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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: 07 Aug 2010, 21:32 
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Location: Denver, Colorado
Homik,

Welcome to the forum, we are all here to assist.

If you have a chance, upload some pics of your build (top and bottom). This way we can see if there are any mis-wires)

Also, one thing to remember is the tube pins are read from the bottom.

Image

When soldering point-to-point, it is easy to confuse pins.

Thanks
Rogers


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PostPosted: 08 Aug 2010, 01:02 
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Joined: 22 Jun 2010, 13:30
Posts: 66
@Homik does the tube glow or get hot? if not that is the problem!

here is my amp
it has a build in diskman and a line in (for pc or other device)
it has 2 tubes the ecc85 (works great) and a em84 for decoration
it has a internal speaker-exit for speaker and a headphone exit for headphones
it is mono because it was my first project and i was terrified that i would ruin it
so it is mono and it works good
i do have a video if someone is interested

Image

Image

Image

Image


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PostPosted: 08 Aug 2010, 09:15 
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Posts: 441
homik wrote:
Though I can't seem to get mine to work. I've tried different power supplies so I'm fairly certain that is not the issue. The issue I'm having is instead of sweet, sweet music coming out my cans (cheapo earbuds for now) I get buzzing. Not even distorted sound, just incessant buzzing. Buzzing is the same on both channels.

I've tried a walwart and the PS i made for it (which makes far better sounding buzzing, but not music :mrgreen: ), and i've checked over the wiring a bazillion times. I've made sure the MOSFET and other things that shouldn't be aren't shorted to ground.
I just can't figure it out. :worried:

I'm using an MP3 player as a source and it works (hooked up the earbuds straight to it and i hear the music fine) and it hasn't exploded, so it doesn't look to be shorted anywhere. Also went with 4k7 resistors for bias instead of pots.

For all i know it could be the wiring (i've made mistakes before... lots of mistakes ;) ) but it would help to know what to look for given the symptoms.

About the hum, did you connect the wallwart directly as power supply ? common problem could be, not enough filtering. A pi filter would be necessary. For simplicity, an example is shown below without values. Several pi filters can be added until hum is gone.
Image
The best wallwarts I've used for similar constructions has output voltages between 16 - 30 VDC, then pi filtered down to 12 - 13 VDC ( it gives a hum free ps ). A simple wallwart can be filtered down to a good result.

Off course best of all would be a 12 V battery or a SMPS ( Switch Mode Power Supply ) for a stable hum free power supply, but costs of these solutions are higher.


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PostPosted: 08 Aug 2010, 17:31 
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Joined: 22 Feb 2010, 20:57
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KrammeAcoustics wrote:
About the hum, did you connect the wallwart directly as power supply ? common problem could be, not enough filtering.

I'm not so much worried about power supply hum yet as much as getting anything to work. The PS i made has a 12VA 12vac Hammond transformer, followed by 2 1000uF caps and an lm7812 and another 220uF cap, and of course bypass caps.
robot797 wrote:
does the tube glow or get hot
if not that is the problem

When power is applied they glow bright for a second or two then fade away. I haven't let it on long enough to see if they start glowing again. When i was building the PS i accidentally made a half wave bridge (talk about making mistakes ;) ) so i may have killed the heaters with that :S
I have 2 more ecc82s but i'm kind of worried about putting them in an potentially killing them too. :hot:
roggom wrote:
If you have a chance, upload some pics of your build (top and bottom). This way we can see if there are any mis-wires)

Also, one thing to remember is the tube pins are read from the bottom.

Ugh, i remember when building a preamp i had to deal with the backwards (at least for me) pinouts. I had to redo the whole thing.

I made extra sure i used the right pinout this time. :king:

Here are some pics, though its a fairly messy PtoP job, even by my standards :?

Image

I'm using the switch on the Alps pot to control the B+ to give the heaters a moment to heat up, so it adds another layer of messiness i'm afraid :worried:

Image

The PS and enclosure came out very nicely though :mrgreen:

Image

Image


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PostPosted: 09 Aug 2010, 06:29 
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Joined: 07 Aug 2010, 06:24
Posts: 44
Location: India
ELO m back again :)
hm... so this is the schematic that i made of the amp but when simulated the results are some what strange :worried:
Attachment:
tube1.JPG

**notice that i've added BIAS resitor of 4.7k cuase without it the output wave was half clipped :eek:
Attachment:
diag1.jpg

As you can see even with the BIAS resistor the upper (+ve half of the wave) is somewhat distorted. is this a common problem ???

