G-PULTEC problems, please help!

[djob]

money saving question...
here it's 230v mains power, and i happen to have a 230v:6.3v valve transformer for the heater, so can i skip buying the stacked transformers and just run straight from the mains power acording to rest of the gpultec psu schematic.

Brilliant approach against overpopulation.
Just don't run straight from mains power.

Thanks much Harpo,
I've now got my hands on a lovely transformer that powered four valves in a big old radio. Puts out 354v x2 (708v), 6.9v, and 5.5v. Heard up to 6.9v is ok on 'the valve wizard' but no center tap on the 6.9v so I'm thinking to create an artificial centre tap with resistors. However seems 354v much too high, any idea on the best work around for that? Cheers everyone!

 

[Harpo]

I've now got my hands on a lovely transformer that powered four valves in a big old radio. Puts out 354v x2 (708v), 6.9v, and 5.5v. Heard up to 6.9v is ok on 'the valve wizard' but no center tap on the 6.9v so I'm thinking to create an artificial centre tap with resistors. However seems 354v much too high, any idea on the best work around for that? Cheers everyone!

Transformer is AC voltage, so 354VAC get rectified to 500V raw DC (or from your 'x2 (708v)' number to even more insane 1001V raw DC. As AC mains voltage isn't a constant and might vary by +/-10%, giving 550VDC (or 1100VDC), your caps need a higher than this number voltage rating. The higher rated caps and resistor(s) for the needed voltage drop probably will cost you more than using the correct transformer. Selling the then not more needed radiator for room heating might further compensate. :

 

[frazzman]

This sounds like a recipe for lost limbs or worse... I suggest buying a custom wound gpultec trafo from donaudio, purpose built for this application with all the windings you need...

 

[Gustav]

Just put the final screw in a two channel version using a lovely case from our own Frank Röllen.

Its duplicated from Jakob's layout, and it does things to the sounds going into my ears that put a smile on my face - or maybe thats the other way around. Sunstroke set in hours ago.

Gustav

 

[Audioman]

Finally today i finish my two unit !! Sound fantastic !!
Thanks to Jakob for the fantastic layout and all the guys of this fantastic Forum !!

 

[Audioman]

Picture Two !!

 

[gyraf]

Very nice and clean build! Well done!

Jakob E.

 

[veve]

How does they sounds?
Is it the PCB Grinder kit?

 

[Gustav]

How does they sounds?
Is it the PCB Grinder kit?

Thats Jakob's original PeQ layout.

Gustav

 

[veve]

Oh Gustav I just realized that you're the man behind Pcb Grinder  ;D.

I've send email to you about the little mistakes on your CTQ page. 

 

[4earstudios]

Hi there

I did much searching but i dont really find an answer to this

I am building a Dual Pultec Enhanced Version. Im in the process of wiring the Led and the bypassboards from silent:arts. My problem as- i am an noob to this - is that i dont know/where exactly these are connected. i ve read i can take the current for the  power led from the heater 6,3v. But how to connect the bypass boards and the led on these, there is nothing writen on them (HWBP36) ( +,-, leds? )

Has anybody used this boards too?

Thx Daniel

 

[gyraf]

I don't think the bypass board is compatible here, we don't have standard opamp voltages available...

You can wire a LED from the 6.3V - use a 220 Ohms to 470 Ohms in series to control LED current.

Jakob E.

 

[4earstudios]

Hi Jakob
Thx for your insight, i´ll let the bypassboard bypassed ;D

Bye Daniel

 

[Harpo]

Im in the process of wiring the Led and the bypassboards from silent:arts. My problem as- i am an noob to this - is that i dont know/where exactly these are connected. i ve read i can take the current for the  power led from the heater 6,3v. But how to connect the bypass boards and the led on these, there is nothing writen on them (HWBP36) ( +,-, leds? )

Just use the type of relais that matches the HWBP36 pcb footprint and your available supply voltage (for instance Omron G5V-2-H1 DC6).
For about 10mA wanted LED forward current in order to not exceed parts limits and LED used as a status display (not building a headlight here) maybe use a (6.3V-1.9V)/0.01A=440 ohm series resistor in between 6.3V supply voltage, LED and 0V. The 1.9V example value will differ depending on colour and type of LED used. Just look up the parts datasheet of your LED and look up the forward voltage Vf parameter.

 

[APL]

I have recently finished and  tested my G pultec. The low boost and cut appear to be working and so is bypass. The Q, high boost and high cut do not seem to be doing anything.

I see others have reported similar problems. I have checked following.

High boost - I have checked continiuity to pot, caps and through switch all appears ok. I get a range of resistances between switch and common (blue ) of sowter inductor eg at 2.3 khz setting resistance is 33.5ohm at 18.7 kHz= 8.5 ohm. At other settings in between, resistance is within this resistance band. So High boost inductor seems to be ok or at least doing something. The capacitor values are also correct.

Q pot- Checking again I suspect I may have problem with pot or more  like joints at pot or molex connecter to PCB. I will stip everything down and sort this.

High Cut - This all appears to ok.

a) I can see that problem with Q pot could affect high boost but would it affect high cut? If not any suggestions?

b) Somebody else  had these symtoms and eventually appears to have concluded he had the in and out mixed up between passive board and the power supply/amp. I have connected out to out and in to in. I assume that is correct?

c) I previously mentioned about the mystery 10k resistor shown attached to the junction of 10k and 1k resistors on low freq circuit, but missing on actual circuit board. Jacob thought it was probably redundant, however I would to add it in case it is relevent to my problems. Can I solder this directly across OUTPUT and GND connection below Bypass switch or is there a better location?

I would be grateful for any suggestions.

 

[APL]

Ignore last post. I resoldered Q pot and a few other connections and it all works fantastic no noise. I did not need to add the 10k resistor.

It sounds good with one OEP output transformer. I just need to replace with the 2 llundahl transformers I just bought in Black market so should sound even better.

Thanks to everybody who helped especially Jacob for help and the design.

 

[veve]

I just realised that there is some differences between the frequencies of the original eq and the Gyraf eq. I bought the original case from Collective Cases so, is it possible to get the original frequencies?

 

[gyraf]

Have you read this thread and the Pultec META?

Jakob E.

 

[veve]

Not the whole tread  :-[

I think now I have to... :-\

Please don't blame me :'(

Anyway, is it difficult to modify to have the original frequencies? If it's then I will buy a front panel with de Gyraf frequencies..

 

[ding]

Dan is a pretty cool guy. I'm sure if you email him and send back the front panel he would be able to help you out here. Not trying to put words in Dan's mouth here so check with him first. I have bought lots of cases and panels from him and have nothing but great things to say about him.