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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 09 Aug 2020, 13:14 
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Joined: 04 Jan 2020, 08:22
Posts: 18
Hi Bruce, thanks for the fast reply, and thanks for you engagement end designs here!

I use the latest on (i sought so at least), posted on page 49, it has the LR8 (soldered on other side of the small bord in latest picture).
It seems to be almost the same as you posted now, the 4,7 uf going to ground (I’m guessing signal ground and not chassis ground) , isn’t there, but 2,2 uf to buss signal instead, can that make a different?
Also a slight change on setpoint resistor for the LR8k4, but I have no problem changing b+ level.

hiss doesn’t change switching in / out the cathode cap, different v+ levels doesn’t change the noise flor (maybe slightly better if lower, type 200 v than 215 that was the original setting, or higher)
The tub I tested is JJ ECC82 / JJ Ecc802s / and a Golden Dragon ECC82.
Br Svante


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PostPosted: 10 Aug 2020, 11:33 
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Hi I have now tried using chokes in the b+ filtering, I had two at home 7 and 15 H /400v, I don’t have any design skills (I’m an mechanical engineer) her, so just tried 2 positions. Placing it close to the tube, didn’t improved the Hiss, but introduced a hum, se the square wave at 20 hz, is easy to spot, the hum could be reduced by changing tuning capacitance on the 1 u cap close to the valve, but did not bother exploring that since the hiss was still there. Then I placed the chokes before the LR8 controllers, didn’t help the hiss, but introduced an audibly ringing at 5 and 6 khz, wiht slightly higher level than the hiss noise.
Maybe it’s the tubes themselves, anyone know tubes that is known to be hiss silent that I can try? (not interested in very expensive NOS variants)
Br Svante


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PostPosted: 10 Aug 2020, 13:54 
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Joined: 24 Oct 2010, 07:05
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My guesses:
1. Have you checked voltages? You should have around 80V (in relation to signal ground) on each heater and around half B+ at the lower tube's anode.
2. What transformer do you use? Is it hot? Buzzing? What rectifier diodes do you use in B+ and the heater circuit? Is hissing stops after you pull the plug from mains (the amplifier should work several seconds after that)?
3. Is there any changes in hiss when you short-circuit the input grid resistor (from the volume control to the ground)?


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PostPosted: 10 Aug 2020, 14:35 
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Joined: 04 Jan 2020, 08:22
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Hi Poty, thancks for your support

I have around 85 volt heater lift, need to check the level on anode (tomorrow, it’s getting late her now)
I uses the recommended Edcor tranny and UF4005 diodes, no buzzing (when amp on but in by-pas mode its absolute quiet.
Hissing doesn’t stop when i pull the plug, keeps on, and gets slightly higher just before the tubes stops working (b+ around 80 v or so)
will check the hiss when shorting input tomorrow,
Br Svante


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PostPosted: 11 Aug 2020, 04:07 
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Joined: 24 Oct 2010, 07:05
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svante wrote:
...when amp on but in by-pas mode its absolute quiet...
No wonder, in bypass mode all active circuits are by-passed.
svante wrote:
Hissing doesn’t stop when i pull the plug, keeps on, and gets slightly higher just before the tubes stops working (b+ around 80 v or so)
Then the source is not transformer or rectification/filtering. Can you also measure the in-out difference voltage across LR8?
svante wrote:
will check the hiss when shorting input tomorrow
You can turn the volume control to zero position to check that.


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PostPosted: 11 Aug 2020, 12:28 
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Hi Poty

At 205 V b+ level, I have 106 v on second plate
If I ground the volume, hiss is maybe not 100% gone, but reduced 10 db at least, same if I ground in between grid resistor and valve pin 1.
The grid resistor I use is Amtrans, and the volume pot TKD, but since its dead quite in passive (signal also passing balance / tone / volume pot), I presume that volume pot isn’t the problem, could in be de grid resistor (bought Amtrans since its recommended for just that usage, should be excellent to suppress oscillation above hearing frequencies on the tube)?

Br Svante


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PostPosted: 11 Aug 2020, 12:30 
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And 251 v in to the LR8

Br Svante


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PostPosted: 11 Aug 2020, 16:34 
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Joined: 24 Oct 2010, 07:05
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svante wrote:
At 205 V b+ level, I have 106 v on second plate...
And 251 v in to the LR8
Both is OK.
svante wrote:
If I ground the volume, hiss is maybe not 100% gone, but reduced 10 db at least, same if I ground in between grid resistor and valve pin 1... The grid resistor I use is Amtrans, and the volume pot TKD...
(you mean pin2?)
I haven't had a noise from resistors for my practice, but cannot eliminate this possibility. In my opinion the main suspects are tubes, but strange thing is that all your tubes are noisy.
By the way - on the photo there is no heaters soldered.


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PostPosted: 12 Aug 2020, 00:02 
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Joined: 04 Jan 2020, 08:22
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Hi Poty

Yes of course pin 2, I also believe it’s the tube, I will purchase some more variants and test, and I will also test low inductance metal type grid resistor.
It might be the normal noise level of the forewatt I’m complaining about, its not very high hiss level, if I played vinyl, it would for sure be below that media noise flor, and my speaker is rather efficient, especially the tweeter, I switch to one beryllium type, and adjusted that level around 1 dB higher than the original soft dome tweeter level (liked it better that way).

Heater and b+ feed was soldered in after i mounted that part in the chassis

Br Svante


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PostPosted: 12 Aug 2020, 10:42 
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Joined: 04 Jan 2020, 08:22
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I Have now tried with metal type (low inductance type) grid resistor, did not hear / measure any different hiss noise. So, I am more convinced it’s the tubes themselves.
Have ordered a couple NOS Sylvania made in 1953, will be interested to hear how they behaves.

BR Svante


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