Why is the 65 Amps London's EF86 channel so chimey....

[dehughes]

...incomparison to my AC30-ish build EF86 channel? I mean, I used stock AC30/4 values, Mercury Magnetic Woden clone trannies, Sozo caps, appropriate resistor values, etc...but I'm finding my EF86 channel to be more strong and tight and ballsy instead of the chimey, airy quality in the London's EF86 side.

Now, is it true that the London's EF86 side is more like a Selmer Zodiac "30" instead of an AC30/4? I find that the plate voltages on the London's EF86 side are about 185v on the plate and 65v on the grid, wheras my EF86 is (again, with the stock AC30/4 values...) landing at about 111v on the plate and about 108v on the grid. Would the voltages themselves lend to such a drastically different tone? Should I try for a larger separation between the plate and grid voltages?

I know I'm kinda rambling....but I'm sort of stream-of-consciousness typing here. My friend just brought his London over and that EF86 channel was all that I wanted my AC30/4 clone to be....(mostly... ). Incredible EF86 channel...


Thanks all...

[UR12]

...incomparison to my AC30-ish build EF86 channel? I mean, I used stock AC30/4 values, Mercury Magnetic Woden clone trannies, Sozo caps, appropriate resistor values, etc...but I'm finding my EF86 channel to be more strong and tight and ballsy instead of the chimey, airy quality in the London's EF86 side.

Now, is it true that the London's EF86 side is more like a Selmer Zodiac "30" instead of an AC30/4? I find that the plate voltages on the London's EF86 side are about 185v on the plate and 65v on the grid, wheras my EF86 is (again, with the stock AC30/4 values...) landing at about 111v on the plate and about 108v on the grid. Would the voltages themselves lend to such a drastically different tone? Should I try for a larger separation between the plate and grid voltages?

I know I'm kinda rambling....but I'm sort of stream-of-consciousness typing here. My friend just brought his London over and that EF86 channel was all that I wanted my AC30/4 clone to be....(mostly... ). Incredible EF86 channel...


Thanks all...

Voltages are one of, if not the most important, thing to duplicate if you are trying to get the same tone. I haven't looked at a schematic of the London but there is one big difference between a AC30/4 and a Zodiac. The Zodiac has the EF86 stage after the tone stack and uses a 12AX7 front end. The AC30 is exactly opposite.

[fzfwyv]

Hey, I just finished building the same amp (the AC30/4 scematic) with a few tweaks.

I have a switch between a 220k (stock value) and a 330k (actually just a 100k in seried with the 220k) going to the EF86 plate. It drops the voltage quite a bit.

I also added a tone control with a .0022 to ground.

A couple other tweaks but I haven't compared my amp to a London, but I have a feeling mine isn't as chimey as the last Vox like amp I heard. Mine is actually more like you mentioned: tighter, focused, and can get pretty aggressive. I like it 'cause the leads really sing.

I also put in a 5 pos switch in place of the brilliant switch. 330pf is as low as I go. I thought the 220 was too bright.

Anyway, I'd be interested in bouncing some ideas back and forth to get a little more chime.

-Rich

[rhinson]

i thought the 65 amps model with the ef86 was the 2-el84 version---this output trannie size differential will make a big difference so you may be comparing apples to oranges. nevertheless, did you actually measure the ef86 voltages in the 65 amp---i've never seen such a disparity between plate and screen in the normal type guitar amps we've seen. you'd have to lower the dropping resistor to that section, as well as substantially increase the cathode resistor/lower the plate resistor and use like a 4.7meg or greater screen resistor to get it that low. doing all this cuts the gain of the tube back which could explain the tone. you'll also
get a more chimey tone by doing what is suggested above by using the variable coupling cap scheme (ala--matchless, et al)---the lower value the coupling cap the more chimey it'll sound. rh

[dehughes]

Hey, I just finished building the same amp (the AC30/4 scematic) with a few tweaks.

I have a switch between a 220k (stock value) and a 330k (actually just a 100k in seried with the 220k) going to the EF86 plate. It drops the voltage quite a bit.

I also added a tone control with a .0022 to ground.

A couple other tweaks but I haven't compared my amp to a London, but I have a feeling mine isn't as chimey as the last Vox like amp I heard. Mine is actually more like you mentioned: tighter, focused, and can get pretty aggressive. I like it 'cause the leads really sing.

I also put in a 5 pos switch in place of the brilliant switch. 330pf is as low as I go. I thought the 220 was too bright.

