01A question - Page 50

gerrittube · 14th January 2021, 05:25 PM

The STF3LN80K5 MOSFET is indeed a great MOSFET for a tube driver stage. It’s a great MOSFET for a concertina too, as many people don’t know yet.

Regards, Gerrit

nashbap · 21st January 2021, 01:50 AM

Hello Everyone,

I have decided to take the plunge into tubes and build a 01A preamp using Ale's Gyrator and Rod Coleman regs. Would appreciate advice on a few questions:

1)I plan on using one B+ supply to feed both channels with no Salas SSHV2 regs. I also plan on utilizing the B+ supply for powering the Source Follower as outlined in Ale's low gain 01A version 6 schematic. What ma draw should I plan for? If the SF is CCS biased at 10ma and the tube around 5 ma can one assume that the total draw for each channel is under 20ma, considering some losses here and there?
2)Given that I plan on building the PSU in a separate box with a 1 meter umbilical to the amp do I need to use a decoupling cap for the B+ at the entry to the gyrator or at the SF? And if so what value?
3)It looks like most recommend the Russian FT3 0.22uf for the output cap? What brand seems to work best for the gyrator cap?
4)Any suppliers of CX301A that folks are happy with? Do I look for tubes that are claimed to have been matched on the tube tester?

Thanks.

nash

mcandmar · 21st January 2021, 02:04 AM

3) Depends on the input impedance of your amplifier. Into a 47k load i settled on .47uf in my build to get the desired low frequency response. Have a play here and see what works for your application RC High-pass Filter Design Tool

I used a K72P Russian Teflon capacitor for the .47uf, and a .1uf FT-2 on the Gyrator board.

4) My advice, buy the cheapest set you can find for building and testing. They are super fragile, i have had a bunch of them die with broken filaments when shipping, and had a couple let go after repeated power on/off's while testing. When you have it all dialled, buy a nice set of matched tubes.

euro21 · 21st January 2021, 07:48 AM

1)
Yes, using one B+ is good solution..... if you use CCS or "gyrator" as 01a anode load. These are high PSRR devices.
Else you must to use complex PSU with low ripple and hum.

SF and CCS or gyrator loaded VAS stage practically independent of the B+ voltage (if it as great as B+= anode voltage + swing peek + 30...40V).

2.)
I use there 47uF // 100nF.

3)
I use in these devices teflon FT3 // V-Cap or V-Cap or Duelund.
The order of quality is the same ... but price expands to the sky. :-(

Rod Coleman · 21st January 2021, 08:44 AM

hi Nash, Any transistor follower (valve follower too, I suspect) needs good supply decoupling.

The decoupling should be right on the drain of the FET, for best control of oscillation risk. The idea is to prevent any part of the supply wiring from thinking about looking inductive enough to form a resonance with stray capacitance.

With FETs, the oscillations can reach 10MHz or more, so a stacked-construction film capacitor is worth seeking out - these have low inductance. 100nF - 220nF.
Add an electrolytic 47-100µF.

nashbap · 21st January 2021, 03:08 PM

Thank you Mark, Bela and Rod for your suggestions.

I took a another look at Ale's 01A version 6. I missed seeing the decoupling caps C1 and C2. My apologies. Rod, I found one stacked film cap thru a Mouser search. Is this appropriate, in // with an electrolyte as suggested?

F612JQ104K250C KEMET | Mouser

Regarding the B+ supply, I was thinking of using this PCB with a MEC. The MEC50 is good for 50ma while the MEC100 for 100ma; which is why I inquired about the maximum current draw from the B+ supply.

MEC Power SUpply

Has anyone used these? Any thoughts?

nash

Rod Coleman · 21st January 2021, 03:26 PM

F612JQ104K250C KEMET | Mouser

Yes, that's a stacked-construction part - will work very well.

nashbap · 21st January 2021, 03:30 PM

Great! Thank you.

mcandmar · 21st January 2021, 07:22 PM

Theory question: I am using Ales Gyrator boards and Coleman filament regulators with cathode bias. What is more important to match, bias voltage or plate voltage?

euro21 · 21st January 2021, 08:38 PM

Anode voltage and bias voltage determines operating point (Ua, Ia at -Vg) ... at specified tube and at given condition.

If the tube changing (another tube, or aging), the operating point also changing.

There are no two identical operating point of two tubes, but if it not too far -relative to each other-, it's irrelevant.

The important thing is tubes gain -preferably- similarity at near operating points.

