EF86 preamplifier suggestions

[Giaime]

Sorry if I didn't write about it: I'm having the transformer custom made, I usually specify 0-8-16ohm secondary on the output transformer...

[octal]

I don't know that one is "better" than the other. What taps do you have on your output transformer? Obviously, if your X-mer has a 8 and 4 ohm taps you can run an internal 8 ohm spkr with the option of adding a external 8 ohm cab. If you have 8 and 16 ohm taps, perhaps a 16 ohm speaker with an optional 16 ohm cab, or an 8 with the option of putting another 8 in series. I generally think that it's better to parallel speakers ...better power sharing if you use mismatched speakers, less risk of damage to the amp if one speaker voice coil blows and opens up.

[Giaime]

I guess I'll continue lonely...

I decided for the Eminence Red Coat Private Jack. What about the impedance? In a small 1x12" combo, is it better to use 8 ohm or 16 ohm, to give the possibility of using an external cabinet instead of the internal speaker (or both toghether)?

[Giaime]

So, I've set my mind on a Celestion Vintage 30, in a small open back cabinet (think Fender BJ for the size and style). Do you think it would be good, or it's too shrill and edgy? My friend has to play rhythm guitar role: he likes bright cones, but the V30 may be too much. Maybe the Eminence Red Coat series are better (which one)?

[Giaime]

Thanks everyone for your replies.

The EF184/6EJ7 is a cheaper alternative to the EF86.

What about the PF86? I can get them cheap, and only a 6ohm resistor is needed to run them on 6.3V.

[jrfrond]

Thank you for your replies.

About the 6 way tone selector switch on the Matchless DC30, do you think it's a keeper or it is better to use a "tone" control knob? I think that the basic function of low-pass filtering is already embedded in the guitar tone knob, so it's useless to duplicate it in the amp: better to have an high-pass tone control like the 6 way switch.

The Matchless rotary switch on the DC30's pentode channel is, in fact, a high-pass filter, switching in gradually larger coupling caps. Very simple and effective. I like this better than a bass control, because your rolloff point is actually changing, not just the level.

[octal]

They just don't sound that good, which I found somewhat disappointing.
-g

Well, if I'd have known that the 'internet hearsay' was from you, I would have taken it a bit more seriously. I didn't remember where I read that....

Nathan

[mooreamps]

I have heard that both of those pentodes "sound bad"-whatever that means.

Good luck!

They just don't sound that good, which I found somewhat disappointing.
Maybe, they would work better as a tremolo oscillator, but even if it could, my first choice would be using a FET for that, and not a tube.


-g

[imbuedblue]

Is there a lesser famous alternative to EF86? I'm willing to experiment. I've heard of E80F, and maybe octal pentodes are more immune to microphonics due to the larger contact area.

The EF184/6EJ7 is a cheaper alternative to the EF86.

Running a 12AX7 in SRPP will get you the harmonically rich, mid-heavy cream of the EF86, but lacks some of the top-end sparkle.

[Giaime]

Thank you for your replies.

About the 6 way tone selector switch on the Matchless DC30, do you think it's a keeper or it is better to use a "tone" control knob? I think that the basic function of low-pass filtering is already embedded in the guitar tone knob, so it's useless to duplicate it in the amp: better to have an high-pass tone control like the 6 way switch.

About the speaker, and the possibility to have an "ext. speaker" jack: would you use an 8Ohm or 16Ohm internal speaker? I think that 16Ohm should be better (less Z ratio in the OT = better sound?), as there are more 16Ohm external speaker enclosures than 8Ohm ones. Or the "ext. speaker" jack could keep the internal speaker active... What do you think?

[octal]

One more thought. If you're going to use the "unused" other input of the LTP, I believe both plate resistors should be equal value. If you keep it "as is" one input will be in balance and the other input will be doubly out of balance.

Nathan.

[octal]

I can get european tubes more easily: I was thinking 6AU6 and 6BA6 (that seems close) and ECF82 (not so close, maybe I can use the triode section as a cathode follower after the pentode stage)...

I have heard that both of those pentodes "sound bad"-whatever that means. I have never tried either myself, so I wouldn't take internet hearsay on them too seriously. I believe one or two really low end guitar amps (Kays, perhaps?) used a 6AU6 as an amp.

Those 6sj7s are cheap enough ($4.51 for NOS from tubesandmore.com) that shipping several to Europe would probably still be cheaper than an EF86.

I cribbed my 6sj7 circuit from the Ampeg Dolphin II schematic:

http://www.el34world.com/charts/Sche...te_Dolphin.pdf

I left off the tone stacks as they were missing values and it seemed like it would load the pentode down too much...

Good luck!

[mooreamps]

Is there a lesser famous alternative to EF86? I'm willing to experiment. I've heard of E80F, and maybe octal pentodes are more immune to microphonics due to the larger contact area.

If you want to go the octal / plexi route, you could do this.



6SL7 > 6SJ7 > C/F > volume ( 100 K ) > bax or gmm tonestack > P/I using 6SL7 > two 6V6.. So, with this layout, you can do it with 5 tubes......

I picked a couple of 12SJ7 recently ; they were only like 5 dollars each. Not as much gain as the EF-86, and they need the extra gain stage in front to drive them.


-g

[Giaime]

I can get european tubes more easily: I was thinking 6AU6 and 6BA6 (that seems close) and ECF82 (not so close, maybe I can use the triode section as a cathode follower after the pentode stage)...

[octal]

Well, you could try the 6sj7. NOS American ones are pretty cheap. I never built a combo with one, but I did build a head (placed directly on top of a 1X12 cabinet) and microphonics didn't seem to be an issue.

Nathan