G-PULTEC problems, please help!

[APL]

Thanks for the info Jacob that sounds simple.

I have just found the "Pultech Meta" page which lists the other Pultec threads. Very useful for new starters saves asking same questions.

 

[APL]

Sorry If this question has been answered before but I cannot find any information.

On the schematic (Rev 3) there is a 10k resistor conected between XLR ground and 2 resistors (1K & 10k) next to switch 3a/b.There is no place on the  PCBGrinder PCB's for this resistor. I have asked Gustav and he confirms there is a discrepancy. He agrees the 10k resistor is present on Rev3 schematic  but his board is Revision 4.

a) is this 10k resistor needed, if so where would the best place to add it?
b) Is there a Rev 4 schematic? The rev 3 schematic is used on the Gyraf and PCBgrinder websites.

Thanks

 

[gyraf]

This 10K is there to simulate the load of the omitted interstage transformer. I don't think it's needed.

Try building without, and see for yourself (remember to reoprt back here) if problematic, you can always solder it to underside of pcb.

There is no new schematic (sch and pcb revision numbers dosn't follow each other)

Jakob E.

 

[APL]

Thanks for the reply Jacob.

I assume it must not be critical or somebody  would have reported by now. I will let you know if there is a problem but it wont be anytime soon - Im slow.

 

[drivebystudios]

Hi there,

I've just finished a BOM for the gPultec. I've seperated it out to make life easy for anyone that wants to substitute Caps, Pots etc.
I'm pretty sure its correct, but if anyone spots anything thats incorrect, messeage me and I'll update it!

Cheers

GPULTEC - Bournes Pots
http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=2cc0c52744

GPULTEC - Other bits
http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=69335a7714

GPULTEC - Panasonic Capacitators
http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=334ceea274

GPULTEC - Pots & Switches
http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=4dea3c693a

GPULTEC - Power PCB
http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=b8e7d2b0da

GPULTEC - Resistors
http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=bfd9240598

 

[APL]

I was just looking at your BOM.

Are you sure about the Lorlin CK2375 switches? the description is 4pole 2/3 position. You need 2 pole 6 position. I went for Lorlin CK1060 from Farnell. I think they are shorting type which apparently have longer life than non shorting.

I have just ordered my components from Farnell and Banzai music if thats any help.

 

[fatheaddrummer]

Hey DrivebyStudios,

Thank you so much for your BOM, this is really cool!! ;-) But I think so too about the switches. It have to be 2x6....

Does anyone have experience with the LL5402 as Input transformer? The Gyraf schematic is suggesting this trafo, but i read that it takes away some low end and a LL1540 would work better. Unfortunately i can't remember where I read it...Any experiences with that?

Best,
Christian

 

[gyraf]

..but i read that it takes away some low end and a LL1540 would work better. Unfortunately i can't remember where I read it...

The G-pultec circuit works quite well as-is, and the 1540 is NOT usable here because of it's high copper resistance.

You'll only start loosing low end if you drive the eq from a high output resistance - but then you wouldn't be able to drive the eq-stage anyway.

If you find the source of this rumor, let me know

Jakob E.

 

[fatheaddrummer]

Ok, now this is clear!
Thank you so much!!

Best,
Christian

 

[dmnieto]

Hi everybody,

I posted a similar question on the rev f, 1176 thread (with mnats board). I am planning to build a g-pultec, but I would like to know if I need to make some changes in my 1176, let me explain.

My intention is to allow signal chain in which the output of the 1176 can drive the g-pultec without bass rolloff. The 1176 has a quite beefy line amp, but i am wondering if i need to do impedance matching as well.

I have currently wired the output so I have a 1:3.16 winding in the EA11148, which is what is needed for the nominal 600 Ohm output.
Now, would it be better to change the wiring so i have a 1:1 winding and a nominal 60 Ohm output?

thanks

 

[drivebystudios]

Sorry... i didn't finish the switches and pots BOM properly...if someone could give me the right mouser part numbers I'll update the BOM!

PS: PCB Grinder is now selling a kit with the lundahls... the package is extremely good value, well worth the price considering time and shipping!!!

 

[dmnieto]

So... should I wire for 60 Ohm output or 600 Ohm? Or it should not matter?

 

[gyraf]

So... should I wire for 60 Ohm output or 600 Ohm? Or it should not matter?

Does not compute - can you rephrase your question?

Jakob E.

 

[dmnieto]

Does not compute - can you rephrase your question?

Jakob E.

Sorry, I asked my question before... I have built a 1176 clone, and I was wondering if I had wired the output transformer for a 600 Ohm output impedance. It is also possible to change the wiring to have a 60 Ohm output impedance.

So my question was, if I wanted to be able to drive the input of g-pultec with the 1176 without inducing a low frequency roll-off, should I rewire the output of the 1176 to 60Ohm, or it does not matter?

 

[gyraf]

Should not matter - 1176 output impedance is very low.

 

[APL]

Driveby: Look at Mouser 10SM160 I think its the  most suitable

Ive just finished PSB board. I got 6.11V heater which is OK, but  I got 272V with 3k3 resistor. Ive never seen any equation posted  to calculate correct Resistance value ( I assume it is a function of tube parameters and input voltage -voltage divider? ) so I started to add series resitors to reduce voltage.It was only when I had a mountain of 4 resistors and I was still too high that I noticed there was a linear relationship between the resistor value and voltage. I may have just discovered ohms law but if its a breakthrough I dedicate my Nobel Physics prize to Jacob.   I drew a graph Volts againt resistor value  for my results a perfect straight line  I then read off resitance at 220V giving 17K. The closest resistor I had was 15k which give 234V on tube.

If you dont know any better. like me, it may be worth going straight from the 3k3 to 15k,if thats still too high draw graph. This worked for me but if this is rubbish I hope somebody will correct me.

 

[dmnieto]

Should not matter - 1176 output impedance is very low.

Thanks Jakob, I guessed so much but I wanted to be sure.

I really appreciate the work you have done on your DIY projects, they are really a wonderful learning experience

 

[fatheaddrummer]

Hey, I have a (maybe silly) question ;-)

In the Gyraf schematic I can find 2 Tubes (I think it's a cathode follower setup?), but in the PCB Layout I am just able to find 1 Tube!? So I am I blind or do I miss some information?

Thank you!!

Best,
Christian

 

[okgb]

12AX/t/u/  tube type's have two sections , Is that what you are seeing ?

 

[fatheaddrummer]

I'm sorry i don't know 12AX/t/u/ tubes, but I'm talking about ECC88 Tubes. In the schematic there are two of them, but the PCB layout just has space for one...

Schematic: http://gyraf.dk/gy_pd/pultec/gy_pd_sch.gif
PCB Layout: http://gyraf.dk/gy_pd/pultec/gy_pd.pdf

Thank you!

Best,
Christian