Yeah--this diverged a bit from my point. I was hoping to glean some information about the product and what Hammond's specs mean, in addition to pointing out to folks that if these PDFs are to be believed, even from the same maker, one transformer described as 325-0-325 might be 50V or more different from another described the same way. (It appears Edcor might be more consistent, but then, they don't make stuff like "drop in" replacements for vintage guitar amps that raise special considerations.)
I'm quite familiar with choosing power transformers. I spent my early DIY years building stuff from whatever I could scrounge and finding ways to make it work. I'm amused that even if you can buy new stuff, it isn't necessarily any less guesswork because you've got to get it in circuit and see what happens.
I'm also not reinventing the wheel on this power supply, as George did a pretty good job with what is on the PCB. And the PCB is already stuffed.
I'm especially curious about an earlier comment suggesting money should be spent on PTs for OPTs! My only problem with PTs--especially in single ended amps--has been mechanical noise. And to be honest, I've got very recent Edcors and Hammonds that hum louder than the vintage stuff I've historically used. I've done fine before with Anteks that are super affordable. The only one that made any noise for me was a low voltage one for a chip amp.
I'd have considered the cheap imported 320-0-320 EI cores that are common on Ebay for this amp, but I wasn't convinced I get the B+ I'm after. I was considering the Antek 3T325 too (115V primary suggests it would also be highish output for something rated like this, and last time I used a 3T325, I have a vague memory that I was getting near 700V end to end on a US line before the rectifiers). But they are out of stock, fitment would have been more difficult, and I wasn't excited about unwinding one of the 6.3V windings a bit to get down to 5V.
I went with the 290CX as it was the cheapest and if the PDFs are to be trusted, is going to give me the highest voltage. This is a CLC, not an LC. If I get too much voltage, I'll just keep dropping the first cap. I bought a few of the Solen 630Vs in various sizes. I also bought a beefy-ish (for a 300B SET amp) 193J choke, so it can probably take a good bit of ripple before it gets too unhappy. And if it can't, I've got two 8lb Stancors in the iron box.
If I can't get the voltage down with a small first cap, I can always add a bit of resistance, whether in series with the choke or by swapping to something else. My iron box also has an old 7H choke with quite a bit more resistance but still enough current handling that could be swapped for the 193J.
Maybe I should have just also had Monolith wind the PT and choke. The S-11s will hopefully be here in a few more days (I'm going for near 400V with the 5k primaries, but not over) and then I just need to find the time to prototype it and see whether the 290CX will get me where I need to go. If its still low, I might sooner snag a Triad R-16 on Ebay or go back to Monolith than try a higher voltage Hammond or Edcor. There just aren't many options listed in the 650-700V range ... unless you look at the Hammond sheets and see that maybe all isn't quite what it would first appear!
Paul
I'm quite familiar with choosing power transformers. I spent my early DIY years building stuff from whatever I could scrounge and finding ways to make it work. I'm amused that even if you can buy new stuff, it isn't necessarily any less guesswork because you've got to get it in circuit and see what happens.
I'm also not reinventing the wheel on this power supply, as George did a pretty good job with what is on the PCB. And the PCB is already stuffed.
I'm especially curious about an earlier comment suggesting money should be spent on PTs for OPTs! My only problem with PTs--especially in single ended amps--has been mechanical noise. And to be honest, I've got very recent Edcors and Hammonds that hum louder than the vintage stuff I've historically used. I've done fine before with Anteks that are super affordable. The only one that made any noise for me was a low voltage one for a chip amp.
I'd have considered the cheap imported 320-0-320 EI cores that are common on Ebay for this amp, but I wasn't convinced I get the B+ I'm after. I was considering the Antek 3T325 too (115V primary suggests it would also be highish output for something rated like this, and last time I used a 3T325, I have a vague memory that I was getting near 700V end to end on a US line before the rectifiers). But they are out of stock, fitment would have been more difficult, and I wasn't excited about unwinding one of the 6.3V windings a bit to get down to 5V.
I went with the 290CX as it was the cheapest and if the PDFs are to be trusted, is going to give me the highest voltage. This is a CLC, not an LC. If I get too much voltage, I'll just keep dropping the first cap. I bought a few of the Solen 630Vs in various sizes. I also bought a beefy-ish (for a 300B SET amp) 193J choke, so it can probably take a good bit of ripple before it gets too unhappy. And if it can't, I've got two 8lb Stancors in the iron box.
