SR45 amplifier
- Thread starter debk
- Start date
Paul Joppa
Moderator
Deb, Xavier, in fact the posters on this thread, you are all A-OK in my book. The link issue has been a grey area, it's not linked from the site but not protected either. So far it hasn't been a problem. I'll consult with Doc B on future plans, perhaps the revised circuit on request with a transformer or C4S. I really didn't want to bring it up but I also don't want the circuit to show up on non-Bottlehead forums.
Paul,
I have total respect for your design abilities and expertise. I have gotten a priceless education following the discussions on this forum over the years. I think Bottlehead products are extremely high quality and reasonably priced. The last thing I want to do is step on anybody's toes.
So I want to make sure it's cool if I purchase the soft start boards and use them to build a 71-a amp.
Michael
I have total respect for your design abilities and expertise. I have gotten a priceless education following the discussions on this forum over the years. I think Bottlehead products are extremely high quality and reasonably priced. The last thing I want to do is step on anybody's toes.
So I want to make sure it's cool if I purchase the soft start boards and use them to build a 71-a amp.
Michael
Paul Joppa
Moderator
No problem there!braubeat said:
OK pals. We have to keep this thread moving even if its only those of us who paid for the original kit and, in consequence, have access to the schematic (just like any other BH product).
I have two comments/questions: First, one of the things that originally discouraged me of using my TL404s in this project was that the OPs were optimized for a 3k load. Having said that I think that there's voltage headroom to increase the regulated voltage a little bit to 350 volts and then operate the 45 at "classic" 275/-56/36mA conditions. Moreover this would reduce the power dissipation needs of the heat sink. I realize there may not be enough B+ at low mains voltage conditions but in my case: A) I have a perennial ultrahigh mains voltage and b) I use power plant conditioner so I always have 119v at my BH gear
Second, why can't one just substitute the plate choke with a C4S as Michael was suggesting? a 36mA C4S with a 20v voltage drop would only be dissipating a quarter of a watt.
Saludos
Saludos
I have two comments/questions: First, one of the things that originally discouraged me of using my TL404s in this project was that the OPs were optimized for a 3k load. Having said that I think that there's voltage headroom to increase the regulated voltage a little bit to 350 volts and then operate the 45 at "classic" 275/-56/36mA conditions. Moreover this would reduce the power dissipation needs of the heat sink. I realize there may not be enough B+ at low mains voltage conditions but in my case: A) I have a perennial ultrahigh mains voltage and b) I use power plant conditioner so I always have 119v at my BH gear
Second, why can't one just substitute the plate choke with a C4S as Michael was suggesting? a 36mA C4S with a 20v voltage drop would only be dissipating a quarter of a watt.
Saludos
Saludos
Paul Joppa
Moderator
Xavier, a plate load dropping 20v would allow about 10vRMS swing, allowing 6v minimum compliance. That's about 0.020 watts in a 5K load ... That said, I do have some plans for a C4S loaded 45 using the Paramount power transformer; the problem is finding a reliable current source device at such high voltages. It's on my list. :^)
You can drop the plate current for a 5K load; I'd go with 30mA at 250-275v. It leaves more current for the shunt reg which is a little starved due to the PT-2 limitations. (That's another reason I want to switch to the PT-7 eventually.)
For those who bought PT-2s with the intention of resurrecting this 5-yr-old design, I'll see if we can send a paper copy of the original notes. For those who want a replacement for the original C4S board, which is no longer available, I recommend the Paramount soft-start kit and I'll throw in a paper copy of the modified circuit diagram showing the connections to that board. That should bring the project to about the level it was originally - it was never a real kit with a real manual, after all!
You can drop the plate current for a 5K load; I'd go with 30mA at 250-275v. It leaves more current for the shunt reg which is a little starved due to the PT-2 limitations. (That's another reason I want to switch to the PT-7 eventually.)
For those who bought PT-2s with the intention of resurrecting this 5-yr-old design, I'll see if we can send a paper copy of the original notes. For those who want a replacement for the original C4S board, which is no longer available, I recommend the Paramount soft-start kit and I'll throw in a paper copy of the modified circuit diagram showing the connections to that board. That should bring the project to about the level it was originally - it was never a real kit with a real manual, after all!
Paul Joppa
Moderator
For this application, the difference with the new boards is insignificant. The differences are 1) a different heat sink (I believe the capacitor is about the same), and 2) there is a trimmer to adjust the driver bias; the older board just has a resistor (the driver is cap-coupled so there is no special need to trim the voltages exactly)
Paul Joppa
Moderator
@Jim, yes I would recommend the paramount 1.1 softstart boards and 5670 driver for use in the paramour II. There are no instructions specific to the Paramour, since it's been out of production for a while now, but it should not be that difficult to figure it out.
I also mention that, because the driver bias is adjustable, you can probably use other tubes such as 12AU7 or 6SN7 if you need less gain.
I also mention that, because the driver bias is adjustable, you can probably use other tubes such as 12AU7 or 6SN7 if you need less gain.
Paul Joppa
Moderator
TWO 6J5s, that would be ... shunt reg, you know... :^)
"Xavier, a plate load dropping 20v would allow about 10vRMS swing, allowing 6v minimum compliance. That's about 0.020 watts in a 5K load"
Thanks Paul. It looks like I still have lots to learn!
You can drop the plate current for a 5K load; I'd go with 30mA at 250-275v. It leaves more current for the shunt reg which is a little starved due to the PT-2 limitations."
Fantastic. I assume the 250-275 is plate to cathode. Right? That's a bias of 50-55 so I need 300-330v at the plate, 315-345 on top of the plate choke. So the design Breg at 320 is fine.
To get a 50v bias the cathode resistor would be 1.66k.
Good for approximately 175mW and approx 6.8% THD.
Now, my big question: would I need to change anything at the C4Ss to account for the 6 mA less I'm running through the 45? Or does the shunt tube just shunts them?
Thanks a lot!
Thanks Paul. It looks like I still have lots to learn!
You can drop the plate current for a 5K load; I'd go with 30mA at 250-275v. It leaves more current for the shunt reg which is a little starved due to the PT-2 limitations."
Fantastic. I assume the 250-275 is plate to cathode. Right? That's a bias of 50-55 so I need 300-330v at the plate, 315-345 on top of the plate choke. So the design Breg at 320 is fine.
To get a 50v bias the cathode resistor would be 1.66k.
Good for approximately 175mW and approx 6.8% THD.
Now, my big question: would I need to change anything at the C4Ss to account for the 6 mA less I'm running through the 45? Or does the shunt tube just shunts them?
Thanks a lot!
Paul Joppa
Moderator
The shunt tube does the work.
