One-Bottle Preamp

[Kingston]

[quote author="Freddy G"]Just in the process of building now.

http://home.cogeco.ca/~lothar/NYDbuild.jpg
http://home.cogeco.ca/~lothar/NYDtopview.jpg
http://home.cogeco.ca/~lothar/NYDturrets.jpg[/quote]

Nice and clean. I wish I had had yours and NYD's (the MILA-1 thread) images for layout tips when I built mine. The hum performance turned out less than ideal on my build. (I'm considering redoing my whole layout, a days project when I get the inspiration)

If at all possible, post some noise specs when you're done. I'd be very interested to have a look. :wink:

 

[hodad]

I had noticed some fairly significant differences in noise levels when I subbed in various AV7's I'd gotten in an odd lot off ebay. So I ordered a batch from AES, hoping to get a batch of GE's to check out. Instead I got a mixed batch. So I started popping in different tubes to see how the noise levels looked with different brands. So far I've tested GE, CBS, & Tung-Sol, & the hands down winner is Tung-Sol. With the Tung-Sols in, one of my channels reaches a very respectable noise level, & the other gets to the "usable at moderate gain settings" point. Obviously I have some layout issues with one channel, but it's interesting how much difference a tube can make.

On another note, I did the dc bias on heater voltage mod, & that seemed to help noise a tiny bit--not a huge difference, but enough to make it worth the half hour I spent doing it.

Tom

 

[khstudio]

[quote author="hodad"]I had noticed some fairly significant differences in noise levels when I subbed in various AV7's I'd gotten in an odd lot off ebay. So I ordered a batch from AES, hoping to get a batch of GE's to check out. Instead I got a mixed batch. So I started popping in different tubes to see how the noise levels looked with different brands. So far I've tested GE, CBS, & Tung-Sol, & the hands down winner is Tung-Sol. With the Tung-Sols in, one of my channels reaches a very respectable noise level, & the other gets to the "usable at moderate gain settings" point. Obviously I have some layout issues with one channel, but it's interesting how much difference a tube can make.

On another note, I did the dc bias on heater voltage mod, & that seemed to help noise a tiny bit--not a huge difference, but enough to make it worth the half hour I spent doing it.

Tom[/quote]

You never mentioned RCA's... I got 4 from AES & hope they are also a top contender :roll:

Kevin

BTW, Thanks for the updates everyone :thumb:

I'm about to dive into one of the NYD pre's but can't decide 1, 2 or MILA ???

 

[khstudio]

[quote author="Kingston"][quote author="Freddy G"]Just in the process of building now.

http://home.cogeco.ca/~lothar/NYDbuild.jpg
http://home.cogeco.ca/~lothar/NYDtopview.jpg
http://home.cogeco.ca/~lothar/NYDturrets.jpg[/quote]

Nice and clean. I wish I had had yours and NYD's (the MILA-1 thread) images for layout tips when I built mine. The hum performance turned out less than ideal on my build. (I'm considering redoing my whole layout, a days project when I get the inspiration)

If at all possible, post some noise specs when you're done. I'd be very interested to have a look. :wink:[/quote]

Got a question... Where is your pin "9" on the tube sockets going.

They don't look right in the pictures :?
Am I missing something? DC filament maybe?

I thought pins 4&5 tie together?

Thanks,
Kevin

 

[skipwave]

[quote author="Freddy G"]Hi Folks,
Some pix of my NewYorkDave 2 bottle-2 channel build.[/quote]

Bea-u-ti-ful. Of course, those microphones in your avatar bring tears to me eyes...... so I kind of expect nice work from you! :grin:

 

[hodad]

Kevin
I did try out an RCA--it was slightly noisier than the Tung-Sol, but not bad. I'm sure that if your layout is better than mine, you'll have less noise than I do regardless.

As to pin 9--4&5 are tied together & connected to one leg of the heater voltage, & pin 9 goes to the other leg.

Tom

 

[khstudio]

That's cool about the RCA's... I guess I'll find out :green:

I was actually reffering to Freddy G's picks - Pins 4-5 & 9.

Kevin

 

[Freddy G]

I was actually reffering to Freddy G's picks - Pins 4-5 & 9.

Yep, big mistake on me :shock: hehe
OK, can someone clear this up for me....on a 12AV7 if you use 6.3VAC then it's 4&5 together and 9 for the other side, right? And if you use 12.6VDC then just use pin 4 on one side and pin 5 on the other?
How about the 5879?
If using 6.3VAC then you use pin 4 on one side and pin 5 on the other?
hmmmm :?:

 

[ciminosound]

How about the 5879?

