New PCB Express build - seeking advice

[mattvon]

Hi all,

New member here! First, I'd like to introduce myself...I'm still somewhat a newbie when it comes to tube amps, but I've built a couple of kits (both Ceriatone) and a couple of VJr conversions (one SE EL34 and one Baby Will). I'm a complete newbie to the Express from a build standpoint--but I've always LOVED the tone.

After spending a couple of weeks reading all I could on here about a scratch build, I decided to try a PCB build first. Given all there is to learn about these amps, I like the idea of starting slowly and learning as I go.

I've been blown away by the awesome support from this group of builders! It's the cool way you all support each other which makes me think I can pull this off. LOL, it's pretty different than over on TGP!

I've read the PCB thread and downloaded all the reference photos I could. RJ is going to help me with a chassis, and rock_mumbles was nice enough to supply me with a PCB.

I also lucked into a nice guy here in Minnesota who was getting out of building tube amps and I was able to score a MASSIVE amount of gear/parts/components--including a complete amp and two partial amps, one of which was an Express clone.

So I've got the Toneslut trannies and carefully went through the BOM and placed my Mouser/AES order. That's all arrived, so I've set about dry-fitting the PCB.

I've run into a couple of immediate questions--some of the components aren't super clear to me, so I've taken a picture of my dry-fit and photoshopped yellow lines and numbers representing the component values I'm unsure of. Could anyone take a quick look and let me know what they should be? Please note the numbers don't represent the schematic or BOM, just for my use.

As a small give-back, I'm planning on putting together a layout for the PCB version I have, "1.0"...hopefully this will help another new guy getting started.

Here's the picture:
[IMG:799:332]http://img.photobucket.com/albums/v519/ ... whole1.jpg[/img]

Thanks in advance! I should also apologize in advance for the million questions I'm likely to have...but I'm hoping to be able to pay it forward once I've learned more.

[rock_mumbles]

#1 and #2 are the bleed resistors for the HV supply 220k 3 watt ... the pcb has two bleed resistors, one on each side of the standby switch, the Express schematic has one (R23 & R24, the two 100 ohm 3W resistors in parallel)

#3 is the 18k dropping resistor (R26a & R26b shown as two 9.1k resistors)

#4 and #5 are the cathode resistor and cap for the 'Lerpoole' they are not used in the Express

#6 is the NFB resistor

[M Fowler]

That is rj's latest version and I never did get a layout from rj on this board.

That is the bias area #4 & #5.

[rock_mumbles]

You'll have to ground (jumper) either #4 or 5 (the cathodes) ... I'll look at my scans and look at the bias supply ...
There is a jumper from the output grid reference resistors on the 'lerpoole' (R17 & R18) to the ground BUS DO NOT install the jumper there, instead install the jumper just to the right of #6 in your picture, that will connect the grid reference resistors (R16 & R17) to the bias supply.

As a reference I labeled the components for the 'lerpoole' on rj's build picture.

[mattvon]

Thanks for all the help! I will order up two 220k 3 watt resistors. I also failed to notice the 1 watt designation for the 470 and 10k resistors on the PI/Presence circuit and ended up with 1/2 watt versions of each, so I need to order the correct ones as well.

Question: I have the pair of 9.1k 3 watt resistors called for in the BOM--could I run them in series to get the required 18K for the dropping resistor? Or am I better off just ordering the right one?

[rock_mumbles]

You use two 9.1k resistors for the 18k dropper ...

For the bleeder resistors I'd make sure to get resistors rated to 750V

[Koop]

This thread is timely for me. I have a complete Express PCB kit enroute from rj. The numbered layout is super helpful, thanks rock_mumbles.

[rock_mumbles]

The numbered layout is for the two EL84 'Lerpoole' using the numbers from the Liverpool schematic posted in the Trainwreck Files .

We should get mattvon to do the same thing with his Exp build ... (hint - hint --- matt you there? take some nice hi-res pics of the populated board and ...)

[Koop]

Thanks for clarifying that. I would've been real confused trying to reconcile the layout with the schematic! Don't mean to hijack this thread, but if someone was kind enough to do a numbered layout for the EL34 Express I would be eternally grateful.

[mattvon]

I will do just that! I'm planning on also making a layout diagram once I've gotten it finished and checked over by the good folks at TAG!

[mattvon]

Okay, small update...I've got what I believe to be the missing components for my build on order from Mouser...even better, I just paid for my chassis from rj, so I should be good to go in a few days!

I also ordered another PCB (for a potential L-pool build) so I'll take a high-res scan of that once it arrives and start the layout documentation.

Thanks for all the support--I appreciate it!

[mattvon]

Okay, while I'm waiting for my chassis to arrive, I took the time to populate my board fully and do a quick documentation of the components...

I would GREATLY appreciate it if you all (paging rock_mumbles...) would take a look at it and make sure I'm not missing anything or have otherwise made a mistake.

Please--this is v1, to anyone out there who is building a PCB, double-check these values!!! I'll update it as I get feedback, and I am still planning on making a full layout once I get a blank PCB and the chassis.

[IMG:799:363]http://img.photobucket.com/albums/v519/ ... ed_v1a.jpg[/img]

**Edited for typo'ed PI cap value...hi-res image on page 2 of this thread**

[Koop]

mattvon, thanks so much. I just got the bits to start this build. I'll work on finishing the cabinet first. When I start populating the board this will be invaluable. It's so great to have a community like this that shares their knowledge and experience.

[mattvon]

Hey, I'm just paying it forward!

All the guys I've had help me, this is the least I can do...but I'd like to make sure my values are correct--I'm hoping rock_mumbles can take a look at it, double-check my work.

[Colossal]

mattvon, your values are correct.