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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: 17 Aug 2020, 11:47 
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Hi Bruce, I was slow to approve a couple of new user posts by ematine and drganic above which have now been passed by with new posts and likely missed by most.

Sorry about that, Gio

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PostPosted: 17 Aug 2020, 21:42 
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Hi, To respond to an earlier posting.


As this is my first tube project I am not sure what right looks like.. I am having terrible hum that increases with volume.. I am using 6n1P's with 220R's and I have detected the following:

1. High Voltage side has 0 ripple, it is perfect and adjusted to 215V
2. Low voltage is 5.99V with 0.152V of AC ripple - not sure if this is expected or acceptable as I know these tubes can run off DC & AC
3. I am getting a malformed signwave across pin 8 and signal ground on BOTH tubes, with pin2 disconnected the wave is 100MV P2P and about 8ms ..

I am assuming this is the hum.. I am using a star ground and have sperate grounds for chasis(earth), high voltage (L/R), low volatage, Signal path (L/R) .. I have added the 1uf on pin 6 B+ and have 1M R on my output through 1K resistors..

Question, should I see so much ripple on the 6V? maybe bad cap? or should I add a 2.2K to elimitate it.. I am using the M317 to regulate the power

The ripple value is not unusual and should not be an issue. If you have significant hum then there are a number of possible problems. First did you add in the positive lift voltage on the heater circuit. I hope you did not ground any part of the heater circuit either. Second the 6N1Ps have more gain and will likely have a higher level of hum over the 12AU7 types. It should not however be noticeable as the preamps are really quiet. I suspect you have a ground loop somewhere. Probably between the input source and volume control. Please post a photo or two of the insides so I can look at it and see if I can spot problems. And finally it may be a problem with your source. If the hum goes up with increase in the volume setting it tends to indicate that it is coming from the signal source.

Good listening
Bruce

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PostPosted: 17 Aug 2020, 21:46 
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Hi, Another answer


Hello Bruce. Sorry for arriving late to this party, and thanks for sharing your design.
I wanted to know if this preamp would work ok with solid state amplifiers (because of the input impedance of those).
Shall the 2.2k resistors be changed to other values for that purpose?


Well it sort of depends on the impedance of the power amps. Typically you would not need to change the resistor values. They are there to insure you don't load down the stage too much and cause it to be non-linear and to compensate for cable capacitance of the interconnects. I would try the preamp wit them in place and see how it sounds.

Good listening
Bruce

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PostPosted: 18 Aug 2020, 10:53 
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Hi
I have now tried the NOS Sylvania tubes, and the hiss noise actually vent up a bit, now it’s also same level at 0-volyme and turning up the knob a bits (the JJ where clearly more quieter at 0-volyme). At full volume I experience same hiss level from the Sylvania tubes as from the JJ.
So I believe my complains is al about the built in noise from the tubes (shielding them doesn’t change anything), So I have to get use to it, I am currently using an AN 300B KIT1 as power amp, and it has a volume knob, so turning the 300B down 30%, and compensate up on the forewatt instead makes the hiss un-noticeably. But I’m planning to build a pure power amp without volyme pot soon (45 or 46 tubes haven’t decided yet), so then it likely will be back
Now its time to decide what tube I like the best musically!

Br Svante


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PostPosted: 18 Aug 2020, 17:14 
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Hi Bruce.. I am attaching a photo,

re your prior response..

yes the low voltage is lifted.. I measure about 70V of lift.. If I jumper (yellow) the star ground directly to the chassis and the hum significantly reduced , this bypasses the X2/150R combination component I am using between my star ground and chassis ground

My input source is a Pioneer DV-45A dvd player plugged into the amp mains, both amp and premap are plugged into the same power socket. Hum level doesn't change, if I disconnect the input device


General grounding I followed
Ground A point grounds input, output, 1MR and volume pot , which is then connected to star with 18 awg solid copper wire)
Ground B point grounds the cathode and 1uf(B+) poly and then connects to star with 18 awg solid copper wire
HV Ground rail connects to the star (14 awg solid copper)

the star is then connected to earth by an X2/150R , as I said, if I jumper this out, the hum is SIGNIFICANTLY reduced

I put a switch to switch the 100uf cathode cap in and out of circuit, with or without cap, hum level remains the same

I really appreciate your help.. thank you


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PostPosted: 19 Aug 2020, 00:28 
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hi
I believe Bruce will give an better answer, but to me it looks as the filament heater pin 9 isn’t conected to anything, and other side of the heater, pin 4 and 5 connected by an orange drop capacitor in between them? Do you really have an filament glow working?

br Svante


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PostPosted: 19 Aug 2020, 00:44 
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Hi again, now I saw that you use 6n1p tubes, so forget my comment about pin 9 for heater, I presume there is some cables to 4 and 5 that is difficult to see in the pictures

Br svante


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PostPosted: 19 Aug 2020, 06:19 
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Correct using the 6n1p


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PostPosted: 20 Aug 2020, 21:51 
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Hi, At least one builder put the volume control at the output side. It might cure your hiss problem. This will work as long as none of your signal sources exceed about 1 volt. Typical Forewatt builds with 12AU7s (and variants) can handle that much and are able to deliver up to +/- 30 volts of output clean. I have used them as drivers for EL84s that way. However.....using a 6N1P complicates the issue. I don't have experience with how well it can handle inputs of that level with its higher gain. I would expect that resistor dividers would be needed at the input to keep it from overloading. Plus I can't be sure how linear it is at anything above a small signal.

Good listening
Bruce

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PostPosted: 23 Aug 2020, 02:19 
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Hi for all tubes you can expect some hiss when your using them and given the scheamtic is correct design.
Unless you got lucky and the low microphony tube for the low to average grade ones.

High end tubes you can expect bit less or low hiss.

For connecting pot on output stage I would recomend 10K pots so your not introducing a huge seires resistance when trying to dry low impedance loads.
Make sure the cap has large enough so theres no base cut off from drviing low impedance load.

Sometimes swapping the tube on left channel to right channel can solve hiss prolbem while using the same tubes.


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