Valve Itch phono

[Coreyk78]

Hi Salas, thank you for posting this design, I've been looking for a tube phono amp that isn't too complicated and it looks like this could be a good one to build.

I have a question about the power supply. I already have a regulated power supply from a project that went in a different direction. It is the PS-1 kit from John Broskie on his glassware site. I would like to use it as the power supply for the Valve Itch. Do you think it would be suitable?

It can provide 50mA @ 300V for the B+ and 2.5A for the heater supply. Would it be a problem to use a single heater supply for all 4 tubes? I guess that I don't understand why there are 2 heater supplies in your design. I haven't looked at the documentation for the PS-1 in a while but I think the heater supply is floating at either 1/4 or 1/2 B+.

I can build a new supply if needed but its always nice to be able to use parts I already have.

[Salas]

The Broskie HVreg will certainly do its ripple kill job well, its analogous to the Mosfet Maida that was used in the first build. Later on you can experiment with the SSHV shunt reg too maybe. I recommend the revised schematic of the second build for the phono itself. There the upper tier tubes had elevated heaters at 1/2B+. The cathodes are sitting high. LM317T were used in those example builds and they are not trustworthy for above 1A constant for heaters in my experience (not LDO much heat), so 2 got used. That allowed to keep the lower tier tubes heaters separately fed and just grounded since there is no problem, their cathodes are very near relative to their cathodes for potential. And all was quiet. With just one heater reg you can't have separate heater elevation potentials, so 1/3B+ should keep the 6H2s just within spec bounds. I hope it will be as quiet.

[Coreyk78]

Thanks for the input. your reply brings me to my next question. What do you mean by upper tier and lower tier tubes?

I apologize, most of my building experience has been using a pcb so I'm still trying to learn.

[Salas]

If you look at the schematic in post #31 there are two tubes near B+ and two tubes near ground. Since two heater regs on different elevation were used in those builds, they shared one 6H2 and one 6SN7 between channels for the upper side since each bottle's got two triodes, and one 6H2 & 6SN7 for the lower side.

[revoli]

Salas

Can you glance at my scrawl attached just to make sure I have interpreted what you are saying correctly. I am planning on using the power shunt and hopefully have captured this correctly, plus as you advise will move some of the PSU circuitry to phono box as shown.

Secondly I have been looking at the heat sink requirements and trying to work out how many need in total and where. The 317's need them, without being too scientific about it these looked like they would be big enough? AAVID THERMALLOY | Semiconductors | Sockets and Heatsinks | Heat Sinks | Transistor Type Packages up to 48°C/W |6296B. They are rated 4.7 '/W whatever that means.....
I think there are some more heatsink requirements in the power shunt but not sure where or how big. Judging by the pics posted in this thread another one of the above sinks may be needed?

I am no expert and just need to be cautious that I am not being stupid!

Thanks for your excellent work.

[Salas]

Your draft is correct, just don't use the 3300uF since your heater regs will be inside the phono, use 100uF. The 4.7C/W sinks for the 317s look big enough. Now for the B+ shunt reg: Give it 320-350V in and 300V out. Set it at 35mA. 10mA will go to both phono channels total. 20V-50V(in-out)x0.035=0.7-1.75W. Using the same type 4.7C/W sink for the input CCS Mosfet will up 8 degC from ambient mostly. Well. Things are different for the output Mosfet. Has to dissipate for 35-10=25-3=22mA (3mA is for the Jfet and BJT inside) times 300V. 6.6W constantly. That will up 31 degC on the 4.7W/C type. Think of a hot box inside (tubes, heater regs, closed) plus that. Maybe 70C or more in the end on that sink. No. At least double that sink's size for the IRF840. Example. Use 105C elcos for everything chemical caps inside the phono.

[revoli]

Thanks Silas. I am getting there just taking me a long time but then not having to rush is part of the beauty of this as a hobby :-). So much enjoyment from the anticipation of great things to come....

[revoli]

Originally Posted by Salas

Went to Mikvous's place today to examine another Itch he made. With my Rev1 changes included.

In the final 2.2uF cap what is the voltage? I am not competent enough to work this out and whilst I started building an Lt-spice model its going to be awhile until I have mastered the package!

Thanks

[revoli]

I would really like to be able to calculate this sort if thing myself Sp the supplementary question is how. I am not keen on just plugging numbers into software to come up with the answers as that does nit develop the same level of understanding. Anyone care to point me in the right direction for some good advice on how to improve my understanding.

[massimo]

Originally Posted by revoli

In the final 2.2uF cap what is the voltage?

As rule of thumb the voltage of output cap should be greater than the p.s. voltage. If the Itch requires 300 V, better use a 400 V cap or greater.