Couple 6SN7 One-Bottle questions

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ihscoutlvr74

Well-known member
Joined
Apr 2, 2008
Messages
68
Gents,

I know its an old topic and I have read the 35 pgs in the meta but I'm finishing up a 6SN7 One Bottle schematic below omitting R1.
ForRafa1_6sn7_pre.jpg


I'm having some hum issues after referencing heaters to ground with 2 100ohm resistors and was wondering if there is anything in my layout that could be affecting this.  I have 2 6SN7wgta's and am rectifying with a 6X4 and each channel has it's own filtering after the 4.7k.  I have a separate tap I could heat the 6X4 with if that would help.  Can someone take a peek at my layout and let me know if there's something I can tweak to reduce hum?  GRN is heaters, blue and gold in back B+, BLK =grnd, white are cathodes.

6SN7_one_bott_guts.gif
 
Move wires while listening. If hum gets worse or better, that's a clue where the problem may be.

Are you really using aluminum rivets as solder-points ? ? ?
 
Yes, I tried using rivets for solder points - big mistake but all components are connected. - My other problem is that once the signal gets to grid #2 the high end is cut dramatically.  In the first stage it's overly bright but once it hits grid 2 I lose a lot of brightness.  I added the RC network used on the BA-2A of 33k ohm and 330pF \ which helped a bit and also added .022uF cap for bypass on output cap which helped some too.  Is there some tweaking of values on cathode end etc that may remedy this?

Thanks, Nathan
 
ihscoutlvr74 said:
Yes, I tried using rivets for solder points - big mistake but all components are connected. - My other problem is that once the signal gets to grid #2 the high end is cut dramatically.  In the first stage it's overly bright but once it hits grid 2 I lose a lot of brightness.

I'm thinking something with those half-connected cold-jointed rivets might cause this. A bad idea indeed. It's a big task but I would redo the whole layout with proper turret boards. The layout itself is quite good.

The grids are the most sensitive points in the entire circuit and I'm guessing some rivet is doing unwanted ohmic effects with the grid creating a low-pass filter.
 
Good advice given already.

All I can add is that I built this design exactly per the schematic shown and it exhibits flat frequency response.

In fact, this design sounds really quite nice and you've reminded me how much I want to (finally) finish the chassis and get racked up before my next big tracking session.
 

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