G-PULTEC problems, please help!

[Gustav]

Very nice unit Pieca! Congratulation

I have a similar problem. I've mesured 12vdc on the heater and 340vdc  without a tube in the socket.. In my first test, the tube died few minutes after I turn the power on so I'm afraid to put another tube to take measurment... The first tube was a free tube so it's not a tragedy  ;D but my others tubes are expensive so I don't want to take some risk ;D

Do you measured with a tube in?

It's my first tube diy so I'm a newbie  ;D

first of all - remember, the voltages you are working with are dangerous.

In order for the tube to work, even if its placed in the circuit, it needs its heater voltage, which is regulated to about 6,3V through your LM317 regulator.  If the regulator gets too hot, it will shut down, so you might see the following behavior.

- Tube glows,
- High voltage is dropped over drop resistor.
- Tube stops glowing.
- Voltage is equal on both sides of the drop resistor (since theres no load (tube not working) on the supply, the resistor will not drop the voltage)

Let the regulator cool and try again. There is probably nothing wrong with your tube, and you can probably get it to glow again.

If you are feeding the circuit 12V, I doubt you can cool your LM317 without using the case as a heat sink. To do this, you need to isolate it electronically from the case.

For my first PeQ, I spent a few days before I realized that my LM317 was shutting down, and I was really confused about the behavior over the drop resistor, so you are not alone, if this turns out to be your problem.

If its not, I would still make sure the LM317 is sufficiently cooled before trying with a new tube.

Gustav

 

[veve]

Thanks for the answer Gustav..

My regulator is not hot that's what I don't understand.. Maybe I have to change it to see whats appen and also check  the board to see if I didn't made a mistake but I'm pretty shure that's not the case..

I think I have to resolve the heater problem first to avoid problems with the tube.

 

[Gustav]

My regulator is not hot that's what I don't understand..

Even with a tube installed? Your measurement of 12VDC indicates that the regulator is not seeing a load  either. You would either get approximately 6,3V with a regulator working on a load, or nothing with the regulator shutting down.

I dont know if theres a way to fake a load over the tube socket to make sure theres no risk of ruining any more tubes if that is what happened.  Someone might be able to help with that.

Gustav

 

[veve]

Maybe I CAN put a resistor in the socket to simulate the heater and see if I get 6,3v. What is the average current in the heater?

 

[Gustav]

Maybe I CAN put a resistor in the socket to simulate the heater and see if I get 6,3v. What is the average current in the heater?

Did you at least try the tube you declared dead?

Gustav

 

[pieca]

Hi all !

After more testing, I've found that there is about 1Db of gain between left and right channel in my build…
My tubes are paired, so I don't suspect them

But I found this :

measure your 10KA high boost pot end-to-end resistances, and add a trimmer (say, 1-2k) to the one that has lesser value. This is probably the lesser of two evils, as pots will be slightly uneven (then again, they are most of the time anyway).

measuring my High boost pot end to end gives me :
9K on the hotter channel
10K7 on the other

So if I put a 2K trimmer in series on my 9K pot ( to get 10K7 total), I should get the same amount of gain on both channels.
Is it correct ?

Is it a preferred place to put the trimmer (Input or output) ?

Thanks again for your help

 

[gyraf]

Put the trimmer at the input end.

Or better yet, find two hi-boost pots that are approximately the same, then trim.

Jakob E.

 

[veve]

The glass is broken so I don't think the tube works again.
I've tried with a new tube and with only the heater tension connected. I've measured 1,27V but the LM317 was'nt too hot.

 

[pieca]

Ok, I've put a trimer

Result : perfect balance between channels +- 0,2 DB from 20hz to 20 kHz ;D

Only 1db High boost difference at full boost… not a big deal

Will try with matched pots when possible

Thanks Gyraf, your project is TERRIFIC !!!!!!!!!!!!!!!!!!!!!!!!!!

 

[MountCyanide]

This was my first tube project and I'm happy to report that it went pretty darn smooth.
I broke out the acid and got to etching.

