} again for examples so they're visible in the finished post. Notice the capitals.
{B}bold{/B}
{I}italicised{/I}
{U}underlined{/U}
{QUOTE}quoted text{/QUOTE}
{IMAGE}image URL here{/IMAGE}
To add a hyperlink into a sentence, eg

Another audio forum is {URL=http://www.audioasylum.com}Audioasylum{/URL}.

The word Audioasylum would show up in the finished post as a hyperlink, blue and underlined.

You can use both HTML and Markup in this forum in the same post, but you can't start a bold (for example) in html and finish it in markup. Start a function in one style, and you must finish it with the same.

You can also "nest" functions, eg in HTML (same idea with Markup too),
{i}813's are the {b}best{/b} tubes{/i}. The entire sentence would be in italics, with the word 'best' bold too.

HTH

Cheers
 
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