G-PULTEC problems, please help!

[telefunk]

ok, my g-pultecs are up and running (and sounding REALLY smooth!) but one slight little problem i seem to have.

This only happens when BOTH of my pultecs are inserted to my Soundcraft 6000 input channels: when I put full HI-boost of 18Khz with both of them with "q"-range in zero, it starts to oscillate. Both of them. And it gets less when I make some extra grounding to the case.
Has it  something to do with impedance??!

 

[gyraf]

There's no way to get the pultec to oscillate by itself (it's a passive eq), so you must have a wireing or setup problem (some output signal making it's way back to input)

Error is probably in the soundcraft and/or in the ground wireing

Jakob E.

 

[mamiti]

Hi,

would anyone be willing to share gerber files for GPultec pcb as I couldn't find them at gyraf.dk?

Thanks,

MT

 

[skal1]

Hey mamiti 

here is the pdf , you can make a pcb from the files


http://gyraf.dk/gy_pd/pultec/gy_pd.pdf

skal1

 

[mamiti]

Hey mamiti 

here is the pdf , you can make a pcb from the files


http://gyraf.dk/gy_pd/pultec/gy_pd.pdf

skal1

Thanks, I've got the pdf already. Thing is that the pcb drill really likes gerber or some other common design file format. PDF is better suited for home-etching. I'm not going to produce these for sale but I just happen to have an access to a great drill so etching is too much of a hassle if there is an alternative.

Anyone?

Cheers,

MT

 

[gyraf]

I don't think we ever made Gerbers for the GPultec...

Jakob E.

 

[mamiti]

I don't think we ever made Gerbers for the GPultec...

Jakob E.

Ok, thanks for the info. I'll try to find a way to import pdf.

Cheers,

MT

 

[mrcase]

hey!

I just finished my first pultec, sounding really nice so far - but I just wanted to clarify how to measure the voltage for the tube correctly.
I´m measuring 290V without the tube in the socket - is this okay or is this way to high? Or do I have to measure this with the tube in the circuit?

thank you all

 

[alexc]

Can anyone explain the effect of using an SRPP with unequal cathode resistances ?
(1K and 470R in the gpultec)

I'm finding on mine I have 250V at the plate of the top tube and around 85V on the
cathode of the top tube. It seems like it should be more like 125V as indicated on the diagram.

Using an ECC88

Thanks

 

[danielb]

Can I use this bridge rectifier 1000VAC(700V RMS)/1.5A?

 

[gyraf]

mrcase: Always measure voltages with tube in place and heated up.

alexc:  The unbalance is on purpose, giving a bit lower output impedance. Only drawback is reduced maximum swing into high-Z, but is outside what we want anyway.

danielb: 700V/1.5A is just fine for the rectifier bridges.

Jakob E.

 

[alexc]

Thx Jakob.

 

[danielb]

Thanks Jacob

Can I i use one of these capacitors for the "4,7uF 250V":

http://elektronik-lavpris.dk/product_info.php?products_id=85892
http://elektronik-lavpris.dk/product_info.php?products_id=102760
http://elektronik-lavpris.dk/product_info.php?products_id=85565

 

[gyraf]

nope, first one is electrolytic, the two next are physically too bit to fit (37mm - we do only have 27½mm spacing - check the pcb).

Jakob E.

 

[audiophreak]

Hi All,
    I purchased two of these - http://www.hammondmfg.com/pdf/5c0030.pdf - the 261G6, and was wondering if i can just hook up the 250vac and the 6.3vac to the appropriate power input pads on the PSU PCB ?  I think the 250vac would work fine, but the 6.3vac when rectified would bring it to maybe 9.2vdc ?  is that enough " differential "  for the LM317 to regulate ?  and would I need to change the " adj. leg " resistor ? 

  any help is always appreciated,
                                            Thanks,
                                                        Chip

 

[Kingston]

is that enough " differential "  for the LM317 to regulate ?  and would I need to change the " adj. leg " resistor ?

It's not enough, or just barely. Realistically when the tubes start pulling current that 9.2VDC drops to maybe 8-8.5VDC. Regulator will drop that 3V more. But you don't really need the regulator in the first place. Replace it with a simple resistor and you will have enough passive filtering for decent DC stability.

Or you can just take the 6.3VAC directly to tubes with carefully planned (or well shielded) wiring.

 

[audiophreak]

Thanks so much Kingston !
     ... so bypass LM317 and add maybe a 1w or 2w dropping resistor after bridge rectifier for 6.3vDC heater ?  

 

[audiophreak]

Hi All,
   
    Got some Questions  ;D

  I am attempting a dual G-Pultec in a 2U case, have used this PT - http://www.hammondmfg.com/pdf/5c0030.pdf - the 261G6 - this PT has a 250vac/ 130ma secondary and a 6.3vac/2.0A secondary. Secondaries are split from terminal block to each PSU-I/O board.  I replaced the 3k3 2w resistor with a 33k 5w and am getting +247vdc after rectifier ( under load ).  Swapped out LM317 with a TL1086 a 1.5A Low Dropout Positive Adjustable Regulator, changed the 1k8 adjustor with a 1k86 and got  +6.26vdc ( under load ) .  so I think I'm good powerwise.

  I've mounted and stacked the control boards to the case floor about an inch behind the front panel. The PSU boards are on the left side towards back of case, so the ( In / GND / Out ) connecting PSU- I/O board to Contolboards, using shielded cable is 6-8 inches long - will that cable length cause a problem ?

  I've read this thread and am searching now, but what is the grounding scheame for this ?  is it just earth ground from IEC connector to case - and thats  it ?  Input shield to XLR ground tab to  " Star Ground " do I run GND shield on output from I/O to XLR ground tab to " Star ground "  ? 

  also, does anyone have the actual frequencies for front panel labeling ?  I seem to remember seeing them somewhere, but not sure where. also I seem to recall some thing about a " enhanced Pultec EQ "  is that  a mod for this project ? or is that a whole other project.

  as always, any and all help appreciated

  Thanks 
 

 

 

[snipsnip]

Hi,

I had issued with mine as a dual build, and its currently in bits waiting to be made as 2 standalone units... so this is just from memory.

I didnt have a star ground on my build. I think the connection on pin 1 will mean it will be grounded to the next piece of kit its plugged in to. I dont think you need to the the audio ground to chassis in this build... but appreciate others opinion here. IEC to chassis is obviously for safety reasons.

Regarding cable length, shouldnt be a problem... I dont think you even need to use shielded wire in this build if you dont want too (again, I appreciate others input here)

 

[audiophreak]

Thanks snipsnip ! 

  I seem to recall a thread where someone said if their Dual unit didnt work out they would just put them in separate cases. I plan on doing the same if I end up with problems I cant figure out. I feel that if the noise or hum ( wont know till I fire it up ) is induced by having two large PTs in the case, I may have found a solution with the PT I'm using, and because its all in one PT, I have room in the case to shield it if shielding it is the solution, or mount outside case.

If grounding scheme is just IEC earth ground to case, I cant see how a " ground loop " can occur , but then again I am still soooo much a newbe  ;D

  I found some pics of other units in the metameta, so I have written down the frequencies , I'm sure they're close enough.
  An Interesting read here - PULTEC - Input Options -Buffers- Imp - TX - JLM Hybrid opamp - does this apply to this tube version ?  and if so , has anyone done it ?  also, is it just a case of adding caps and inductor values to add/increace  frequency selections ?

I do appologies if any of this has been covered, I've just finihed reading the G-Pultec threads from the metameta and my eyes/brains are I little fuzzy  ;D

Thanks again snipsnip and to All