G-PULTEC problems, please help!

[gyraf]

What I usually do with this type of problem is simply to cut the remaining unwanted copper with a sharp knife..?

Jakob E.

 

[Majestic12]

My second Pultec is ready. This one is for a friend of mine. Looks as beautiful as the first one

 

[MicDaddy]

8)

Lookin' good, nice and clean Majestic

 

[Majestic12]

BTW, is there a specific reason why the bypass circuitry is the way it is? Wouldn't it be much easier and better to use a switch to simply switch the Input directly to the output?
In the Gyraf circuit, the the bypass doesn't prevent the signal from going through the transformers and gainstage.

 

[MicDaddy]

I like the signal in bypass 

 

[PeteC]

Jakob,
thanks - you're right of course - redrawing the board is a rather extreme solution to the problem.

In the end as we botched up 1 of the filter boards I have hand re-drawn it and etched - its electrically sound even if it looks a little amateur.

BTW - thanks for putting such great projects in the hands of keen hobbyist engineers like myself who are really musicians. its much appreciated.  My GGSL is a great bit of kit - so I cant wait to complete the 2 G-Pultecs.

Thanks again
PeteC

 

[Songguy]

Hi guys,

If I wanted to add an unbalanced 1/4 input to my g-pultec is it really as simple as wiring it to the board and mounting the  jack?
Cheers,
Chris

 

[Majestic12]

Yes, that's all you need to do.

 

[PeteC]

Just finished etching and drilling the last of my 4 boards for the G Pultec pair I am building - getting very excited - Like a big kid again .. ;D

Pete

 

[karloff70]

Hi chaps....

I bought a diy Pultec off someone and it is rather 'ghetto'.....and has issues that I can not grasp. The main one at the moment is it powers up ok, works initially (valve glows, if not very much...) then gradually over the next minute or two it stops glowing and descends into thin distortion and out........any clues/ideas would be appreciated very much!

 

[audiophreak]

Hi,
    I'm still very much a newb , but I might put a DMM on the B+ ( could check it at the tube side leg of the 3k3 2w resistor )  to see if that stays stable ( should be around +245vdc ).  Then check the heater voltage if it satys stable  ( could be checked at the middle pin of the regulator - should be around 6.3vdc ). If all of that checks out, try swapping  in another tube .

  Hope this helps - BE CAREFUL  !!

 

 

[ncoak]

Hi chaps....

I bought a diy Pultec off someone and it is rather 'ghetto'.....and has issues that I can not grasp. The main one at the moment is it powers up ok, works initially (valve glows, if not very much...) then gradually over the next minute or two it stops glowing and descends into thin distortion and out........any clues/ideas would be appreciated very much!

possibly too small a heatsink on the regulator - someone had a similar issue on the first page of this thread.

 

[karloff70]

Thanks guys!! I'll measure (carefully...) and get a bigger sink, as the one in there is indeed smaller than e.g. the one in the Pultec earlier on this page.........hmmm, makes me think the seller told me porkies, as if that is the case the thing would never have been happy as is.....

 

[PeteC]

Hi All,
Another one is born ....and its twin is nearly here too.....
I just completed the first of my pair of G-P's and its working fine first time  ;D

Just the artwork to do now.

Does anyone have any ready-made panel artwork that has the frequencies on it ?  I'm using Mac OSX

The second G-P just needs the case drilling now and final wiring.

So thanks to Jakob and this fantastic forum, I now have a GSSL  and 2 G-P's in my project studio, and have etched the boards for a Dual Green pre.  Also on the list is a DIY Tube Mic, but I may have to sell some gear to buy a good capsule i think.

Meanwhile any help on artwork much appreciated, I'm using Lazertran Injet on Black panels.

Cheers
PeteC

 

[Nick Franklin]

Hi Pete,

PM me your email and I'll send you the artwork. I've got tons of advice for using the lazertran product too.

Nick

Hi All,
Another one is born ....and its twin is nearly here too.....
I just completed the first of my pair of G-P's and its working fine first time  ;D

Just the artwork to do now.

Does anyone have any ready-made panel artwork that has the frequencies on it ?  I'm using Mac OSX

The second G-P just needs the case drilling now and final wiring.

So thanks to Jakob and this fantastic forum, I now have a GSSL  and 2 G-P's in my project studio, and have etched the boards for a Dual Green pre.  Also on the list is a DIY Tube Mic, but I may have to sell some gear to buy a good capsule i think.

Meanwhile any help on artwork much appreciated, I'm using Lazertran Injet on Black panels.

Cheers
PeteC

 

[PeteC]

Hi All,

a bit deflated tonight as I tested the first of my newly finished G-P's as an insert on some tracks in Mixbus.

I seem to be getting a lot of distortion when using the unit as an insert. Especially from the low boost. In fact the unit only seems to stay clean if the sends are quite low.

How do I go about testing to see if its my sends and return that are too hot - or whether I have a problem with my unit.
It sounds like blocking distortion so I'm wondering whether my caps are OK etc etc 

Not sure where to start so any advice on a methodical approach to tracking the issue down would be great.  I'm using allegedly good Mullard NOS ECC88's so I'm hoping the tube is good . I will try subs to see what gives.

Any help much appreciated - a lot of late nights have gone onto building these EQ's !!!

Rgds
Pete

 

[Nick Franklin]

Are the tubes you're using definitely good?

 

[PeteC]

I think so Nick ,

I just swapped one for an E88CC - and exactly same voltages and symptoms -

after a bit of testing I noticed that my HT is sitting at 279v and heaters at 6.23 v -  so I think I ned to drop another 30V or so across the power supply.

I'm reading 18v across the 3k3 resistor so reckon drawing 5.45ma , to drop another 30v i think i need another 5K5 or so resistance to get under 250V for the HT

I wonder whether this is the problem ? would a too hot HT show these issues ?

I just ran some tracks in mixbus, and found that with the sends all down low then the blocking distortion was gone, and the EQ sounded great - maybe I'm just to hot with te faders on my mixes usually !?

Still concerned that there is something wrong with a cap in my filter section though.

PS thanks Nick for the great help earlier on teh panel graphics - really really helpful - much appreciated.

Rgds
Pete

 

[gyraf]

I'm pretty sure that you have a level problem.

What sort of levels are you feeding the eq with?

The GPultec output stage is happiest running the old-fashioned standard +4dB as in analogue tape recorders, which means some 10dB headroom above this before nasty sneaks in.

Try to output a 100Hz full-level sinewave from your system, and verify with a multimeter that it's not much more than +14dB - ca. 3.9V AC

Jakob E.

 

[PeteC]

thanks Jakob,  I will try that

I forgot to add that I'm running unbalanced inputs at moment until i get more LL5402's for each unit

I'm sending out from MIxbus on my Mac into an Edirol FA-101 interface , and then using the send and returns on the interface.
I dont know what levels the signals are usually but will check the peak AC on the send leg to see what I'm feeding the EQ.  Its been fine with my GSSL.

meanwhile i will add some more resistance to the dropper between the two caps. At the input leg of the 3K3 I'm reading 297v and 279 at the output leg at the moment.

Rgds
Pete