Pentode (EF86) pre-amps and combo's?

[Isaac Stuckey]

My favorite for a single knob simple tone control so far, is like a tweed deluxe... Look up the schematic for the 5e3.

[Ingo]

Tubenit,
That tweed OD special schematic looks really interesting, I liked the tone, slightly interested in building one now. That would be cool.

Also, Ingo, You mentioned the EF804, is that a direct replacement for the EF86 pinwise? Does it have the same gain properties? Like would it be less gain kind of like the difference between a 12ax7 and a 12ay7 or is it similar?

Hi Isaac

The EF804 from Telefunken is a long living version from the EF86 and is less microphonic. It is a direct replacement pinwise and has the same electric values as the EF86. Even this tube is more expensive, it´s worth a try

Best regards
Ingo

[Isaac Stuckey]

That's very cool, will have to try one of those eventually.

[JMPGuitars]

I'm curious about them too, but the JJ EF806S is $30 compared to the EF804 for $70...and I'm happy with the EF806S. I think it's funny that I don't want to spend that much on tubes considering what some people pay for NOS.

[Isaac Stuckey]

Is your EF806s basically the same thing as Ingo described?

[JMPGuitars]

Yes. Direct replacement for EF86, and supposedly less microphonic. So far I've only built them in heads and they sound amazing. I built a combo version I need a cabinet for, I'll see how that does with the EF806S.

[Isaac Stuckey]

Cool, will look into that once I get around to building another AC15 clone.

[saransk]

I built the EF-86 mod that is included in the Tube Depot's 18 watt "kit."
Pretty easy change for the original "Normal" channel 12AX7.
Buy a new socket, much easier just to rewire from the ground up

I'm familiar with the tube because of the QUAD preamps I had for years. (The Brits love these tubes)

I mounted the socket with rubber "O" rings between it and the chassis and included the "rf" cap. One thing I do use is a tube shield which holds the tube rather tightly in the socket. This may help cut down on the microphonics. Since the tube is a high gain, I never would have used it without a shield.

I've also added one with both the "small" rotary tone control (6 positions) and the "large" control (from W***r with 12 positions.

Good shielded cable from the inputs is a must.
Don't use an inexpensive tube - the RFT EF86 is pretty decent in my amp
Haven't tried EF806 that is sold as a replacement, probably will try the JJ one just to see.

[JMPGuitars]

I mounted the socket with rubber "O" rings between it and the chassis and included the "rf" cap. One thing I do use is a tube shield which holds the tube rather tightly in the socket. This may help cut down on the microphonics. Since the tube is a high gain, I never would have used it without a shield.

I've also added one with both the "small" rotary tone control (6 positions) and the "large" control (from W***r with 12 positions.

Good shielded cable from the inputs is a must.
Don't use an inexpensive tube - the RFT EF86 is pretty decent in my amp
Haven't tried EF806 that is sold as a replacement, probably will try the JJ one just to see.

That's interesting, I was going to use rubber o-rings also. I love the tone of the EF806, but it is a little microphonic when the head sits on top of the closed-back cabinet...which I guess should be expected. I know a lot of people say to just not put the head directly on top of the cab, but real-world situations, that's not always an option so I'm trying to work around it.

I already use tube shields, but I'm going to try the o-rings out and see if it works better. I'm curious also about the EF804 if it really is less microphonic than the EF806. For almost triple the price, it better be.

I'm also curious about an octal substitute like the 6SJ7 or RCA 5693. I don't know what it would sound like, but if it sounds similar to the EF86 but without the microphonics, that would be awesome and much less expensive.

[legin71]

First post!

My view is if you like the sound of the EF86 then you should use it. I was reading an interview with DrZ the other day and he uses them even though they are microphonic. He was saying that if you tap the tube lightly with a pencil you can hear how microphonic it is. His solution is to find the least microphonic tube and put that into the first preamp stage. As every EF86 IS microphonic, this seems like a decent enough solution to me. You have to say that Dr Z is pretty clever and probably designed his circuit a bit better than we could to help minimise microphonics.
I really liked some of the other suggestions with fibre washers.

[JMPGuitars]

Dr. Z is definitely brilliant, but his solution there is based on having lots of EF86s to choose from. They're not cheap tubes, so for the average person, buying 10 tubes and tapping each to see which is best, is not all that realistic.

But I agree, using rubber grommets and/or fiber washers to reduce the microphonics is a good way to go. The other option is that if you're using a head, don't put it directly on top of the speaker cabinet.

[JMPGuitars]

I've been doing some more research, and I'm going to try out some RFT EF86 tubes. They seem to be available on ebay and a couple other tube shops, ranging pretty widely in price. From what I've read though, they're supposed to sound fantastic with ZERO microphonics.

[Isaac Stuckey]

Don't forget to post your results.

[JMPGuitars]

Don't forget to post your results.

Of course! And I'll do an audio/video sample too. I'm also planning on doing a power tube comparison between JJ and TAD and Tung Sol (new production). I'm not happy with the amount of JJs I've had to send back, so time to compare other options.

I'm also considering trying out some tube rings and see how they work.

[StarGeezers]

With our great success using the 5725, just thinking that up front of a Marshall 18Watt circuit would be Teriffic .. Plenty of gain , Sweet sound, but a diminutive 7 pin socket ... Rugged tiny tube , very pedal friendly ... and we paid a buck a piece for ours ...

May be perfect to downsize the 18Watt chassis for a nice smaller /lighter combo cab ... Using the TLBox (Wattkins) , we’re no longer so dependent on large combo cabs ... Great for we “old guys”

[Isaac Stuckey]

The 5725 sounds interesting, but is there a version of it in a 9 pin socket? Or maybe I could make a converter so I wouldn't have to use a smaller socket in the chassis, but the pin converter would work for this. Like a mini yellow jacket.

[JMPGuitars]

The 5725 sounds interesting, but is there a version of it in a 9 pin socket? Or maybe I could make a converter so I wouldn't have to use a smaller socket in the chassis, but the pin converter would work for this. Like a mini yellow jacket.

There are, but from what I've seen so far, they're overpriced. Just do a google search for "6AQ5 to 6P1 adapter" and some stuff will pop up. (and I have no idea about the pin layout...)

[Isaac Stuckey]

I could probably just as easily buy some parts and make one myself. But I'm not doing anything with pentodes right now, especially since the last AC15 I built is the top boost, instead of the normal channel so no EF86, and personally I like the top boost better so far.

[AC Cobra]

I was going to get a RTF ef86, but they did t have them in stock at tube depot, and I was a little worried if ebay would be legit, but I do think those are worth enouh to make fake copys of. I ended up getting the tung sol ef86 partly because I dont want to rely on nos tubes.
As far as the tung sol power tubes I just put a set of 6L6G's in another amp and they sound fantastic!! That may not mean much for the EL 84's in a 18 watt though, and that is what matters.
I was looking at the schematic for the ef 86 being used as a overdrive tube, but Im not into doing quite that. I was wondering if anyone has tried using one in the second stage to get more harmonics and compression. I was thinking 1 stage of a 12 AU7 or (dont hate me for sugesting it) a transistor.
I guess Ill just wonder for a while as my amp is on hold because Im too busy building guitara right now(which is a good thing)

[Isaac Stuckey]

Wulllll, Then finish the guitar, and the amp, then record a video of them together.