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Tubelab SE 300b Build Thread

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mkane77g

mkane77g

Member
Joined 2014
Looking at some pic in this thread it appears some have the pcb mounted fairly tight against the chassis. Were some of the parts mounted on the back side of the board to accommodate this. Is it possible to remotely attach the tube sockets so they can be bolted to the chassis to take some strain off the board while rolling tubes?
To many questions and I've just begun. Sorry.
 
Z

zman01

Member
Joined 2011
It's always good to ask questions beforehand. :)

By "back side" you mean underneath, right? Yes, that is possible and will make it possible to have a fit closer to the top panel. With 45 tubes I am guessing that heat dissipation will not be a major issue; I recall one builder installing a low speed fan for a 300B build with a few of the semiconductors mounted on the bottom.

It will be good if you get the heat-sinks planned before you finalize chassis and fitting.
 
J

jdrouin

Member
Joined 2012
The OPTs you mentioned would be fine for getting a working unit going, though if they make 5K ones with lower wattage ratings, those would be OK too. The ones you linked to are rated for 15W, but since a 45 only puts out about 1.7W, you'd probably be fine with a 3W or 5W model.

The choke needs to have the same resistance as R4, which is 150 ohm. Not sure about the inductance rating. I used a Triton C-14X for my 300B implementation because it's what George used. Read through the TSE pages (overview, assembly, schematic, etc.) multiple times to see what he recommends for a 45 build. The information is written organically so it can take multiple passes, like Moby Dick; I still find new info when I go back through it. My guess is the Triton choke would be fine but I was only interested in 300B info when I read through it.

Also, I mounted resistors on the top of the board and capacitors underneath in order to get it closer to the chassis top plate. I soldered my tube sockets right onto the board and have found it to be stable. If you make good strong solder joints, tube rolling will be just fine.

On my amp, the board is mounted to bolts that go through the top of the chassis, with nuts and washers to keep everything tightly in place. That arrangements also allows you to raise or lower the board according to your needs as the project evolves. My board sits roughly 3/4" below the chassis top plate, which is enough to show the tubes while allowing space for resistor and IC heat to dissipate.
 
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mkane77g

mkane77g

Member
Joined 2014
J

jdrouin

Member
Joined 2012
With a primary impedance of 10K and secondary of 32 ohm, are you sure those are the right OPTs for you? I'm not sure what the impedance of your speakers is, but most people go with an 8 ohm or 16 ohm secondary to match their speaker impedance, and generally use a 5K primary for the 45 tube.
 
W

w5jag

Member
Joined 2007
The Hammond 125 series has adjustable impedances and loads.

The primary can be set at 2.5K, 5K, or 10K.

The secondary can be set to 4, 8, 16, or 32 ohms.

They are good transformers in my opinion. Personally, for only a few dollars more, and assuming you have the extra room on your chassis, the 125ESE would be a better choice. It has 9H primary inductance, which, while not great, is a lot more than the Edcor XSE15. I do not believe there is a published inductance spec for the 125CSE.

I am using the 125ESE on my TSE. Some measurements were made on that amp and you can see them, including pictures of it's square wave response at 3.5 watt output, on the last page of the 801 TSE thread, probably two or three pages back by now.

Win W5JAG
 
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J

jdrouin

Member
Joined 2012
Board is looking good so far. Just remember to check the mechanical stability of all the solder joints.

As for a choke, in the 45 section of the Tubes and Applications page, George suggests a DC resistance of 150-200 ohm, and says that the higher resistance Hammond 158M will work. You'll want a good 200mA of current capacity too.

In the 2A3 and 300B sections he indicates a couple others. All told:

* Hammond T-193J -- 10H, 200 Ohm, 200mA
* Triad C-14X -- 6H, 150 ohm, 200mA
* Hammond 158M -- 10H, 262 Ohm, 100mA

Any of these is in the ballpark, though the 158M is high in resistance and low in current capacity. I would go with with the T-193J or the Triad, though I'd search this forum first to see what others are using successfully in their 45 builds.

You might find better prices at different venues. Check alliedelec.com, mouser.com, digikey.com, https://www.tubesandmore.com/, https://tubedepot.com/, Your Store, audioXpress | audioXpress Magazine. Advancing the Evolution of Audio Technology - Since 1970, https://www.parts-express.com/, madisound.com, and angela.com.

As for OPTs, if you're looking for nicer ones later on, the Magnequest RH-40 (5K: 8ohm, 16ohm; 40mA, 5W -- $125 ea.) or a custom wound Electra-Print (i.e. 5k, 8ohm, 50mA, 3W -- $120 ea.) would work.

I ordered Electra-Prints for my 300B (5K: 8ohm, 100mA, 15W) and like them, though I'd personally go with the Magnequest.

Of course, there are much more expensive options if you want to go with Hashimoto, Tango, Sowter (SA02 -- 156 GBP / $196 ea.), Lundhal (LL1663 -- $145 ea.), etc..
 
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