G-PULTEC problems, please help!

[scott_humphrey]

Hi All,
       Finally got some pix of my Dual G-Pultec !!!   

    I used the Hammond 261G6 power trans, it has a 250V C.T. @ 130 ma secondary 6.3V @ 2A secondary. I replaced the 3k3 2w resistor with a 33k 5w resistor to bring the rectified 380vdc down to 240vdc.  I replaced the LM317 with a TL1086, its a low voltage drop out regulator and a drop in replacement, although Kingston mentioned that just a dropping resistor could be used as after rectification its about 7.8vdc.
     The front panel was done at Prodigy Engineering, I think I may have crowded the left side as I wanted to keep as much room as possible between filter boards and power switch. Collin at AML now carries all the pots for this all in 1/4 inch shafts.
    I haven't done extensive testing yet, but so far it sounds Fantastic !  - clean, fat, big bottom end ... and Smoooooooth   ;D
    no hum or buzz or grounding issues - I only have IEC ground to chassis, I have a ground wire in place to connect to pin1 XLR inputs, but haven't tried it yet

  Here is a link to some pix - http://picasaweb.google.com/audiophreeek/DualGPultec?feat=directlink

  If anyone wants the panel graphic, I have it in Illustrator , just email me.
  All questions / comments welcome


  Big THANKS to Jakob E. / Gyraf , Kingston , snipsnip , benlindell ,  and to this great forum.


   

She's a real beaut, Clark!

 

[audiophreak]

Thanks Scott !
                      I love the sound of this thing so much, as soon as I finish my current project ( a quad of NewYorkDave One Bottles ) ....  I'm gonna build another one 

 

[ncoak]

just wrapping up sourcing everything for my g-pultec - last item on the list is a socket for the tube. i've scouted around online, all the 9-pin sockets i've seen look like the pins are too large for the holes on the gyraf board. can anyone point me to an appropriate socket? unfortunately my local stores don't carry them so i can't just take a quick look...the wonders of the internet age

 

[snipsnip]

I couldn't find ones either. I drilled out the pcb holes a bit.

 

[ncoak]

curses!

came across this thread for anyone in the same boat...will post results when they arrive.

http://www.groupdiy.com/index.php?topic=7392.0

edit: received the sockets and the pins were indeed too big; trimmed them down to size no problem.

 

[audiophreak]

Hi,
  I've used these - http://cgi.ebay.com/tube-sockets-9-pin-pc-gold-ceramic-25-pc-bag-wholesale-/330528394271?pt=Vintage_Electronics_R2&hash=item4cf5070c1f#ht_500wt_1156

  I've built a lot of tube gear so I got the bag of 25, at that price , even with shipping it comes out to just over $2 a socket.
  Not sure if its the same seller , but havent had any problems ... yet  ;D

 

[leadbreath]

hi

could someone please tell me the current drawn for the g-pultec circuit??

cheers
mick

 

[audiophreak]

Look up the Tube Data sheet, I think the heaters are about 400ma and the B+ is around 15-20ma  then of course LED or lamp  

 

[ncoak]

where exactly should i be taking the various voltage measurements - black probe to ground, red probe to ?

 

[ncoak]

if i'm interpreting the overlay correctly, i should be able to measure ~250v at pin 4 and 6.3v at pin 6 - just want to verify that i'm measuring with respect to ground here...and that touching a probe to these pins with the other probe to ground (case/star ground) won't leave me cooked like a thanksgiving turkey  ;D

 

[kazper]

You want to take your voltage readings across the 2 wires... IE the black and red wires from your T2 Antek transformer. With using the 6v secondaries you should be very hot on your T2 primaries (actaual transformer, not as in use/backwards. I'd recommend taking your readings with the tube out, get voltages close then try with a tube in it.

Kaz

 

[ncoak]

ok...so i've got the transformers sorted, getting a nice 236v going into the board - led attached to the 470r by LM317 lights up as it should, lovely.

...until i plug the tube into the socket, at which point i get no LED action, and the tube doesn't heat up. i've tried 2 different tubes so i'm pretty sure that's not the issue. any ideas of what i should look for to get this going? learning as i go here so i'm not exactly sure between which two points i should be taking voltage measurements around the tube - if anyone could shed some light it'd be greatly appreciated.

please excuse my noobness!

 

[audiophreak]

Hi,
    I'm still a Noob too.  I wouldn't take the feed for the LED from the 470r as thats part of the ADJ. circuit to set heater voltage. I soldered a wire to the heater + tube socket pin on the bottom of the PCB with a 420r in-line to the LED.

  Look at the PCB Layout on Gyrafs Web page and just follow the traces to the tube socket pins to check heater and B+ voltages, black meter lead to star ground or heater ground, red meter lead to heater+ or B+ pin on tube socket - BE CAREFUL  !!!

 

[ncoak]

thanks audiophreak - i've been mulling this over and studying the circuit, definitely going to take your advice on the LED.

edit: noob alert

 

[ncoak]

got this guy up and running, sounds great! 226v between tube pins 4 & 5, 6.3v between 5 & 6. moving the led made all the difference of course - learned quite a bit in the process of this build. thanks to everybody for the help, and of course to jakob for making it all possible.

 

[audiophreak]

Congrats    Glad to hear it .... Enjoy !!!

 

[muffy1975]

Guys,

The first 2 low frequencies don't work in boost mode on my g pultec? has anyone got his or fixed this problem? i believe these two frequencies are covered by a 2u2 cap and a 1u cap.

help please

michael de A ???

 

[funkymonksf]

Does anyone have a bom for this project?

Oh pretty please!

-Brice

 

[gyraf]

The first 2 low frequencies don't work in boost mode on my g pultec? has anyone got his or fixed this problem? i believe these two frequencies are covered by a 2u2 cap and a 1u cap.

..make sure (with ohm-meter) there's connection through the frequency switch and into the capacitors - that's the only thing that can go wrong there, I think..

Jakob E.

 

[muffy1975]

With Regards B.O.M,

for the filter section, most people are using polypropylene capacitors for the LF sections ( Wima MKP4 or MKP10 ) or other boutique polyprops etc.

For the high section they are using polystyrene caps, sometimes in series to build up the value required. made by xicon from Mouser these are cheap and rock. Some people are using silver mica caps but they are 10 times the price.

The switches are 2 pole 6 positions switches MBB. The pots I believe are 10k lin, 100k log, 10k log, 2k2 lin and 1k lin.

The resistors are 1/4 watt metal film etc.

The PCB with the tube......all the values that you need are stated in the PDF. Actually so are all the values for the filter section.

Go for F&T caps for the big 220uf caps and the 4700uf cap. They are great PSU caps.

Michael