Ok, we won’t belabor it anymore - just suffice it to say that a 4 diode bridge should be used unless there is compelling reason to use a tube rectifier. It’s just a matter of what secondary voltage to choose here. Use the 150 in series (or 300 in parallel) for 360V at load, the 275 for 340 volts, or the 250 for 310. All at a 60 watt DC load, at the first cap. If you need more accurate estimates, run it in PSUD. Personally, I would be inclined to use the 275 volt if I was buying a new trafo specifically for this. You do want some overhead for the second level RC or LC filtering, but not too much. Regulation will be better with these than with that doubler (where a 150 volt would be needed just to get the 315V at load).
That's what I thought at first, but then what's been said here and what I've read elsewhere made me doubt that.
OK, so if you use the entire secondary with the full-wave bridge (Wheatstone bridge) then you'll get the entire 500VAC * 1.414 = 707VDC, but at half the rated current capacity of the transformer. Correct?
That's a kind of voltage doubler compared to the full-wave center-tapped configuration of the same transformer.
1) If you use the 500VCT 200mA transformer as full-wave rectified with its center tap connected to ground you'll get 250VAC (half the secondary) * 1.414 = 353VDC unloaded, with 200mA load current capacity.
2) If you use that same 500VCT 200mA transformer but leave the CT disconnected, and use a full-wave bridge across the entire secondary, with negative end to ground, you'll get 707VDC unloaded, but with 100mA load current capacity.
Does everyone agree that is correct?
And... To make things simpler...
If you need to create an approximately +300VDC plate supply and you're in North America, you can use an isolation transformer designed for 230V stepdown to 115V, but wired backwards so you get 230VAC across the 'secondary'. You could use the Triad N-68X (50VA), which is available for $14.19 plus shipping.
Using a full-wave bridge across that:
230VAC * 1.414 = 311VDC unloaded, approximately 200mA load current capacity.
Triad Magnetics - N-68X - Transformer, Isolation, Bobbin, 1, Freq 50/60Hz, Pri 115/230VAC, Sec 115VAC - Allied Electronics & Automation
The Antek 280V 50VA toroid will be better, but this is cheaper.
--
If you need to create an approximately +300VDC plate supply and you're in North America, you can use an isolation transformer designed for 230V stepdown to 115V, but wired backwards so you get 230VAC across the 'secondary'. You could use the Triad N-68X (50VA), which is available for $14.19 plus shipping.
Using a full-wave bridge across that:
230VAC * 1.414 = 311VDC unloaded, approximately 200mA load current capacity.
Triad Magnetics - N-68X - Transformer, Isolation, Bobbin, 1, Freq 50/60Hz, Pri 115/230VAC, Sec 115VAC - Allied Electronics & Automation
The Antek 280V 50VA toroid will be better, but this is cheaper.
--
Having the heater windings already there is worth something too. Approximately the cost of a separate 6.3 volt transformer, to be precise. Unless you want to wrap that winding yourself on the isolation transformer.
One plus to not having the heater windings on the plate supply transformer is that there won't be any coupling of switching spikes from the plate supply to the heater windings. That's a bigger deal in a preamp, but it doesn't hurt to keep those separate if you can.
But yes, correct -- It does work out about equal if you purchase a transformer with the heater secondaries included.
But yes, correct -- It does work out about equal if you purchase a transformer with the heater secondaries included.
Or use any 120V isolation transformer with a Delon.
I use this in all of my amp designs. In my case there's a quadrupler for the front end stages, too.
I use this in all of my amp designs. In my case there's a quadrupler for the front end stages, too.
Attachments
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Search for Hammond's document gives the relations of current ratings and voltage outputs, versus different rectifier configurations, center tap, bridge, 1/2 wave, cap input filters, etc.
For a couple of examples:
1. Secondary current ratings apply for Resistive loads (real resistors).
2. A secondary with a current rating of 2 amps into a resistor; that is rectified by solid state diodes, will typically only give 1.1A or 1.2A into a Capacitor input filter.
You can get it to run more current than that, but it will get hot!
Cap input filters get DCV up to as high as 1.414 x RMS volts.
Choke input filters get DCV up to as high as 0.9 x RMS volts.
In both cases, there are losses that will make the voltage less than those numbers.
1.414 / 0.9 = 1.57.
If you need a 300VRMS secondary with a cap input filter to get the DC voltage you want, you will need a 471VRMS secondary to get the same DC voltage if you use a choke input filter . . .
. . . So why use a choke input filter???
Cooler transformer
No capacitor transient current that generates hum and high frequency noise (it can couple into the amplifier circuitry, primarily via ground loops).
But those transients couples into the filament secondary too.
