Seeking EF86 amp suggestions

[smackoj]

Hi; I ordered a couple vintage EF86 tubes to see if I like the tone diff.  if any of you forum gents have a favorite amp or design you would like to suggest I'd be glad to have a look at it?

thanks  jack d
 

[MakerDP]

My favorite is the Matchless DC30. I built a 15-watt version of one. LOVE the EF86 channel.

Another popular one is a Marshall 18 watter TMB with an EF86 in the non-TMB channel instead of the single 12AX7.

[jojokeo]

Hi Jack,
One of my favorite uses is EF86 > cathode follower > tone stack > EL84 or 6V6 for single ended. If push-pull is wanted then into phase inverter and power tubes. Very easy, basic, and very nice. I've also done two cascaded which is a bit overkill but also works well. I've heard the Tilt switch is nice which morphs pentode to cathode but I prefer either/or and then a variable gain control. Then there's the Vox idea of only the pentode followed by various coupling cap sizes into either single ended tube of your choice or pi > pp tubes.

[kagliostro]

Derived by this

http://www.bensykora.com/7cylinder.html

a friend is building this (with the standard PS, no the alternative one)





http://www.diyitalia.eu/forum/download/file.php?id=10619&mode=view

http://www.diyitalia.eu/forum/download/file.php?id=10617&mode=view

K

[smackoj]

thanks amigos. great suggestions and there is a lot of info, although much of it is related to hi-fi and phono preamp designs, on the internet. I found this one schemo which lists about 6 different amps/amp builder's designs and gives the different values used for setting up the EF86 tube. Here is a copy of it for those who have an interest.
 

[MakerDP]

Hey Kagliostro... that pot on the cathode bypass of the EF86... does that let you adjust how much "bypass effect" the capacitor has on the cathode? I've never seen anything like that before.

[kagliostro]

Yep


Is a trick I found on a Merlin's book that some guy experimented with satisfaction, same thing for the morph control
(the 1M pot connected to ground and the 0.1 and 0.47 cap)


K

[MakerDP]

Merlins book??? I must have missed that. Now I have something to do during my break today!

[kagliostro]

You can find it on the first preamp book

Pag. 29 Fig. 1.20 for the variable gain control

Pag. 95 Fig. 3.29 for the morph circuit

K

[smackoj]

Here is my sorta finished EF86 project. I went with a preamp rather than a complete amp to get it done quickly and then test the sound before committing to a slower build. I used an old Champ style SE amp carcass and kept the PT which works really well for a preamp.  I did not add anything but a volume control to speed up the build and I have a second 9 pin socket wired up to accept the more available 12a_7 type tubes.  I used the Matchless DC30 parts values you see listed above along with the EF86 standard wiring schemo.  I figured why not go with a amp builder's values that I know will be as good as it gets like the venerable Matchless.

I think it sounds fantastic thru my vintage SS Tel Ray amp with a 60's era alnico mag speaker. A very noticeable change in tone characteristics from the traditional mini 9 pin type tubes. Love it a lot.

Here are a couple pictures of my 'ghetto' cruisin' EF86 preamp.   

[MakerDP]

Nice job smackoj. I _really_ like my Matchless DC clone (Trinity TC15). Every time I play it out somewhere I get a ton of good comments about it. Then when I tell them I built a $4500 amp myself for less than $700 they almost do a backflip.  It also holds a special place in my heart because it was the first amp I built.

Kagliostro... I have Merlin's 2nd edition. Looks like that info isn't in there, unless it's in a totally different place. I'll have to scour the book some more.

[kagliostro]

Pag. 57 Fig. 2.18 for the morph circuit

About the variable gain control (or boost) seems that on the second edition isn't present

you can see something like it on Pag. 260 Fig. 14.7, look to the boost switch that excludes a resistor that is in series with the bypass cap

You can look also at Pag. 166 Fig. 9.12 where a pot is connected in series with a bypass capacitor as a Presence Control

K

[smackoj]

I had never heard of Matchless and then one day I strolled into Russo's Music in Omahaha, Neebraskee and found a twin twelve model brand new on the floor. I was immediately in love with the sound and workmanship. Unfortunately I didn't have 3 grand in my pocket that day or it would have been mine! Top notch stuff IMO.

 

[MakerDP]

Thanks K. I suspected as much. Maybe I'll ask Merlin about it over on AX84. He's still very active there.