If I can't get the voltage down with a small first cap, I can always add a bit of resistance, whether in series with the choke or by swapping to something else. My iron box also has an old 7H choke with quite a bit more resistance but still enough current handling that could be swapped for the 193J.
Maybe I should have just also had Monolith wind the PT and choke. The S-11s will hopefully be here in a few more days (I'm going for near 400V with the 5k primaries, but not over) and then I just need to find the time to prototype it and see whether the 290CX will get me where I need to go. If its still low, I might sooner snag a Triad R-16 on Ebay or go back to Monolith than try a higher voltage Hammond or Edcor. There just aren't many options listed in the 650-700V range ... unless you look at the Hammond sheets and see that maybe all isn't quite what it would first appear!
Paul
The choke that works well for my choke input power supplies is the Hammond 193H, 5H @ 200mA; 65 Ohms DCR; 2.5 Lbs.
Most often, I do not use any small capacitor before the choke.
The Hammond 193J is 10H @ 200mA; 82 Ohms DCR; 5.5 Lbs.
If it is the same quality as the H version, it will work very well.
Most often, I do not use any small capacitor before the choke.
The Hammond 193J is 10H @ 200mA; 82 Ohms DCR; 5.5 Lbs.
If it is the same quality as the H version, it will work very well.
Hi Paul
The 290CX is rated for 650Vct @ 207 mA. If you doing CLC then you should really try to not draw more than 150mA. You will likely discover that the transformer will get pretty hot if you go beyond this, with possible physical vibrations.
My simulations using PSU-II suggest that an 5uF input cap could get you around 390VDC after the 10Hy 193J or 193h choke when using GZ34 full-wave rectification and drawing 180mA. Of course the actual B+ voltage will strongly depend on your mains voltage. I see that the 290CX specs are based on 120VAC primaries. If you have 115VAC then you might want to increase the input cap, but then you will probably need to exchange GZ34 for something else such as the 5AU4 which can handle larger value input caps. With 5AU4 you will probably need 15uF or more for the input cap.
Sadly, both of these 'audio amplifier' rectifiers do not allow for the kind of soft-start that you get with TV damper diodes. In my experience, the GZ34 is a little softer than the 5AU4 though.
Also, regarding the input cap, I think it was mentioned already, but this really needs to be a decent quality stable film cap. You don't want this cap value to drift... In the past, motor run caps were recommended. Today we also have DC Link caps which are IMHO a great alternative.
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I appreciate you running the simulations. As you mention, swapping rectifiers will be another option for me. My line voltage tends to be pretty high, so we'll see.
I am curious to hear about folks experiences with DC Link caps. After I glued fancy series 'lytics into my 845 monos and bypassed them with fancy film caps a few months ago, I realized that would have been smaller, cheaper, and likely better in every way.
I have motor runs in various sizes, including a case (30) of brand new Aerovox 16.5UF 1000V/1200V peak sitting around for another planned 845 project (ideally, all film caps in giant old Mac chassis ....). One of those might not fit here. But I'll find something that works for size, capacity, and quality.
As I indicated, my history with salvaged power transformers and chokes means I have some experience messing with power supply components until the voltage ends up where it needs to be. And if the 290CX is just too much, well, back to the list I started with!
Paul
I am curious to hear about folks experiences with DC Link caps. After I glued fancy series 'lytics into my 845 monos and bypassed them with fancy film caps a few months ago, I realized that would have been smaller, cheaper, and likely better in every way.
I have motor runs in various sizes, including a case (30) of brand new Aerovox 16.5UF 1000V/1200V peak sitting around for another planned 845 project (ideally, all film caps in giant old Mac chassis ....). One of those might not fit here. But I'll find something that works for size, capacity, and quality.
As I indicated, my history with salvaged power transformers and chokes means I have some experience messing with power supply components until the voltage ends up where it needs to be. And if the 290CX is just too much, well, back to the list I started with!
Paul
Hi Paul
Many in this hobby attempt (early on) to build a SE 300b amp on the cheap, wonder why it doesn't sound as they had hoped, then blame the 300b.