You can use a secondary with a lower current rateing
Yes, there are tradeoffs to using a choke input filter
Cost
Weight
Real Estate (room)
Magnetic Spray that can transmit hum (so orient properly, and space properly)
You have to have a higher voltage secondary
Do not just count the number of advantages and disadvantages, give all factors the consideration versus what is most important to you.
For me, I use choke input filters whenever I can.
"Doctors and Lawyers are just practicing" Me too!
For a couple of examples:
1. Secondary current ratings apply for Resistive loads (real resistors).
2. A secondary with a current rating of 2 amps into a resistor; that is rectified by solid state diodes, will typically only give 1.1A or 1.2A into a Capacitor input filter.
You can get it to run more current than that, but it will get hot!
Cap input filters get DCV up to as high as 1.414 x RMS volts.
Choke input filters get DCV up to as high as 0.9 x RMS volts.
In both cases, there are losses that will make the voltage less than those numbers.
1.414 / 0.9 = 1.57.
If you need a 300VRMS secondary with a cap input filter to get the DC voltage you want, you will need a 471VRMS secondary to get the same DC voltage if you use a choke input filter . . .
. . . So why use a choke input filter???
Cooler transformer
No capacitor transient current that generates hum and high frequency noise (it can couple into the amplifier circuitry, primarily via ground loops).
But those transients couples into the filament secondary too.
You can use a secondary with a lower current rateing
Yes, there are tradeoffs to using a choke input filter
Cost
Weight
Real Estate (room)
Magnetic Spray that can transmit hum (so orient properly, and space properly)
You have to have a higher voltage secondary
Do not just count the number of advantages and disadvantages, give all factors the consideration versus what is most important to you.
For me, I use choke input filters whenever I can.
"Doctors and Lawyers are just practicing" Me too!
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to verify:
triode strapping would be just connecting the grid to the plate with a 100 ohm resistor?
should I do a separate resistor and capacitor on each cathode for the output tubes? If so, do I keep the values the same?
triode strapping would be just connecting the grid to the plate with a 100 ohm resistor?
should I do a separate resistor and capacitor on each cathode for the output tubes? If so, do I keep the values the same?
Yes, or just a piece of wire. The supressor grid (g2), not the screen grid (g1).
Shared resistor and cap as you have now is ok ; separate would better match the tubes' output if they aren't. Double the values in that case, i.e. 6v6 PP UL bias point
And to remove the feedback loop: disconnect the 1k/1000pf from the opt and tie them to ground.
Then... listen and let us know how it sounds to your ears 😉
Shared resistor and cap as you have now is ok ; separate would better match the tubes' output if they aren't. Double the values in that case, i.e. 6v6 PP UL bias point
And to remove the feedback loop: disconnect the 1k/1000pf from the opt and tie them to ground.
Then... listen and let us know how it sounds to your ears 😉
Klimon,
Your Post # 49 said:
"The supressor grid (g2), not the screen grid (g1)."
Please help me understand that statement.
Instead, I believe it is more like this:
6V6 Beam Power Tube
g1 Control Grid
g2 Screen Grid
No Suppressor Grid. Instead the Beam Formers are connected to the Cathode.
Or this:
EL34 Pentode
g1 Control Grid
g2 Screen Grid
g3 Suppressor Grid.
Your Post # 49 said:
"The supressor grid (g2), not the screen grid (g1)."
Please help me understand that statement.
Instead, I believe it is more like this:
6V6 Beam Power Tube
g1 Control Grid
g2 Screen Grid
No Suppressor Grid. Instead the Beam Formers are connected to the Cathode.
Or this:
EL34 Pentode
g1 Control Grid
g2 Screen Grid
g3 Suppressor Grid.
Apologies for reviving this thread but I had a very similar question and didn't feel it was worth starting a whole new one.
I bought on a whim for a good price a pair of Hashimoto HWC-30-8, which are 8K primary and rated for 30W and am looking for a project for them.
I'm already building an EL84 Tubelab SPP with other OPT so am not interested in another EL84.
Ideally, I can build something that is 20W-30W, since I don't think I will ever have truly high efficiency speakers. (I'm using Troels Gravesen 3WC right now).
I have many 12AX7/12AU7/12AT7, 5842, D3a, 6922/6DJ8 so would prefer to use those for the input/PI stage if possible.
Lastly, I prefer B+ below 400V.
One hurdle I have now is to know how to determine which tube would work well with an 8K OPT, meaning, what parameters do I need to look at in the datasheet to determine this?
If possible, I'd like to use 6L6-GC or EL34 in UL, or KT-88 in triode (like the Luxman MQ88-Uc), but I don't know if any of these make sense for 8K OPT.
