Dual Lite amp project

[sluckey]

I just finished another small box project. It's a combination of my Hammond AO-39 conversions. The dual lite contains a Vox AC-15 normal preamp and a Marshall 18W Lite IIB preamp. This will fit very well in Doug's blank 12 x 6.5 x 2.5 chassis. Here's the link...

     http://sluckeyamps.com/dual_lite/dual_lite.htm

[kagliostro]

 

Nice Amp Steve 

   

EDIT: Steve if I remember well in your version of the Vox AC15, between the mod, there was a way to put the input in series

Have you tried something like that also here ? Can you give it a try ?

Franco

[sluckey]

That's a good idea Franco. I may just give it a try.

[kagliostro]

Thanks

Franco

[vibrolax]

A very attractive build.   Dual preamp things make me curious about replacing the channel switch with something like a balance control to mix the two preamps.

Well done.

[shooter]

Very nice, thanks for setting the bar!, BTW, I'd check the seat on your 5Y3

[sluckey]

Dual preamp things make me curious about replacing the channel switch with something like a balance control to mix the two preamps.

Now that's another good idea. Thanks.

[sluckey]

Very nice, thanks for setting the bar!, BTW, I'd check the seat on your 5Y3

It's a virgin NOS socket. I had to crank and shove to get it down that much. It ain't gonna fall out. Maybe it will relax a bit when it warms up and I'll be able to get it all the way in.

Hmm, reminds me of an old joke.   

[kagliostro]

.......... something like a balance control to mix the two preamps.

I don't know what will happen having a balance pot at the input (  )

if the balance is to be placed between the two outputs of the first tubes (paralleling the input)

you'll be on the same situation about which Doug asked for his Plexi 6v6

and there the best solution is to have two separated volume controls

so, to me, the best solution, instead of a balance pot, will be this

(I've find it some time ago, but don't remember where  )



Oh, but the amp is finished and you haven't enaugh holes on the faceplate .... this is a problem

Franco

[DummyLoad]

Very nice, thanks for setting the bar!, BTW, I'd check the seat on your 5Y3

It's a virgin NOS socket. I had to crank and shove to get it down that much. It ain't gonna fall out. Maybe it will relax a bit when it warms up and I'll be able to get it all the way in.

Hmm, reminds me of an old joke.   

is it possible that some solder got pulled down into one of the pin cups by capillary action? that's happened to me before. i used a magnifying glass find it and re-flowed the pin with the chassis right side up and cleaned up with some solder wick. couldn't get all of the solder out, but got enough to allow the tube to fully seat.


--pete

[sluckey]

is it possible that some solder got pulled down into one of the pin cups by capillary action?

That's the first thing I checked when I first has such a hard time seating the tube. I just tried a different tube. Slipped in fine. That particular 5Y3 just has some fat legs. Actually, it has some oversize factory solder blobs on a couple pins. Couple scrapes with a razor knife fixed it right up.

[sluckey]

Just for you Franco...

I played around this morning with cascading the preamps. I first connected the EF86 preamp output into the 12AX7 preamp. Didn't care for that.

Then I connected the 12AX7 output into the EF86. Much better. Plenty of nice distortion, but trying to roll back for a nice clean or slightly overdriven sound was not easy. Really didn't sound good to me with anything except full out distortion. Think American Woman.

I didn't try to optimize any of the gain other than twisting knobs. The 12AX7 into the EF86 has possibilities for anyone that wants to experiment. I'm gonna just stay with my original circuit. I already have a few buzz saw pedals and I can always turn my little PeeWee into a Herzog!   

[kagliostro]

Many Thanks Steve

those are precious infos


have you tried to jump the inputs ?

Franco

[sluckey]

have you tried to jump the inputs ?

No. That would end up causing a lot of signal cancellation since the preamp outputs connect to opposite sides of a differential amplifier (LTP PI). I suppose I could sum the preamp outputs with a couple resistors to feed one input to the PI. That would make it possible to jump the inputs. But, this amp is done. It's just what I expected. I have both my lite amps in one box. I like the way it sounds.   

[billcreller]

Beautiful work there Steve !!

[kagliostro]

Thanks Steve

I didn't considered you are using two different intakes on the PI

Ciao

Franco

[DummyLoad]

that's a neat concept & some very nice work.


--pete 

[Toxophilite]

Lovely workmanship and cool looking amp!
THanks

[johngovan]

Sorry for bumping the old thread. I just wanted to ask, what kind of capacitor did you use in this build? Thank you.

