pix of Custom built guitar amps/cabs

[thermionix]

Those look great Bruno!  Thanks for the tips.  I'll have to look for some painter's pliers.

[stallik]

I know them as canvas stretching pliers. Cheap as chips online

[tubelectron]

Yes, I have been in trouble to find the English correct term for pince à tentures, pince de tapissier...

You're right, it's a cheap accessory (I bought mine from England via eBay !). Another affordable instrument is an agrafeuse électrique that is to say an electric stapler or electric stapling gun with 10x6 and 10x10 staples. I even would say that these are compulsory if you expect a perfect result (or nearly) with vegetal grillcloth.

A+!

[thomasha]

Hi, I finished one too!
But the cab already had the tolex on it (still not as good as tubeelctron's though), I just added the new grill cloth, speaker and tube amplifier.
It all started from a burned transistor amp, that still has some nice IC for chorus that I will be using in another build.

The circuit started with the circuit from Doug: http://www.dougcircuits.com/neon.html
Unfortunately the AC4 build page is down.
I used in mine an OPAMP LFO, cause the Neon light wasn't working in a periodic way, it was more like a random tremolo.

The imput has 4 configurations, EF86, 12ax7, both in series, both in parallel, which gives some nice different tones, from clean to mean.

here some pics:







I'm still finishing another wah in a 159a, wait for it!

[thermionix]

That EF86, is it a Siemens?

[tubelectron]

Hi thomasha,

Why you did not use the "bias vary" type of tremolo that was on the original AC4 and replace it with a photocell trem (an lately with an OP LFO) ? Did you experienced throb / thump in the speaker while trem on ? Or is it a simple choice of your own ?

Nonetheless, it's a funny amp which have all the ingredients to sound good ! And it seems that you managed all right to put your VOX-like grillcloth satisfactorily...

A+!

[amptramp]

Are you sure the output transformer is connected like that?  This appears to be a humbucking transformer where the input power goes in on the tap, the output power to the lower voltage supplies goes to the end nearest to the tap and the plate goes to the output end farthest from the tap.  The following radio schematic:



does not show the relative scale of the output transformer winding but the bottom end of the primary is at about the 2.5% point of the entire winding from the tap.

[thermionix]

I don't think that's a tapped transformer, just has a wire drawn through it.

[thomasha]

Hi!

The EF86 is a RFT, it has no visible grid. I had it laying around.

The thing with the tremolo was that I wanted to save one tube for the extra gain stage. I liked the neon lamp idea, but my lamp was acting crazy and I didn't had other to test. I also used a ORP062, the "vintage" kind of LDR. It came with a box full of subminiature tubes that I got over ebay. I saw that there were some amplifiers from Dynacord that used it as a LDR.

In the end, I wanted to stay with the two gain stages, but already had the tremolo hole in the chassis and the faceplate. So, I decided to build the Opamp version. At least it goes faster than the other tremolos that I tested (I built a supro copy with tremolo some time ago)


Sorry about the wire drawing thing, it is a normal transformer. But I have one Radio transformer which has this humbucking winding. It has a really low resistance in that winding, is it really helpfull to run the preamp power supply through it? I mean in guitar amplifiers?

Another thing that I see now, instead of the first resistor I'm using a small choke that I had.
You can see it right next to the turret board on the left side of the picture.

[thermionix]

RFT, yes.  I recognized the logo but couldn't remember.  East Germany, West Germany, close enough!

[tubelectron]

Qualification of a switchable Dual-Power 100W/3W output stage for the biggest of my 3 project :



My Boogie MKIIA is used as a bench for testing the circuit :



It works as expected, but needs impovements in tone in the 3W (single-ended) mode.

A+!

[vigilante397]

switchable Dual-Power 100W/3W output stage

Seriously?  How are you switching from 100W to 3W without just building two completely separate output stages with their own dedicated tubes? Je ne comprende pas

[tubelectron]

switchable Dual-Power 100W/3W output stage

Seriously?  How are you switching from 100W to 3W without just building two completely separate output stages with their own dedicated tubes? Je ne comprende pas

You nearly guessed it right, vigilante397 : there are dedicated tubes for each power selection, but they share some common parts, notably the output transformer.

A+!

[thomasha]

That's interesting, I assume the 100w has a PP transformer. Are you using the reverb Transformer for the low wattage version, half or the player to plates winding of the PP transformer?

The tube must really have a low impedance at the primary?

[tubelectron]

That's interesting, I assume the 100w has a PP transformer. Are you using the reverb Transformer for the low wattage version, half or the player to plates winding of the PP transformer?

The tube must really have a low impedance at the primary?

Yes, that's it, thomasha : I use the half primary of the output transformer. The 100W stage is disabled, and the 3W single-ended stage is enabled by a flick of a DPDT switch.

A+!

[tubelectron]

Here is a sample to have an idea of the tone in the 3W position :

https://soundcloud.com/tubelectron/r05-0008-dpmp3

It's probably more a 1W than a 3W : I didn't measured the power yet. But it's not really important because that position is intended for home use, and being overdriven "à la vintage" (no hi-gain).

The guitar has a 5-position Strat-like switching, with a HSH disposition : Gretsch FilterTron X2, Danelectro Lipstick X1. Each PU position is tested, starting from the Neck one.

Your comments about the tone (not about the playing, of course  ) are welcome : you guess that I'm interested in their justification, more than their simple statements.

A+!

[tubelectron]

Final improvements, tone of the revised version of the circuit :

https://soundcloud.com/tubelectron/r05-0001-dual-power-lo-31-08-17mp3/s-Rpag0

I don't think that I can go much further unless if I greatly complicate the circuit, with no certainity to obtain really better sonic results. So I will admit that the qualification is met  ...

The overdriven tone is only produced by the single ended stage of the LO position, through the output transformer and speaker. The preamp section stays pure clean all along.





A+!

[wavley]

A cool amp I built for a guy

[stallik]

^ That's a very smart build

[wavley]

^ That's a very smart build

Thanks!  I'm pretty happy with it. It's mostly a Weber kit, but built on a Hoffman turret board.  Those Hoffman boards are fantastic and really facilitate clean wiring.