My old (1963) RCA Victor console stereo (fully serviced/modded by me of course) STILL has its Original (date code 1962) RCA branded 5AS4A rectifier tube - feeding B+ to 17 tubes.
Even the 1960's era Realistic "Lifetime Gold Pin" 7189A output tubes are strong and kick booty.
Just in case I need to replace the rectifier, I've got a healthy stock of NOS RCA and GE 5U4GT's tucked away.
"They sure made them good back then!"
Finished it up. Before the RIAA turret board:
I found a pair of 0.01uF Orange Drop caps so I clipped out the Soviet PIO caps that I had in there previously.
With the RIAA board:
With the 6C4 cathode follower, I slapped on a pair of 4.7uF caps to drive 10k loads. Absolutely no problems. The preamp measured <0.05% THD with 5mV input at 1kHz. No audible hum with the AC heaters. It sounds really, really good--that's the extent of my "audiophile" vocabulary.
I found a pair of 0.01uF Orange Drop caps so I clipped out the Soviet PIO caps that I had in there previously.
With the RIAA board:
With the 6C4 cathode follower, I slapped on a pair of 4.7uF caps to drive 10k loads. Absolutely no problems. The preamp measured <0.05% THD with 5mV input at 1kHz. No audible hum with the AC heaters. It sounds really, really good--that's the extent of my "audiophile" vocabulary.
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Schematic as built:
Minor value changes were because I mostly used whatever parts I had on hand. The only things I got from Mouser was the chassis, the choke, the 2 big 22k resistors, the RCA jacks, and the 4 22uF caps. The wonky 82uF + 0.1uF cathode bypass capacitors were from a previous built that I had salvaged. I added an additional filtering stage to get the ripple down even more. According to PSUDII, the ripple at the supply of the 5879 tube was 58nV. I ran the second stage hotter than the original schematic to get more linearity, but I don't think it matters. Oh well, I'm burning an extra 0.25mA per channel for nothing.
Well, after I listened to Meddle, I opened up my newly acquired 2018 remix of Animals. The bass rumble on Pigs (Three Different Ones) was unbelievable.
Minor value changes were because I mostly used whatever parts I had on hand. The only things I got from Mouser was the chassis, the choke, the 2 big 22k resistors, the RCA jacks, and the 4 22uF caps. The wonky 82uF + 0.1uF cathode bypass capacitors were from a previous built that I had salvaged. I added an additional filtering stage to get the ripple down even more. According to PSUDII, the ripple at the supply of the 5879 tube was 58nV. I ran the second stage hotter than the original schematic to get more linearity, but I don't think it matters. Oh well, I'm burning an extra 0.25mA per channel for nothing.
Well, after I listened to Meddle, I opened up my newly acquired 2018 remix of Animals. The bass rumble on Pigs (Three Different Ones) was unbelievable.
Nicely done 
! Just a remark to one of your alterations: A screen decoupling capactor only needs to be tied to the pentode's cathode if there's some NFB signal injected into it. Your preamp surely performs the same if you return the capacitor to ground again.
Best regards!
! Just a remark to one of your alterations: A screen decoupling capactor only needs to be tied to the pentode's cathode if there's some NFB signal injected into it. Your preamp surely performs the same if you return the capacitor to ground again.Best regards!
Bravo! 👏 Very neat wiring, specially the filaments. That contributes to low hum/noise despite the AC heaters.
Happy listening!
Happy listening!
Metal tube should be quieter due the metal shell acting as a shield, provided it is grounded at one of the pins. Metal tubes like 6SJ7 and 6SF5 are excellent for phono or microphone preamps.