Universal PCB to cater for 18watt derivatives

[jamesrr]

Over at Wattkins we've been working on the development of a 'Universal' PCB to cater for the simple construction of many different amps. Whilst the PCB itself could be used to construct 'non-18 Watt' amps, it most certainly has been constructed with the 18watt community in mind.

Indeed, the heritage of this PCB can be traced back directly to 18WATT.COM and Terry Stinger's (AKA Z-Stingray) Baby Will & Superlite PCBs. Before his untimely passing away, Terry produced a '5E3' PCB to similar exacting specifications and donated the PCB design to Wattkins for production and use under a Creative Commons Non-Commercial licence model. This PCB has been fabricated & sold through the group for quite a few years now.

Over that time we have felt that a more generic design could be developed allowing the simple creation of a multitude of amps including the 18 Watt family.

That time is nigh

The PCB will fit nicely in a 'standard' 16x8 chassis and there is a pre-drilled 16x8x2.5 heavy gauge aluminium chassis also available through Wattkins if you wish to minimise the drilling. The design process for the chassis is documented here.
It will also fit in a Valve Junior chassis like the Baby Will if you really need it to !

The PCB looks like this: -


It really is extremely flexible to use. It supports Octal PCB sockets directly soldered to the PCB for EL34, 6K6, 6V6, 6L6 etc power tubes as well as having PCB cutouts to allow simple connection to 'external' chassis mounted Noval sockets for EL84s.

The Pre-Amp sockets support wiring for 12Ax7 heaters as well as the 'Russian' pins 4,5 only style. You can also put an EF86 Pentode up front if desired.

So with this PCB you could easily construct a LiteIIb, Superlite, Superlite with MOSFET cathode follower, EF86 driven LiteIIb and EL34 powered 36Watt versions of them...

I've put together an initial schematic & layout for a LiteIIb type amp to provide an indication of the capability.

The design process we went through to produce the new PCB is documented here.

Please feel free to ask any questions but contain them to 18 watt related ones on this website...
If you're wanting to discuss other styles of amp please feel free to do so over at Wattkins & PPWatt.

We should have pricing and availability info soon.

regards,

JamesR

[jamesrr]

We've finalised the PCB design & had the factory fabricate 2 prototype PCBs for us.

I've built the first amp as a "Superlite 6V6". Here is the fully populated PCB


I built a 6V6 version as my test bed chassis is setup with cutouts for Octal sockets and I needed to test the design as quickly & easily as possible. Whilst the PCB is designed to directly solder in Octal Power Tube sockets, we have large cutouts that allow the traditional 18watt Noval sockets to be used for EL84s You just need to run wires from the pads to the socket lugs and attach the Noval socket direct to the chassis rather than to the PCB itself.



Here is a picture of the PCB installed in my test chassis: -



...and here is the 'outside': -


I've finished the following "Superlite 6V6" (and a LiteII "U") schematic and layout.

It's similar to the 2.7 v4 SuperliteIIb Rock Mumbles documented with the following significant differences: -

Antek AS-1T300 PT
Edcor GXPP15-16-8K OT
MOSFET cathode follower driven TMB tone stack
6V6S power tubes
330K Power tube Grid resistors (vs 470K more appropriate for EL84s)
330 Ohm cathode bias resistor (vs 150R suited for EL84s)
47 uF cathode bypass cap vs 2200 uF as I thought it would be super hot anyway !

(I used a fixed 330K/680K Gain stage rather than a Gain Control Pot as I only had 4 Pots in my test bed chassis)

The voltages I got are:-

HT 408v
A - 393v after R4 180R
B - 375v after R5 2.2K
C - 315v after R6 12K
D - 273v after R39 12K

V1 Pins:-
1 203v
3 1.88v
6 147v
8 0.87v

V2 Pins:-
1 234v
3 75v
6 238v
8 75v

V3/4 Pins:-
3 389v
4 373v
8 26v

Power Tube Cathode Resistor (R28) 330R

Using the Weber Bias Calculator that calculates as giving 14 watts plate dissipation per tube which is right on the money for the 6V6S power tubes I'm using.

We should have these PCBs available for sale in a couple of weeks or so. I'm very pleased with them.

cheers,

James

[zaphod_phil]

Nice looking job!

[CurtissRobin]

That does look good. I'll have to make some time to visit wattkins.com and pore over that thread.

KennyO

[jamesrr]

My boy's band came round a week or so ago and I managed to get them to play the 6V6 Superlite for me to record. I'm afraid I only have a Zoom recorder so the quality isn't brilliant but it gives a reasonable impression of the amp. It sounds a lot better in real life !

The audio clip on Youtube is here: -

http://www.youtube.com/watch?v=VmPV1pOtqLc&

The full production run of the PCBs is in now, so I'll have a couple more to use shortly.

For the next one I'm planning on an EL34 "36 Watt". I'll post the schematic, layout, build pics (and hopefully a sound clip !) over in the 36 watt folder in the coming weeks.

[JMPGuitars]

A 36 Watt EL34? That's something I'd love to build.

[crgfrench]

I just picked up a Valve Jr combo for $50. I have a Universal PCB sitting on my desk just waiting to be populated as a Fullerwell ("Denim Deluxe") 18 Watt circuit. This is going to be fun.
First things first, replace the front panel badge:

Logo Epictone.png