I don't need an exact design but just a head start in which direction to start looking for existing projects.
If this makes more sense as a new thread I can do that as well. Thanks
I bought on a whim for a good price a pair of Hashimoto HWC-30-8, which are 8K primary and rated for 30W and am looking for a project for them.
I'm already building an EL84 Tubelab SPP with other OPT so am not interested in another EL84.
Ideally, I can build something that is 20W-30W, since I don't think I will ever have truly high efficiency speakers. (I'm using Troels Gravesen 3WC right now).
I have many 12AX7/12AU7/12AT7, 5842, D3a, 6922/6DJ8 so would prefer to use those for the input/PI stage if possible.
Lastly, I prefer B+ below 400V.
One hurdle I have now is to know how to determine which tube would work well with an 8K OPT, meaning, what parameters do I need to look at in the datasheet to determine this?
If possible, I'd like to use 6L6-GC or EL34 in UL, or KT-88 in triode (like the Luxman MQ88-Uc), but I don't know if any of these make sense for 8K OPT.
I don't need an exact design but just a head start in which direction to start looking for existing projects.
If this makes more sense as a new thread I can do that as well. Thanks
I built a variant of an Eico HF-89, fits your requiremet. It's a very classic schematic, no tricks, I get 28W average before clipping. The ouptut tubes 6P3S-E can be replaced by 6L6GC or 5881, or EL34 adjusting the bias.
Those Hashimoto HWC-30-8 OPTs are rated for a max plate current of 80mA per side. GU50 would normally be operated with 70 to 100mA plate current per tube. If the OPTs can take that then GU50 would work. 8k primary would be just about perfect for a pair of GU50, either in pentode with no more than 300V on the screen grids, or triode at up to 400V plate-cathode. UL is not how I'd use GU50s, as you'd want to use them with at least 400V on the plates, and that would be too high voltage for their screens. But in the end I think the problem is that you'll be using the OPTs at the limit of their current capabilities.
KT88 is also a big tube that would typically be used with high-ish plate currents. Something like 400V and 75 to 90mA per tube. KT88 has robust screen grids that can take 400V. But again, there's that 80mA per side limitation of the HWC-30-8 OPTs.
How about a nice push-pull triode amp? Perhaps push-pull EL34 with 400V plate-cathode and 50mA per tube? You'd get about 10 to 13W per channel out, mostly class A operation. If you use 6P3S-E or 6L6GC instead, you'd get less power, but they would also work well in triode into an 8k primary. While EL34 and 6L6-oids in PP pentode or UL are usually used with 5k to 6.6k primaries, 8k is perfect for them in triode mode.
There's also PP 6V6 pentode or UL with a 320V B+. 8k would be good for that. PP 6V6 should get you 10W UL or 15W pentode.
Just a thought. The problem with triode-wired EL34 or 6L6, or 6V6 in pentode or UL is that you do get less power out of them.
KT88 is also a big tube that would typically be used with high-ish plate currents. Something like 400V and 75 to 90mA per tube. KT88 has robust screen grids that can take 400V. But again, there's that 80mA per side limitation of the HWC-30-8 OPTs.
How about a nice push-pull triode amp? Perhaps push-pull EL34 with 400V plate-cathode and 50mA per tube? You'd get about 10 to 13W per channel out, mostly class A operation. If you use 6P3S-E or 6L6GC instead, you'd get less power, but they would also work well in triode into an 8k primary. While EL34 and 6L6-oids in PP pentode or UL are usually used with 5k to 6.6k primaries, 8k is perfect for them in triode mode.
There's also PP 6V6 pentode or UL with a 320V B+. 8k would be good for that. PP 6V6 should get you 10W UL or 15W pentode.
Just a thought. The problem with triode-wired EL34 or 6L6, or 6V6 in pentode or UL is that you do get less power out of them.
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Thanks for the thoughts... I'll take some time to look into these options.
I have some projects I need to finish first, I just wanted to get a head start on the overall direction for what I can do with the HWC-30-8.
Those projects include a TU-8200R and Tubelab SPP.
The TU-8200 should be about 8W with 6L6-GC in UL.
For the SPP, I have custom Sowter OPT with 25% UL winding, which based on the Mullard datasheet should provide around 14-15W...
The 6V6 or triode EL34/6L6 is interesting but at 10-13W, I wouldn't gain much in terms of power, but are there other advantages?
For example, with the EL34 in triode, is the damping factor improved over the EL84 UL?
I have some projects I need to finish first, I just wanted to get a head start on the overall direction for what I can do with the HWC-30-8.
Those projects include a TU-8200R and Tubelab SPP.