[sluckey]

F&T 2x32 can, IC axial caps, Sprague bypass caps, and Xicon polypropylene coupling caps.

[johngovan]

F&T 2x32 can, IC axial caps, Sprague bypass caps, and Xicon polypropylene coupling caps.

Thank you so much sluckey! Appreciate it. :)

[boodle]

Working on a Dual Lite that will have unusual tube compliment: 5879 and 4 ECL84's for about 10W.  I am trying this mix because NOS tubes for the entire amp come in at $14!

Looking at the schematic, it looks like Sluckey used 18W resistor values in the PI and PA.
Q for those who have made one or something similar...What impact would having a more Vox like PI and PA have on the tone?  (Change the grid leaks on the power tubes to 220K, change Rk in the PI to 1.2K, and bring the grid resistors down to 1.5K on the power tubes.)

I am guessing a cleaner PA for the amp.  Besides that dynamic difference, what sonic changes should I expect?

Thanks, All!

[sluckey]

I can't speak to sonic differences, especially since you will be using different tubes. But I can say. the dual lite is my favorite amp because of sound and size and the Vox preamp is preference, although the Marshall sounds good too.

[72Blazer]

Sluckey, what kind of iron does this amp require?  Tried the old link at the top of the thread but no luck there.

[bmccowan]

With help from the Forum members, especially Tubenit, I built a 2xECL84 amp - the thread is here:
https://el34world.com/Forum/index.php?topic=28856.msg317622#msg317622 It might have some useful info for you.
Nice amp. I intend at some point to try those power tubes with a 5879 preamp which I have used quite a bit in the V1, or V2 position.
I used a Musical Power Supplies PT for that amp, keeping the B+ voltage in a reasonable range for the ECL84s.

[DummyLoad]

Sluckey, what kind of iron does this amp require?  Tried the old link at the top of the thread but no luck there.

http://sluckeyamps.com/dual_lite/dual_lite.htm

[mresistor]

Sluckey, what kind of iron does this amp require?  Tried the old link at the top of the thread but no luck there.

He used the PT out of an Hammond AO-39 chassis, and so did I.   Not sure about the OT but I used a Hammond 1750PA.

[sluckey]

I salvaged the PT and OT from a Hammond AO-39 chassis.

[boodle]

bmccowan...I have also built a tubenit amp, the SoLowWatt CPI.  Sound great.  I did it point-to-point in a tiny chassis and that was a nightmare, but worked as designed. I will be sure to keep an eye on the B+ for the ECL84's.  Thanks for the heads up.

I don't think anyone had built Tubenit's CPI version of the SoLowWatt, so I will post some pictures of the rat's nest interior and audio files when I can get to that.

Tubenit's amp gave me the idea to pursue the Dual Lite with the same tubes.

sluckey...glad to hear that it is your fav.  I will build it as designed first and give it some time to settle.  I'm building this one in the chassis and cabinet of an oddball Traynor, the TS-15.  The Traynor is a solid state amp that has a little cult following.  I happened upon a chassis and cabinet that had been stripped of all amp parts and speakers for cheap.  One interesting thing about the cab is that it is a 2X8, so it has the speaker surface area somewhere between a 10 and a 12, but is very responsive dynamically.

So, in the end, the amp will be a very unique thing: a 10W Sluckey Dual Lite with unusual tubes in a 2X8 cab.

Fingers crossed!

[boodle]

One more question (for now!) about the Dual Lite. 

I assume that the output of the parallel triodes on the 18W pre-amp side invert the input signal like a single triode plate signal.

Does the Pentode preamp also invert the input at the plate output?

I ask because I am wanting to have a "Both" option on the channel switch and would want both channels to have the same signal phasing.

[sluckey]

One more question (for now!) about the Dual Lite. 

I assume that the output of the parallel triodes on the 18W pre-amp side invert the input signal like a single triode plate signal.

Does the Pentode preamp also invert the input at the plate output?

I ask because I am wanting to have a "Both" option on the channel switch and would want both channels to have the same signal phasing.

The output of both preamps are inverted from the input. However, you can't use a "both" option because one channel feeds the inverting input of the LTP-PI and the other channel feeds the non-inverting input of the LTP-PI. The results would be major cancellation and would sound thin and weak.

In order to send the guitar signal through "both" channels you would need to mix the channels using a couple 220K resistors, then send the combined signal through the top input of the LTP-PI. The lower input would be grounded.

[boodle]

Sluckey,
So the resulting schematic (using the original tube compliment) would look like the pdf attached?
Also, if correct, would you suggest changing the value of the circled cap?
Thanks!

