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I've added an ef86 channel to a Lightning 15w using the following method:
[img][img]http://i32.photobucket.com/albums/d26/ab3640au/LightningSchematicwithmodshownforef.jpg[/img][/img]
[img][img]http://i32.photobucket.com/albums/d26/ab3640au/LightningSchematicofef86channel.jpg[/img][/img]
Essentially, I've taken this from Mark Durham's Vajra 18watt variant (on the 18watt forum), however the values in the ef86 channel are very much like those used in the early AC15's and AC30's.
I'm using the Westlabs trannie set, so the PT can handle the extra tube without any problems. The good thing is that both channels sound great, but very different - Lightning channel is chimey with lots of sparkle, while the ef86 channel is fatter with a faster attack; and has more gain.
Having said all that .. I have one problem that I need to resolve. I'm getting some ugly buzz/distortion in the ef86 channel, but ONLY when I have the Volume set low (2-3) and Master on high (anything above 6). If I turn up the Volume, the buzz goes away. If I turn down the Master, the buzz goes away .. it's weird! I really haven't had the opportunity yet to crank both Master & Volume at the same time in this channel, so I'm not sure whether the buzz/distortion will occur or not. I'm wondering whether there might be too much gain happening in the ef86 channel or whether it might have to do with how I've connected this channel at the PI (note: I'm now wondering whether I should have left the PI as it was and simply added another 220k resistor for the ef86 connection - in that way, the voltage divider would tame the gain a bit.
Any thoughts??

REGARDS

Barry M

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Barry M

What you have in that channel is an EF86 configured, 18W Tremolo tone stack. You should be able to make this work fine. I couldn't trace everything, but take a look at a DC-30 schematic and connect this up to the PI the same way. Should work.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Coco .. thanks for the reply. I checked the dc-30 schematic and I definitely have connected it the same way (other side of PI). Probably the biggest difference with my ef86 preamp circuit is that I've used some different resistor/cap values, when compared to the dc-30. Mine have come from the "Vajra 18", which in turn came from early Vox circuits, so it should work but has more gain than the stock dc-30 values. I'm going to try a few things today, to see if I can kill off the buzz. Firstly, I'm going to restore the PI to it's "stock" Lightning configuration, then add a 220k resistor beside the 220k resistor for the Lightning channel (r9 on the schematic) and connect the ef86 channel from there. This will work, but probably result in some ef86 gain being dumped (via the voltage divider). If the buzz problem relates to the gain in this channel, then my problem should disappear. If this doesn't work, then I'll look further at my lead dress, particularly to the PI and ef86 tube. Lastly, I'll change the resistor/cap ef86 channel values to the dc-30 values if the problem is still there. I'll post my results when done ..

Barry M

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Barry M

Stephen (Coco) .. good news! I connected the ef86 preamp to the same side of the PI as the stock Lightning preamp .. just added another 220k resistor beside r9. The buzz is now gone. I'm thinking that it perhaps the vox resistor/cap values that I used in the ef86 preamp, coupled with the method of connection to the PI was resulting in too much gain ..
The ef86 channel has lost a bit of gain (it probably had too much before) due to the voltage divider, but is much more versatile now. I can get some real nice clean tones, but still push it if needed for plenty of dirt.
I'm sure that it could also have worked via the other side of the PI, however I would have needed to reduce the amount of gain by changing resistor & cap values.
Merry Xmas to all ..

REGARDS


Barry M

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Barry M

Barry, Good news! How about posting the final configuration so others could use it.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Stephen .. no problem with posting the configuration .. give me a couple of days on this as I want to do a little tweaking first Once that's done, I'll post .. Merry Xmas ..

REGARDS

Barry M

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Barry M

Update .. I've made one change to the ef86 channel and "I think" I'm happy with it. I replaced the 500k Volume pot with a 1 Meg pot (audio taper) and the ef86 channel now has a little more "edge" than before. Daz (from this forum) is coming around tomorrow (he's down here in Melbourne from Sydney for the Xmas holidays) and I'll get him to provide a second opinion before I post the final configuration here. There's no doubt that you could play around "lots" with the gain levels in the ef86 channel .. I want something that will clean up nicely, if required, but get nice & dirty when cranked without the tone turning to mud! I'll let you know once Daz has a play tomorrow ..
Also .. I've completed two other Lightning clones in the last week (the most recent completed amp is mine) .. so I've been busy!

