Modified Sluckey "Dual Lite" Project

[HARodgers]

Hi all,
I've been working on a modified version of Sluckey's Dual Lite (Bias and rectifier switching, 18w Cascade, master volume, switchable feedback) and wondered if anyone could see any issues or potential improvements that could be made?

The main questions I have are:
-Is the value of the dual pot for the master volume correct, given the original 470K resistors?
-‎What would be the best value for the resistor that connects the feedback circuit to ground, and does the feedback circuit need connecting before the 0.22uF capacitors as well?
-‎Will a fixed bias circuit work with the various channels or will the necessary values be too far apart to use fixed bias?
-How would you go about choosing a choke for the first stage of the filter? The one used on the AC-15 circuit the dual lite takes from is a Hammond 193B (https://www.hammfg.com/part/193B) - would this be suitable?

Thanks in advance for any advice or other potential modifications to add.

[sluckey]

The main questions I have are:

-Is the value of the dual pot for the master volume correct, given the original 470K resistors?

yes

-‎What would be the best value for the resistor that connects the feedback circuit to ground, and does the feedback circuit need connecting before the 0.22uF capacitors as well?

I've never seen an amp with feedback connected as you show it. I would connect the NFB with presence control the same as seen in a typical Marshall amp. Then use two 220K mixing resistors to connect the two preamps to the top input of the PI. Read this info about the LTP PI...

     http://www.aikenamps.com/index.php/the-long-tail-pair

-‎Will a fixed bias circuit work with the various channels or will the necessary values be too far apart to use fixed bias?

Fixed bias only affects the output tubes. Doesn't matter how many channels you have. What's up with your bias supply? I like to keep the bias circuit simple. Here's my November amp with simple bias circuit. You may be interested in the NFB circuit too...

     http://sluckeyamps.com/november/november.pdf

-How would you go about choosing a choke for the first stage of the filter? The one used on the AC-15 circuit the dual lite takes from is a Hammond 193B (https://www.hammfg.com/part/193B) - would this be suitable?

My Dual Lite power supply is modeled from the Marshall 18 watt amp, not the Vox AC-15. If I were going to use a choke I'd get the small Fender choke from Doug and just replace the 2.2K resistor in the B+ string. But, if you rather have the AC-15 power supply you will need a BIG choke (such as 193B) because all current (including output tubes' plate current) for the entire amp flows through the choke. Just copy the AC-15 power supply...

     http://sluckeyamps.com/VAC15/Vox_AC15.pdf

I think no choke, small choke, or big choke will all sound good in this amp. I chose to use no choke mainly because this was purposely built as a Lite amp, using a small 12" long chassis. My Dual Lite is mounted in a small Vox cab. I don't have any pics but it looks just like my L'il Maggie amp. See the last 3 pics on this page...

     http://sluckeyamps.com/lil_maggie/lil_maggie.htm

[HARodgers]

Thanks again for the help. I think over complication is my main issue with builds!

I've moved the circuit round after reading the article on LTP PI and looking at the November amp, and have decided against the choke. Does this look more reasonable?

[RonFast]

I too am just starting to build the Sluckey Dual Lite. I have built a few amps now and am getting pretty comfortable putting these projects together, but I am stumped with assembling the caps on the 2 pole 6 pos MBB "Brilliance switch". Sluckey, would you be able to show a close-up or direct me to a clearer description of how to assemble it? Thanks

[sluckey]

Notice on the schematic and layout that half the switch contacts are colored gold and the other half are colored silver? That's done on purpose to make it easier to visualize wiring the switch. The two lugs near the center of the switch are the two wipers and the lugs around the perimeter are the individual position contacts. Use your ohm meter to determine which contacts belong to which wipers. Once you do that put a jumper between all seven lugs for half the switch. I just laced them all up. Don't solder yet. This half of the switch simply serves as a convenient way to mount all the caps. Now solder one end of a wire to the wiper of this group of contacts. This wire will eventually go to the board. Now solder one end of another wire to the gold wiper. This wire will eventually go to the volume pot. Finally, using the attached drawing, solder the six caps to the switch. This should also solder the lace wire on the silver lugs.

It will be much easier to do all this soldering with the switch in a bench vise. If you don't have a vise, just mount the switch to the chassis with the shaft on the inside. This puts all the switch lugs on the outside of the chassis and will make it more fun to do all the soldering.

When all the caps are soldered to the switch, mount the switch correctly in the chassis and connect the two wires, one to the board, one to the volume control.

[RonFast]

Thank you Sluckey, I really appreciate all of the advice and support you give us.

[RonFast]

Again i really appreciate the support. 
Sluckey, 2 more questions:
(I am going from your original schematic)

I would like to use a Master Volume, where in the circuit would you place it?

I would like to use this amp to occas plug my Pod HD5500x into. Would a passive Effects Send/Return require major surgery?

[sluckey]

I would like to use a Master Volume, where in the circuit would you place it?

You're the second person to ask for a MV mod recently. Maybe I should include the mod in the pdf. See attachment...

I would like to use this amp to occas plug my Pod HD5500x into. Would a passive Effects Send/Return require major surgery?

Easy. Just put the jacks between a volume control wiper and the PI input coupling cap. Look at this schematic if you need more info...

     http://sluckeyamps.com/november/november.pdf

[RonFast]

Wow! Thanks for the quick reply. That is exactly what I needed to hear

[RonFast]

Hi Sluckey, I am at the final stages of the Dual Lite and wiring up the master volume. What is the resistance of the 2 resistors soldered to the pots. The diagram looks like it is red red green which is 2.2 Meg? Is that right? Thanks

[sluckey]

2.2M is correct.

[RonFast]

Thanks again!

[Glenn]

I built sluckeys dual lite with the ppmiv last week.
The vox side was very loud, so I put in the ppmiv. It works quite well, but I found the amp doesn’t quite have the chime it did after installing the ppmiv. It still sounds great though so I’m leaving it, because I like the grunt i can get with the ef86 tube.
Good luck with your build...

[HARodgers]

To everyone who's built a dual lite, what speaker(s) did you match the amp with? and what was the rough rms output? I was considering matching this with an Celestion Alnico blue, but I was skeptical as to the 15Wrms rating (especially with the Hammond transformers being rated at 20w)

[sluckey]

I like the Vox side with a Celestion Blue. Lot's of chime. I don't play hard enough to destroy the speaker. A pair of Blues would probably handle anything the dual lite can put out.

I also have a 2x12 with Celestion Heritage G12H(55) and G12H(75). Vox and Marshall sound good through this cab.

My Dual Lite is actually mounted inside a Vox Pathfinder cab with a single 8" Vox Bulldog speaker. Sounds pretty good with that too.

[PRR]

> what was the rough rms output?

Two EL84 at 325V, that's commonly rated "18 Watts".

The Celestion Alnico blue has a monster 1.75" voice coil. I'm sure it won't burn on a hard-worked 18W amp. The suspension may not handle all that motion gracefully so it "compresses" (distorts) around its 15W rating. As hi-fi or PA, this is a poor fit. As high-flavor guitar, it may shine.