I finished my 18 Watt head with EF86 normal channel and Mass

[Wayne_Alexander]

I finished it today. I bought one of Graydon's head kits and modified it by replacing the normal channel with an EF86, wired like the stock AC15/AC30-4 EF86 channel. I can't make photo links work, but here's the address of a photo of the right side of the tagboard, modified to make the EF86 components fit.

http://community.webshots.com/sym/image ... qnn_ph.jpg

or http://community.webshots.com/photo/436 ... 2849vgAqnn

I put a little terminal strip to join the shielded inputs into the 68K resistors that feed into pin 9, the rest of it fit on the main board, I just added one eyelet at the bottom right and one in the bottom row a few over from the right side. I wired the tone controls exactly like the stock tremolo channel. It's a little bright, so I may modify that a bit if I can figure out how.

The EF86 is louder and gainier and ballsier than the 12ax7; it sounds bell-like and chimy and Voxy at low volumes and REALLY gainy at the top end--kinda like Eddie Van Halen on the first album. It's a slightly different character of sound than the 12ax7 makes, I really like it.

I also added a Mass motor (little speaker without a cone) on top of the chassis, and tried to wire it with a 15ohm Rheostat that Graydon supplied, but I couldn't figure out how to do that, so I followed the stock Mass schematic from the Weber site [with a 100 ohm pot and a 100 ohm resistor], without the line-out. I put in a switch -- one position routes the signal from the impedance selector straight to the speaker jack, the other position routes the signal to the Mass per the Weber schematic.

With the switch straight to the speaker jack the Mass is still in the circuit (it would take an additional switch to totally remove it from the circuit, because the hot wire coming from the pot is attached at the input of the speaker jack) though the volume is 100% with the pot full up, and stays about the same until the last little bit of rotation on the pot, then the volume drops some, maybe 12db.

With the switch routing the signal to the Mass, the amp is more a bedroom amp--with the pot all the way up it's probably cutting 25 or 30db, and now the pot attenuates increasingly with rotation, but the volume gets really low. This may not be wired right, but it works for now and the switch is a gig level versus bedroom level switch. The Mass adds very little color to the tone, just allows it to get that screaming gain at lower volume levels, and it sounds way better than a master volume would.

[markh]

Very nice looking build, Wayne. Did you notice any microphonics problems with th EF86?

You could probably use a DPDT switch to completely switch out the MASS when you're not using it. One side would connect the output jack to either the hot side of the MASS or the OT, and the other would connect or disconnect the MASS input to the OT.

--mark

[Wayne_Alexander]

Mark, the EF86 I'm using {Phillips} is a little microphonic, but not enough to matter when playing. I'll try other EF86's over time. Good idea on the switch, I'm currently using only one side of a DPDT, I could run the hot wire from the pot that follows the mass through the unused side of the switch so it's disconnected totally when it's switched off. I'll try that.

[Wayne_Alexander]

I had trouble with the wiring for the Mass motor, but Graydon sent me the schematic he uses and now all is well. I've just left myself one speaker jack, filling the other one with the knob on the Mass, and I wired the DPDT switch next to that to switch the signal either direct to the jack with the Mass out of the circuit, or through the Mass. Now that I've got it wired right, the Mass cuts about 5-6 db at the highest setting, and then can be attenuated all the way down to a whisper. It's a noticeable volume jump when it's switched out of the circuit, even full-up, but I think it's perfect and it makes it so I can use this amp without a THD Hotplate or other external attenuator. I recommend this to all of you.

On another subject, my Phillips EF86 has now gotten pretty microphonic (actually mechanical vibration inside the tube body, it doesn't seem to be heard through the speakers even though it's quite loud standing nearby). I'm ordering a couple of other EF86's to try, a NOS Mullard and a Svetlana. I'll report on those when they arrive. I can say that the EF86 channel is a lot louder than the 12ax7 and somewhat gainier when dimed, probably 8 db or so louder. Having had a stock 18 Watt, I like the EF86 normal channel a lot better. I kept the tremolo channel stock because I like the tremolo and the tone of that is fine as well.

[Wayne_Alexander]

As I posted elsewhere (in the Tone controls in EF86 mod post) I rewired the phase inverter and power supply a la "Jason's PI Mod" which is pretty much the same as the early AC30/AC15. That cut the gain and volume a little in the EF86 channel, and cut the gain and volume a bit more in the 12AX7 tremolo channel. Now the 12AX7 channel full up has only AC/DC levels of gain, and the volume and gain on the EF86 channel match the 12AX7 channel when the EF86 channel is turned to about 6 on the volume dial. The EF86 has gain levels around those of the first Van Halen album at 10 on the volume dial, and is a lot louder (8db?) than the other channel. The EF86 has a Voxier clean sound, the 12AX7 has a Marshallier clean sound. I've tried three different EF86's now, a Phillips (worked fine) Mullard (I prefer it only slightly over the Phillips, it sounds very similar) and a Sovtek, which sounds almost as good but has a bit more background noise and feeds back more. With the revised PI/Power supply wiring, I find I'll use the EF86 when I want to play dirty, and the 12AX7 when I want to play with a little grit but also want tremolo. I wish there were a way to beef up the gain on the stock 12AX7 tremolo channel so I could get closer in volume and gain to the EF86. Do any of you have any ideas?

[markh]

There is a complex interdependancy between the two halve of the triode in the trem channel, so there's not much to play with there. The only thing I can think of would be to add a triode stage between the volume control and the PI (which would require another tube).

--mark

[Wayne_Alexander]

Mark, that's what I thought too. The AC30 PI and power supply wiring suits the EF86 a bit bettter (It's still an out of control hurricane in a little glass bottle), so as long as that channel is what I'll mainly use on the amp, it'll work fine.

Thanks.

[Shea]

I've been using Svetlana EF86s from Antique Electronic Supply, and I haven't had any problems with microphonics or noise.

Hmm, maybe they're the same as Sovteks, since they have the S logo.

Shea