21st January 2021, 01:50 AM	#492
nashbap diyAudio Member Join Date: Jul 2012 Location: New Jersey USA	Hello Everyone, I have decided to take the plunge into tubes and build a 01A preamp using Ale's Gyrator and Rod Coleman regs. Would appreciate advice on a few questions: 1)I plan on using one B+ supply to feed both channels with no Salas SSHV2 regs. I also plan on utilizing the B+ supply for powering the Source Follower as outlined in Ale's low gain 01A version 6 schematic. What ma draw should I plan for? If the SF is CCS biased at 10ma and the tube around 5 ma can one assume that the total draw for each channel is under 20ma, considering some losses here and there? 2)Given that I plan on building the PSU in a separate box with a 1 meter umbilical to the amp do I need to use a decoupling cap for the B+ at the entry to the gyrator or at the SF? And if so what value? 3)It looks like most recommend the Russian FT3 0.22uf for the output cap? What brand seems to work best for the gyrator cap? 4)Any suppliers of CX301A that folks are happy with? Do I look for tubes that are claimed to have been matched on the tube tester? Thanks. nash __________________ F5TV3, AVC, BA3b pre, Salas DCG3b, OBL-15, SonyVfet2pair monos, Millett Nutube Bal pre

21st January 2021, 03:08 PM	#496
nashbap diyAudio Member Join Date: Jul 2012 Location: New Jersey USA	Thank you Mark, Bela and Rod for your suggestions. I took a another look at Ale's 01A version 6. I missed seeing the decoupling caps C1 and C2. My apologies. Rod, I found one stacked film cap thru a Mouser search. Is this appropriate, in // with an electrolyte as suggested? F612JQ104K250C KEMET \| Mouser Regarding the B+ supply, I was thinking of using this PCB with a MEC. The MEC50 is good for 50ma while the MEC100 for 100ma; which is why I inquired about the maximum current draw from the B+ supply. MEC Power SUpply Has anyone used these? Any thoughts? nash __________________ F5TV3, AVC, BA3b pre, Salas DCG3b, OBL-15, SonyVfet2pair monos, Millett Nutube Bal pre

21st January 2021, 03:30 PM	#498
nashbap diyAudio Member Join Date: Jul 2012 Location: New Jersey USA	Great! Thank you. __________________ F5TV3, AVC, BA3b pre, Salas DCG3b, OBL-15, SonyVfet2pair monos, Millett Nutube Bal pre

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14th January 2021, 05:25 PM	#491
gerrittube diyAudio Member Join Date: Jan 2018 Location: Holten	The STF3LN80K5 MOSFET is indeed a great MOSFET for a tube driver stage. It’s a great MOSFET for a concertina too, as many people don’t know yet. Regards, Gerrit

21st January 2021, 02:04 AM	#493
mcandmar diyAudio Member Join Date: Feb 2012 Location: Dublin	3) Depends on the input impedance of your amplifier. Into a 47k load i settled on .47uf in my build to get the desired low frequency response. Have a play here and see what works for your application RC High-pass Filter Design Tool I used a K72P Russian Teflon capacitor for the .47uf, and a .1uf FT-2 on the Gyrator board. 4) My advice, buy the cheapest set you can find for building and testing. They are super fragile, i have had a bunch of them die with broken filaments when shipping, and had a couple let go after repeated power on/off's while testing. When you have it all dialled, buy a nice set of matched tubes.

21st January 2021, 07:48 AM	#494
euro21 diyAudio Member Join Date: Sep 2004 Location: Budapest	1) Yes, using one B+ is good solution..... if you use CCS or "gyrator" as 01a anode load. These are high PSRR devices. Else you must to use complex PSU with low ripple and hum. SF and CCS or gyrator loaded VAS stage practically independent of the B+ voltage (if it as great as B+= anode voltage + swing peek + 30...40V). 2.) I use there 47uF // 100nF. 3) I use in these devices teflon FT3 // V-Cap or V-Cap or Duelund. The order of quality is the same ... but price expands to the sky. :-(

21st January 2021, 08:44 AM	#495
Rod Coleman садовник diyAudio Member Join Date: Jul 2004 Location: Warwickshire UK	hi Nash, Any transistor follower (valve follower too, I suspect) needs good supply decoupling. The decoupling should be right on the drain of the FET, for best control of oscillation risk. The idea is to prevent any part of the supply wiring from thinking about looking inductive enough to form a resonance with stray capacitance. With FETs, the oscillations can reach 10MHz or more, so a stacked-construction film capacitor is worth seeking out - these have low inductance. 100nF - 220nF. Add an electrolytic 47-100µF.

21st January 2021, 03:26 PM	#497
Rod Coleman садовник diyAudio Member Join Date: Jul 2004 Location: Warwickshire UK	F612JQ104K250C KEMET \| Mouser Yes, that's a stacked-construction part - will work very well.

21st January 2021, 07:22 PM	#499
mcandmar diyAudio Member Join Date: Feb 2012 Location: Dublin	Theory question: I am using Ales Gyrator boards and Coleman filament regulators with cathode bias. What is more important to match, bias voltage or plate voltage?

21st January 2021, 08:38 PM	#500
euro21 diyAudio Member Join Date: Sep 2004 Location: Budapest	Anode voltage and bias voltage determines operating point (Ua, Ia at -Vg) ... at specified tube and at given condition. If the tube changing (another tube, or aging), the operating point also changing. There are no two identical operating point of two tubes, but if it not too far -relative to each other-, it's irrelevant. The important thing is tubes gain -preferably- similarity at near operating points.