I used the Don Audio toroid (and inductor) and I got stuck for a moment when the high voltages were too-- well, high. The 18k /10-watt resistor fix that I found earlier in this thread worked a charm at knocking the juice right down to where it needed to be. I used the Collective Case and this piece sounds grand. I busted my tube virginity and I kept calm by keeping an eye on the permanently hooked up multimeter that made sure the bleeder resistors were doing their jobs. I'm certainly digging this piece.

But---- being a fiend of transistor sound --- and a fiend of learning this stuff--- I just had to make a solid state version.  I did a bunch of searches and fact-schematic-gathering and decided on the pretty well worn path of the 2520. I just etched and built a bunch of 312's from scratch so the API circuit was very familiar to me. I did a sort of fusion of the Gyraf input (with lundahl 5402) and the 325 circuit in Photoshop.  And, of course, used the Gyraf Filter PCB.

( Yes, that's a Mnats/Hairball DIY-990 in there. I hadn't prepared the gar2520 yet at this point. It sounded very good in there. But that's not the kind of good I was going for with this.)

I routed and manipulated everything for a nice tight and custom layout that could use 5mm terminals. Initially wiring up a Cinemag CMOQ2S as one often does with 2520 amps I recalled an old Scully 280 that I've had for decades just stashed away in a closet that was ripe with transformers. There's a 600:600 Freed tranny (32035) that seemed would be appropriate so I wired it up and sure enough--- I dug it. I find it more subdued than the CMOQ.  A bit mellow and dare I say vintage. Well, certainly. It's pretty damn old. And lovely sounding. A nice pairing for the aggressive gar2520. (Not that gar's is more aggressive than any 2520, I mean 2520's being  aggressive in general.)

Opted for Fastron Inductors. Because if I was going solid state and aggressive I might as well try these little sub-dollar suckers. I dig em. Temporary unengraved front panel. Oddly in Neve Grey-Blue.

Gotta say -- besides all of this learning for me- this is so damn gratifying!  But the best part is : IT WORKS. I'm stoked. I pulled. it. off.  Woo.  Additionally, I'd be more than happy to share the etch file. Just say the word. Thanks GroupDIY. Having a blast.

 

[Gustav]

This was my first tube project and I'm happy to report that it went pretty darn smooth.
I broke out the acid and got to etching.

I used the Don Audio toroid (and inductor) and I got stuck for a moment when the high voltages were too-- well, high. The 18k /10-watt resistor fix that I found earlier in this thread worked a charm at knocking the juice right down to where it needed to be. I used the Collective Case and this piece sounds grand. I busted my tube virginity and I kept calm by keeping an eye on the permanently hooked up multimeter that made sure the bleeder resistors were doing their jobs. I'm certainly digging this piece.

But---- being a fiend of transistor sound --- and a fiend of learning this stuff--- I just had to make a solid state version.  I did a bunch of searches and fact-schematic-gathering and decided on the pretty well worn path of the 2520. I just etched and built a bunch of 312's from scratch so the API circuit was very familiar to me. I did a sort of fusion of the Gyraf input (with lundahl 5402) and the 325 circuit in Photoshop.  And, of course, used the Gyraf Filter PCB.

( Yes, that's a Mnats/Hairball DIY-990 in there. I hadn't prepared the gar2520 yet at this point. It sounded very good in there. But that's not the kind of good I was going for with this.)

I routed and manipulated everything for a nice tight and custom layout that could use 5mm terminals. Initially wiring up a Cinemag CMOQ2S as one often does with 2520 amps I recalled an old Scully 280 that I've had for decades just stashed away in a closet that was ripe with transformers. There's a 600:600 Freed tranny (32035) that seemed would be appropriate so I wired it up and sure enough--- I dug it. I find it more subdued than the CMOQ.  A bit mellow and dare I say vintage. Well, certainly. It's pretty damn old. And lovely sounding. A nice pairing for the aggressive gar2520. (Not that gar's is more aggressive than any 2520, I mean 2520's being  aggressive in general.)

