G-PULTEC problems, please help!

Ok thank's..

I will built my Pultec first and see if it works... Then after I will advise with the front panel  ;D

Hi all,
I've had one of my pultecs sitting on the shelf a while, I always thought it sounded "good" but never "great". Today I put it under the microscope and noticed in RMAA that there was a wide +3db sub bass boost ~25hz going on both with all knobs zero'd AND in bypass.
Any ideas where to look, possible wrong component ? Aside from this all else is well, no noise and all freq positions work fine... Appreciate any insight

frazzman said:

Hi all,
I've had one of my pultecs sitting on the shelf a while, I always thought it sounded "good" but never "great". Today I put it under the microscope and noticed in RMAA that there was a wide +3db sub bass boost ~25hz going on both with all knobs zero'd AND in bypass.
Any ideas where to look, possible wrong component ? Aside from this all else is well, no noise and all freq positions work fine... Appreciate any insight

Click to expand...

Looks like I'm not the only one who has observed this frequency response:

https://groupdiy.com/index.php?topic=21818.0

That user reports simular behavior.

Is this boost 'normal'?

If so, why? And how could it be changed? I think that boost produces a kind of 'wooly' sound...?

Resonance between output capacitor, transformer primary, and whatever load you give it?

Try with a larger output capacitor and see if that helps - e.g. a 10uF

"wooly" is not in that area, at least in my nomenclature

Jakob E.

Hello everyone!
I have a Gyraf pultec I built a few years ago, that recently started to show some problems.

Symptoms: Low freq cut pot does nothing (Low freq boost works normal), AND the HF "bandwidth" pot reduces HF when turned clockwise. When the HF bandwidth pot is full CCW, there is HF gain at the correct freq. It looks like from the schematic that these could be relate to the same fault, but since I'm not smart enough to know, that's why I'm here.

Anyone care to bite on what the fault might be??

Thanks in advance!
Cheers
mike

Nothing in there that wears out - try replacing the pots in question..

Jakob E.

Thanks Jacob!
I'll try that.
m

Shoot me if this is a simple search solution!

My own PCB etch of  this thing... didn't print it from gyraf layout, just made my own, so who knows...

With the EQ "IN" and all the controls down... I'm getting about 1db signal loss? This is normal?

jwhmca said:

With the EQ "IN" and all the controls down... I'm getting about 1db signal loss? This is normal?

Click to expand...

A matter of component tolerance - specially the exact value of the 10K hi-boost pot, which forms upper part of the overall-attenuator of the filter in bypass

Jakob E.

I made a stereo version of the PCBgrinder pultec, and it sounds great! But I've noticed that the left channel is about 0,5 or 1 dB lower than the right channel, and when I boost the highs all the way the differance is a little annoying. How can i compencate for that?

Allso i see that the plate voltage on the left is 240V, and the right is 245V.

Raw gain in a ECC88 varies a couple of dB. Try swapping/replacing tube?

Hi guys,
I'm getting conflicting information everywhere I look... For the power switch, is it SPST, SPDT or DPDT??
Cheers!!

naths101 said:

Hi guys,
I'm getting conflicting information everywhere I look... For the power switch, is it SPST, SPDT or DPDT??
Cheers!!

Click to expand...

You can use either SPST, SPDT, DPST or DPDT. But DPST would be best.

Majestic12 said:

You can use either SPST, SPDT, DPST or DPDT. But DPST would be best.

Click to expand...

thanks mate!

Hi everyone! I just finished soldering and mounting pcbs and other parts for this project...But get into these problems...
On first test the eq seems working but at really low volume...had mounted both input and output lundhals...Had also a lot
of noise... I am a beginner so I tried to disconnect the filters board to try to figure out where the problem might be...but the
background noise still remains...Thanks for any help!!!
Emanuele

hey guys. i wanted to know, how i need to wire a 4 pole pot (e.g. something like this: http://de.mouser.com/Search/ProductDetail.aspx?R=CK2375virtualkey12200000virtualkey10WA177) to swith the pultec on and off?

this is how my frontpanel looks

weiss said:

hey guys. i wanted to know, how i need to wire a 4 pole pot (e.g. something like this: http://de.mouser.com/Search/ProductDetail.aspx?R=CK2375virtualkey12200000virtualkey10WA177) to swith the pultec on and off?

this is how my frontpanel looks

Click to expand...

Something like this switch with 45° indexing for switching mains voltage (whatever your mains voltage might be).
(not a pot and you don't need 4 switch poles. Your link shows a Lorlin type rotary switch with 30° indexing, capable of switching 150mA and 6.35mm (not 6mm) spindle diameter)
Please update your profile with your location data.

Harpo said:

Something like this switch with 45° indexing for switching mains voltage (whatever your mains voltage might be).
(not a pot and you don't need 4 switch poles. Your link shows a Lorlin type rotary switch with 30° indexing, capable of switching 150mA and 6.35mm (not 6mm) spindle diameter)
Please update your profile with your location data.

Click to expand...

okay so i need to buy a new one
thanks

weiss

Emanuele,
I dont think anybody answerered your question about noise. Try looking back through posts here. Im no expert but possible problems may be
1 faulty tube
2 the power transformer interfering with inductors. Solution move transformer or shield inductors
3 Grounding is a common reason.See post #439 17 Sept 2013 for correct method

Hope you find the cause of problem .
PS Remember to Check and recheck you solder joints and continuity

Hi everyone,

I'm currently building a stereo gyraf Pultec based on PcbGrinder's CTQ PCB.
There is no fuse on this pcb, and I need to put a fuse in front of my transformer (from don audio)
What is the correct fuse value for 2 boards?

Thanks for your help