P.S when i ran the simulation for a little time the graph shocked me :P but increasing time showed the actual output.

Thanks,
newBiE RoHan


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PostPosted: 09 Aug 2010, 09:12 
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Joined: 08 May 2009, 08:20
Posts: 918
Location: Duesseldorf, Germany
Hi Rohan,

the bias idea went a bit wrong. If you don't ommit the P1 (your schematic) you set 2 bias points on the circuit..
By using the potentiometer and the bias resistor, the bias starts to drift away, because there is no single fixed point for
biasing the mosfet. The bias may run stable after a while, when the tube is heated up and the emission is stable (tube bias)...
The 4k7 resistor is meant to use instead of the potentiometer. With using a higher voltage you also have to change the "fixed" bias
resistor value or you must re-adjust the potentiometer.
Attachment:
tube1_new.JPG

I hope that was a little help.


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Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 09 Aug 2010, 09:55 
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Location: India
hm..
oopsie forgot to add in capacitor time functions :) thats why the output was clipped, some somehow if you closely see the sine wave output "IT IS DISTORTED ON THE UPPER HALF" any comments....
also,
since tina can actually Simulate or Produce almost real scenario sounds the output was not the tube kind that i've herd of :( does the mosfet buffer destroy the in sequence distortion harmonics?

P.s thanks but a few offtopic questions,
can this be tweaked into a purely tube driven amp incorporating two tubes for greater current outputs =) coupled with a transformer

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"Problems cannot be solved by the same level of thinking that created them" -Albert Einstein


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PostPosted: 09 Aug 2010, 10:19 
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Joined: 03 Aug 2008, 20:22
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Location: Denver, Colorado
Homik,

Nice build,

Now it was difficult to see the tube pins, but with the dead tube in place, measure pins 4&5. One should be at b+ (12v or your power supply potential) and the other at ground. The tube heaters will work with 12v ac or dc, but ac would reveal some bad hum at such a low voltage.

Next, I see you have two semiconductors for each heatsink, I am sure you used mica insulators, but did you use a screw insulator as well? They are small nylon and prevent the screw from touching the inside or outside of the tab hole.Here is an example http://www.richco-inc.com/partdrawings/MNI.pdf

Pins 1 and 6 should be at about 10.5~11 volts and pin 9 should be disconnected, but measure about 6 volts (heater center tap). The others 2,3,7,8 should be in the millivolt range.

Rogers


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PostPosted: 09 Aug 2010, 10:44 
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Location: Denver, Colorado
Rohan wrote:
oopsie forgot to add in capacitor time functions :) thats why the output was clipped, some somehow if you closely see the sine wave output "IT IS DISTORTED ON THE UPPER HALF" any comments....
also,
since tina can actually Simulate or Produce almost real scenario sounds the output was not the tube kind that i've herd of :( does the mosfet buffer destroy the in sequence distortion harmonics?

P.s thanks but a few offtopic questions,
can this be tweaked into a purely tube driven amp incorporating two tubes for greater current outputs =) coupled with a transformer

IN Tina you can adjust the setting for the potentiometer anywhere from 1 to 99 %. As is you are set at midpoint so 50k bringing your dc voltage to about 4 volts at the source. Start making adjustments and you will see that the simulation signal should round off. You may have to change the potentiometer value as well.

As far as all tube, yes it can be done. This project is designed as an introduction to tubes and hybrids. A second tube can be used in place of the mosfet, but the voltages will have to be significantly increased to provide enough output.


For a completely different, but all tube unit I like SRPP triode:

http://gilmore2.chem.northwestern.edu/p ... n1_prj.htm

http://gilmore2.chem.northwestern.edu/p ... igurations.

http://www.tubecad.com/may2000/page2.html

Rogers


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PostPosted: 09 Aug 2010, 12:11 
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Joined: 22 Feb 2010, 20:57
Posts: 8
I can see now that those pics are fairly useless for debugging. :down:
So i drew up a wiring diagram. One thing i forgot to show in the diagram is the 1k resistor to ground after the output cap.

This is viewing from the bottom.

Image

Roger: I'll whip out my DMM later and see if everything checks out.

And yes, the semis are isolated with mica and nylon washers.


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