The Phantom SR45 Build - Snow Creek Shuttle Episode 1-A Bottlehead Saga

[ssssly]

Roughly 20 years ago I was introduced to the Bottlehead community via the DIY speaker building community. And after building my first Bottlehead kit, a pair of Paramours, I was hooked.

With considerable assistance from PJ, PB, CB, Voltsecond, Wardsweb and others, I built Foreplays (I, II and III), S.E.X I and II, Paramounts, an Eros, two BeePres, a Crack, some Quickies and repaired and/or customized piles of classic Dynaco, HH Scott, Altec and Macintosh gear.

Then, I was injured in the line of duty. Loosing much of the motor control in my right hand and finding myself unable to hold a soldering iron still enough build anything. So in true do it yourself fashion, I went to school to learn mechatronics engineering. Figured if I couldn't hold an iron, at least I could build the robots to hold one for me. And while successful in building said robots. It still wasn't as satisfying.

Then it was suggested to me to adopt smithing as a form of physical therapy. So I learned metalworking. Welding, then blacksmithing, then copper and silver smithing. Working from larger to smaller until now. Where I have reached the point that I can once again build by hand (Not to mention the robots).

Prior to my injury I had plans to build a SR-45.

Now, at long last I give you "The Snow Creek Shuffle-Episode I: The Phantom SR45" build thread.

PS..my apologies to PB and PJ if this spurs requests for the long oop SR45 board.





 

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I like big caps and I cannot lie.

To provide them some extra breathing room I decided to go with some spare Paramount top plates. Sanded to a low polish, 2000 grit, then primed and painted Hammer tone copper.

Machined Teflon tube sockets.

Custom resin printed hole shrinker.

All brass hardware.

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PT-7 power transformer.

Prototype OT-2 output transformer and PC-3 plate choke I traded PJ some OG PT-2s for.

NOS paper wound C-7X in Rust-Oleum white.

Underside of the resin hole shrinker.

Random unbranded RCA and binding posts I picked up at an electronics market in Seoul, Korea.

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Black resin printed hole drilling guides/standoffs to accommodate the OT-2 and PC-3 on the Paramount Chassis

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Safety ground wiring.

[Thermioniclife]

Quite an inspirational tale. Well done, looking good and best wishes.

[Paul Birkeland]

I remember selling an extra set or two of those boards a long time ago, but I couldn't remember who ended up with them.

[ssssly]

 

I remember selling an extra set or two of those boards a long time ago, but I couldn't remember who ended up with them.

Also when I convinced QueenBee to do one last run of PT-2s for the project. That included the PT-2s I traded with PJ for the OT-2s and PC-3s in this amp and now power his 6J5 Paramours.

The remaining 2 NOS PT-2s I have will be going into my Paramour rebuild in a later episode of "the Shuffle".

I'm planning on doing them with fully 3D printed and electroformed in place wiring. As an interim proof of concept for a method of 3D printing transformers that I've been developing.

[2wo]

If I remember correctly, the original SR45 kit used the then current C3S boards. Took a lot of jumpers but doable...John

[Doc B.]

3D printed transformers gets my attention. Will be interested to hear how this develops.

[ssssly]

3D printed transformers gets my attention. Will be interested to hear how this develops.

Doc,

Would be more than happy to include anyone from Bottlehead in the project in any way they would like. My EE work is focused on digital motion controllers and I/O for them. I'm designing a manufacturing method based on known designs. Y'all know way more about tx design and implementation than I.

So if there is a transformer design you would like to test via this method, I'd be happy to.

[ssssly]

If I remember correctly, the original SR45 kit used the then current C3S boards. Took a lot of jumpers but doable...John

Sorry, what is doable?

[ssssly]

Speaking of TX design and implementation.

PT-7 has marked 150v, 6.3v and 3.15v out with corresponding 0v for the 150v and 6.3v.

Need 300v and 2.5v.

First blush, just instal a voltage doubler for 300v. Or is there a better way here?

Drop the 3.15v to 2.5v with a voltage divider, no problem.

Where should I pull the 0V leg for that though? 

[Paul Joppa]

Yes, the PT-3/7/10 uses doublers for high voltages. For lower voltages (such as Crack), the winding is used with a fullwave bridge.

In the MonAmour, the 6.3v center-tapped winding was rectified with the usual FWCT arrangement; it's OK to use half the winding to power a 2A3 or 45 with AC. Be aware that either arrangement biases the 6.3v terminals to the cathode voltage of the 2A3 or 45 - around 50-60 volts depending on the specific design. It's important that the winding be AC grounded because it also serves as an electrostatic shield for the high-voltage winding. Usually the cathode bypass cap provides the grounding function

[ssssly]

To make sure I understand you correctly, pin 4 is the center tap for the secondary and therefore common for both the 6.3v and 3.15v.

Normally those legs would be phase corrected with full wave bridge rectifiers but since both legs are being used as AC heaters, it's not necessary.

And the cathode bypass cap is sufficient for the ground path for AC shielding in that configuration for the otherwise standard SR45 circuit.