WE417A / 12B4A mic pre schematics

heya gang

here's something i made for rafafredd, it's an adaption of my B&K pre. sorry, i've lost patience with trying to do in the box, so i hope you can read my crappy drawings :thumb:





there's a heater psu missing, but it's 7VAC -> ordinary 35A bridge -> CLC with 1H + 3 x 47.000yF, biased up 40V

more here:

http://www.sismofyt.net/diy_audio_gear.html

if anyone have any interest in this project, i'll be happy to explain my thoughts behind this pre

forgot, the input trannie is a high ratio ('bout 1:15) jørgen schou and can't be bought today. but i've had good luck with the lundahl LL1577 (1:14). with high output sources it can clip (nicely), so maybe wired it 1:7 (switchable perhaps). i use it mostly with ribbons, so i don't hit it hard

i should probably have included a 1k gridstopper for the 12B4 (right up to the pin, like the four on the WE471A) and the first cap in the psu should be 47yF / 630VDC just to be safe. and a 470k / 1W B+ bleeder :roll:

eta: the voltages written are

WE471 plate 130V / cathode 650mV / 26mA

12B4A plate 130V / cathode 17V / 22mA

don't like the 5842 in this setup. component choice, layout and psu will have a great effect on the sound when you only got 8 parts directly in the signalpath :wink:

cheers,

ole

HI !!
how are you ?
long time no see

:roll:
or is it just me that's been MIA lately ?

I like the 417a but right now I'm using NOS 5842, have you any thoughts on the CJ single bottle preamp? I'm using 1:15 beyer trafos on the inputs and Gefell m930s will clip the daylights out of them. 20db pad is needed on the inputs and some kind of attenuation is needed on the outputs too!

I run my plates at 150vdc, solidstate rectification, large caps and some value of resistor, also run the heaters at 6.3vdc fully regulated by a voltage regulator.. JRC makes a 6.3v regulator, go figure.

another idea, use the 417 as a gain stage after a LCR EQ for makeup gain.. I think that combination would rock..

Hey, very nice you posted it, Ole!

I´m building it...

You mentioned shockmounting the 471a tbes, and I´ve finally found a nice way to do it. I´ll get some pics done.

I´m also thinking about getting pretty radical on your conceptions and soldering directly to the tube pins, what do you think about it? CJ did it once in a headphone amp. It´s kinda crazy, I know.

[quote author="Svart"] I like the 417a but right now I'm using NOS 5842, have you any thoughts on the CJ single bottle preamp? [/quote]

the WEs have a nicer tone - in this project - and also tends to be less microphonic. i do like the 5842 and i use them alot, but mostly as output drivers, not as input tubes

i've only skimmed the CJ thread, but that's not the way i'd do it :wink: :green:

[quote author="Svart"] I'm using 1:15 beyer trafos on the inputs and Gefell m930s will clip the daylights out of them. 20db pad is needed on the inputs and some kind of attenuation is needed on the outputs too! [/quote]

yeah. the JS i use seem to be unclippable with the mics i use which are not high output LDCs. i also do not use a cathode bypass cap which increases the WE471A gain. it also totally messes wit the sound, imho. large value lytics and low voltage signals don't get a long well

this is not a good pre for recording kicks. it's nice for vocals and acustic instruments

[quote author="Svart"] I run my plates at 150vdc, solidstate rectification, large caps and some value of resistor, also run the heaters at 6.3vdc fully regulated by a voltage regulator.. JRC makes a 6.3v regulator, go figure. [/quote]

run the plates higher (or are you talking about the actual plate voltage, not the B+?) and run the tubes hot. i think the sound best in the 25-30mA region. i like to run my heaters at 6V, not 6,3V

[quote author="Kev"]HI !!? [/quote]

HELLO KEV!!

[quote author="Kev"]how are you ?[/quote]

exellent thank very much - and you?

[quote author="Kev"]long time no see[/quote]

yes :grin:

[quote author="Kev"]or is it just me that's been MIA lately ?[/quote]

you're always MIA :green:

[quote author="Svart"]another idea, use the 417 as a gain stage after a LCR EQ for makeup gain.. I think that combination would rock..[/quote]

yes, it would. that's what i do with my 5842s, use them as output drivers

[quote author="rafafredd"]Hey, very nice you posted it, Ole!

I´m building it...

You mentioned shockmounting the 471a tbes, and I´ve finally found a nice way to do it. I´ll get some pics done.

