Western Electric 417A Tube Preamp

[rafafredd]

Is your EDCOR 15k:600 gaped?

here is a quote from the auction listing:

These transformer are special design custom made for Tube Pre-amp. ( 6dj8. 417a. 5687 ).
The Transformer Core is Z-10 with air gap .It allow dc. current not over than 30ma. So the pre-amp circuit do not need any expensive couple capacitor.

Primary impedance : 15k ohm ( DC.current not over 30ma.)

Secondary impedance : ( 600 ohm series ) ( 150 ohm parallel )

Frequency Response + --1.5db 20Hz-----25K Hz

Weight 1 KG. with packing.

 

[Svart]

nope they aren't gapped, i used a big old polyester cap..

 

[Svart]

i've been playing with my setup lately and found these pres to have an unparalleled ability to give clear gain. I can hear stuff in the background that the mics picked up that none of my other tube or SS preamps can do. I used some little beyer input trafos that can't handle a hot mic so I made some 20 db pads then bypassed the series resistors with diodes for the phantom to reach the mic less inhibited.

I also put a 100k pot between the cap and the output trafos and changed them out to 6k:600. Now I have output level adjustment capabilities.

The pres are still on the noisy side but will still clip the recorder easy if the ouput atten. is all the way up even with a 20db pad on the inputs so I am sure it's just a helluva lot of gain.

:thumb:

the 7788, how would you hook that up? I'm all for some more cheap single tube pres after this..

 

[rafafredd]

then bypassed the series resistors with diodes for the phantom to reach the mic less inhibited.

I can´t understand. What does that means?

 

[kiira]

[quote author="rafafredd"]

then bypassed the series resistors with diodes for the phantom to reach the mic less inhibited.

I can´t understand. What does that means?[/quote]

LOL! I couldn't understand that either but I thought it was just me. :razz:

This thread made me remember my 417a's though so I went to find them I thought the'd maybe gotten lost like my Greyhill switches (boohoo!) but they were in my tube box. yay.

Kiira

 

[Svart]

the mics are phantom powered. Putting 1k resistors in series will greatly reduce the current to the mic in case it's a mic that needs a lot of OOMPH from the phantom supply. I added diodes in parallel with the resistors so that the phantom power current can flow through the diode and not really through the resistor.

With my mics, the phantom at the mic with the pad is 28v. probably plenty to work with but with the diodes it's 35v. not optimal still but works ok. I can't tell the difference really, but I think the lower voltage affects the low end some.

 

[Svart]

I know it's unconventional and likely flawed but I was just giving it a try..

Also it doesn't seem that the tubes are very linear, I think the low end is actually sloping off pretty heavily. This works great for the overheads since I don't need to EQ the bottom end at all! boosting/cutting less than 600hz seems to do nothing at all, 700hz is there though. I think the 5842/417a tubes don't reproduce below 700hz very well. The top end is beautifully clear though! I'll have a clip here shortly.

 

[ioaudio]

[quote author="Svart"]the mics are phantom powered. Putting 1k resistors in series will greatly reduce the current to the mic in case it's a mic that needs a lot of OOMPH from the phantom supply. I added diodes in parallel with the resistors so that the phantom power current can flow through the diode and not really through the resistor.[/quote]

http://www.jensen-transformers.com/as/as016.pdf

see how its normally done. put the 6,8k resistors directly on the mic input xlr and the pad after that. avoids the struggle. :thumb:

 

[Svart]

Yes I know. These pads are in line at the mics themselves since the mics don't have pads on them.

 

[ioaudio]

ahh- i seeeeeeeeeeeeee.

i wondered, you should heve known that with over 3000 posts :grin:

 

[Svart]

:green:

Yeah I bet most of that was rambling too.

I appreciate your help though.

I still can't get over these preamps.

I stuck some 20uf polypro caps I had between the tube output and the transformer in place of the 1uf caps I had and the tone changed but did not change the response.

I'm going to have to make a ton of these now!

 

[MatthewF]

It seems to have been a while since people have been talking about these 417A based pres. I just picked up some 5842s on ebay for a seemingly good price. The same seller has another pair available here;

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=330279000101

I hope these valves will be suitable, I think I'll use this circuit as my first foray into P2P tube circuit construction due to its low parts count...

Cheers!

Matthew

 

[CJ]

Good price, JAN stuff is premium.

Now if I could just get this Lars output done...

I'm shakin a stick boss, I'm shakin a stick.

(Cool Hand Luke)

 

[craptical]

Ahh, got them! Thanks Matthew! :thumb:

/Dave

 

[haiku-ish]

Hi, fisrt post here
i made this preamp ! great sound, my goto preamp since i'v build it.
i've also added a DI input.

JAN 5842

thanks a lot for sharing your schem and ideas...

 

[Wagtbtoobz]

Hmmm, an Alcatel 1:28 input , it should sound good ?    Pierre

 

[haiku-ish]

Hi Pierre  ;-) !!

yes an ortf

sounds really good !!

 

[strangeandbouncy]

Hi,


  I know I am very late to the party, but does anyone possibly have the schematic for this . . . .


    just found a 417 in an old box of stuff . . . .


    Kindest regards,


    ANdyP

 

[hobiesound]

while reading i was thinking the same as strangeandbouncy .... fork it over i say!

 

[zebra50]

   just found a 417 in an old box of stuff . . . .

As you do...  

Nice. That's one big red capacitor!