I'm looking at using an 2a3 SE valve amp, the tubelab SE diy project.
The gumf says it can be used to drive other amps, so I was wondering if I could put it in line from my DAC to the F5.
The DAC puts out 2.6v < 800 ohm
I built the F5 by following instructions and gleaning a kindergarten level of understanding about the technical side of things.
My interest would be to build the SE amp, but recognizing it probably lacks the muscle to drive my FR speakers that are 89db efficient, so use the F5 to add gain and presumably retain that seductive tube sound.
Any thoughts? Or is it an overly simplistic idea?
Many thanks in advance for your help.
The gumf says it can be used to drive other amps, so I was wondering if I could put it in line from my DAC to the F5.
The DAC puts out 2.6v < 800 ohm
I built the F5 by following instructions and gleaning a kindergarten level of understanding about the technical side of things.
My interest would be to build the SE amp, but recognizing it probably lacks the muscle to drive my FR speakers that are 89db efficient, so use the F5 to add gain and presumably retain that seductive tube sound.
Any thoughts? Or is it an overly simplistic idea?
Many thanks in advance for your help.
Ok, thanks.
I had concerns about introducing to much noise into the F5 and cooking something. Should I mention perhaps that the current limiting stage has been omitted in my amp.
Would it be wise to wire in a potentiometer in the SE to limit the juice, initially, then place resistors in line if distortion or smoke become a problem?
Kindergarten questions no doubt, thank you so much for your time.
Money, wife and children mean one build per 10 year cycle - F4 will have to wait
I had concerns about introducing to much noise into the F5 and cooking something. Should I mention perhaps that the current limiting stage has been omitted in my amp.
Would it be wise to wire in a potentiometer in the SE to limit the juice, initially, then place resistors in line if distortion or smoke become a problem?
Kindergarten questions no doubt, thank you so much for your time.
Money, wife and children mean one build per 10 year cycle - F4 will have to wait
I lifted this from the diy page.
The 2A3 is essentially two 45′s in parallel in the same envelope. The filament current is 2.5 amps per tube. The 2A3 also has a 300 volt maximum plate voltage rating, although several new production “2A3 types” have higher ratings. The higher plate current drawn by the 2A3 will bring the plate voltage to about 300 volts when used with a 550 volt transformer and a choke in place of R4. The choke should be rated for 150 to 200 mA. I use the Triad C-14X or the Hammond T193J. The B+ voltage is then fine tuned to the desired value by changing C4. Start with a very low value for C4 (4.7 uF at 450 volts) and increase if needed.
The 2A3 will make about 4 watts with a 2.5 K ohm load, 3.5 watts with a 3 K ohm load and 2.5 watts with a 5 K ohm load. The distortion and damping factor improves with increasing load impedance. Most users use a 3 K ohm transformer with 2A3 tubes.
The filament current for two 2A3 tubes is 5 amps. A power transformer with at least 6 Amp capability on the 6.3 volt winding is required. A center tap on the 6.3 volt winding is required. The filament regulator IC will require a supplemental heat sink with 2A3′s. I use the heat sink from an old Pentium IC. I have used a Hammond 270HX power transformer in a 2A3 only amplifier.
The 2A3 should be biased in the 50 to 60 mA range.
Is that a little long winded but helpful?
The 2A3 is essentially two 45′s in parallel in the same envelope. The filament current is 2.5 amps per tube. The 2A3 also has a 300 volt maximum plate voltage rating, although several new production “2A3 types” have higher ratings. The higher plate current drawn by the 2A3 will bring the plate voltage to about 300 volts when used with a 550 volt transformer and a choke in place of R4. The choke should be rated for 150 to 200 mA. I use the Triad C-14X or the Hammond T193J. The B+ voltage is then fine tuned to the desired value by changing C4. Start with a very low value for C4 (4.7 uF at 450 volts) and increase if needed.
The 2A3 will make about 4 watts with a 2.5 K ohm load, 3.5 watts with a 3 K ohm load and 2.5 watts with a 5 K ohm load. The distortion and damping factor improves with increasing load impedance. Most users use a 3 K ohm transformer with 2A3 tubes.
