Double Shot..my new project, tube preamp..layout & pcb

[dschwartz]

hi there..
i want to share my latest project with you..
it´s a two independent channel tube preamp. The OD channel it´s a dual rectifier preamp, with a switch between the bypass caps and ground for two states of gain...
The clean channel is gain stage 1 bypassed to gain stage 4, and both bypass caps not connected to ground..the clean channel gain voicing is made at the gain pot..point to point to suit taste...

use a dpdt switch to change channel and disconnect ground from bypass caps..

the tonestack board is pretty standard, choose your preferred values there

The power section is based on real mctube idea....two transformers (one 120-12 and 6-120 in america.. i use 220-12/12-220 in Chile)..

a separate box contains the transformers and the rectifying board...the filtering and regulation board goes inside the main box...power is transmitted trough a 3 wire power cable (340VDC, 17VDC, and ground)

Missing the 5th stage? well.. it´s a MOSFET BUFFER!!!!!! hehehe...well, if RG sez that they are good..who am i to disagree???

I did the layout and boards by hand, with a graphic editing SW...so if you see an error please point it out!!!
I´m currently building it and will post the results as soon it works...

the layouts:


the boards:


Any questions and observations are welcome!!!

[MetalGod]

Looks like you've put alot of work into this project - can't wait to see the finished article.

Got a schematic?

[Pushtone]

That looks great.
A high voltage tube project is a wonderful thing to share.
I like the separate boards.

If I where to build it I think I would go with a large power transformer and use the MAINs AC.
What the advantage of the back to back transformers over using MAINs AC?
I've looked at the Real McTube before but can't see the advantage now. I'll have another peek.

A schematic would really help us check your layout.

Another question...
Are you planning on soldering the tube pins directly to the PCB?
What are the large yellowish rectangles on the main board?
Is this going to be in a "pedal" chassis?

Thanks for sharing.

[anchovie]

If I where to build it I think I would go with a large power transformer and use the MAINs AC.
What the advantage of the back to back transformers over using MAINs AC?
I've looked at the Real McTube before but can't see the advantage now. I'll have another peek.

The back-to-back transformers isolate the tube HT supply from the mains power supply. Simply rectifying the mains AC is an incredibly dangerous thing to do!

[brett]

For sure, nobody should to rectify mains (mains in my area are only specified to have spikes less than 2000 VAC !  Hopefully, they are brief !). 
The advantage of two transformers back-to-back is that they are cheap (re-cycled?), not expensive amp transformers (eg Hammonds).  Of course, if someone builds cheap low-current, high voltage transformers, they would be great for such a project.  How much is the transformer in the Epi Junior, I wonder ?
cheers 

[John Lyons]

Looks good Daniel. I would make the traces a bit larger though if you can. Either that or use heavy copper for PCB. 2 oz or more.

Yes, the back to back transformer thing is cheap and also that you can get 12v from the first transformer and 100+ ish volts from the second, clever!

ALthough Weber and Hoffman have inexpensive transformers for pre amps...

John

[Aharon]

That looks great.
A high voltage tube project is a wonderful thing to share.
I like the separate boards.

If I where to build it I think I would go with a large power transformer and use the MAINs AC.
What the advantage of the back to back transformers over using MAINs AC?
I've looked at the Real McTube before but can't see the advantage now. I'll have another peek.

A schematic would really help us check your layout.

Another question...
Are you planning on soldering the tube pins directly to the PCB?
What are the large yellowish rectangles on the main board?
Is this going to be in a "pedal" chassis?

Thanks for sharing.

Looks like the big yellow things are relays..................
Aharon

[stephanovitch]

Whithout schematic, it's difficult to find mistakes on yours PCBs

[dschwartz]

sorry for the lack of an schematic..i did it with livewire but when i was finishing an error ocurred and the file got corrupted..damn!!

Yes, the yellow things are relays..5 volts that´s why there´s a voltage divider on the power board (the two unmarked resistors)

since we have 220Volts main here, a back to back pair of 12v transformers will give me around 320 volts DC rectified.. not bad..

yes it will be a pedal..

no, i wont solder the tube pins..i will use sockets..
i noticed some traces were thin..but i will use solder to make them thicker where high voltage pass...maybe in a new version i´ll make them thicker..

i´m gonna make the schematic, so i´ll post it when it´s ready..
i´m so proud of this, i hope it works..

[dschwartz]

i finished the power supply part..i got 290 volts DC will this voiltage be enough?? the rectifier preamp sez 340 volts..so..do i have to change some parts?

[dschwartz]

the power supply:



the preamp:


imho the switching is pretty clever.....
any comment is VERY appreciated!!

[Paul Marossy]

Looks like a nice project so far! 

[dschwartz]

one thing i left out.. sorry.. the mosfet can be a IRF822 or alike...

[dschwartz]

I did the layout by hand following my instincts..

Can someone help me by detecting risks of oscilations, noise??

i mean, are the B+, signal and ground traces placed correctly so the build won´t have any layout-related issues?

[stephanovitch]

Have you add mods on the original rectifier schematic?

[dschwartz]

hmm only the switching part is a mod..
also..the mosfet buffer instead of a triode buffer, and the tonestack is scaled down by 10 (like dr boogie´s) to lower output impedance..

i´m thinking about lowering the first coupling cap, too.. but all the rest of the parts are the same..

[stephanovitch]

C14 is not on the original schematics

[stephanovitch]

There is a 5nF caps but to ground probably next to tube for decoupling supply

[dschwartz]

i´ve found two versions of that cap (both of them 5nF..i´ll use 2.2nF) one goes from B+ to ground, and other from B+ to plate in parellel with the resistor.. i was confused so i studied what are they for and other preamp schems, and decided that the correct position was in parallel with the resistor...as low pass filter avoiding oscilations..

[stephanovitch]

Look at this recent schematic I've found:
http://www.neufgiga.com/index.php?m=c9ae77e8&a=7d397569&share=LNK8998473c92cb4c44d