[BUILD] The Rude Tube IVORY ====== Official build & support thread

[dmp]

Thanks Bern, it's the 5402 the problem, i actually checked the wiring to be sure and it just doesn't sound right with the 5402. it actually distort quite a lot and the overall low end is definitely lower.

The circuit can't drive a output transformer well, much less a 1:1 ratio. At a minimum you would want a 15k:600 (5::1 ratio) but then you lose gain and would need makeup gain to have line level. In my testing, even with a 10:1 step down output transformer the tone suffers.
I am working on adding a makeup gain stage that can drive a transformer as a solution.
As designed, I think this works great for unbalanced in, unbalanced out at instrument level but it does not work for balanced in/out with line level.

 

[bernbrue]

You're probably right. A cathode follower as final tube stage would have been fine for transformer balanced output. I've used mine completely unbalanced and that work great.
Bernd

 

[gaetan]

The circuit can't drive a output transformer well, much less a 1:1 ratio. At a minimum you would want a 15k:600 (5::1 ratio) but then you lose gain and would need makeup gain to have line level. In my testing, even with a 10:1 step down output transformer the tone suffers.
I am working on adding a makeup gain stage that can drive a transformer as a solution.
As designed, I think this works great for unbalanced in, unbalanced out at instrument level but it does not work for balanced in/out with line level.

I have some spare Gyraf srpp pcbs, might do the trick.

 

[gaetan]

With some serious head scratching, lots of fails, i managed to get it to work with a gyraf SRPP circuit so i get balanced outputs with 5402 and without affecting the tone. and it actually sounds really nice.

I couldn't run both boards from the same power transformer as it was making some noise and i am actually going recreate the SRPP tube stage without the pcb onboad power supply, 

My question is can one powersuply board handle 4 tubes or should i use 2 boards?

 

[bernbrue]

The board is not the problem. Check if your power transformer delivers enough power. Heater should have around 2A.
Bernd

 

[gaetan]

The board is not the problem. Check if your power transformer delivers enough power. Heater should have around 2A.
Bernd

it's rated 2.5, but to be honest i don't mind having 2 power trafo. I'll do more experiments.

What a fun project, thanks Bern!

 

[gaetan]

Here is the machine, it took me a while to get it to sound the way i wanted and i finally found the right tweaks and it sounds insanely good.

 

[labak]

Hello Gaetan,

Such a nice beast.

Could you tell us more of you did at the end with G-pultec stage? What about Transformers?

Thank you.

 

[gaetan]

Hello Gaetan,

Such a nice beast.

Could you tell us more of you did at the end with G-pultec stage? What about Transformers?

Thank you.

input transformers are Edcor 600/15 which turned out to be a great for testing as the output is easy to swap to center tap to get less signal. i used a dual G-pultec board from PCB grinder with lundahl 5402 . i modified the output knob and added some extra resistors to reduce 20dB or so. the Gpultec runs off a secondary transformer as i struggled with a ground loop. if i remember well the floor noise is around -80dB now.
If i had to redo it i would run the rude tube into the EQ section of the Gpultec without input trafo, so i have the 20 dB of reduction already and there is a slight reduction in the low end that requires a little boost on the output.

One last fix i need to do is the bias control, i think i have a 5k pot into R15 and i will change to a multi turn to get more precision.
the current through that pot goes up to 1.25 ma with the pot fully clockwise so i just added a 100ohm resistor to get the needle in the middle when it sounds right. i think it is great for recalls to have that meter if you decide to go with a bias pot.

I would have shown the inside but i have tried so many things that it now looks like a spaghetti dish. quite embarrassing.

 

[museic]

I'm finally back to this project.... got it all wired up today. Just a few questions.
My b+ is hovering around 360 v. Tube is glowing normally. Is this high enough to worry about? I didn't do sound check yet because of the high value.

What is the purpose of the v+ rail? Phantom power?

 

[bernbrue]

360V measured with tube plugged in? Much too high! What transformer have you got?
V+ is for relays, lights or whatever you want to use it for.
Bernd

 

[museic]

Yes with the tube plugged in. It's the triad vpt230-110. The transformer is putting out 270v ac.

 

[bernbrue]

Less would have been ok as well. The tube  has a maximum rating at 300V. Try to bring down the voltage by increasing R3. You can take 1K or 2x 470R in series. They must be 3W or more.
Bernd

 

[museic]

I have 4x 470r in series. Only Brought it down to 346v.

 

[museic]

It seems my problem would be my transformer putting out too high of voltage. Should I try a new transformer? Is it very common that a transformer puts out too much voltage?

 

[bernbrue]

Can you measure the AC voltage the transformer puts out?  Turn your multimeter to ac and check the voltage the psu gets from the transformer. You can keep this transformer for another project.
Bernd

 

[museic]

Yeah it's putting out 272v. Weird because it's rated for 2x115 or 230v.

 

[museic]

I talked with triad magnetics about the  vpt 230-110 transformer. They said it doesn't have enough load on it to pull it down to the specified voltage. So for future reference it seems that transformer won't work in this circuit. Or is there some trick to add a bigger load?

 

[bernbrue]

Hi,
Is this the data sheet for your transformer? So has it got two secondary windings?
https://www.mouser.com/ds/2/410/media-1067313.pdf
You can use one secondary winding only. Don’t forget to isolate the wires of the other secondary winding

Cheers
Bernd

 

[kambo]

actually i have the same transformer, its paralleled, and it works! may be double check ur resistor values on PSU board!