A Very Nice Tube Phono Preamp

I have been looking at different options concerning components and their availability in different sources. Salectric, can you give advice on W and V ratings of 100K and 10K resistors and 0.1 uF capacitor added between B+ and heater supply -, or do you recommend certain brands/types for these? I suppose these are added for hum prevention. One of my old amps I built had a same kind of arrangement.
 
I have been looking at different options concerning components and their availability in different sources. Salectric, can you give advice on W and V ratings of 100K and 10K resistors and 0.1 uF capacitor added between B+ and heater supply -, or do you recommend certain brands/types for these? I suppose these are added for hum prevention. One of my old amps I built had a same kind of arrangement.

The parts you are referring to establish a DC reference point for the heater supply, which I use for sound quality reasons, not hum. I have tried the preamp without the DC reference (just connect the (-) side of the heater line to ground instead of the network shown on my schematic). There is no hum either way. The DC reference sounds slightly different and I prefer the sound with it rather than with the direct connection.

The exact values of the resistors and capacitor are not critical at all. The two resistors are just a voltage divider to reduce the B+ voltage to a lower voltage. A reference in the 10 to 30 volt range is fine.

Many preamps and amps with a network like this use a large value cap like 100uf. I tried a number of values and didn’t find any advantage to the higher values. What I did find is that the type of cap used affects sound quality. A good film cap typically sounds better than a large electrolytic so I recommend a low value (0.1uf to 0.47uf) film cap. I happen to like an old film cap made by Fiable that I bought over 40 years ago. I had a few left so that’s what I used.

The voltage rating of the cap should be comfortably above the DC voltage used as the heater reference. Anything rated at 50vdc or greater is fine.

You can use Ohms Law to find the current flowing through the voltage divider network, and from that determine the wattage dissipated by each resistor. The total current through the resistors is roughly 2 ma, so the 100K resistor has 0.4w dissipation. I would use a 2w or greater for the 100K. The 10K can be 1/2w. I used a Mills 12w for the 100K because I had one in my parts box, and I used a Dale CMF 1/2w metal film for the 10K.
 
I have started the build of the phono pre. I will stick precisely to Salectric's schematic but the components will be mostly different. Similarities concerning components are the transformers and chokes by Hammond and resistors in RIAA section by Vishay. I will include a SUT in the amplifier chassis, and that will be Lundahl LL1931 with amorphous cobalt core and Cardas copper wire. The output transformer will be Lundahl LL2756 interstage transformer customized to 12 mA.

All filter capacitors are Kemet C4QA-series polypropylene film capacitors that I have used successfully in my previous 300B project. Only electrolytic capacitors are those for heater supply (Nichicon). 0.1 and 0.033 uF capacitors in the amplifier part are Miflex KPCU-01 series copper foil capacitors. Resistors other than RIAA section are from Kiwame, Mills, TDK and Takman.

Tubes I sourced from eBay. D3a's are used Telefunken labeled by Siemens, 5687s are Philips new NOS and the 5R4GY is a used one by GE.

Amp and PS will be built in separate chassis. The frames are made of wood and the top covers are 3mm aluminum plate. I have designed the layout and drilled the top plates that are now at a paint shop. Wooden chassis frames are also under construction by a friend who is a skilled carpenter.

I hope to get the top plates next week and start the assembly work that is the best part of the project. I'll post some pictures when there is more to show.
 
Excellent project! You should end up with a very nice phono preamp with those components. My only suggestions are:

1. Use 3 LEDs instead of 4 on each 5687. This increases the current and improves the sound.

2. After it’s up and running, I suggest you try Raytheon 5687 instead of JAN Phillips. I have tried a good number of 5687 types and I like the Raytheons best by far. The JAN Phillips are actually my top choice in some other gear but not the phono preamp, for whatever reason.
 
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