The filament current for two 2A3 tubes is 5 amps. A power transformer with at least 6 Amp capability on the 6.3 volt winding is required. A center tap on the 6.3 volt winding is required. The filament regulator IC will require a supplemental heat sink with 2A3′s. I use the heat sink from an old Pentium IC. I have used a Hammond 270HX power transformer in a 2A3 only amplifier.
The 2A3 should be biased in the 50 to 60 mA range.
Is that a little long winded but helpful?
you'll wasting gain , severely , using F5 as booster amp for flea watt 2A3 amp
you have an option to load lightly output of 2A3 amp , (say 16 to 20R) , thus having greater output swing than in case of 8R speakers
that way voltage swing will be more than sufficient to feed F4 , while having lowish THD
go to FW , read F4 user manual
you have an option to load lightly output of 2A3 amp , (say 16 to 20R) , thus having greater output swing than in case of 8R speakers
that way voltage swing will be more than sufficient to feed F4 , while having lowish THD
go to FW , read F4 user manual
You'll be using all of the voltage gain from the Tube amp so you'll hear more of the tube sound if you use the F4.
If you only need say 4Vrms dynamic peaks at the speaker, then you only need 6dB voltage gain (assuming 2Vrms from cd player/source)
If the Valve amp has for example 15dB gain and the F5 has 15dB gain you'll be attenuating the signal right down so you have below 0.7V rms coming out of the valve amp to get 4Vrms out of the F5.
I you connect it to an F4 you'll be using 4V rms from the tube amp to give you 4V rms out the F4 and into your speaker.
So you'll be hearing more of the tube amp and throwing away less signal at the front end.
Edit: I slapped this together very quickly just to illustrate what is happening, the exact numbers could be a bit off but not important to cry over
If you only need say 4Vrms dynamic peaks at the speaker, then you only need 6dB voltage gain (assuming 2Vrms from cd player/source)
If the Valve amp has for example 15dB gain and the F5 has 15dB gain you'll be attenuating the signal right down so you have below 0.7V rms coming out of the valve amp to get 4Vrms out of the F5.
I you connect it to an F4 you'll be using 4V rms from the tube amp to give you 4V rms out the F4 and into your speaker.
So you'll be hearing more of the tube amp and throwing away less signal at the front end.
Edit: I slapped this together very quickly just to illustrate what is happening, the exact numbers could be a bit off but not important to cry over
Last edited:
Lorien,
This is madness, if you ask me. The "tube" sound is subjective, and I am sure the qualities that you like can be achieved for the cost of a few resistors, literally.
I remember somebody advising to use carbon resistors on the F5 to make it less clinical. Metal film resistors are famously accurate and precise, with excellent characteristics across the board, but this man claimed that his amp was too clinical. Nelson Pass, in his wisdom, advised against carbon resistors, but suggested two resistor changes, and was specific about them. The man changed his amp accordingly, replacing all carbons to metal film, to the new values, at a cost of £3 maybe, and said he was delighted that the fist now had a silky velvet glove....sounds good dunnit? - a silky velvet glove! Sounds valvey to me.....I'll find the values and let you know in a pm, or on Facebook.
This is madness, if you ask me. The "tube" sound is subjective, and I am sure the qualities that you like can be achieved for the cost of a few resistors, literally.
I remember somebody advising to use carbon resistors on the F5 to make it less clinical. Metal film resistors are famously accurate and precise, with excellent characteristics across the board, but this man claimed that his amp was too clinical. Nelson Pass, in his wisdom, advised against carbon resistors, but suggested two resistor changes, and was specific about them. The man changed his amp accordingly, replacing all carbons to metal film, to the new values, at a cost of £3 maybe, and said he was delighted that the fist now had a silky velvet glove....sounds good dunnit? - a silky velvet glove! Sounds valvey to me.....I'll find the values and let you know in a pm, or on Facebook.
"increase the value of the feedback resistors from 2 X 100 ohms and 10
ohms to 1 X 100 ohms and 22 ohms"
Erm - am I missing something? Increase 2x100 ohm to 1x100 ohm?
And the fella says he puts in 2x100 ohm, but that's the original spec as listed on the first watt site. Not an increase of anything.
ohms to 1 X 100 ohms and 22 ohms"
Erm - am I missing something? Increase 2x100 ohm to 1x100 ohm?
And the fella says he puts in 2x100 ohm, but that's the original spec as listed on the first watt site. Not an increase of anything.
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