Sluckey Dual Lite British - New Build

[Raoul Duke]

Steve,
Quick question regarding transformers. I’m going to use the Heyboer set you recommended and was studying your chassis plans. My question is “are the transformer positions on the plan the result of your research while designing the amp”?

It appears that they are 90 degrees shifted from one another and the OT seems to have a little bit of distance from the PT ; which appears to me to be intentional. I’m sure I can scale it to a pretty exact measurement if these positions are indeed tried and true. I have to make the PT cutout and want to be sure I get it right. Not a lot of variation with the PT vs OT - but I figure every millimeter counts. Any advice is certainly appreciated!

Also - I agree that this amp will be a nice compliment to the Tweedle. It’s always an eye opener for me when I hear first hand how loud these relatively small amps actually are.

Got a Mouser box today and spent a little time this evening sorting through and organizing. Hoping to make the board tomorrow, then start marking the chassis in preparation for cutting. Went with a BUD 13x7x2 and hoping it’ll be strong enough - seems a little light. Guess we’ll see.

I’ll post some pictures as I progress and turn this into a build thread if there’s interest and it’s permissible with the Mods - or I can certainly start one elsewhere here if more appropriate.

Thanks again!

[dorrisant]

Marc, pardon me if I am stating what you already know...

Most times I tape off all secondaries on the PT and connect the primary to AC power. I then attach the OT secondary of choice to a preamp. I run the OT's amplified signal to a set of headphones (with volume control) and start to find the quietest orientation right there on my bench. Once I find the closest possible quiet orientation, I have the absolute minimum distance between the PT and OT. This can be adjusted to fit the layout needs if they need to be located further apart. This physical distance can be checked directly on the chassis if wanted at this point. I have had zero trouble with this method and once the dimensions are discovered, they can be transferred to other builds using the same TX part numbers.

This method is back of hand after a few times and removes any doubt much like the question you're asking Steve.

Hope this helps.

[TUBEDUDE]

I always use this headphone technique. Of course generally, the more distance between the two, the better. But the orientation is more important. I've used the same sets on many 18W builds. Repeating the position and orientation did not find the optimum alignment. For a fairly standard build process i expected them to respond more uniformly. So even identical parts will require a check to insure minimum hum. Also, be aware that on some sets the minimum may require a bracket to mount the OT on its side to get the null. I used a section of angle aluminum for this on two occasions.

[sluckey]

My question is “are the transformer positions on the plan the result of your research while designing the amp”?

The transformer positions are "tried and true". However, they are not exact. I wanted the edge of the PT to be inset 1/2" from the edge of the chassis. And I wanted the center of the OT to be on a center line between the output tube sockets. Notice I did not show any exact positions for either transformer. Slight adjustments to the position of either transformer is OK.

BTW, I don't use headphones. I doubt Leo or Jim used them either.

[TUBEDUDE]

To be fair, Leo setup his layouts for ease of manufacturing in great quantity. There is no room for individual positioning on an assembly line cranking out thousands of chassis. He never would have expended the time. He just rotated 90° and said good enough. This is fine tuning for the best performance, something only possible in a handmade amp.

[Raoul Duke]

I definitely appreciate the experienced perspectives offered here, thank you all!

Dorrisant, TD - I’ve heard of this process before but never fully understood the step-by-step of it. Is there a sticky or other reference I might check out being the “untrained enthusiast” that I am just to ensure I execute this safely and correctly if attempted? I’m always eager to do the homework required to learn, understand, and apply the lessons introduced here on this excellent board.

Steve - looking at your designs and reading your advice to the many folks here I figured you had a method to their placement. The practical, subtle details and forethought are received, understood, and appreciated!

Thanks again guys!

[Raoul Duke]

Being a fan of safety-based mods that don’t affect the sound; I’m looking to put a bleeder resistor in this amp and based on what I think I understand, it would go from the “A” node tab on the cap can to ground. Is it in fact that simple?

Also - got the turret board done yesterday; my first one:

[johnnyreece]

Nice work!

