Thinking of building the SV300B Push-Pull

[Cifrocco]

Still looking for a tube amp to build, have now come across the issue of Glass Audio showing the SV300B Push-Pull by Kobayashi. A little daunting, and uses some hard to find parts, so I'm wondering about part substitutions, if anyone cares to give me some advice.

The power supply has two Tamura A-4004 chokes. Each one shows a parallel connection. Was wondering if I could replace it with a Plitron PAT-4174-00 (I have 4!). The Plitron is just one straight winding and specified as being for a C-L-C filtering configuration. Would this work in place of the A-4004?

Also in that same circuit the designer is using 100uF 800V Mylar film, non-polarized capacitors where one normally finds the usual large, polarized, electrolytic filter capacitors. I'm guessing I could just use good quality electrolytics (two in series due to high voltage) and be done with it?

Below is the part of the schematic in question:

[Miles Prower]

Originally Posted by Cifrocco

The power supply has two Tamura A-4004 chokes. Each one shows a parallel connection. Was wondering if I could replace it with a Plitron PAT-4174-00 (I have 4!). The Plitron is just one straight winding and specified as being for a C-L-C filtering configuration. Would this work in place of the A-4004?

The Plitron chokes probably won't work since this design is a choke input filter. With a choke input, the choke passes the entire ripple current. If you have a reservoir capacitor up front, the ripple current that the choke has to pass is lessened considerably. I'd expect to see problems with core saturation if you tried to use it as the input element in a choke input filter.

Also in that same circuit the designer is using 100uF 800V Mylar film, non-polarized capacitors where one normally finds the usual large, polarized, electrolytic filter capacitors. I'm guessing I could just use good quality electrolytics (two in series due to high voltage) and be done with it?

That's overkill, especially in a PP amp where the PS isn't in the signal path, due to cancellation at the primary center tap. Here, I'd just get a couple of 220uF / 450Vdc electrolytics, wire 'em in series with a couple of 100K voltage balancing resistors paralleling each capacitor. That will certainly be good enough here.

[limono]

Well, I don't see a choke input PSU .It's a cap input with a series tube damper diode for slow start and to filter HF "hasch" of solid state rectifier , so your Plitron chokes should be fine or maybe even better than Tamura's. Film caps in PSU are for "sound " reason. If you want to keep "voicing" of the amp you should follow design as close as possible.Whats important is that you arrive at simillar B+. Good luck!

[andyjevans]

Instead of using a single damper diode for slow start, would it not sound better with two dampers instead of the solid state diodes? Don't really get this.

Andy

[Rod Coleman]

The current passed by the damper is almost dc. The drop is therefore a lot lower than if it were taking the peak rectifier current (Ampere level).

The designer has made the first stage (SS diodes, 100u film cap) very low impedance compared to valve rectifiers and elkos. This will provide stiffer B+, and very fast recovery from overloads.

Combined with the heavy bleed resistor (75K), the turn-OFF of the rectifiers will also be fast, suggesting that the designer is tailoring the HF emissions. The choice of SS diode will be important to match the original intent. Otherwise, Cree Silicon Carbide may be a good starting point.

The damper diode is there to provide a slow rise of B+, and chop off reverse current pulses.

Whether any of this makes a difference in the sound that's important to you depends on the rest of the amplifier, the rest of your system, and how hard you run it into overload.

I find the first cap after the rectifier to set the whole flavour of any amplifier, and that proper audio grade MKPs improve anything from DHT SETs all the way down to EL84 PP guitar amps.

I don't know about Mylar films in this position, but I can recommend ANSAR CPA series, and the AMPOHMs, now made by LCR:

Polypropylene Capacitors

[Cifrocco]

Thank you for all the advice, much appreciated.

[planet10]

Originally Posted by Rod Coleman

I find the first cap after the rectifier to set the whole flavour of any amplifier, and that proper audio grade MKPs improve anything from DHT SETs all the way down to EL84 PP guitar amps.

We found that using poly caps in the power supply made a BIG difference in performance, and use nothing but now... the BIG solen polys in our case.

dave

[cprom]

Don't know if you have start your project yet. Mine finished last year.