seavote

Hamptone LCMP tube micpre question
« on: January 03, 2008, 08:28:36 PM »
i'm considering an LCMP tube pre build:
http://www.hamptone.com/figure1.htm
http://www.hamptone.com/tape_op_art.htm

the metal work is no problem. i'll use the recommended power supplies from mouser. this leaves the audio board to DIY.  My problem is that i dont understand how to hook up the jensen jt115
http://www.jensen-transformers.com/datashts/115kepc.pdf

to the LCMP audio PCB
http://www.hamptone.com/LCMP_CV.htm
4 pins on each side of the jt115. 6 pins on the pcb where the input transfomer is connected. what am i missing?
Everyday is a gift. Thats why it's called the present


mad.ax

Hamptone LCMP tube micpre question
« Reply #1 on: January 04, 2008, 05:58:07 AM »
Hummm...
Looking at the PCB, I count 12 pins for the input transformer (XT in), and 8 for the output transformer (XT out).
On XT out, 2 pins are soldered to the ground so at first sight it may look like 6 pins... But the JT115 is an input transformer, right? Not an output one.

On the JT115 you need to use only 6 of the 8 pins
1 is input hot
4 is input cold
5 is output hot
6, 7, and 8 to the ground


For XT in, only four of the twelwe pins are usefull on the PCB, they are labelled 4,5,6, and 7.
4 is output hot        connect to 5 on the JT115
5 is output ground   connect to 8 on the JT115
6 is input hot          connect to 1 on the JT115
7 is output cold      connect to 4 on the JT115

you can use the two pins on both side of the one labelled 5 on the PCB to connect pins 6 and 7 from the transformer, or tie 6, 7, and 8 on the JT115.

Happy new year!
Axel

seavote

heater question
« Reply #2 on: January 04, 2008, 10:43:19 PM »
Yes jt115 is an input transformer. i havent decided on an out put transformer yet. thanks for your help. perhaps you can indulge another question. the LCMP uses  50.4 VDC  to supply the 4 tubes heaters(wired in series). am i right in thinking that if i build one channel (that's my plan)
and add another when i can swing the $$$$. i must add some type of "dummy load" to the heater circuit?  if so, would i calculate it the following way?  2 tubes are used in each channel:1 6072 and 1 12au7.    each tube wired in series requires 12. [email protected]  so 300ma (two tubes in a channel) divided by 25.2vdc   equals 11.904 ohms.
can i use a 12 ohm resistor ,to ground,for a dummy load? i hope so as this will mean i'm starting to understand what i'm doing better. :wink:
Everyday is a gift. Thats why it's called the present

mad.ax

Hamptone LCMP tube micpre question
« Reply #3 on: January 05, 2008, 06:50:59 AM »
almost there! But be carefull, a 12 Ohms resistor would  draw way too much current!

You assumed that R = I/U that's your error.

 R = U/I wich means R = 25,2V divided by 0,300A = 82 Ohms

Now that you have the value for your dummy load resistor, you should worry about the power dissipated in it...

P = U X I = 25,2 X 0,3 = 7,56 Watts. For safety margin let's use some 15 Watts. So you need a 82 Ohms/15W resistor...  Not so common, and not so cheap...

Since you plan to build the second channel someday you could go another route;
Wire the heater circuit on 2 more Noval sockets, and plug in a couple of whatever old 12xx7 you may have in your junk boxe... Here is your perfect dummy load...

Axel

rafafredd

Hamptone LCMP tube micpre question
« Reply #4 on: January 05, 2008, 01:26:37 PM »
I donĀ“t get c8...??? Just take it out!?  :?

seavote

Hamptone LCMP tube micpre question
« Reply #5 on: January 06, 2008, 04:38:56 PM »
mad ax, thanks. the best solution is the simplest.i'm ordering double caps and resistors anyway so i will make 2 pcbs and populate them. trannies,XLRs and switches on the second channel will come later. i have a bunch of 12au7s (uos) ,im sure i can find 2 extras that work.does anyone know what output transformer came with the LCMP kit. the jensen 4:1 output transformer is about $125 and i'm looking to go cheaper.
Everyday is a gift. Thats why it's called the present

pantsonfire

Hamptone LCMP tube micpre question
« Reply #6 on: January 06, 2008, 07:23:49 PM »
I don't know what came in the original kit, but I used an Edcor WSM15k/600 in my PTP LCMP and it sounds great. $10USD. Maybe Edcor makes a version that would work with a pcb. Also, if you email Scott Hampton, I'm sure he'd be glad to give you the info you're looking for.

best of luck.


 

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