5879 Data Sheet

 

[khstudio]

[quote author="Freddy G"]

I was actually reffering to Freddy G's picks - Pins 4-5 & 9.

Yep, big mistake on me :shock: hehe
OK, can someone clear this up for me....on a 12AV7 if you use 6.3VAC then it's 4&5 together and 9 for the other side, right? And if you use 12.6VDC then just use pin 4 on one side and pin 5 on the other?
How about the 5879?
If using 6.3VAC then you use pin 4 on one side and pin 5 on the other?
hmmmm :?:[/quote]

I'm not sure how to hook up DC filament's but I NEED to learn.

Can I turn a standard 6.3v AC filament into DC & how :?:
:EDIT: I know how, I meant I would like to know how it works on tubes normally hooked up to 6.3v &/or this pre-amp???

I've read something about the "Sony standard" (I think) when it comes to DC fil but don't know anything about it.

Thanks,
Kevin

 

[Kingston]

[quote author="khstudio"]I'm not sure how to hook up DC filament's but I NEED to learn.

Can I turn a standard 6.3v AC filament into DC & how :?:
:EDIT: I know how, I meant I would like to know how it works on tubes normally hooked up to 6.3v &/or this pre-amp???[/quote]

The wiring is exactly the same as AC and DC. Basically, if you decide to run the preamp (and not just this two-bottle) as DC, you just convert the AC to DC at the PSU end... if the PSU has the juice for it. If you decide to do this, you'll basically lose about half of the available current to rectifying and filtering at the PSU.

Looking at NYD's noise figures, DC heaters should be quite unnecessary. You could try the AC heater virtual center tap bias trick as well. (look at the MILA schematics)

 

[emrr]

You will find a significant change in noise if you burn all the tubes in before testing audio. Tubes that have been sitting for years, used or NOS, usually have a burn-in period in which they improve with regards to noise. I believe getting stray electrons migrated to the elements is the main object. Reference the Radiotron vol. 4 for info about building a burn-in jig for selecting tubes.

[quote author="hodad"]I had noticed some fairly significant differences in noise levels when I subbed in various AV7's I'd gotten in an odd lot off ebay. So I ordered a batch from AES, hoping to get a batch of GE's to check out. Instead I got a mixed batch. So I started popping in different tubes to see how the noise levels looked with different brands. So far I've tested GE, CBS, & Tung-Sol, & the hands down winner is Tung-Sol. With the Tung-Sols in, one of my channels reaches a very respectable noise level, & the other gets to the "usable at moderate gain settings" point. Obviously I have some layout issues with one channel, but it's interesting how much difference a tube can make.

On another note, I did the dc bias on heater voltage mod, & that seemed to help noise a tiny bit--not a huge difference, but enough to make it worth the half hour I spent doing it.

Tom[/quote]


EDIT: PRR mentioned burn in back on page 4.

 

[khstudio]

[quote author="Kingston"][quote author="khstudio"]I'm not sure how to hook up DC filament's but I NEED to learn.

Can I turn a standard 6.3v AC filament into DC & how :?:
:EDIT: I know how, I meant I would like to know how it works on tubes normally hooked up to 6.3v &/or this pre-amp???[/quote]

The wiring is exactly the same as AC and DC. Basically, if you decide to run the preamp (and not just this two-bottle) as DC, you just convert the AC to DC at the PSU end... if the PSU has the juice for it. If you decide to do this, you'll basically lose about half of the available current to rectifying and filtering at the PSU.

Looking at NYD's noise figures, DC heaters should be quite unnecessary. You could try the AC heater virtual center tap bias trick as well. (look at the MILA schematics)[/quote]

That's right... I forgot about loosing current. :thumb:
I read that before.

Also, look again at Daves chart on page 1, it says (With DC on the heaters)

The Power tranny I have should have enough current to do it but I don't have ANY experience doing this. Could someone please draw something up or give me more details, also, how to wire to the tubes. (I don't want to ruin the tubes, I've on'y got 4 of them.