Best Wishes

Barry M

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Barry M

Further UPDATE ..
Daz came around today and played through the Lighting/ef86 amp and was quite impressed. He commented that the ef86 channel wasn't as gainy as the one he'd tried on a DC-30 - I'm sure that mine has been somewhat "tamed" by the voltage divider on the Lightning side of the PI. As a result, we're able to get some nice clean and dirty tones with no mush or mud when the ef86 channel is really pushed. Daz said that you couldn't really crank the volume on the dc-30 above "6", before it got too mushy. FWIW .. here are my voltages:

V1 (ef86) - pin 1, 123v; pin 3, 2.8v; pin 6, 121v; pin 8, 2.8v
V2 (12ax7) - pins 1+6, 142v; pins 3+8, 1.4v
V3 (12ax7) - pin 1, 170v; pin 3, 1.4v; pin 6, 277v; pin 8, 170v
V4, V5 (el84) - pin 3, 8.1v; pin 7, 366v; pin 9, 252v
V6 (5ar4) - pin 4+6, 291vac; pin 8, 368v

I also measured the voltage before and after the 22k resistor on the B+ line - 364v "before" and 337v "after".

The only thing I might consider here is increasing the B+ voltage a little - I read something over on the 18watt forum about this .. I'll need to check it out first before I modify the amp any more. I'll ask Daz to post his opinion here once he get's back to Sydney (and has access to the www).

Regards


Barry M

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Barry M

Interesting comment on the DC-30. The 30W lightning I built also gets pretty dirty with MV over the top. Maybe you've hit on a better configuration for a second channel. What are you doing to isolate the EF86 from vibration? Which manufacturer are you using? I hear they are pretty sensitive.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Stephen .. in order to deal with the microphonics associated with ef86 tubes, the first decision I made was to do this amp as a head. Secondly, I purchased some silicone tube dampers (rings) off an ebay seller (mr.resenter) - I used one of these to mount the socket on the chassis and two others around the tube itself. As for the ef86 tubes, I got those off ebay as well for 99c each! (I was lucky). They were all good pulls, which tested the same as a new tube - I got a Mullard, UK Philips, Valco and Holland Philips Miniwatt. Currently I'm using the miniwatt in the head. There's no doubt that the ef86 has LOTS of gain and can really be pushed over the top, however in my experience with it (so far), it needs a little taming to prevent it getting mushy & farty when really driven. I'll keep you posted ..

REGARDS

Barry M

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Barry M

ok .. I'm happy with the ef86 channel now! I'll see what I can do in putting a schematic together (I'm not too good at drawing them though ..) in a new thread over the next few days. Essentially, the main change I've had was to change the plate resistor from 220k to 330k and screen resistor from 1meg to 2.2meg (suggestions from Mark Durham at 18watt.com). Now the ef86 channel more closely matches the dc-30 in component values, except the PI connection and B+ voltage. As already mentioned, I've connected the PI to the same side as the Lightning channel (with voltage divider), so I'm dumping some gain. However, my B+ voltage is about 364v (before the 22k resistor, which drops it down to about 337v), which will result in more gain than the dc-30 (before the voltage divider does it's "thing" in evening out things a little). My final voltages:

V1 (ef86) - pin 1, 75v; pins 3+8, 1.8v; pin 6, 128v
V2 (12ax7) - pins 1+6, 142v; pins 3+8, 1.4v
V3 (12ax7) - pin 1, 170v; pin 3, 1.4v; pin 6, 277v; pin 8, 170v
V4 (12ax7 PI) - pin 1, 258v; pin 2, 46v; pin 3, 70v; pin 6, 260v; pin 7, 47v; pin 8, 70v
V4, V5 (el84) - pin 3, 8.1v; pin 7, 366v; pin 9, 252v
V6 (5ar4) - pin 4+6, 291vac; pin 8, 368v

