G-PULTEC problems, please help!

[Majestic12]

That's it....I'm such a stupid guy. Used a ECC83 (12AX7) instead of an ECC88. Must have read the schematic wrong (it's hard to read the .gif files on Gustavs website). Confused 88 with 83.....


Changing the tube should fix it, thank you guys

 

[PeteC]

Let us know !!

hope it works out for you.

Pete

 

[Majestic12]

Problem solved. After swapping the tube for an ECC88 and setting the resistor to 15K I got 252 V HT voltage.
Unit seems to work as it should, there is only a slight bass roll-off at around 40Hz even when turned to bypass and with attenuators turned down.

 

[Songguy]

Hi all,
Potentiometer question:
Will I have any problems if I use a 10k audio taper pot rated at 200v instead of 500v?

Many Thanks,
Chris

 

[Majestic12]

No, shouldn't be a problem.

 

[audiophreak]

  Hey  Majestic12 ,  got this from a few pages back , thought you might benifit from it , I think I have my B+ sitting about 238vdc .

Does the higher voltages for the HV+ matter?  I'm trying to understand what it does and why the 30-40V difference would matter.

It matters - because we're already stretching the ECC88's voltage capability to the edge (it's anode voltage is rated some 90-120V depending on what datasheet you consult)

Ca. half of our HT voltage appears across each half of the ECC88 - so the suggested 250V HT shouldn't be exceeded by too much.

On very-high-overvoltage units, there is a tendency of premature burn out of the tube.

Adjust voltage by trying different value resistors between resevoir caps - circuit sounds good between 200 and 250V.

Jakob E.

 

[keefaz]

Unit seems to work as it should, there is only a slight bass roll-off at around 40Hz even when turned to bypass and with attenuators turned down.

Is there the same bass roll-off when you connect the output of your 1176 comp in the gpultec input (eg connect the 1176 between your sound source and gpultec) ?

 

[PeteC]

just curious .....

has anyone tried messing with LED cathode bias or a CCS in the tube stage of the G-Pultec ?
I've used these on my audio and guitar amps with success - just wondering really before I start to build my pair.

Rgds
Pete

 

[benlindell]

Where's the best spot to take power for a 6.3V lamp?

 

[audiophreak]

Hi Ben ,
          I used an LED for less current draw and soldered leads to the tube socket pins for the heater under the PCB. 
 

 

[snipsnip]

Where's the best spot to take power for a 6.3V lamp?

you can just take it straight from the secondary and drop it with a 2 watt resistor.

 

[benlindell]

Where's the best spot to take power for a 6.3V lamp?

you can just take it straight from the secondary and drop it with a 2 watt resistor.

What value resistor? I'm not so hip with my formulas.

 

[idylldon]

Where's the best spot to take power for a 6.3V lamp?

you can just take it straight from the secondary and drop it with a 2 watt resistor.

What value resistor? I'm not so hip with my formulas.

Use Ohm's law.  Piece of cake.

Cheers,
--
Don

 

[benlindell]

So 6.3v and .15amps means around 42ohms right?

 

[Majestic12]

R=U/I

6,3V/0.15A = 42 Ohm

But 150mA current only for the lamp seems much. Don't know if the regulator can handle the current.

 

[PeteC]

quick question ...
I'm building 2 G-Pultecs,

I have all my parts ordered and in my stash except for the 4.7uF output coupling caps

I have some very nice 2.2uF caps surplus from a hifi project - could I sub these without loss of low freq signals on the output or will this be detrimental to the sound ??  ( I only have one for each EQ though otherwise I'd try to pair them up to get 4.4Uf.  )

Dont want to compromise the units as I'm using gold pin mullards for the SRPP stages.

Any advice very welcomed - especially help to understand how the cap value affects the freq - I'm not sure which resistance in the output circuit  is reacting with the cap for the RC value 

cheers
PeteC

 

[PeteC]

bump..sorry..... can anyone help me out on this ?

Cheers
PeteC

 

[audiophreak]

try this  -  http://www.muzique.com/schem/filter.htm

 

 

[PeteC]

thanks - I'll play around with that -

still not sure what the impedance of next stage is - ie the impedance looking into the Lundhal output TX and loading of next piece of kit.
Rgds
Pete

 

[PeteC]

Can anyone help me here ........
I'm building 2 G Pultecs at the moment from Gyraf's excellent resource.

today my neighbor helped me develop and etch all 4 boards for both units.

The 2 main boards ( PSU and tube stage ) went great - but we hit problems trying to get the filter boards to etch properly due to the position of 2 very close traces at the edges of the boards

His solution is for us to edit the layout so we have more space to play with ( and seing as he is doing all the helping out for me I cant really argue with that - so after a couple of aborted attempts we stopped using more photo resist board.

Question is - does anyone have an editable version of the pcb layout I could edit to move tracks around ?

I realise that many of you will have been able to etch the boards,  just as they are designed , quite successfully - but we had some problems with the closeness of these 2 tracks.

Can anyone advise on a way to overcome this or a way to convert and edit the pdf? Or is there an Eagle version etc somewhere ? 

All help much appreciated. - Cant wait to get these units built and running in my set up.

Rgds
PeteC