My tranny's heater = 3v-0-3v

Thanks,
Kevin

 

[pstamler]

That tranny's a little skimpy to use for 6.3V DC filaments. If it's really 3-0-3 (6V center tapped) then a full-wave bridge will give you only 6V of DC under nominal conditions (a little under the desired 6.3V but not horribly so). But it'll give you only 5.1V when your line voltage is 10% low, not an uncommon situation in the summertime, and that's really too low for most tubes to be happy. And it limits you to a single filter capacitor, which will need to be a whopper to cut the hum down to manageable levels.

If all you have for filaments is that transformer, then I think you're getter off sticking to AC filaments and hoisting them up 60V or so. But if you can use a 10V transformer, then your unreg output voltage at 10% low line level will be about 10.2V. Drop 2V in a (high-power) dropping resistor and a second capacitor, then drop 2V in a 3-terminal regulator and you're there. (I use 5V regulators with two 1N4003 diodes in series between the regulator's ground terminal and the actual ground for a total output voltage of 6.2V, close enough.)

Once you have 6V (more or less) of DC, for a regular 12A*7 type tube, hook + to pin 9 and - to pins 4 & 5 jumpered together (or vice versa; the tube won't care).

What's nice and safe about this is that if your DC supply is 6V, even if you hook it up wrong you can't blow up a 12V tube, just underpower it.

Peace,
Paul

 

[pstamler]

Oh, and don't forget when you calculate how much heatsink on the regulator, do it on the basis of dropping 5V across the reg., which is about what you'll be doing when the line voltage climbs to 10% high.

Peace,
Paul

 

[khstudio]

That tranny's a little skimpy to use for 6.3V DC filaments.

I'm sorry, I wasn't reffering to the "Actual" voltage I was reffering to the Heater/filament section of my Power tranny. (normally 6.3v AC under load)

Can I make that work & How?

Kevin

 

[Kingston]

[quote author="khstudio"]

That tranny's a little skimpy to use for 6.3V DC filaments.

I'm sorry, I wasn't reffering to the "Actual" voltage I was reffering to the Heater/filament section of my Power tranny. (normally 6.3v AC under load)

Can I make that work & How?

Kevin[/quote]

mr. stamler just put it in a nutshell:


[quote author="pstamler"]That tranny's a little skimpy to use for 6.3V DC filaments. If it's really 3-0-3 (6V center tapped) then a full-wave bridge will give you only 6V of DC under nominal conditions (a little under the desired 6.3V but not horribly so). But it'll give you only 5.1V when your line voltage is 10% low, not an uncommon situation in the summertime, and that's really too low for most tubes to be happy. And it limits you to a single filter capacitor, which will need to be a whopper to cut the hum down to manageable levels.

If all you have for filaments is that transformer, then I think you're getter off sticking to AC filaments and hoisting them up 60V or so. [/quote]

It won't hurt to try the AC filaments biased with a 30-60v center tap. See if/how it works and forget the DC heaters for a while. The hum difference between AC and DC should be only 2-5dB, depending on your wiring, nothing to worry about. again, see the MILA-1 schematics for further info.

 

[pstamler]

Still a little skimpy. The formula for a full-wave bridge rectifier circuit (as mentioned in another thread) is:

Smoothed DCV = (ACV * 1.414) - 2.5

The 2.5V is the drop in the recifier diodes. A 6.3VAC winding will give you 6.4VDC, which sounds just right, but then look at what happens when line voltage is 10% low: the DC output is then 5.5V. Too low.

When designing a power supply you always need to take line fluctuations into account. And, in the case of a filament supply, it's always more effective to use a 2-stage filter, which entails losing some DC across the resistor between stages.

Peace,
Paul

 

[khstudio]

OK, cool :thumb:

I will try the AC filaments biased.


Kevin

 

[Marik]

[quote author="pstamler"]Still a little skimpy. The formula for a full-wave bridge rectifier circuit (as mentioned in another thread) is:

Smoothed DCV = (ACV * 1.414) - 2.5

The 2.5V is the drop in the recifier diodes. A 6.3VAC winding will give you 6.4VDC, which sounds just right, but then look at what happens when line voltage is 10% low: the DC output is then 5.5V. Too low.

When designing a power supply you always need to take line fluctuations into account. And, in the case of a filament supply, it's always more effective to use a 2-stage filter, which entails losing some DC across the resistor between stages.

Peace,
Paul[/quote]

Unless I am missing something (sorry did not read much before last couple messages), with 3-0-3 you get 6x1.41=8.46V. You still have some margin to smooth it out even further with a small value resistor and cap.