slp-90 clone, decent preamp!

[807tubenut]

Got mine built tonight, my aikido octal/6sn7gt is a little darker then this slp-90 clone from fleabay, all in all im enjoying it, nice and quiet!

An externally hosted image should be here but it was not working when we last tested it.

Like it better with telefunkens thrown into the mix.

An externally hosted image should be here but it was not working when we last tested it.

 

[Dr Freeman]

hi,

which one do you prefer?
how does cary sound overall?
Thanks

 

[807tubenut]

hi,

which one do you prefer?
how does cary sound overall?
Thanks

The slp-90 with Telefunken tubes is still my favorite after many years, it sits beside the aikido.

 

[Dr Freeman]

hi
the 2sk310 in the PSU of Cary it's discontinued. Any idea for substitute?

 

[807tubenut]

NTE67 Is available, But if you look around, the Original can be found.

 

[maton00]

You can use almost any mosfet with at least 400 VDS rating like a FQPF5N50, IRF740, IRF840..... For a linear HV regulator I whouldnt care for RDSON, swithing speed or anything besides current and VDS, Power dissipation, perhaps VGS and and if it has an internal zenner, if not use a external zenner to clamp VGS to less than the needed to fully turn the Mosfet and the regulator will be almost indestructible....Well only if the circuit is properly heatsinked and shortcircuit protected.

 

[Dr Freeman]

You can use almost any mosfet with at least 400 VDS rating like a FQPF5N50, IRF740, IRF840..... For a linear HV regulator I whouldnt care for RDSON, swithing speed or anything besides current and VDS, Power dissipation, perhaps VGS and and if it has an internal zenner, if not use a external zenner to clamp VGS to less than the needed to fully turn the Mosfet and the regulator will be almost indestructible....Well only if the circuit is properly heatsinked and shortcircuit protected.

Thank you,


See PSu attached.
Would the transistors indicated by you be fine?
IRF730?

 

[Dr Freeman]

The slp-90 with Telefunken tubes is still my favorite after many years, it sits beside the aikido.

So between SLP-90 and Aikido 9 Pin which one would you recommend? in terms of sound, noise hum .... and last but not least difficulty of realization.
I've built an Aikido ACF-2 and I am very happy with him but his gain (buffer) is a bit low and I would like to make one of the two.

 

[807tubenut]

I like the Cary best for my listening. The wife and I prefer instrumental music while we work in the "lab", and the slp-90 clone, driving my DCPP with 6JM6 tubes driving a set of schaub lorenz coils. I tend to use the Octal aikido for bench testing.

 

[maton00]

Thank you,


See PSu attached.
Would the transistors indicated by you be fine?
IRF730?

It will do nicely I would put a 6.2-10V zenner between Gate and Source and a grid stopper but it will require invasive mods to the PCB

That circuit has some errors check the 9013 or the NPN transistor has placed wrong in the diagram with Collector and Emitter pins swaped.
Collector must go to mosfet grid node and Emitter to the output, also it needs to exist a resistor between base and Emitter to turn the Mosfet off when current goes up (looks that the PCB has built in a current limiter when VBE in the NPN transistor is near 0.65V). For preamp duty a 10-22 ohms will limit to 65-30mA.

 

[maton00]

Schematic updated

 

[Dr Freeman]

I like the Cary best for my listening. The wife and I prefer instrumental music while we work in the "lab", and the slp-90 clone, driving my DCPP with 6JM6 tubes driving a set of schaub lorenz coils. I tend to use the Octal aikido for bench testing.

@807tubenut

Please confim me the secondaries voltage in yor PSU in the schematic attached?
They should be:


250V AC Rectifier 6X4

6.3V AC Filament 6X4
15V AC Heather tube driver


Thank You

 

[Dr Freeman]

View attachment 856306
Schematic updated

Thank you for help,
but I've checked and my schematic matches exactly with the phisical PCB.

 

[maton00]

Okay then BG2 (9013 transistor) isnt doing anything, what I can say about the original "aparent intention" of the designer in the first schematic is that it almost shows a current limiter, that may also create a HV controlled delay in combination with the output capacitance (current controlled HV ramp) until it almost charges that capacitor.
It can be a deliberate mistake to confuse other copycat designers, but it wouldnt make harm if conected as showed in the original schem. It can also shutdown or limit output current if correctly set in case a tube run away or shorts.

 

[gerrittube]

BG2 is a current limiter. Max. current depends on the voltage across the MOSFET’s source resistor. I would expect a value there of a couple of Ohms, please check!

Regards, Gerrit

 

[Dr Freeman]

@807tubenut
Which PSU did you use for your Aikido preamp?
Can you post schematic Please?

 

[rongon]

I don't know if this is relevant, but here's a schematic from 1994 of the original Cary Audio Designs SLP-90 preamp and psu. It doesn't look like what you're talking about.
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