Hi Everyone,
I just received a new pair of 9.5K primary OPTs from Muse Coils. First of all, as you know from my prior posts, Muse Coils iron is first rate. Unbelievable quality. These OPTs were made specifically for GM70s. I am pursuing a new design and have a few questions
1. What do you think about a B+ in the 500-600V range? Too low? Any adverse impact sonically?
2. anyone running excessively starved filaments on a GM70? I am thinking about 10-20% starved. In reading Steve Bench's article, this reduces distortion considerably, but I am not sure if the tube's life would be reduced or power output be reduced with starved filaments.
3. Any thoughts on a driver that you like? I have a couple of options regarding input 1) 2Vrms from the DAC or 2) 2Vrms from DAC then running thru a 600:15K input transformer. Either of these input choices would feed the driver tube.
Thanks! Pat
I just received a new pair of 9.5K primary OPTs from Muse Coils. First of all, as you know from my prior posts, Muse Coils iron is first rate. Unbelievable quality. These OPTs were made specifically for GM70s. I am pursuing a new design and have a few questions
1. What do you think about a B+ in the 500-600V range? Too low? Any adverse impact sonically?
2. anyone running excessively starved filaments on a GM70? I am thinking about 10-20% starved. In reading Steve Bench's article, this reduces distortion considerably, but I am not sure if the tube's life would be reduced or power output be reduced with starved filaments.
3. Any thoughts on a driver that you like? I have a couple of options regarding input 1) 2Vrms from the DAC or 2) 2Vrms from DAC then running thru a 600:15K input transformer. Either of these input choices would feed the driver tube.
Thanks! Pat
Looks like you could expect 5-6W in class A1 and quite a bit more if the grid is pushed into class A2.
Rather 3-4W in A1 (600V, 100mA), than 5-6W.
About 7W at +20V grid peek.
If you use such low anode voltage, the output impedance of tube is 2k..2k2 so even 5-6k OPT is usable (with little bit higher distortion).
1.) IMHO higher anode voltage (850-900V, 100mA, 9-10k OPT) is more practicable (about 8W in A1, 16W at +20V).
2.) Starved filament for power tube? Why?
3.) Driver (two stage, even with SF/CF).
If you use high/er/ Ua, higher negative bias for 100-120mA op. point, you need even 180-220Vpp grid swing.
220Vpp requires 110Vp/2.828Vp gain, about 39x, which is about 32dB.
With 2dB headroom, at least 50x gain requiring.
Primarily I like high gm trioded pentode.
D3a (E280F, E180F), C3g, 6E5P etc.
About 7W at +20V grid peek.
If you use such low anode voltage, the output impedance of tube is 2k..2k2 so even 5-6k OPT is usable (with little bit higher distortion).
1.) IMHO higher anode voltage (850-900V, 100mA, 9-10k OPT) is more practicable (about 8W in A1, 16W at +20V).
2.) Starved filament for power tube? Why?
3.) Driver (two stage, even with SF/CF).
If you use high/er/ Ua, higher negative bias for 100-120mA op. point, you need even 180-220Vpp grid swing.
220Vpp requires 110Vp/2.828Vp gain, about 39x, which is about 32dB.
With 2dB headroom, at least 50x gain requiring.
Primarily I like high gm trioded pentode.
D3a (E280F, E180F), C3g, 6E5P etc.
Hi Pat,
You cannot expect high power output with a B+ of 500-600 Vdc on a GM70 and 9.5k primary impedance.
From my recollection, you had a 800V CT capable power transformer. You could increase the voltage by slightly changing from choke input to capacitor input. Use PSUD2 to fine-tune the necessary value.
Here's a 10k loadline, where you can expect ~ 22W into A1 for 100mA bias. You can safely bias these transformers into 100mA, they have flux density headroom and will give you 1.5T @ 25W @ 25Hz
No need to starve the filaments IMHO.
You cannot expect high power output with a B+ of 500-600 Vdc on a GM70 and 9.5k primary impedance.
From my recollection, you had a 800V CT capable power transformer. You could increase the voltage by slightly changing from choke input to capacitor input. Use PSUD2 to fine-tune the necessary value.
Here's a 10k loadline, where you can expect ~ 22W into A1 for 100mA bias. You can safely bias these transformers into 100mA, they have flux density headroom and will give you 1.5T @ 25W @ 25Hz
No need to starve the filaments IMHO.
I never heard of Muse Coils and went to check out their site. Impressive looking products but no information. No location, no price, no specs, nothing.
@astouffer
I take personal responsibility for the contents of the Muse Coils site. It needs to be updated for sure. Consider its looks as beta version. However I am currently working on the future scientific, philosophical content and product list. It was launched with the primary intent of offering and developing transformers with unique requirements by customers, hence the reason of no price list and standardized products, as I offer a huge variety between parameters, building materials, core and wire choices, etc. I am currently a low-scale manufacturer and cannot afford to keep in stock a huge diversity standardized products. Purchase was and still done by communication contact form and specs are specifically measured and sent for each unique product.
My products are also based on the choice of materials related to the sound quality of devices, which is heavily considered as snake oil by the majority of audio enthusiasts, and is research that I'm currently working on, gathering data, and publications with measurements will have to be included on the website as well.
In the future, you can expect a few, I'm aiming for 2-3 standardized products maximum as a start, aiming at products with unique features with no market analogue. Probably available as both low-cost and boutique versions simultaneously.
There is an attached datasheet of a product from my portfolio. The datasheet lacks a few important things, such as footprint, size and weight. These will also be added in the future.
I take personal responsibility for the contents of the Muse Coils site. It needs to be updated for sure. Consider its looks as beta version. However I am currently working on the future scientific, philosophical content and product list. It was launched with the primary intent of offering and developing transformers with unique requirements by customers, hence the reason of no price list and standardized products, as I offer a huge variety between parameters, building materials, core and wire choices, etc. I am currently a low-scale manufacturer and cannot afford to keep in stock a huge diversity standardized products. Purchase was and still done by communication contact form and specs are specifically measured and sent for each unique product.
My products are also based on the choice of materials related to the sound quality of devices, which is heavily considered as snake oil by the majority of audio enthusiasts, and is research that I'm currently working on, gathering data, and publications with measurements will have to be included on the website as well.
In the future, you can expect a few, I'm aiming for 2-3 standardized products maximum as a start, aiming at products with unique features with no market analogue. Probably available as both low-cost and boutique versions simultaneously.
There is an attached datasheet of a product from my portfolio. The datasheet lacks a few important things, such as footprint, size and weight. These will also be added in the future.
As others have pointed out, low plate voltage with that transformer is not great idea.
In my opinion it's not a great idea in general because lots of electricity is going to be wasted for little return. The GM70 requires almost 2x the filament power of the 845/211.
IMHO, you either go for the full potato with 1KV+ anode voltage or find a 5K transformer to get at least 8W or so.
GM-70 ... I tested A LOT with them and I love those tubes and they really show their true potential at 1200VDC 80mA. Simply and truly amazing sound.
