• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Frank's Ultimate Tube Preamp

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#201
joan2 said:


if you can post the physical dimensions of your trafo we can make a good guess as to its va rating....

i emailed jojo re: lm12 project, did you get a copy? if not you can email me....

i am proud of what has turned out in my gainclone thread in the 'other' forum, i am proud of you guys....

there's a big world out there, and let's not limit ourselves and widen our knowledge....there's a lot to be learned...

the fun part of it all is that it is free for the taking.....
Click to expand...


Joan2

Here is the physical dimension of the transformer.

Thickness = 4.8 cm
Width = 7.2 cm
Height = 8.7 cm

Primary 110Vac
Secondary 6Vac & 125Vac

I haven't got a copy of the LM12 project, But I did try to experiment on it using an inverted configuration it worked out fine.

For now I will try my hands on tubes since this will be my first time to build preamp. I really need to learn about tubes.

Thanks
 
#202
hi,

looks like a traffo with a 1in center leg stacked to a 1 3/4 in thichness (sorry i still can not shake off the english system which i grew up with!) so you're good for at least 70va which is more than enough for your tube preamp...

one caveat though, your 110 volt primary is a casue for concern, you ever heard about murphy?

take care!!!

tony
 
#203
joan2 said:
hi,

looks like a traffo with a 1in center leg stacked to a 1 3/4 in thichness (sorry i still can not shake off the english system which i grew up with!) so you're good for at least 70va which is more than enough for your tube preamp...

one caveat though, your 110 volt primary is a casue for concern, you ever heard about murphy?

take care!!!

tony
Click to expand...

Again Thank you very much.

Now I can start building the preamp.

Pardon my ignorance what about murphy?
 
#207
Re: Re: Murphy's Law (not EDDY)....

fdegrove said:
Hi,

O'Toole's Commentary
Murphy was an optimist.

Cheers,😉
Click to expand...


hi Frank,

i mentioned him, because it is always a good practice to leave 'murphy' out of our deisgns.....as much as possible...

btw, will you object if i design a solid state voltage regulator for power supply to your 'ultimate tube preamp'?


tony
 
#210
Hi,

Here it is, it is the same for the phono stage so if you want to build the entire preamp you'll need 4 of each or 2 for the line section only.

Cheers,😉
 

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#212
Hi,

Frank, have you previously addressed why you use silicon rather than tube rectifiers?
Click to expand...

Not extensively other than that within the context of the preamp design and in conjunction with the tubed regulator I can't hear the difference.

Other than that I prefer tube rectifiers with a particular penchant towards the hybrid design which seems to offer an acceptable compromise both technically and sonically.

Ultimately what sounds best is entirely subjective and system dependent to a large extent.

Cheers,😉
 
#213
Your design seems ideally suited to use an isolation transformer as the powertx. I'm thinking of certain EI designs by Elgar and MGE (Topaz) offering 0.0005pF capacitance between the windings, and claiming noise reduction of the order of 146dB common-mode, 60dB transverse. One would of course have to add a second transformer for the heater supplies, but that's preferred from a sonic vantage point in any event.
 
#214
Hi,

Your design seems ideally suited to use an isolation transformer as the powertx. I'm thinking of certain EI designs by Elgar and MGE (Topaz) offering 0.0005pF capacitance between the windings, and claiming noise reduction of the order of 146dB common-mode, 60dB transverse.
Click to expand...

You could if you live in a country where you have a 240V mains.

I try to not use off the shelf xformers as most are below standard (mine anyway) so I have them custom made by a winder I trust.
The little extra you pay gives you a xformer with all the goodies you want: good line regulation, no noise, no heat, a static shield between primary and secondary and in case you have several secondaries wound on the same iron you can tell him to minimise interwinding influences where it matters most.

IMHO a good powerxformer is the heart of a timeless concept and is never money down the drain.

Other than that I try to pay attention to good isolation from the mains so the music just gets amplified without (I'd hope) external influences.

Series regulators are only one way to go about that, chokes are fine too but are bulkier and probably more expensive to get right.

All in al, to me at least, it's easier to design a good regulator than to find an excellent choke and once you've designed some regs for several current ranges and voltages you can reuse them in other designs very easily.

Cheers,😉
 
#216
Hi,

Can I also use the 12FQ7 tube on this preamp design?
Click to expand...

You could but keep in mind that the values were optimized for the 12BH7A whereas the 6CG7/6FQ7 is a noval version of the 6SN7 and heater variants.

if not do you have a design for these tubes.
Click to expand...

No, other than the occasional Luxman design using it I don't see it used very often.

Last production runs I know of were done by Ei but I haven't seen much of those lately.

Cheers,😉

P.S. Keep in mind that the pinout isn't the same either.
 
#217
hi,

I try to not use off the shelf xformers as most are below standard (mine anyway) so I have them custom made by a winder I trust.
The little extra you pay gives you a xformer with all the goodies you want: good line regulation, no noise, no heat, a static shield between primary and secondary and in case you have several secondaries wound on the same iron you can tell him to minimise interwinding influences where it matters most.

IMHO a good powerxformer is the heart of a timeless concept and is never money down the drain.
Click to expand...

me too.....i make all power traffos i use in my projects myself...

i find this very much to my liking:
http://www.turneraudio.com.au/index.html
http://www.turneraudio.com.au/htmlwebpgs02/poweramps.htm
http://www.turneraudio.com.au/htmlwebpgs02/powersupplies.htm


tony
 
#218
fdegrove said:
Hi,



You could but keep in mind that the values were optimized for the 12BH7A whereas the 6CG7/6FQ7 is a noval version of the 6SN7 and heater variants.



No, other than the occasional Luxman design using it I don't see it used very often.

Last production runs I know of were done by Ei but I haven't seen much of those lately.

Cheers,😉

P.S. Keep in mind that the pinout isn't the same either.
Click to expand...



Thanks for the info.

Just this morning I broke one of my 12BH7A tube when I accidentally drop my portable grinder. I managed to find 4pcs. of 12FQ7 from my dads pile of stuff and wonder if I could use it.

I'm on the process of building the preamp I still have 3pcs will keep the third one for replacement if ever one got busted, "I hope not cross my fingers". I'll keep you posted regarding the status of the project.

Again thanks.
 
#219
Hi,

If it were me breaking a tube_something that actually seldom happens_ I get in this funny funeral mood....:bawling:

I'm on the process of building the preamp I still have 3pcs will keep the third one for replacement if ever one got busted, "I hope not cross my fingers".
Click to expand...

Under the conditions they operate and provided you run the heater at 12VDC, they should last you a lifetime....
Which is probably much longer than you'll keep the preamp anyway...🙂

Cheers,😉
 
#220
Tube sensitivity............

If it were me breaking a tube_something that actually seldom happens_ I get in this funny funeral mood.
Click to expand...

Me too !

Once the cat knocked down a box of tubes and one 6l6 popped on to the tiled floor. I almost got a heart attack ! Luckily the tube ( and box of tubes ) was not damaged.

Cheers.
Ashok.
 
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