This OPT https://primarywindings.com/product/500 ... ansformer/ has 100mA DC current at the primary - any good? Quiescent Ia = 63mA and the theoretical peak - point (A) on the chart is 133mA. I would expect some heat to be generated but the tube is unlikely to ever reach that peak. It would take some really heavy sustained overdrive to get it there!
The 20W output is overkill but regarding that bandwidth, if the manufacturers claims are true it has a much better low end response than the Hammond. A 15Hz roll-off versus a 100Hz roll-off if I remember it well.
What's your experience there? I heard about them through Merlin's website. They look good on paper at least!
Excellent to deal with, helpful and good value transformers. I got the multi tap PT as well for the 3 levels of B+. EL34 SE is loud at the full B+, but more importantly sounds great.
I'm in England so it was very easy for me to buy. I miss the old days of USA Classictone and even MM at not bad prices, even with shipping and taxes.
What's your experience there? I heard about them through Merlin's website. They look good on paper at least!
Excellent to deal with, helpful and good value transformers. I got the multi tap PT as well for the 3 levels of B+. EL34 SE is loud at the full B+, but more importantly sounds great.
I'm in England so it was very easy for me to buy. I miss the old days of USA Classictone and even MM at not bad prices, even with shipping and taxes.
You had me at "sounds great"! I'm here in the Czech Republic - an expat. as English as fish and chips. No reason to think they have struggled with Brexit though, the European shipping rates look okay. As far as the going rates go, they are one of the more reasonably priced suppliers. MM - fuggedaboudit!
What's your experience there? I heard about them through Merlin's website. They look good on paper at least!
Excellent to deal with, helpful and good value transformers. I got the multi tap PT as well for the 3 levels of B+. EL34 SE is loud at the full B+, but more importantly sounds great.
I'm in England so it was very easy for me to buy. I miss the old days of USA Classictone and even MM at not bad prices, even with shipping and taxes.
You had me at "sounds great"! I'm here in the Czech Republic - an expat. as English as fish and chips. No reason to think they have struggled with Brexit though, the European shipping rates look okay. As far as the going rates go, they are one of the more reasonably priced suppliers. MM - fuggedaboudit!
Your OPT with a 3k primary scares me as the EL34 has an output Z closer to 5k according to my calculations. Still, if it works
Yes that's the PT. When you look at all tyne calculations for primary load, 5k would be ideal, but running at higher plate v and using 16r speaker would bring that to nearer 3k.
FWIW I'm using a NOS Siemens EL34 and a 4r speaker off the 4 r tap. Nothing gets hot even after hours. I can't remember the plate voltage offhand but it's high with bridge diode recto.
I just went 5F2A and tweaked cathode resistor and screen/ grid to suit SE EL34. There's plenty of examples such as AX84 and RJ's Eagle.
I have since added a simple MV to control pedal input levels.
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rogb wrote: ↑Wed Jun 21, 2023 2:00 pm
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Excellent to deal with, helpful and good value transformers. I got the multi tap PT as well for the 3 levels of B+. EL34 SE is loud at the full B+, but more importantly sounds great.
I'm in England so it was very easy for me to buy. I miss the old days of USA Classictone and even MM at not bad prices, even with shipping and taxes.
You had me at "sounds great"! I'm here in the Czech Republic - an expat. as English as fish and chips. No reason to think they have struggled with Brexit though, the European shipping rates look okay. As far as the going rates go, they are one of the more reasonably priced suppliers. MM - fuggedaboudit!
Your OPT with a 3k primary scares me as the EL34 has an output Z closer to 5k according to my calculations. Still, if it works
Yes that's the PT. When you look at all tyne calculations for primary load, 5k would be ideal, but running at higher plate v and using 16r speaker would bring that to nearer 3k.
FWIW I'm using a NOS Siemens EL34 and a 4r speaker off the 4 r tap. Nothing gets hot even after hours. I can't remember the plate voltage offhand but it's high with bridge diode recto.
I just went 5F2A and tweaked cathode resistor and screen/ grid to suit SE EL34. There's plenty of examples such as AX84 and RJ's Eagle.
I have since added a simple MV to control pedal input levels.
20230428_175424.jpg20230428_161720.jpg
I've just been reading the London Power page on power scaling https://londonpower.com/power-scaling-faq. It looks very interesting. I was looking at the same PT but I hadn't thought about the power scaling possibilities. In your bottom image, I think I see your rotary switch for B+ on the right. It's a neat looking build you have there. I think Primary Windings designed this PT for solid-state rectification (there isn't a separate coil tap for a tube rectifier) and so the voltages they mention are probably pretty close to yours: 360V/260V/115V - full, half and 1/10th power. Is 1/10th power really that usable? Now that you brought it up though, it sounds like a really good idea to include.
I imagine your preamp is more or less 5F2A topology but the possibilities are very broad here. Something I want to include is a harp channel and I've been talking with a guy in Germany about a collaboration on this build. I'm not sure he would want me to identify him by name, but here's his website: https://harpamps.de/en/home.html.
Lots of ideas are just floating around in my noggin at the moment but it's encouraging to hear about the performance of the OT with your build and I think I could get away with the 3k5, 10W OT that Primary Windings offers: https://primarywindings.com/product/kt88_10w/ . The differences between yours and mine are likely not that significant. Most of the time the amp isn't going to be anywhere near its peak output.
You had me at "sounds great"! I'm here in the Czech Republic - an expat. as English as fish and chips. No reason to think they have struggled with Brexit though, the European shipping rates look okay. As far as the going rates go, they are one of the more reasonably priced suppliers. MM - fuggedaboudit!
