SR45 amplifier

[xcortes]

01A looks good. Battery heated filaments too at 5v and 0.25 mA (same as the 71A actually).

Paul, I think PGP 8.1s would be a tad better here than the PT-2s right?

I'm ready to go for it.

[Paul Joppa]

01A looks good. Battery heated filaments too at 5v and 0.25 mA (same as the 71A actually).

Paul, I think PGP 8.1s would be a tad better here than the PT-2s right?

I'm ready to go for it.

PT-2 has more magnetic headroom, but the voltages etc. are significantly different. I'd need at least a conceptual design and voltage budget to comment further.

[braubeat]

I'm ready to build one too. Lets go for it.

Michael

[debk]

Now that we have the PT2 transformer group buy, is it possible to get the boards for the SR45.
I may be mistaken but from the schematic in the SR45 upgrade manual, the board looks like it is the same board from the extended FPIII.  Of course the component values are different.

Debra

Hey Deb - remind me next week - I'm out of town again all this week and my notebooks are at home. The original SR45 board preceeded the current "soft-start" board, and it would be expensive to make just a few - plus the newest version (4.4) is better in several ways. I'll just have to make sure what the wiring changes might be.

Paul

Just reminding you about boards for the SR45

Hope you had a good trip

Deb

[Paul Joppa]

Thanks, Deb - I had a great trip.

I can't seem to locate the SR45 conversion page - does anyone have the link at hand?

Meanwhile I'll mark up my schematic to show terminal labels and parts as used on the current (v4.4) board. I assume the original web page had a schematic? Hopefully that will be enough information to revive the design. The new boards are available as the "soft-start" kit for Paramount, including a trimpot for setting the driver bias precisely; you get a new driver socket (useful) and a 5670 tube (less useful).

It appears that the clip-on heat sink will work as long as your power line voltage is not much above 120v. This was always a marginal aspect of the original SR45 design.

By the way, the original used the 6CM7. The 6CS7 is very similar, but looks a bit more linear in the published curves. IIRC the pinout is a bit different, but just mention it in case someone wants to experiment.

[xcortes]

The instructions and schematic were never published but were supplied with the original kit instead. I have my own copy that could send to you Paul or to anyone BH authorizes me to do so.

Saludos

ps. Paul: I have a Board Meeting and Quarterly Earnings release coming next week so I really shouldn't be thinking about the 71As project. BUT so far what I have in mind is 01Aa driving 71As. Battery heated filaments. Independent PS for driver and power tubes with RS080 and exo-01 on the 01A and pgp 8.1s and (maybe Dowdys) on the 71A tube's one. DC, SR and C4S loaded each. I triamp but for this iteration I will only build two pairs because I wan't to try to direct couple the Ionovac tweeters (another project). I already have the two pair of TL404s, and most of the ps iron for both sets. I'll try to post a first attempt of a schematic next week. You mentioned "crazy enough", right? Let's set a new world record for Dunken factor.

[debk]

SR45 upgrade manual

http://www.bottlehead.com/et/adobespc/paramourII/SR45%20upgrade%20manual.pdf



Deb

[xcortes]

Good!

[Paul Joppa]

Thanks, Deb. Turns out, I had downloaded it a while back but failed to file it where I could find it! That manual has the schematic which I propose to modify. (Actually it is a later version than what I have in my files - I'll check but I think I just added the RC stability network to the shunt reg part.) Notice that it's version 3.5 - there was actually quite a lot of development before the kit was offered!

[Paul Birkeland]

I made up a few sets of custom boards for this circuit a while back.  They mount just above the power transformer, hold a large heatsink, and free up lots of space around the heatsinks.  



(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fimg526.imageshack.us%2Fimg526%2F9276%2Fdsc0193ij.jpg&hash=ca2cbf76e89c56adf8fbdd883792f27f817a6dc1)
I don't have a ton of documentation on these, but the connections are not too complicated.

[2wo]

That is the one I was thinking of. I have always been a little worried about the small heat sink on mine. This also looks easier to implement then the original PCB. Granted it was not the original purpose but it is a bit of a Kluge with all the jumpers.

Would you consider having a few more made, or make the file available?...John       

[Paul Birkeland]

I will talk to Doc/PJ on Monday about this.  Last time I made a few, he and PJ gave me their blessings, I'd just want to double check that this is still OK.

[braubeat]

Xavier,

If you are using two power supplies you might have enough voltage headroom to have c4s loads on the shunt regulators and on the plates of both tubes. Of course this would cut down on the Dunkel factor.

Michael

[Paul Joppa]

I guess I have to say this, lest the thread get out of hand.

I have NOT placed this design, or the circuit diagram, in the public domain. When it was a semi-kit, I got some recompense from the sales. And, as I said early in this thread, I am working on a second-generation version from which I expect to get some income if it does become a kit.

I don't have a problem with a few enthusiastic Bottleheads making versions for themselves, especially if it involves purchase of PT-2s and/or C4S boards, both of which produce some income for me. It does become a problem for me if I lose ownership of the design. It's more a legal issue than a financial one - my monetary compensation is small, but it does validate ownership of the design.

Intellectual property is a very tough issue, which we as a society are barely starting to deal with in an age where copying and disseminating have become so much easier. I'm sure the whole concept will see huge changes over the next couple centuries. Meanwhile we muddle through as best we can.

[xcortes]

Hear hear!

And good to know a revision could end up in a kit. I'll do a pair (already ordered the pt-2) to see what the buzz is about with my 755As. And if you guys eventually come out with a full kit count me on!

Saludos