I´m also thinking about getting pretty radical on your conceptions and soldering directly to the tube pins, what do you think about it? CJ did it once in a headphone amp. It´s kinda crazy, I know.[/quote]

yeah, they're microphonic. hang them, so you can tune the resonance freq, or else it's useless

dunno 'bout soldering them in. they won't last forever. why do you wanna do that?

whoooaaa, what a beautiful amp! i love it!

yes, it would. that's what i do with my 5842s, use them as output drivers

Click to expand...

awesome, good to hear that I'm on the right track.

B+ is 150vdc exactly. I guess I could raise that? They have awesome headroom as it is, much more than the recorder they go into for sure..

[quote author="Svart"]

yes, it would. that's what i do with my 5842s, use them as output drivers

Click to expand...

awesome, good to hear that I'm on the right track.

B+ is 150vdc exactly. I guess I could raise that? They have awesome headroom as it is, much more than the recorder they go into for sure..[/quote]

yeah, my experience tells me 150VDC is way to little. 130VDC / 26mA across the plate is where i think it sounds the best, imo that is. the tube will be running at 80% of it's max wattage, which is peachy

do you have the cathode resistor bypassed with a cap? try removing that one

[quote author="sismofyt"][quote author="Svart"]another idea, use the 417 as a gain stage after a LCR EQ for makeup gain.. I think that combination would rock..[/quote]

yes, it would. that's what i do with my 5842s, use them as output drivers[/quote]

foo. I thought the 5842 and the 417a were the same tube. :-( I have two 5842s.

edit: forgot to say that amp looks way nice.

Kiira

kiira said:

[quote author="sismofyt"]foo. I thought the 5842 and the 417a were the same tube. :-( I have two 5842s.

edit: forgot to say that amp looks way nice.

Kiira

Click to expand...

well, they're are very close. but my experience (20 WEs, +100 5842s, all raytheons) tells me that the 5842 tends to be more microphonic and in my pre circuit the 471A sounds a little better. the 5842 can sound a little 'glassy' and hard, especially if it doesn't get enough juice

but you can swap around as you please, they're electrically the same

thanx for the nice word about the B&K thingy. i like, and take great pride, in mechanical engineering :wink:

I thought I was doing something original when I soldered direct to tube, but as it turns out, this was fairly common practice on some of the tube/condenser mics.
You can never do anything completely original, so I should have known.

I built a plastiic sleeve for the tube and lined it with coreprene pad (does not compress over time), and it helped a lot.

Use loose wires if you solder direct so that the stiffness of the wire does not transmit vibration to the tube.

Where the hell did Kiira come from?
Acid flashback, or for real?

[quote author="CJ"]I thought I was doing something original when I soldered direct to tube, but as it turns out, this was fairly common practice on some of the tube/condenser mics.
You can never do anything completely original, so I should have known.

I built a plastiic sleeve for the tube and lined it with coreprene pad (does not compress over time), and it helped a lot.

Use loose wires if you solder direct so that the stiffness of the wire does not transmit vibration to the tube.

Where the hell did Kiira come from?
Acid flashback, or for real?[/quote]

it's common with miniature tubes and nuvistors. nuemann does it. i think some AC701s are soldered in as well. i once had an amp with soldered EL34s... ARRRRGGHHHHHH!!!!!!!! damn, fukkin' bean counters

i'd also be worried about damaging the tube with too much heat..? i always start getting all sweaty and paranoid when i have to jam in tubes in tight sockets..

you're an original, that's good enough :wink:

that plastic sleeve thingy was that due to microphonics (we're talking WE471A here, right?)

i'm pretty sure kiira came from her mothers womb, but i wasn't there, so..

I got caught in one of those time/space discontinuum thingies and ended up being a British double agent in WWII Germany. Man, the fashions back then!

anyway... I'm back to my usual century and my old job as a fry cook. No more dating SS officers for me!

Agent Kiira

mmmm valves and fries, I think Kiira is a keeper!

[quote author="kiira"]I got caught in one of those time/space discontinuum thingies and ended up being a British double agent in WWII Germany. Man, the fashions back then!

anyway... I'm back to my usual century and my old job as a fry cook. No more dating SS officers for me!

Agent Kiira[/quote]

actually, it was cj who finally cracked open a flux capacitor so we could make a groupdiy timemachine to get you back to germany in 1943 to get a stash of VF14s

there's still some pcbs in the black market if you're quick

glad you're back safe. dating was not part of the mission