EF86 "18 Watt" amp

[tunghaichuan]

The Brown Note 18W Lite IIB amp that I'm building and documenting in this thread (http://www.thefret.net/showthread.php?t=8502) is not the first 18 watt amp I've built. The first 18 watt project I built is detailed here:

http://www.diycustomamps.com/ef86_18w.htm

A couple of new pix showing the "updated" front panel:

http://www.diycustomamps.com/images/18w/ef86_18W4.jpg

http://www.diycustomamps.com/images/18w/ef86_18W5.jpg

This amp is not really an 18 watter, it is actually more like a simplified version of the Vox AC-15 with the pentode preamp tube and cut control. I hadn't played it in a while and after pulling it out and playing it a bit yesterday, I was surprised to hear how good it sounds. Very fat and chimey. It takes pedals very well.

The output transformer in that amp is very special: it was a NOS Bedrock Amps OT made to run in near Class A operation. It is a 20 watt unit. The power transformer is a Custom Coil unit. I'm using another just like it in the Brown Note 18W project.

On downside of this amp is that the preamp tube, a 6267 (industrial EF86), is microphonic. So cranking it up all the way only induces squeal. I can't use a clean booster to drive the front end either :( I'd like to try a few modern EF86 tubes, but these are pricey and there are no guaranties that they will not be microphonic as well.

The face and back plates are made of laminated paper. They look okay but are kind of cheesy. I plan on sending out the CorelDraw files to BNP Lasers to have proper plastic or metal plates made for the amp. I don't like the black writing on the white background so I think I'm going to go with a black face plate with white writing.

One thing that concerns me about this amp is the the a 6CA4/EZ81 tube rectifier shares the filament winding with the EL84s, 12AX7 and 6267/EF86. If the recto ever shorts, it will take out the tubes and the OT. I may pull the socket and put in an octal socket so I can run a 5Y3 or 5V4 off of the 5V winding on the PT.

The amp really needs a cabinet and I really need to acquire some woodworking skills :D

A very worthwhile project, and very Voxy tones out of it. With the right pedals, it will do a Marshall impersonation as well.

tung

[duhvoodooman]

On downside of this amp is that the preamp tube, a 6267 (industrial EF86), is microphonic. So cranking it up all the way only induces squeal. I can't use a clean booster to drive the front end either :( I'd like to try a few modern EF86 tubes, but these are pricey and there are no guaranties that they will not be microphonic as well.
From what I've read, microphonicity (is that a word?) is a chronic problem with EF86 tubes. Isn't there somebody out there who makes a sturdier version? Eurotubes claims that the JJ EF806/6267 has good microphonics performance, but they go for $27 a pop, so I assume that's what you're referring to with the "pricey" comment....


The amp really needs a cabinet and I really need to acquire some woodworking skills
Amen, bruddah! That's an area where I have ZILCH skills/experience. I drool over what I see guys like M29 and Shiner do!

Dude, you REALLY have to figure out a way to record some demo clips and start posting them here! I (and I'm sure many others) are dying to hear what some of these little gems of yours sound like!!! :poke: ;)

[tunghaichuan]

From what I've read, microphonicity (is that a word?) is a chronic problem with EF86 tubes. Isn't there somebody out there who makes a sturdier version? Eurotubes claims that the JJ EF806/6267 has good microphonics performance, but they go for $27 a pop, so I assume that's what you're referring to with the "pricey" comment....


I'm such a cheap b*stard, the thought of shelling out $27 for a modern production tube gives me the the willies :D I think the only thing manufacturers can do is heavily screen out the really microphonic tubes. I remember reading an article a few years ago in one of the tube magazines that I subscribe to saying that almost all preamp tubes are somewhat microphonic. It is just that most 12AX7s fall in an acceptable range. I had high hopes for the 6267 tubes, they are supposed to be low noise/microphonics:

http://www.nj7p.org/Tube4.php?tube=6267




Amen, bruddah! That's an area where I have ZILCH skills/experience. I drool over what I see guys like M29 and Shiner do!


I'd like to be able to build Trainwreck-quality cabinets. They are not very practical for gigging musicians, but they sure look cool.

I have a few routers and a dovetail jig with a box joint template. I just need to get a table saw and build a cross cutting jig or get a chop saw. Maybe someday...



Dude, you REALLY have to figure out a way to record some demo clips and start posting them here! I (and I'm sure many others) are dying to hear what some of these little gems of yours sound like!!! :poke: ;)

I'm working on it :D I'm going to try to get something recorded today. The downside is that y'all will have to listen to my crappy playing to hear what the amp sounds like. :rotflmao:

tung