Okay so I got another gift from my father in law. A beautiful pair of Unitran 9U14 outputs. A unitran Power transformer and A unitran inductor for the power supply. (He's cleaning out his house as he doesn't build anything anymore because of the age so he gives these things to me).
So I'm gonna build a little integrated amp with them.
I looked up the unitran and these seem to be very nice outputs.
Specifications say -1db from 10Hz to 100kHz 😱
Ra-a is around 8k, Good for some EL84 or something like that.
So the goal is to go for low distortion & wide bandwidth.
I have found the 6CZ5 tube and these look very nice. Something like a scaled up EL84 with lower distortion.
It does around 21.5w with only 1% of distortion.
7k5 Raa and 350v on the plates.
As the transformer has a wide bandwidth I was planning to use some global feedback and maybe some local CFB using the secondaries.
The power transformer Has 350v or 425v dual windings. I think they used a tube rectifier with this.
Using the 350v and semiconductor diodesI would end up with around 480v Raw voltage and that is a little bit to much. Maybe a choke input would be a good idea. Would be nice to use this transformer.
So next step is the general principle. I was thinking to use A pentode/triode combination.
Pentode fo the first stage. Triode for the phase split and let it directly drive the outputs.
The pentode has high gain so some feedback doesn't mess up the sensitivity.
Something like an 6AN8 I think.
Then for the preamp I was thinking about a 12AX7 and 12AU7. I want A baxandall tone control in there as it would be used as an integrated amp.
First stage 12AU7 kathode follower for driving the Baxandall tone control.
A 12AX7 + 12AU7 kathode follower for gain and also driving the baxandall using feedback.
Volume and balanced would be straight forward as will be the input selection.
RIAA phono input could be a nice add on. Something with a pentode at the input maybe. Haven't decide that part yet.
When the amp is finished I'm probably gonna give it to my father in law so he can enjoy it. (He still likes to listen to music and he loves tubes).
Any suggestions are welcome
So I'm gonna build a little integrated amp with them.
I looked up the unitran and these seem to be very nice outputs.
Specifications say -1db from 10Hz to 100kHz 😱
Ra-a is around 8k, Good for some EL84 or something like that.
So the goal is to go for low distortion & wide bandwidth.
I have found the 6CZ5 tube and these look very nice. Something like a scaled up EL84 with lower distortion.
It does around 21.5w with only 1% of distortion.
7k5 Raa and 350v on the plates.
As the transformer has a wide bandwidth I was planning to use some global feedback and maybe some local CFB using the secondaries.
The power transformer Has 350v or 425v dual windings. I think they used a tube rectifier with this.
Using the 350v and semiconductor diodesI would end up with around 480v Raw voltage and that is a little bit to much. Maybe a choke input would be a good idea. Would be nice to use this transformer.
So next step is the general principle. I was thinking to use A pentode/triode combination.
Pentode fo the first stage. Triode for the phase split and let it directly drive the outputs.
The pentode has high gain so some feedback doesn't mess up the sensitivity.
Something like an 6AN8 I think.
Then for the preamp I was thinking about a 12AX7 and 12AU7. I want A baxandall tone control in there as it would be used as an integrated amp.
First stage 12AU7 kathode follower for driving the Baxandall tone control.
A 12AX7 + 12AU7 kathode follower for gain and also driving the baxandall using feedback.
Volume and balanced would be straight forward as will be the input selection.
RIAA phono input could be a nice add on. Something with a pentode at the input maybe. Haven't decide that part yet.
When the amp is finished I'm probably gonna give it to my father in law so he can enjoy it. (He still likes to listen to music and he loves tubes).
Any suggestions are welcome
I've said it before and say it again. Really good tone controls are complex. The provided Max Robinson "unity gain" setup requires 2 bottles per channel. That can be reduced to 1 bottle per channel by substituting DC coupled ZVN0545A source followers for the cap. coupled cathode followers. I regard 100% defeatable tone controls as essential. Comparatively few recordings benefit from the presence of tone controls. "Unity gain" greatly simplifies the task of making the tone controls defeatable.
Pentodes introduce partition noise. 🙁 In order to use a pentode in the 1st gain block of a phono preamp, its gm must be very high. Otherwise, satisfactory S/N performance will not be realized. The 6AC7 has the requisite high gm.
IMO, a 6922 cascode is an excellent alternative to a pentode, in the 1st gain block role. Partition noise is not present and, like a pentode, adverse CMiller interactions with the cart. or SUT are a non-issue. FWIW, think of a cascode as a "synthetic" pentode.
Pentodes introduce partition noise. 🙁 In order to use a pentode in the 1st gain block of a phono preamp, its gm must be very high. Otherwise, satisfactory S/N performance will not be realized. The 6AC7 has the requisite high gm.
IMO, a 6922 cascode is an excellent alternative to a pentode, in the 1st gain block role. Partition noise is not present and, like a pentode, adverse CMiller interactions with the cart. or SUT are a non-issue. FWIW, think of a cascode as a "synthetic" pentode.
