I looked at the data for the EF86 tube today, and noticed something I hadn't seen before.
On my DC30 clone, I didn't connect pin 2 and 7, because the schematic didn't say anything about that. But I see that pin 2 and 7 are for the internal shielding.
I looked at another schematic, and there pin 8 (supressor grid) is connected to pin 7, and pin 3 (cathode) is connected to pin 2.
This way, pin 8 and 3 are connected through the internal shield, and not directely connected with a wire between the pins.
Is this how it should be wired?
Is it important that pin 8 and 3 are connected through the shield, or could the shield just be connected to pin 8&3, which are already connected?
Or should the shield be grounded directely?
Tommy
EF86 wiring
Moderators: pompeiisneaks, Colossal
Re: EF86 wiring
Tempus edax rerum
Re: EF86 wiring
Ok.
Need to register to see it...looks like it could take some time before my account is activated.
Tommy
Need to register to see it...looks like it could take some time before my account is activated.
Tommy
Re: EF86 wiring
Here you go:
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Eardrums!!! We don't need no stinkin' eardrums!
Re: EF86 wiring
Thanks.
If it's not grounded, should I expect more noise?
Tommy
If it's not grounded, should I expect more noise?
Tommy
Re: EF86 wiring
Okay. It is worthwhile reading...it helped me with my EF86 build. I essentially copied the AC15 circuit but with the 6-position rotary switch a la the DC30.Tdale wrote:Ok.
Need to register to see it...looks like it could take some time before my account is activated.
Tommy
Tempus edax rerum
Re: EF86 wiring
Yes and no. It really depends.Tdale wrote:Thanks.
If it's not grounded, should I expect more noise?
Tommy
Eardrums!!! We don't need no stinkin' eardrums!
Re: EF86 wiring
I've always grounded the shield (2 and 7) and never had any noise issues except what I would refer to as "regular" tube noise. Meaning some samples of EF86 are noisier than others. Oddly enough the noisiest EF86 I have is an old Mullard but it sounds great and the quietest is a new Sovtek and it sounds terrible. The only tube design I've seen where 2 and 7 are not grounded directly is the Dr Z KT-45. I would have to check but I think they went to pin 3 and 8. And it's quiet too.
I have found a couple things after having messed with various circuits and EF-86s.
I like the 220K plate resistor better than the 330K value Matchless used. Seems to sound a little softer maybe less "pentatonic" read: less bright or harsh.
A single EF-86 into a phase invertor sounds pretty good, more gain and edgier than a single 12AX7 stage, but an EF86 stage cascaded into a 12AX7 gain stage sounds better. The 12AX7 seems to tame the EF86 down a lttle but you get lots of gain. Probably more than you need but you can throw some away. In fact my current iteration is a standard Marshall 18-watt style pre-amp preceded by an EF86 with a 500K gain control followed by a 500k/500k voltage divider and 500pF bypass cap. This is then fed via switching jack into the front end of the Marshall -18 pre-amp so you can have either or. This set-up has almost as much distortion as three cascaded 12AX7s (almost).
I think the EF86 front ended amp needs tone controls other than just the 6-position coupling cap choices of the DC 30. For instance a high cut is definately worth having at a minimum. But I found the rotary switch very limiting.
Try a EF86 in a plexi-style pre-amp, cathode follower, tone stack, etc. That has more gain than the standard plexi or jumpered inputs with nice bite but without the full saturation of the JCM 800 style 3-stage. Too much fun. One of these days I'm going to really make an effort at an Octal tube pre-amp.
I have found a couple things after having messed with various circuits and EF-86s.
I like the 220K plate resistor better than the 330K value Matchless used. Seems to sound a little softer maybe less "pentatonic" read: less bright or harsh.
