SR45 amplifier

[2wo]

The 12AT7 was used only for the driver, I kept the 6CM7 as the reg...John

[Jim R.]

An update on my gain/volume situation...

Ok, first, this is really hard to admit, especially since I did the samething three times in a row when swapping speakers: I got an instant nearly 6 db gain simply by connecting the speakers in phase ;-).  How I did that, especially with these speaker cables (which are so obviously different on positive and negative sides) is a complete mystery, but that alone made a nice difference.  Another mistake I made wa to not play the amps or speakers long enough for them to wake up and for the nickel core demagnetization to happen.  So all that together got me about another full 99 db or thereabouts, which is a full step on the coarse volume control.

I could not locate the vcap CuTFs, so I just put the cd player on repeat and let the system play while I finished organizing my toolbox and moved almost of the remaining junk out of my listeninr room and set the area rug in place, and sure enough after an hour or so things really started to come into focus, gain some far more substantial weight and far better top to bottom balance, clarity and tonality.  I also have to remember that a substantial part of this system is brand new, including all but one set of interconnects and the CD player.

So, as things got better and better over the course of a few hours, it became pretty clear that I'm going to stick with these amps, but also probably keep the Orcas in the listening room.  That will mean chopping the stand height down somewhat as they were sized for another room and a much higher couch.  Oh, and all this was sans subs again.  I'm still kicking myself how I could have connected the left speaker out of phase originally, and then two more times when switching in orcas and then back to nagas, and only caught it today when I put the Orcas back in -- I guess I was just on autopilot and did the same thing everytime and today as I was pluggin the cables in something clicked and I thought, this is not right.

Other than that and a somewhat flakey 6j5 on the left side of he preamp, all seems to be coming along nicely now, and I've got a NOS pair of RCA 6j5s in my mailbox right now which I'll go fetch tomorrow.  Then if I can't find the cutf caps, I just got an unused, unwanted pair of .1 uF Mundorf SGOs for half price, so I may throw those in too.

Despite all this, the listening after the first couple of hours was really nice.  Computer and dac and room treatments are next.

-- Jim

[xcortes]

A CL 90 at the mains input reduces the current inrush and hence the magnetization of the Ni cores. I'm not sure if it's 100 percent true but I think at least they help as I don't need a lot of time for my amps to sound open (and my horns are 106 to 110 dB efficient so there's not that strong a signal going through.

[Grainger49]

I put switches on my Paramours.  I just short from the transformer side of the Parafeed cap to the opposite end of the OT primary.  With the primary shorted I wait 30s to a minute and turn the switches off.  A SPST is all you need.  I even got them from Radio Shack.

[Jim R.]

Thanks, guys.  Xavier, I've just not had very good luck with the ICLs in the past as they were had a fairly noticeable negative impact on dynamics.  And with your ultra sensitive drivers I'm not sure you'd hear this on your system.  BTW, totally awesome setup with the Edgar horns and MI drivers!  If I only had a space big enough...

Grainger, I did think of this too, but for some reason I'm still not fully comfortable with this idea either, but I haven't completely ruled it out either.  I willhave some room leftover in my larger chassis when I rebuild these amps with the Dowdy chokes, nickelEXO-145s and 6DN7 drivers, so maybe I'll add a time delay relay in side that has no possibility of being activated after the first activation.  I also plan on using Neutrik PowerCons for the power connection, as they can function as a power switch as well.

I had an idea on where my CuTF caps might be, so when I get down there today hopefully I can get these installed and sit back and listen some more.  And of course I'll have to hook the subs back up for the full effect.
-- Jim

[Grainger49]

Jim,

If you are uneasy about leaving the switches shorted you can buy spring return switches.  You will have to hold the switch in the shorted position for 30-60s then release it for each amp.

[Jim R.]

No, actually I'm more uneasy about the possibility of discharging a fully charged parafeed cap through the cathode resistor.

-- Jim

[Paul Joppa]

If I understand this discussion correctly, the output transformer primary shorting switch does not discharge anything. There is no DC voltage across, or current through, a parallel feed output transformer. (If there's no music, there is no AC voltage or current either!)

Ideally, you would leave the output transformer shorted until the tubes have warmed up and are conducting, and short it again before switching the power off.

[debk]

I have almost all the parts to build the SR45, except the iron.

Would the BH-5 work just as well as the TFA-2004jr?  If I am not mistaken they are both 3K impedance.
I don't know how the BH-6 plate choke compares to the BCP-15 (40ma/50H)

Appreciate any advice

Thanks
Debra

[Paul Joppa]

The BH-5 is a modified TFA-2004Jr, with slightly different coil geometry and materials. Electrically they are identical.

The BH-6 is a modified BCP-15-50mA, with slightly different coil geometry and materials. Electrically they are identical. It is gapped for 40 henries at 50mA.

For what it's worth, the BH-2 (SEX upgrade) is modified BCP-15-40mA, with slightly different coil geometry and materials. Electrically they are identical. It is gapped for 50 henries at 40mA.

The BH-xx products were developed by Mike to optimize cost-effectiveness, that is with refined but not labor-intensive coil geometry and materials, and in channel frames with solder tabs. All of the items mentioned are highly suitable for use in the original SR-45, and the performance differences are small.

[debk]

Thanks Paul, I appreciate it


Debra

[johnsonad]

Paul,

If you guys end up selling this as a kit with a base plate could you please make it oversized? This would allow us tweakers to put much larger iron on top and fiddle around underneath. Maybe something on the BeePre scale? 

Regards,

Aaron

[Paul Joppa]

My new quote: "Every case is special, but there are no special cases".

It just doesn't make sense from a business perspective to compromise a design for a few, or to customize individual kits.

It is (in my opinion) more practical to handle different needs as a separate custom job. For example, for a modest charge one of us could place the layout on a larger panel with wider edges, and have it made by Front Panel Express and drop-shipped to you. That way, the manual instructions (including the pictures) would not need to change. Eileen could separately sell you a larger base in any of our standard sizes if you didn't want to make your own.

I know it seems a waste if you have some base parts left over, but the real cost of custom packing is much greater than the cost of the wasted wood.

Note, all the above are my own ideas on Friday evening with a nice cocktail in front of me; Doc B may have other thoughts next week so don't hold me to this!

[johnsonad]

Lol, Paul I'm three glasses of wine in so I understand.  What you are proposing would be ideal. I've been fooling around with a Paramount built idea using FS100 plate chokes and full 2004's and thinking how I'm going to fit it. I would happily pay for some level of ability to customize on the source end. As you know my SR45 build will be a one off too. If Bottlehead can support such customization, I am all for it!

[Paul Birkeland]

If a shunt regulated power amp enters our kit lineup, it may already be monoblocks on 10" x 12" or 12" x 12" chassis plates, so we will have very, very little room to grow any larger.

Also, an amplifier that is fully shunt regulated is the least flexible of all possible designs, as even something that seems as mundane as changing to a larger plate choke with more copper may have some undesirable consequences.  The same goes for the BeePre and Eros, the refinement level of these designs makes them more sensitive to changing parts.

-PB