REGARDS

Barry M

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Barry M

I had the pleasure of meeting barry and his amps whilst in melbourne.
He's done some really nice work and tried out a few of his 18watt and lightning variants.
the ef86 lightning is nice little amp, I tried it out prior to his current mod.
Lightning channel had all the characteristic chime and dirt we all know - in fact maybe alittle nicer than a real lightning - more punch to me but it could be the BBQ speaker and sozos he was using.
The EF86 channel was a nice addition, very different sound, less chimey, more midrange thicker sound but plenty of harmonics. very nice! I was expecting Barry to take advantage of the very gainy nature of EF86 like the dc-30 i recently tried, but in fact it only had a little dirt on tap (less than lightning channel), barry made more usable.
The dc-30 Ef86 channel is very gainy, to a point past 6 on the gain dial it gets fuzzy and bass get characteristic matchless flabbiness, pretty much useless. I think with the matchless rotary tone control and circuit values, it gives the most gain, I say about 3 times Barry's channel (prior to his current mod).
But sounds like Barry has now found a happy medium where the gain knob is usuable throughout the whole range. I can see why he has some happy customers!!
There's a post by dirty amps somewhere here suggesting a few mods to a dc30 circuit more usuable on the ef86 channel.

Daz .. thanks for the comments & feedback on the ef86 addition. As you said, I've made one further change since you tried the ef86 channel and I'm much happier with the gain level now. When you tried it, it had some nice tone, but not quite enough characteristic "ef86 gain" - it sounds heaps better now but still doesn't get mushy. Im my (short) experience with the ef86 tube so far, I've found it to be extremely sensitive to small component value changes or B+ voltage changes - more so than a 12ax7 tube. A few small changes can change things a lot with an ef86. I'll get the new owner (who runs a recording studio) to record both channels in the next week or so and post some mp3 files here ..

REGARDS

Barry M

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Barry M

Ok .. forget all I've said in this thread about connecting the ef86 channel to the same side of the PI as the "Lightning channel". Yeah .. ok .. it works, but the voltage divider is dumping too much gain. I ended up taking a different approach and am MUCH happier with the results.

It's now connected in much the same way as the original schematics shown in the first post of this thread, except I've changed the 22k resistor on the B+ supply line to the ef86. Essentially, the following applies:

1. Lightning channel is stock
2. EF86 channel is based on the Vox AC15 component values (220k plate resistor, 1 meg screen resistor etc)
3. EF86 channel is connected to the opposite side of the PI
4. EF86 channel has its own filter cap (16uf) and B+ line (see Mark Durham’s Vajra 18 on the 18watt forum for more detail)
5. You need to get the B+ voltage down to around 300vdc (after the 2watt dropping resistor). My voltage before this was 368vdc, so I found that a value of 60k worked for me – the voltage is VERY important; any variation makes a big difference
6. Used the Marshall 18watt tremolo channel tone stack for the EF86 channel
7. Used 1meg audio pot for volume control and 500k audio pot for tone

I'm using the Westlabs PT (and choke/OT) and the PT will handle the current of the extra ef86 tube.

The Lightning/ef86 Head is like having two separate amps at your disposal. The Lightning sounds exactly like a good Lightning should, while the ef86 channel is very rich (harmonically), fat and sustains forever (even when the gain is backed off). Now that I'm happy with it, I'll put together a layout shortly for posting.

REGARDS

Barry M

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Barry M

Very nice. I'm know I'm looking forward to that. Let me know if I can help in any way to get this posted. Clips would be nice as well.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Layout? Please do, I'd be up for building one of those since hearing it firsthand!

Daz .. it sounds much better since you heard it .. much more gain in the ef86 channel, however it doesn't get farty at all with the volume set high. It still cleans up nicely too, so there's plenty of versatility.
I've actually decided to build myself a lightning/ef86 channel head and sell the completed lightning chassis that I originally built for myself .. that's how much I like the ef86 channel in this amp!! I'll put together a proper layout and post plenty of pics of this forthcoming build, for those that are interested in building it.

REGARDS

Barry Marie

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Barry M