The Snow Creek Shuffle Sr45, Pmount, Pmour, SEX Rebuilds

[ssssly]

After building Bottlehead kits and hording associated parts for 20 years it has come time form a mass round of builds/rebuilds.

I recently came across a box of transformers in my audio parts closet and decided it was finally time to build the SR-45s I have been planning for more than 10 years. Unfortunately the OT-2s I need to complete that build are back ordered for another month. So I figured that while I wait for the OT-2s, I might as well update and build some other Bottlehead gear in the meantime. 

What I've got.

Two Bee-Pres (PT-7)
Paramounts (PT-4, PC-2, FC-1, OT-1)
Eros (PT-5)
Pre BH upgrade MQ Iron Sex
SEX (PT-3, PC-1)
Paramour I (Hammond, C-7x, T7010)
Foreplay III (PT-3)
     
     And the following pile of iron

     (4)PT-2
     (1)PT-3
     (2)PT-7
     (2)PC-2
     (2)BCP-15
     (2)EXO-03
     (2)BCM-11
     (2)TFA 2004
     (4)155J
     (6)T7010
     (1)360AX
     

The SR45s build will take up PT-2s, OT-2, BCP-15 and C-7Xs.

And now for the Snow Creek shuffle.

I was planning on using the TFA-2004 and EXO-03 for the SR-45s, but PJ said to keep them for a 300B build. So into the Paramounts they go with the Pmount PC-2s moved to power supply filters.

Which frees up the OT-1s.

Leaving me:

     (2)PT-2
     (1)PT-3
     (2)PT-7
     (2)OT-1
     (2)PC-2  24H, 75mA
     (2)BCM-11 12H, 100mA, 145 ohm
   

Looking at that list makes me think I should build a pair of upgraded Paramour IIs. (PT-2, OT-1, PC-2 Plate, BCM-11 Power Supply)

Which leaves me the two SEX Amps, which I have never really been super fond of. At least not for critical listening. Nor can I find anything about the MQ Iron in them.

So modify them or cannibalize them?

(3)PT-3
(2)PT-7
(2)MQ SEX Outputs
(2)MQ SEX Plate Chokes
(2)PC-1

Assuming the MQ irons in the SEX are similar to the later BH-1 & BH-2...PB mentioned using them with PT-7s to build DC heated 45 amps. Which sounds like a good use for them, can't find info on the PC-1s possible power supply filters.

Which would bring the post shuffle list to:

AMP (Power, Output, Plate Choke, Power supply filter)

SR45 1 (PT-2, OT-2, BCP-15, C-7X)
SR45 2 (PT-7, MQ SEX OT, MQ SEX PC, PC-1)
Paramount (PT-4, TFA-2004, EXO-03, PC-2)
Paramour (PT-2, OT-1, PC-2, BCM-11)

Does this make sense or is there a better arrangement?




     
     

[Paul Birkeland]

Man, there's a lot in your post and juggling what you're up to with pretty much the same problem I deal with on a daily basis with my own iron stash is challenging!

Why two SR-45 amps?  I don't think the SEX OPTs are well suited to a SR-45 build, but those are somewhat hard to find and it's probably not such a bad idea to just resell them.

The Paramour with the OT-1 and PC-2 may work better with the PT-7 running closer to the typical 2A3 operating point (say maybe 275V/52mA).  I believe the PT-7 would be a bit happier providing the extra high voltage current compared to the PT-2, but PJ would be better suited to comment on that. 

[ssssly]

Why two SR-45 amps?

Two different systems. One for the horn section of my bi-amped Altec Magnificents upstairs. One for my full range driver room downstairs.  That and to use up parts.

I like my Paramours. Something about the sweetness of that circuit appeals to me despite the noisy background. So I'm definitely going to rebuild a pair. And try to get a blacker background without losing warmth. Paramount's are great, but I miss the extra sweetness sometimes.

After the Paramount TFA-2004 swap and Paramour build...the parts I had left seemed to match one of your suggestions from my SR45 post. So I figured why not.

If you weren't using my boards, I'd use the PT-7s with the BH-1 operating at 4K and the BCP-15/BH-2 plate choke with a different operating point.  That would get you DC heaters in the process, but it would be a ground-up design.

On the assumption that the MQ iron in that SEX was similar to the later BH-1, BH-2 combo.

But I'm not married to a second 45 Amp. Just figured I'd like it more than an updated SEX. Which is a good sounding AMP. Just not good enough to make the rotation with my other BH AMPS. I originally used it for headphones, but I like my Crack better so haven't turned it on for years.

