Hi Rod Coleman!
where do you go now?? i like meet you!
What about the Filament for DHT??
Thank you!
where do you go now?? i like meet you!
What about the Filament for DHT??
Thank you!
Hi QuangHao, New Version of Heater PCBs are being fabricated now. They will be here next week, and made available shortly after.
The new PCB is built around the circuit used since 2004, and preferred by most amp builders that tried it, compared to other heating methods.
I wanted to add a voltage-servo, to adjust current until the filament voltage achieves rated value (eg 5V for 300B). But listening test showed it was clearly audible, degrading the current drive sound! So that has gone.
The new PCB is now only 79 x 21mm (see attached dimensioned drawing).
Compared to the previous circuit, the ripple rejection is much improved, and a sealed cermet multiturn trimmer added, to fine tune the current.
But most of all, you get open, articulate current-drive DHT sound.
The new PCB is built around the circuit used since 2004, and preferred by most amp builders that tried it, compared to other heating methods.
I wanted to add a voltage-servo, to adjust current until the filament voltage achieves rated value (eg 5V for 300B). But listening test showed it was clearly audible, degrading the current drive sound! So that has gone.
The new PCB is now only 79 x 21mm (see attached dimensioned drawing).
Compared to the previous circuit, the ripple rejection is much improved, and a sealed cermet multiturn trimmer added, to fine tune the current.
But most of all, you get open, articulate current-drive DHT sound.
Attachments
Hi Rod,
Might as well put me down for a couple as well.. Seems like an elegant solution to use in my next transformer coupled 26 PRE..
Kevin
Might as well put me down for a couple as well.. Seems like an elegant solution to use in my next transformer coupled 26 PRE..
Kevin
Thanks Kevin! The higher ripple rejection & noise filtering should be just the thing for the #26.
I'm planning a configuration (with this PCB) that normally drives 250mA filaments (00A, 01A, 3A/109B, 4021 etc), but increases current to #26 level (1.05A) when a jumper (PC motherboard type) is attached. Like a 'Guest Mode', where a 26 comes to stay when you want a change from the Resident DHT!
I'm planning a configuration (with this PCB) that normally drives 250mA filaments (00A, 01A, 3A/109B, 4021 etc), but increases current to #26 level (1.05A) when a jumper (PC motherboard type) is attached. Like a 'Guest Mode', where a 26 comes to stay when you want a change from the Resident DHT!
This is exactly what I need as it will allow for easy swaps between my reference 26, and the 12/112(A), 01A that I also want to run in the next version of my pre.. I have a circuit, but I'd rather use yours as it seems rather better thought out and is the result of a lot of study whereas mine is just... textbook..
Kevin
Hello Rod,
I'd like to order 4 of them please. If you ever do a PP version, I'd like a couple of them as well. I assume I can use these single tube boards in pairs for a PP amp channel.
Thanks,
John
I'd like to order 4 of them please. If you ever do a PP version, I'd like a couple of them as well. I assume I can use these single tube boards in pairs for a PP amp channel.
Thanks,
John
I am in. How many? It depends, 2 boards, most probably 4. Rod what is the max current/power those puppies can handle?
Hello,
I'd like 4 boards, if you don't mind. Is there a chance you'd offer a complete kit of parts?
Regards,
David
I'd like 4 boards, if you don't mind. Is there a chance you'd offer a complete kit of parts?
Regards,
David
hello David, I prefer to ship with all parts as a kit - the performance depends greatly on using certain Japanese transistors. The MJE150xx series and the like really degrade the ripple-rejection and low-voltage control.
I'll probably offer them assembled too, if anyone prefers that way.
hello Gianluca, I am testing at current up to 3A now, so GM70 (20V 3A) is a standard build, no problem.
Higher power is possible - let me know the tube & I'll work out how big the heatsink has to be!!
Hi Rod
I am interested in GM70 ( 20v 3A) and 75tl (5V 6.25A). I would also like it as a kit,if possible.
Regards,
Mark
I am interested in GM70 ( 20v 3A) and 75tl (5V 6.25A). I would also like it as a kit,if possible.
Regards,
Mark
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Joined 2009
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This is a big red flag for me - I'd like to use them with 6C4C, but I'm wondering whether your approach has enough design margin with respect to the parts used. I want to know that the amplifier is repairable in the future without being reliant on hard to find parts (except the bottles of course!) ???