Full tone stack off of an EF86?

[dartanion]

Adding a cathode follower is so simple and such an elegant solution to this issue, I recommend it to those who want a tmb with an EF86. No need to futz with tonestack values, unless you really want to. We've talked about the EF86 ad nauseum over on SEwatt and came up with a few options for pentode/triode tubes. The 6U8 is a popular one, but there are tons of others that would work too (6AN8, 7199, etc.). It's worth considering.

For the EF86 builds that I have done, I normally just use a simple tone control and sometimes a rotary switch like a DC30. It just depends on what the client wants. The rotary switch is nice as you can tune that channel for the guitar being used or the room.

[dehughes]

Adding a cathode follower is so simple and such an elegant solution to this issue, I recommend it to those who want a tmb with an EF86. No need to futz with tonestack values, unless you really want to. We've talked about the EF86 ad nauseum over on SEwatt and came up with a few options for pentode/triode tubes. The 6U8 is a popular one, but there are tons of others that would work too (6AN8, 7199, etc.). It's worth considering.

For the EF86 builds that I have done, I normally just use a simple tone control and sometimes a rotary switch like a DC30. It just depends on what the client wants. The rotary switch is nice as you can tune that channel for the guitar being used or the room.

Nice. So, running a cathode follower off of the EF86's cathode will allow one to use "standard" (r.e., Fender/Marshall) TS values? OR are you saying one needs to then run a 12AX7 cathode follower setup between the EF86 and the tone stack?

[dartanion]

EF86 plate to CF, then tmb ts. This is why I suggest a pentode/triode tube for your situation. You get that pentode tone, plus you have a triode for the CF all in one tube. No need to drill another hole. No need to change standard ts values (unless you want to). This setup will get you where you want to go, but then it's up to you to tweak to taste. Besides, EF86s are a big pain in the ass to find good ones, new, used, NOS, whatever.

Alternatively, you can use a single tone control like 18watt trem tone control. Relatively low loss and works pretty well with an EF86. I posted a layout for one on the 18watt.com downloads area.

[Merlinb]

Interesting...this is what the Rt. 66 does, yes?

I don't know that schematic.

So, I could still have a "mid" pot if I choose....it would just need a "floor" of about 50k..so a 50k pot on top of a 50k resistor, maybe?

Well in practice you'd just use a 50k or 100k mid pot, since the resistor wouldn't really do anything except limit the range of control.

[klingo]

the rt. 66 does this https://tubeamparchive.com/download/file.php?id=8365

it's a quite low loss T/B tone control that sounds good. treble pot adds high-mids distortion as well when turned up, and the bass pot set the amount of...bass.
IMHO it work well for blues/rock tone but doesn't have the mid scooped tone that some people like.

[dehughes]

EF86 plate to CF, then tmb ts. This is why I suggest a pentode/triode tube for your situation. You get that pentode tone, plus you have a triode for the CF all in one tube. No need to drill another hole. No need to change standard ts values (unless you want to). This setup will get you where you want to go, but then it's up to you to tweak to taste. Besides, EF86s are a big pain in the ass to find good ones, new, used, NOS, whatever.

Alternatively, you can use a single tone control like 18watt trem tone control. Relatively low loss and works pretty well with an EF86. I posted a layout for one on the 18watt.com downloads area.

Hey dart...this one?

http://www.18watt.com/files/ef86_layout.jpg

I'll save that for sure.

As for the CF idea...not bad! However, I would indeed need to drill another hole, as I only have two 9-pin holes on this chassis. For your idea I'd need an EF86, another 12AX7 to use as a cathode follower, and then another 12AX7 for the PI, yes?

[dehughes]

the rt. 66 does this https://tubeamparchive.com/download/file.php?id=8365

it's a quite low loss T/B tone control that sounds good. treble pot adds high-mids distortion as well when turned up, and the bass pot set the amount of...bass.
IMHO it work well for blues/rock tone but doesn't have the mid scooped tone that some people like.

Exactly. And I'd still like to get somewhere close to the scooped mid-Fender-y thing, even with an EF86...

So Merlinb, on the schematic linked above, would the "midrange control" essentially be the 100k to ground on the Bass pot?

[dartanion]

David,

I am recommending using an alternative tube to an EF86, such as the 6U8, 6AN8, 7199, or a litany of other pentode/triode tubes. There are tons of different TV tubes that are noval socket pentode triode tubes that have proven to work well in guitar amps. There are some clips on SEwatt of a 6U8 channel amp that sound pretty much like an EF86. A tube like this used one noval socket and gives you the pentode and triode, therefore no more holes need to be drilled. The great thing is that NOS 6U8s are under $10 whereas NOS or New EF86s are more, with NOS being really expensive.