From my experience, the best 'cheap' SE 300b only needs approx. 310VDC supply. Build an LCRC supply or an LCLC supply. Use a 5Hy choke as your first choke. Make sure it is rated high enough for choke input supply (so it won't vibrate). 5VDC on the cathode. Fixed bias.
(Ok, ok, if you can get higher B+ that is going to be better, but NOT if you are going to use a cap-input supply. Also, if you are going for a Miata style PSU then that is also a totally different beast which I won't comment on but to say it can also be an excellent choice too. Here I am only discussing old-school PSU's.)
My suggestion:
1. Do an LCLC (or LCRC as 6A3sUMMER suggested) supply. You probably can get away with 5Hy on the first choke (as 6A3sUMMER also suggested). Use GZ34 since your transformer has a 5V winding for the heater. You will hear the difference with choke input even if your B+ is a bit on the low side. A quick simulation using PSU-II suggests you can get around 315VDC after the 5Hy choke for an LC supply when using GZ34 and a Hammond 290CX transformer.
2. Use fixed bias. Your 290CX has a 50v secondary for negative grid bias. Fantastic! Cap couple your Mosfet follower stage to the Grid. Use an inexpensive polypropylene and foil coupling cap to start with - you will likely be pleasantly surprised. Don't forget to use a grid stopper.
3. Use DC on your heaters. If possible use a proven regulator circuit for each 300b. Use a decent wire wound 10 Ohm resistor -ve heater to ground for each 300b so you can easily measure+calculate your 300b current.
4. If your budget is constrained, don't over-spend on the OPT's. You can always upgrade them later if needed. The power supply is inherently in the audio circuit for SE builds. A fancy OPT will not fix a poorly considered PSU.
5. You can even upgrade this cap coupled amp to interstage transformer at some point if you wish. Or you can try using snake-oil boutique coupling caps - whatever floats your boat...
I have seen some fantastic looking SE 300b amps that actually sound quite mediocre. Expensive OPT's from various boutique manufacturers and fancy chassis. Every one of these fails had a poorly considered power supply. Pretty much every one started with a cap-input supply too...
Many in this hobby attempt (early on) to build a SE 300b amp on the cheap, wonder why it doesn't sound as they had hoped, then blame the 300b.
From my experience, the best 'cheap' SE 300b only needs approx. 310VDC supply. Build an LCRC supply or an LCLC supply. Use a 5Hy choke as your first choke. Make sure it is rated high enough for choke input supply (so it won't vibrate). 5VDC on the cathode. Fixed bias.
(Ok, ok, if you can get higher B+ that is going to be better, but NOT if you are going to use a cap-input supply. Also, if you are going for a Miata style PSU then that is also a totally different beast which I won't comment on but to say it can also be an excellent choice too. Here I am only discussing old-school PSU's.)
My suggestion:
1. Do an LCLC (or LCRC as 6A3sUMMER suggested) supply. You probably can get away with 5Hy on the first choke (as 6A3sUMMER also suggested). Use GZ34 since your transformer has a 5V winding for the heater. You will hear the difference with choke input even if your B+ is a bit on the low side. A quick simulation using PSU-II suggests you can get around 315VDC after the 5Hy choke for an LC supply when using GZ34 and a Hammond 290CX transformer.
2. Use fixed bias. Your 290CX has a 50v secondary for negative grid bias. Fantastic! Cap couple your Mosfet follower stage to the Grid. Use an inexpensive polypropylene and foil coupling cap to start with - you will likely be pleasantly surprised. Don't forget to use a grid stopper.
3. Use DC on your heaters. If possible use a proven regulator circuit for each 300b. Use a decent wire wound 10 Ohm resistor -ve heater to ground for each 300b so you can easily measure+calculate your 300b current.
4. If your budget is constrained, don't over-spend on the OPT's. You can always upgrade them later if needed. The power supply is inherently in the audio circuit for SE builds. A fancy OPT will not fix a poorly considered PSU.
5. You can even upgrade this cap coupled amp to interstage transformer at some point if you wish. Or you can try using snake-oil boutique coupling caps - whatever floats your boat...
I have seen some fantastic looking SE 300b amps that actually sound quite mediocre. Expensive OPT's from various boutique manufacturers and fancy chassis. Every one of these fails had a poorly considered power supply. Pretty much every one started with a cap-input supply too...
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