Opted for Fastron Inductors. Because if I was going solid state and aggressive I might as well try these little sub-dollar suckers. I dig em. Temporary unengraved front panel. Oddly in Neve Grey-Blue.

Gotta say -- besides all of this learning for me- this is so damn gratifying!  But the best part is : IT WORKS. I'm stoked. I pulled. it. off.  Woo.  Additionally, I'd be more than happy to share the etch file. Just say the word. Thanks GroupDIY. Having a blast.

Self etching  ;D

Gustav

 

[Rocinante]

Gustav,
That's awesome man.  Seriously. Here I am reading and rereading this thread, silently trying to troubleshoot my own Pultec in the hope that I find someone who has had similar issues and there you go and present some bad ass modification indicative of the gdiy spirit and with genuine modesty show us all what else can be done (which along with other talented gdiy members also portrays your understanding of the design).
My hat goes off to you there sir. I'm sure it sounds magnificent.

 

[Gustav]

Gustav,
That's awesome man.  Seriously. Here I am reading and rereading this thread, silently trying to troubleshoot my own Pultec in the hope that I find someone who has had similar issues and there you go and present some bad ass modification indicative of the gdiy spirit and with genuine modesty show us all what else can be done (which along with other talented gdiy members also portrays your understanding of the design).
My hat goes off to you there sir. I'm sure it sounds magnificent.

Hi Rocinante.

I quoted the full post and commented, which must have made it appear like my post, but I can't take credit for the self etch gain stage swap.

But since were on the subject, I did remove the  gain stage for a project myself.

Even did a quick lay out in Eagle for a two channel version.

https://pcbgrinder.com/download/Random/BTUBEDRIVER.pdf

You can use the existing board for a channel, though.

Gustav

 

[MountCyanide]

Yeah, that was me.
Perhaps I seem overstoked but I started all of this diy in January of this year.
Each consequent fix of this audio electro-addiction requires a higher dose.
Plus, copying circuits and mashing them up and tweaking em seems to makes for really good learning.

 

[Rocinante]

Lol. Oops. I guess its an optical illusion or finally paying off the brain alterations/ damage I did in my youth.
Amazing stuff then Mount cyanide. I havent gotten to self etching yet but im positive I see at least a 312 in the future.
I am currently waiting for some 18k resistors to arrive as I am pretty sure thats what's the issue with my build.
I too used the Don Audio xfmr and am having some audio trouble; I can just barely hear it if I crank my monitor way up. I ran a scope across as well as a cap/guitar cord probe and I have signal and continuality through the whole filter section. It seems to stop just before the output xfmr. My readings on the srpp are like others pretty weird/off.  I'm guessing/ hoping this 18k swap (which I just ran out of that value of course dammit) will be the solution. 
Its a great build anyway and I certainly learned a lot referring to this thread.

 

[MountCyanide]

Thanks dude.
Make sure it's a high watt 18k.
I used a 10.

 

[gyraf]

I don't think you need that high-powered a dropping resistor for high voltage:

The ECC88 SRPP stage draws only ca. 5mA, which equates to 1W per 200V dropped across it (UxI=P: 200Vx0.005A=1W).

Remember that it's often easier to just add another resistor in series than to find the exact value you're after.

And then two ½W resistors can dissipate the whole 1W, providing they share load equally.

Jakob E.

 

[MountCyanide]

Oh ok. I was following previous advice --and further promoting (slight) misinformation haa.

 

[djfatum]

what power transformer should be for G-Pultec ???

Andrzej

 

[Gustav]

what power transformer should be for G-Pultec ???

Andrzej

9V or 12V and 220V secondaries - or use Jakobs solution with two trafos attached.

I am not sure why it says 15VAC for the first trafo, I would use two 12VAC transformers, but I am sure Jakob will explain the reasoning behind it.

Gustav