[sluckey]

I’m looking to put a bleeder resistor in this amp and based on what I think I understand, it would go from the “A” node tab on the cap can to ground. Is it in fact that simple?

Yes

Nice looking board. I see you decided to do revision 1.

[Raoul Duke]

Thanks for the confirmation Steve.
Couldn’t resist, really curious about blending the channels.

I used to have a JTM45 clone that I used on an ABY box with my old ‘67 AC30 and really liked the two together at times. I know these are different circuits to what I’m building here; but figured I’d try it out and see how it sounds.

Hoping to do the chassis PT cutout today - just a little hesitant because I don’t have the PT on hand - but I’ve found plenty of references on line regarding the cutout size and mounting post centers. I’ll probably measure everything 17 more times and then try it, lol.

[sluckey]

Hoping to do the chassis PT cutout today - just a little hesitant because I don’t have the PT on hand

I know you're eager but I'd wait on the PT. There's plenty of other holes to make.

[lonote]

Being a fan of safety-based mods that don’t affect the sound; I’m looking to put a bleeder resistor in this amp and based on what I think I understand, it would go from the “A” node tab on the cap can to ground. Is it in fact that simple?

It is that simple.

However, if you use 2 resistors & one cap (2 more extra parts), you not only have the bleeder feature but you have created a positive voltage reference point to elevate your heaters for added hum reduction. You don't HAVE to elevate the heaters, but the option is there.

I borrowed this directly from one of Sluckey's other amp designs (snippet of his schematic attached). It works well & I plan to make it a standard feature. You can adjust the elevation voltage by changing resistor values.

And to your original intent, the B+ drains off quite quickly.

Sluckey Bleed Resistors-Elevated Heaters.jpg

EDIT: PS- Headphone trick also works well, worth the few minutes it takes.

[Raoul Duke]

Thanks lonote, great points - very useful.

Hoping to do the chassis PT cutout today - just a little hesitant because I don’t have the PT on hand

I know you're eager but I'd wait on the PT. There's plenty of other holes to make.

I know you’re right, I’ll hold off until I have it here. Thanks for being the voice of reason, lol.

Still trying to decide whether the chassis will “hang” in the cab (like a Fender) or “sit” in the cab (like a Marshall). I know Ken Fischer used BUD chassis’ and sat them (with reinforcing dowels), but I think the iron I’m using is lighter than 30w+ TW iron.

I have an original Dean Markley CD60 (serial #002) with an open-ended aluminum chassis that’s thinner gauge than the BUD and the iron is huge (looks a lot like Mesa sized “of the day”) and while it has pulled down a little since assembly 40+ years ago - it hasn’t moved in the 10+ years I’ve owned it and everything stays tight.

Thoughts?

[Colossal]

Being a fan of safety-based mods that don’t affect the sound; I’m looking to put a bleeder resistor in this amp and based on what I think I understand, it would go from the “A” node tab on the cap can to ground. Is it in fact that simple?

It is that simple.

However, if you use 2 resistors & one cap (2 more extra parts), you not only have the bleeder feature but you have created a positive voltage reference point to elevate your heaters for added hum reduction. You don't HAVE to elevate the heaters, but the option is there.

I borrowed this directly from one of Sluckey's other amp designs (snippet of his schematic attached). It works well & I plan to make it a standard feature. You can adjust the elevation voltage by changing resistor values.

And to your original intent, the B+ drains off quite quickly.

Sluckey Bleed Resistors-Elevated Heaters.jpg



EDIT: PS- Headphone trick also works well, worth the few minutes it takes.

This is a great post. Elevating heaters makes for a quieter amp, is especially useful for any amp with a cathodyne or cathode follower, and as lonote points out, serves as a power supply bleed when the amp is powered down. I elevate the heaters in any amp I build. I typically target +50-60VDC for elevation.

[LOUDthud]

The bleeder in lonote's post won't discharge the filter caps unless the Standby Switch is left in the Play position. Better to move it to the other side of the Standby.