A single EF-86 into a phase invertor sounds pretty good, more gain and edgier than a single 12AX7 stage, but an EF86 stage cascaded into a 12AX7 gain stage sounds better. The 12AX7 seems to tame the EF86 down a lttle but you get lots of gain. Probably more than you need but you can throw some away. In fact my current iteration is a standard Marshall 18-watt style pre-amp preceded by an EF86 with a 500K gain control followed by a 500k/500k voltage divider and 500pF bypass cap. This is then fed via switching jack into the front end of the Marshall -18 pre-amp so you can have either or. This set-up has almost as much distortion as three cascaded 12AX7s (almost).
I think the EF86 front ended amp needs tone controls other than just the 6-position coupling cap choices of the DC 30. For instance a high cut is definately worth having at a minimum. But I found the rotary switch very limiting.
Try a EF86 in a plexi-style pre-amp, cathode follower, tone stack, etc. That has more gain than the standard plexi or jumpered inputs with nice bite but without the full saturation of the JCM 800 style 3-stage. Too much fun. One of these days I'm going to really make an effort at an Octal tube pre-amp.
Re: EF86 wiring
Should I replace the cathode resistor too, or is it only the plate resistor that should be changed to 220K?
I got a JJ-EF806 tube, which is the same as a EF86. It sounds good, but is very microphonic compared to a Mullard I have. It's also a bit brighter than the Mullard, which is tight and warm sounding.
Tommy
I got a JJ-EF806 tube, which is the same as a EF86. It sounds good, but is very microphonic compared to a Mullard I have. It's also a bit brighter than the Mullard, which is tight and warm sounding.
Tommy
Re: EF86 wiring
I like the Mullard too. Mine is very warm and dark.
No you don't have to change the cathode from 2.2K with a 220K plate. But you sure can. I suggest trying different combinations. It has to work with the rest of the circuit. So just like a 12AX7 you can play with the cathode and plate freely to achieve the desired frequency shaping and current swing. Matchless and some Dr Zs use the 330K with a 2.2K cathode maybe to wring a little more gain out because they are one tube stage pre-amps. I've tried 1.5K/22mF and even the Marshall set-up of using a 0.68 mF cap with a 2.7K on the cathode and plate resistors between 100K and 470K. Depends, if your only using one stage versus cascading stages and what the output section is and what tone your going for. I wouldn't stray too far off the beaten path though, those typical values are used for a reason, and why reinvent the wheel?
What I was saying about the 6-position rotary was that I found it limiting as the only tone control. But that's not to say that switchable coupling should be ruled out. You can use a 3-way toggle to get a pretty good range of coupling caps, just make sure the caps are between the high voltage plate and the switch itself to keep the DC out of it. The switchable coupling caps can help dial in the sound when trying different cathode and plates. A lot of times I will bread board up the cathode and try different values with different fixed plates. You can use a pot for trying cathode values, it's scratchy, but can get you into the range, I don't use pots for plate resistor trials, too much voltage. I just temporarily solder them in.
No you don't have to change the cathode from 2.2K with a 220K plate. But you sure can. I suggest trying different combinations. It has to work with the rest of the circuit. So just like a 12AX7 you can play with the cathode and plate freely to achieve the desired frequency shaping and current swing. Matchless and some Dr Zs use the 330K with a 2.2K cathode maybe to wring a little more gain out because they are one tube stage pre-amps. I've tried 1.5K/22mF and even the Marshall set-up of using a 0.68 mF cap with a 2.7K on the cathode and plate resistors between 100K and 470K. Depends, if your only using one stage versus cascading stages and what the output section is and what tone your going for. I wouldn't stray too far off the beaten path though, those typical values are used for a reason, and why reinvent the wheel?
What I was saying about the 6-position rotary was that I found it limiting as the only tone control. But that's not to say that switchable coupling should be ruled out. You can use a 3-way toggle to get a pretty good range of coupling caps, just make sure the caps are between the high voltage plate and the switch itself to keep the DC out of it. The switchable coupling caps can help dial in the sound when trying different cathode and plates. A lot of times I will bread board up the cathode and try different values with different fixed plates. You can use a pot for trying cathode values, it's scratchy, but can get you into the range, I don't use pots for plate resistor trials, too much voltage. I just temporarily solder them in.