At one point I was debating trying to redesign them into push pulls for sub amps for a slot loaded design sub with a boatload of small sensitive drivers. But they don't sell the drivers anymore and I never built them.

But If there is a better choice for how to use that iron that I missed, I'm all for it.

My Bee-Pres are early first runs. As is my Eros. But other than PS filters not much to do with iron there.

I've never heard or seen the schematics for the post Crack headphone amps. So dunno.

But basically, I'm trying to build the best versions of what I can with what I have on hand. Or with bare minimal additional purchases. 10 years seems long enough to hold on to stuff planning it's best application.

Time to make it useful.

[Paul Birkeland]

I believe the SEX iron upgrade would be an 8K:8 output transformer but the plate choke that went with it is certainly suitable for use with a #45.

[Paul Joppa]

Hilarious - I too have a collection that I puzzle what to do with...  ^:P

For the Paramour, I still lean to the PT-2 because of its shielded 2.5v winding. It can take a bit of increased current draw, especially if you add a some resistance between the power transformer and the rectifiers to get the voltage down - as PB suggests, you want a bit less voltage and a bit more current in the 2A3; just changing the cathode resistor to 1000 instead of 1200 ohms will do the job.

Also as PB suggests, the second 45 amp is the more problematic one. The MQ transformer has an 8K primary, which would reduce the available power with a 45 to something like 1.3 watts. It would have lower distortion though, and better damping factor than a more normal 45. So it's a maybe.

On the other hand, I do have a pair of prototype OT-2s which had a few too many primary turns, giving them a 4500-ohm primary, very close to the standard 45 specs. If you used a PT-7 for the Paramour, I'd happily swap you for the PT-2s - the Paramour was my first design for Bottlehead, and PC-2 my first power transformer design so it would be cool to have a pair.

Have I muddied the water enough yet?   :^P

[Paul Birkeland]

Have I muddied the water enough yet?   :^P

Yes, we have to have some kind of weird three way trade where I end up with his TFA-2004s

[ssssly]

Muddy Waters sounds good. In fact I think I will put "Muddy, Brass and the Blues" on.

So if I trade you the PT-s for the 4500K OT-2s that would give me:

Two PT-7 Powered SR45s. One with PB;s power supply board, one without. One with standard OT-2s, one with the 4500k OT-2s and the BCP-15s, C-7Xs, MQ SEX Chokes and PC-1s to split between them as appropriate.

Paramount (PT-4, TFA-2004, EXO-03, PC-2)
Paramour (PT-2, OT-1, PC-2, BCM-11)

And an 8K MQ output to find something to do with. Which actually makes me think I should just leave the MQ SEX intact and get another plate choke specific for the second SR45.

If the rest of the iron allocations make sense, that sounds good to me.

[ssssly]

Yes, we have to have some kind of weird three way trade where I end up with his TFA-2004s

Been waiting a decade to hear those things magnetized. Gotta at least let me turn them on in something first.

[Paul Birkeland]

And an 8K MQ output to find something to do with.

[Paul Joppa]

I thought of the 10, but it only goes up to 425v - didn't follow up with the 801!

I appear to have a pair of PC-3s on hand, to match the OT-2s. I'll throw them in with the PT-2 prototypes.

This is from my inventory spreadsheet - I'd better make sure they're all really here!

[ssssly]

That could be interesting.

And if you have stuff to trade, I'm a parts horder. BH, Heathkit, Dynaco, Altec, JBL, VPI, Fostex, tubes (by the box load, more than 20 repair shops' full stock from out of business sales) , oil, wax and motor run caps, NOS teflon and phenolic tube sockets, high quality wire and parts from military aircraft and signals equipment, old power station voltage, amperage and indicator dials, weird early 2000s unobtanium (I have Manger bending wave drivers someplace).

I like to trade.

[johnsonad]

LOL, I love this thread. 

[ssssly]

PJ

Of the two sets of PT-2s I, one pair is from the first production run of the Paramour II. Very early in that run. I ordered them prior to their release. But they have been painted white. Well, had a couple extra layers of shellac applied to them, then we're painted white as I do with all my power transformers.

The other pair is brand new in the box and sticky bubble wrap from when I special ordered them around 2013. After they were OOP.

Which pair would you like for your collection?

[Paul Joppa]

I'd prefer the unpainted, since I tend to prefer bare metal or black paint.

Perhaps we should move this to PMs?

[Thermioniclife]

Oh man this was getting very interesting. A three person horse trade is not an everyday occurrence.