Anyway, I'd be interested in bouncing some ideas back and forth to get a little more chime.

-Rich

Bounce away. I could use all the ideas I can come across and don't mind sharing what I've discovered so far. I'm running a tone knob myself, but with a .0047uf to ground... I was JUST contemplating doing the 5-way switch thing, too....I'd do 6, but I only have 5 turret lug positions free.

What values did you use on the 5-way? Did you use 5.1M resistors between the caps, or did you use a shorting switch?

[dehughes]

i thought the 65 amps model with the ef86 was the 2-el84 version---this output trannie size differential will make a big difference so you may be comparing apples to oranges. nevertheless, did you actually measure the ef86 voltages in the 65 amp---i've never seen such a disparity between plate and screen in the normal type guitar amps we've seen. you'd have to lower the dropping resistor to that section, as well as substantially increase the cathode resistor/lower the plate resistor and use like a 4.7meg or greater screen resistor to get it that low. doing all this cuts the gain of the tube back which could explain the tone. rh

Yup, 2 x EL84. I know OTs make a difference, but this is clearly a preamp thing as it is all happening quite well at low volumes... Yup, I did measure the voltages myself, just 4 hours ago. My friend who owns the amp was there to witness, and I measured twice just to be sure...they seemed weird to me, also, but that's what we found. Maybe you're right about tweaking out the Rk, Rp and Rs to get that tone....something was happening, and MAN was it cool. Very cool...

[rhinson]

it's probably a combo of all the factors---esp the 6way cap selector. that's cool you actually measured/verified the voltages. didn't happen to notice/document the parts values did you? rh

[dehughes]

it's probably a combo of all the factors---esp the 6way cap selector. that's cool you actually measured/verified the voltages. didn't happen to notice/document the parts values did you? rh

PM sent...

E-mail me.

[jelle]

Hi Dehughes,

I'd interested to know the values for the EF86 preamp.

Can you mail it to me by PM?

Thanks,

Jelle

[drz400]

I'd love to see a London Schematic if anyone has one
PLease PM

[jaysg]

I'm not sure the schematic would be that interesting. Take the 18W design, update the layout, use Sozo caps, the DC30 cap selector instead of the tone control I'm showing, add a Cut control after the PI, and go through several OT revisions with MM...Dan's very honest about these amps. The added value is roadworthyness and component selection, not anything hidden. They made the combo the same size as an AC-30, so it would fit a pre-existing anvil case. schmart!

[edit]In looking at the 65Amp site and the cascode thread, I'm now thinking that they've replaced the ef-86 circuit with a 12ax7 cascode on both 18 and 36W amps. It looks like the website has been updated, however, there are still references to the ef-86 that should have been changed.

[dehughes]

Interesting...

I guess I should state my intent in starting this thread:

I'm not intending to copy or duplicate or rip-off anything from the London, but rather am trying to get a grasp on what it is that they do to achieve the sounds they are getting out of that amp. I think it is a fantastic amp, but while it is super cool I don't want a clone of it. I dig my amp as-is, but think it could benefit from some of the clarity that the London seems to get out of its EF86 side.

There, that's that. Thanks for the free tech lession guys! I greatly appreciate all your time and information...

[dehughes]

Well, I connected a 1M resistor in parallel with the .1uf cap on the EF86 grid (forming a divider with the 1M resistor from the filter cap to the grid itself...) and this took the voltage from about 120v down to 77v or so on the grid, and RAISED the voltage on the plate from 125v to about 172v. Interesting....anyone know why that happened? I wager it makes sense, but I'm a bit too tired to process.... Also, I tried running about 2M on the grid (no resistor to ground...just increased resistance to the grid) and this yielded similar voltage results. What exactly is going on with that? I'm sure if I knew more about Ohm's Law, etc., it would make sense, but I figured that 2M in front vs. a 1M/1M voltage divider would yield different results...

However, the voltage change did, in fact, make the EF86 smoother, softer, and more articulate, albeit a bit quieter overall. I do like that effect, but actually prefer to run it like the AC30/4 normally does, with the 220k on the plate and the 1M on the screen. This keeps the channel warm and thick, but with enough articulation to let my SG speak clearly enough. Still though, it is good to know of some options for running an EF86...

[chief mushroom cloud]

...I know OTs make a difference, but this is clearly a preamp thing as it is all happening quite well at low volumes... Yup, I did measure the voltages myself, just 4 hours ago...

Did you measure the OT winding ratio?