Gibson Amp Kits - GA 40?

[Diablo]

I'm thinking I might like to build a Gibson GA 40 Les Paul amp after hearing videos of the Victoria Electro King. Anyone know if there are kits available anywhere? I could scratch build it or convert some other kit, but I'm feeling lazy. The GA 40 uses some oddball tubes which I just happen to have.

[pentatone]

Diablo -
as far as I know there is no kit available.

I recently built a GA 40 minus the tremolo channel from scratch around a 60s 15" Isophone speaker I got for free. I got the revised schematic by a German forum fellow and it really was an easy build.
I decided to try to make an amp as cheap as possible and only had to invest 270,-- Euros in parts since I already had the speaker.
I constructed a custom cab where the 15" speaker and the chassis fit and built the baffle floating like the old Tweed Fenders.
The tone is marvellous - my "keep-it-amp" if somebody would force me to reduce my arsenal to only one remaining.

I don't know if it is allowed here to link to another forum - maybe somebody can enlighten me.
I posted a couple of pics there since I dont have any ressource for posting pics in the www.

[Diablo]

Thanks Pentatone. I think I'll draw up a layout from the schematic. I'll bend my own chassis up at work from aluminum, and make it a head. Too bad there are no faceplates available, so I'll have to get one custom made if I want it fancy.

You have my permission to post a link - I don't think anyone minds.

[pentatone]

Diablo -

optically my amp has nothing to do with the GA 40 or the Vic either but at least I got the tone for little dough.

I hope you can zoom the pics without going through the registration process.
http://www.tube-town.de/ttforum/index.php?topic=8873.0

[Diablo]

Thanks Pentatone for the link, unfortunately it requires registration.

[fyl]

Try http://www.harpamps.com/gibson/pg_0181.jpg for the schematics.

[Diablo]

Thanks FYL, now I all I need is a good wiring and board layout.

[Diablo]

Someone was kind enough to post a layout on a different GA40 thread, but it didn't match the GA-40 Les Paul amp, so I drew up a layout. Now, I'm looking over the schematic to select the right PT, choke and OT. The AC voltage at the 5Y3 rectifier plates is 300, so I matched it with the AC30 style PT from Ted Weber.

https://taweber.powweb.com/store/pt30sch.jpg

It looks to be overkill, but it has the right (300V) taps on the secondary.

The choke filters all the amp current including the power tubes, so I matched it with a Tweed-style 5-8H - 200mA/125 ohm choke (WO14684) from Weber. I figure a little more Henrys won't hurt anything.

I'm selecting a Deluxe Reverb OT with 6.6K primary/8 ohm. (WO41318)
https://taweber.powweb.com/store/041318sch.jpg

If someone thinks I've made a bad choice, please let me know before I order the transformers....thanks in advance.

[pentatone]

Diablo -

I'm a bit delayed, sorry.
What's going on with your project? Any progress?


I used a Hammond 125E OT which allows me to fiddle around a bit with the impedance ratios. Primarily I bought it because my speaker has an impedance of 4.5 Ohm (strange, isn't it?). I was pretty insecure if I could get good results with an OT with a fixed impedance ratio and wanted to keep a bit of freedom to try out different ratios. I ended with a ratio of 1600:1 (7200:4.5 - which is pretty similar to the primary impedance of the OT you are considering to use).
IMO you can't go wrong with a Deluxe Reverb OT.

When it comes to Chokes and Henries - that is a miracle I wasn't able to discover, yet. I use a Hammond 159S.


Many gretings!

[Diablo]

Thanks Pentatone for the info. I haven't started my project yet, as I still have to order the parts. Once I get the transformers, I'll draw up a sketch for the chassis layout. At work, we have a first-class metal shop for prototype sheet metal parts. My plan is to use the CAD & water jet to cut all the chassis holes. I'll make the chassis out of either stainless steel or aluminum. I've been going back and forth in my mind whether to build just a head or a combo amp, and that's kind of delayed me ordering the parts.

[pentatone]

Diablo -
you are a lucky guy with all these nice devices for cutting the holes. I am a dentist and decided to abuse some of the drills.
BTW - I have had good results by using good tweezers and a lockable needleholder - that makes keeping the wires and parts (resistors, caps) in position while soldering so much easier.

Years ago I was a big fan of heads but over the time became too lazy to carry two pieces around so that I prefer combos now which I can grab with one handle.

Please keep us posted!