Your OPT with a 3k primary scares me as the EL34 has an output Z closer to 5k according to my calculations. Still, if it works
Yes that's the PT. When you look at all tyne calculations for primary load, 5k would be ideal, but running at higher plate v and using 16r speaker would bring that to nearer 3k.
FWIW I'm using a NOS Siemens EL34 and a 4r speaker off the 4 r tap. Nothing gets hot even after hours. I can't remember the plate voltage offhand but it's high with bridge diode recto.
I just went 5F2A and tweaked cathode resistor and screen/ grid to suit SE EL34. There's plenty of examples such as AX84 and RJ's Eagle.
I have since added a simple MV to control pedal input levels.
20230428_175424.jpg20230428_161720.jpg
I've just been reading the London Power page on power scaling https://londonpower.com/power-scaling-faq. It looks very interesting. I was looking at the same PT but I hadn't thought about the power scaling possibilities. In your bottom image, I think I see your rotary switch for B+ on the right. It's a neat looking build you have there. I think Primary Windings designed this PT for solid-state rectification (there isn't a separate coil tap for a tube rectifier) and so the voltages they mention are probably pretty close to yours: 360V/260V/115V - full, half and 1/10th power. Is 1/10th power really that usable? Now that you brought it up though, it sounds like a really good idea to include.
I imagine your preamp is more or less 5F2A topology but the possibilities are very broad here. Something I want to include is a harp channel and I've been talking with a guy in Germany about a collaboration on this build. I'm not sure he would want me to identify him by name, but here's his website: https://harpamps.de/en/home.html.
Lots of ideas are just floating around in my noggin at the moment but it's encouraging to hear about the performance of the OT with your build and I think I could get away with the 3k5, 10W OT that Primary Windings offers: https://primarywindings.com/product/kt88_10w/ . The differences between yours and mine are likely not that significant. Most of the time the amp isn't going to be anywhere near its peak output.
Nice build Rog - thanks for sharing.
My first ever build was an Ampmaker SE from Barry. His transformers were made by Primary Windings.
1/10th power is pretty handy at home but really I use the full power and dial it in with MV.
Yes that's the PT. When you look at all tyne calculations for primary load, 5k would be ideal, but running at higher plate v and using 16r speaker would bring that to nearer 3k.
FWIW I'm using a NOS Siemens EL34 and a 4r speaker off the 4 r tap. Nothing gets hot even after hours. I can't remember the plate voltage offhand but it's high with bridge diode recto.
I just went 5F2A and tweaked cathode resistor and screen/ grid to suit SE EL34. There's plenty of examples such as AX84 and RJ's Eagle.
I have since added a simple MV to control pedal input levels.
20230428_175424.jpg20230428_161720.jpg
I've just been reading the London Power page on power scaling https://londonpower.com/power-scaling-faq. It looks very interesting. I was looking at the same PT but I hadn't thought about the power scaling possibilities. In your bottom image, I think I see your rotary switch for B+ on the right. It's a neat looking build you have there. I think Primary Windings designed this PT for solid-state rectification (there isn't a separate coil tap for a tube rectifier) and so the voltages they mention are probably pretty close to yours: 360V/260V/115V - full, half and 1/10th power. Is 1/10th power really that usable? Now that you brought it up though, it sounds like a really good idea to include.
I imagine your preamp is more or less 5F2A topology but the possibilities are very broad here. Something I want to include is a harp channel and I've been talking with a guy in Germany about a collaboration on this build. I'm not sure he would want me to identify him by name, but here's his website: https://harpamps.de/en/home.html.
Lots of ideas are just floating around in my noggin at the moment but it's encouraging to hear about the performance of the OT with your build and I think I could get away with the 3k5, 10W OT that Primary Windings offers: https://primarywindings.com/product/kt88_10w/ . The differences between yours and mine are likely not that significant. Most of the time the amp isn't going to be anywhere near its peak output.
Nice build Rog - thanks for sharing.
My first ever build was an Ampmaker SE from Barry. His transformers were made by Primary Windings.
1/10th power is pretty handy at home but really I use the full power and dial it in with MV.
I'm ashamed to say I don't know who Barry is but he seems like a man with impeccable taste. I love what you have done with your design. I hope I won't disappoint you with mine.
What's your experience there? I heard about them through Merlin's website. They look good on paper at least!
Excellent to deal with, helpful and good value transformers. I got the multi tap PT as well for the 3 levels of B+. EL34 SE is loud at the full B+, but more importantly sounds great.
I'm in England so it was very easy for me to buy. I miss the old days of USA Classictone and even MM at not bad prices, even with shipping and taxes.
Hi Rog/anyone else who can elucidate...
I'm getting very busy now as my day job kicks in, so naturally, it's time to resurrect this project!
A question is whether the tremolo circuit would have enough juice to drive it if we dropped the voltage to both the preamp section and the power section, and a possible solution is to scale the power only for the power tube but leave the preamp plates at their full voltage. I am interested in how you scaled the power to your amp, was it the full preamp and power amp sections, or did you limit it to scaling the power at the power section only? Supro have obviously managed it so that the tremolo is operational at its 5W setting - it has three: 1W/5W and 15W using a 6L6. However, I've not been able to find any comments about its usefulness of the tremolo at the lowest (1W) power setting. As I understand it, at the lower voltages, the low voltage may not be enough to drive the tremolo circuit. Really, just curious about how you would implement the tremolo with the power scaling offered by the multi-tap PT.