The TU-8200 should be about 8W with 6L6-GC in UL.
For the SPP, I have custom Sowter OPT with 25% UL winding, which based on the Mullard datasheet should provide around 14-15W...
The 6V6 or triode EL34/6L6 is interesting but at 10-13W, I wouldn't gain much in terms of power, but are there other advantages?
For example, with the EL34 in triode, is the damping factor improved over the EL84 UL?
Yes, I know exactly what you mean. There are so many ways to build a good 10W per channel tube amp, from Tubelab SPP, Baby Huey, Bevois Valley, Dyna ST35 using PP EL84, or Williamson 6L6-triode amplifiers. Then there are lots of designs that make about 20W per channel like the Dynaco ST70, Eico ST70, Mullard 5-20, etc. But 50Wpc? Things get much more expensive, big and heavy.
Maybe you'd enjoy a PP Triode amp that uses no or very little global negative feedback, to try out a different flavor?
BTW, the difference between 10W and 20W is really not much. I think you'd need to bump up to >40W to actually hear a major difference in volume capability.
The downside is that an 8k primary OPT capable of >50W is harder to make than an 8k ohm 20W-capable OPT. That means the 50W transformer is going to be more expensive and perhaps not sound as nice in the end.
Tubes and tube amp output transformers have to work within major limitations.
Big power from tubes requires a lot of effort and money.
https://www.diyaudio.com/community/threads/gu-50-pp-amp-project-any-favs.164165/
https://www.diyaudio.com/community/threads/pyramid-ix-monoblock-200w-from-4x-gu-50.224306/
Maybe you'd enjoy a PP Triode amp that uses no or very little global negative feedback, to try out a different flavor?
BTW, the difference between 10W and 20W is really not much. I think you'd need to bump up to >40W to actually hear a major difference in volume capability.
The downside is that an 8k primary OPT capable of >50W is harder to make than an 8k ohm 20W-capable OPT. That means the 50W transformer is going to be more expensive and perhaps not sound as nice in the end.
Tubes and tube amp output transformers have to work within major limitations.
Big power from tubes requires a lot of effort and money.
https://www.diyaudio.com/community/threads/gu-50-pp-amp-project-any-favs.164165/
https://www.diyaudio.com/community/threads/pyramid-ix-monoblock-200w-from-4x-gu-50.224306/
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itsikhefez,
1. If you have a digital oscilloscope, then do this for a week of listening to your stereo.
Set your scope to Infinite persistence mode (shows the total history of the signal, so you can see the maximum + and maximum - voltage over time, Vpeak + and Vpeak -),
And connect the probe at your amplifier output (to your speaker input).
Given an 8 Ohm actual load impedance, the power is Vpeak squared / (8 x 2) = Watts
Why do this? To get an estimate of how much amplifier power you might need.
2. If your Hashimoto does not have UL taps, you should not plan to add all the extra complex circuitry required to make the amplifier be UL.
Does the Hashimoto only have an 8 Ohm output tap?
A 6 Ohm speaker on it will make the primary 8000 (6/8) = 6000 Ohms
Many 8 Ohm speakers have minimum impedance of 6 Ohms, and some models as low as 4 Ohm minimum impedance.
Take a DMM, and read the DCR of your loudspeaker, the AC impedance of the speaker will be that low at one or more frequency areas.
Think of the complete stereo as a system. No one part of it is used in isolation from the other parts.
Design for output power. Design for Finesse. Design for looks. Only you know.
Have fun designing, building, and listening!
1. If you have a digital oscilloscope, then do this for a week of listening to your stereo.
Set your scope to Infinite persistence mode (shows the total history of the signal, so you can see the maximum + and maximum - voltage over time, Vpeak + and Vpeak -),
And connect the probe at your amplifier output (to your speaker input).
Given an 8 Ohm actual load impedance, the power is Vpeak squared / (8 x 2) = Watts
Why do this? To get an estimate of how much amplifier power you might need.
2. If your Hashimoto does not have UL taps, you should not plan to add all the extra complex circuitry required to make the amplifier be UL.
Does the Hashimoto only have an 8 Ohm output tap?
A 6 Ohm speaker on it will make the primary 8000 (6/8) = 6000 Ohms
Many 8 Ohm speakers have minimum impedance of 6 Ohms, and some models as low as 4 Ohm minimum impedance.
Take a DMM, and read the DCR of your loudspeaker, the AC impedance of the speaker will be that low at one or more frequency areas.
Think of the complete stereo as a system. No one part of it is used in isolation from the other parts.
Design for output power. Design for Finesse. Design for looks. Only you know.
Have fun designing, building, and listening!