[sluckey]

Sluckey,
So the resulting schematic (using the original tube compliment) would look like the pdf attached?
Also, if correct, would you suggest changing the value of the circled cap?

You got it! Change the cap to .1µF. And use a C&K 7211 ON-ON-ON switch. Center position would be "Both". For example, look at my Phoenix, All American Dual Lite...

     http://sluckeyamps.com/phoenix/phoenix.pdf

[boodle]

You are and continue to be The Man!  Thanks. 

Working on a layout using the DIY software.  Will post in a new thread when finished with the layout and schematic to see if I am missing anything.

[boodle]

I am using the DIY software for the layout and I am hoping to use the ExpressSCH software for the schematic. 

Does anyone have a .sch file for an AC30 with an EF86 preamp channel and/or a .sch file for an amp that is close to the Dual Lite?  This would help speed up the schematic process significantly.

I have some Tubenit .sch files that I can start with: HoSo56 ECL84, SoLowWatt 12A_7, SoLowWatt CPI.  Hoping to get one closer to the Dual Lite and one for a quad of power tubes as my amp will use a 5879 and the 4 triodes of the ECL84's for preamp work and all four of the ECL84 pentodes for output power.

[bmccowan]

Are you aware of the large index of ExpressSCH files that Doug maintains here? There are many Voxy schematics there and many 5879s.
Cutting and pasting from one sch file to another is not very intuitive, but there are good instructions for doing so.
What can be frustrating with combining sections from multiple files, is figuring out when to use the snap feature and when to turn it off.

[boodle]

Thanks, bmccowan.  I searched for them and only found gif's and pdf's yesterday.  I'll try again.
I'll play with snap/not snap.

[boodle]

Ok, I searched again with zero luck.  I tried to search "expressSCH" and zero results returned.  Still only finding pdf's and gif's.

Lil help!

[sluckey]

Boodle, I have the original Visio files for the Dual Lite and AC-30.4 Lite. I can make these files available in Visio or pdf format.

[boodle]

Sluckey and bcm,
After much poking around, I have finally found the sch files!  Thanks for the heads up that it exists.

Sluckey, I have your pdf's for those, but appreciate your willingness to send them.

[sluckey]

I don't recall ever putting the AC-30 Lite on the net, so I'll attach the pdf here. If nothing else you can maybe use it as a guide while doing your DIYLC work.

[boodle]

Sluckey,
Thanks!

I believe I now have all the sch and other files that I need.  All is right in the world (the el34world at least).

[bmccowan]

After much poking around, I have finally found the sch files!

I shoulda, coulda, pointed you right to them, but you probably found some other great stuff while poking around.
I'm curious what you are thinking for the other channel? All triode preamp or a different mix-up of triode and pentode?
I have built amps with V1 pentode > V2 dual triode
and amps with the reverse V1 dual triode > V2 pentode - these are two favorites - a Matchless Clubman style and another that is sort of a HoSo 56 meets Dr Z.
I always thought it'd be fun to do a dual-lite with opposite V1 - V2 configurations.

[capohk]

Hi all, first post. Wanted to express my thanks to Sluckey for the great resources for this project. I've just finished wiring up mine and fired it up. Some noise and hiss which I will need to try and chase down, but everything lights up and makes noise so I'm pretty happy.

I made mine with the guts of a 60's Bolex projector amp - this had a tube complement of 2x Tungsram el84, 2x Phillips Miniwatt ecc83 and 2x Minwatt ef86 among others so pretty spot on for this project. The OT has secondary taps for 4 and 8 ohm speakers and the PT had two 6.3v secondary taps for heaters, but not centre tapped, used hum pots instead so I've put one in my build. No CT on the HT secondary. I went with SS rectifier and a 150r sag resistor.

Voltages come out a little low but the bias seems spot on so I guess it is ok.
SS rectifier - 318V
B+ (after sag resistor) - 305
Cathode Resistor 130r
Voltage drop across K resistor - 11

Calculated plate dissipation is 11.9W ie 99.2%

I do wish that there was some kind of one-stop shop for hum, buzz and hiss troubleshooting - it would really help me at this stage of my amp-building learning. I did flip the layout around so that the tubes are on the same side of the chassis as the pots - I'm not sure if this will have an effect on the noise floor. I still used shielded cable for the inputs, the heaters are in twisted pairs and the grounding scheme is split with each filter cap grounded to it's own stage.

Anyway, thanks again Steve - I'm sure this will be a great amp. My edited schematic is below for reference. I'll post some pics anon. All feedback welcome of course.

Cheers

Capo