If you want to give this a try, you won't be burning serious cash on an experiment. The tubestore.com has 6EA8/6U8 for $6.95. I'm sure most tube sellers have them too.

[briane]

Interesting. Would you be so kind as to tell me how you built the preamp? I don't think I'll run a paralleled 12AX7 after the EF86 like you did, but the component values would probably point me in the right direction. And yes, I was thinking of running the EF86 in Pentode as well.

Well I would have to open her up to recall exactly....but the essence was that of the standard mode ef86 pentode operation, fed into a typical v1A style dumble TS circuit (with different values), though a smaller sloper resistor (I recall 82k), and larger cathode bypass cap (220 uf?) were the prime ingredients. Taking the output off the volume the parallell 12ax7 was styled similar to the typical v1B preamp.

Before my next comments let me say I greatly respect dartanion, but personally I dont share the exact viewpoint.

The CF after the ef86 works, but results in a noticable frequency change....Which I personally did not care for. I found that running in pentode mode I did have enough juice to drive the TS, though I recall the volume pot is turned up just a hair more than is typically expected. The key was adjusting pre-amp components so the frequency was not so noticably shunted in the high end.

I have done a number of builds with the 6an8 and 6au8, and while they work just fine, I have never found the tone of those tubes to be as magical as an ef86. To my ear they have a grating value that wears out the ear after a few hours. Same thing with the dual ef86. In my mind I just tend to think of it like too much pentode, and the ear likes a little triode mixed in, but thats really an oversimplification. That said those other tubes are probably easier/cheaper to aquire, and likely less fidigety than the ef86. That likely is just a personal taste factor.

FYI, I spent 2 years finding the component values that I wanted to stay with for that crazy build. It was a long, hard road to travel, but I was also doing more than just monkeying with the pre-amp. I ended up gutting the amp once, and rebuilding it multiple times.

[dartanion]

Briane,

You are absolutely on the money about preference. I like straight up pentode ef86 channels, but setting them up with a tmb took away too much gain and balls for my liking. It will work, but it depends on your goals for the build. A cf does alter the tone, but to me, it is a good tonal change. In David's case, a cheap and fun experiment would be to try something like a 6U8. IIRC, he's a consumate amp tweaker, so I thought he may enjoy it.

There are lots of options here, so it's really a matter of taste. There are other noval based pentodes out there too. Some very close to an ef86 without the high price tag and microphonic nightmares.

[briane]

Dartanion, thanks for taking those comments with the knowledge its my personal preference, and will not reflect the views of others.

I admit the tmb with the ef86 is a strange beast. The only time I have ever used it was on my version of the SSS, which was intended as a clean only amp. In that case I even found some gain loss through the TMB to be desirable. It definetly loses some aggression, aka balls.

Yes, for the builder that wants to understand the difference theres no substitue for trying it out, and with a variety of types of tubes...Thats where I came up with my views. And given the small cost of investment, and that it only takes a couple of hours to swap an amp over, its a really valuable learning experience.

cheers david, you have lots of options to move forward with!

[dehughes]

Great. Thanks guys. I love the different viewpoints....one can learn a lot that way. I'll re-read the posts and see what I land on. And yes, I'm a neurotic amp-tweaker.....love to hear "this vs. that".

I think I may have a few old stock 6U8/6AN8/7199 tubes upstairs...I'll have to check...

[dartanion]

Not a problem guys. You can learn things from anyone and trust your own ears. Some of the most hyped gear and mods may be not your cup of tea. I personally have a love/hate relationship with the ef86. Love the tone when they aren't microphic, I also hate the price for good NOS.

[FunkyE9th]

Has anyone tried to use a cathodyne inverter? It only needs one triode, so it will free up a triode. Just wondering if that will be enough to make up for the gain loss via a TMB. An LTP (at least the ones I've worked with) has a gain of ~26. You should be able to get a gain of ~59 with the extra triode. Just wondering if that's enough to make up for the loss. I have never looked at the gain loss of a TMB...

[Darkbluemurder]

Some of the 65Amps models use a EF86 with a tone stack, e.g. the Soho. The topology there is EF86 - gain control - second gain stage plus cathode follower - tone stack w/ bump circuit - PI - power amp.