Sun Audio SV-2A3

[wmy45]

Dear All,


I am a beginner trying to diy a sun audio sv-2a3 amp. But i have some questions about the transformers. I do not intend to make a purchase of the originals, they would cost me a bomb =/ any advice? My plan now is to get the ratings and look for cheaper alternatives!

SPT150 power/main transformer: what is the VA rating?

SCH515 choke: I understand the significance of the choke, but how do i select one?? i can't seem to find any information on this choke =/

output transformers i have found. Not top notch, but i believe will do the job =)

My output transformers:

http://singapore.rs-online.com/web/s...duct&R=2106475


The schematics for SV-2A3:

http://www.ys-audio.com/wce/sunaudiosv2a3.JPG



What are the items within the dotted lines? There is one labeled N.L. a RC filter. but without ratings...and the capacitors tied to the choke, are they implied to be optional? why the dotted line huh?


I look forward to receiving the enlightenment from anyone in this esteemed forum on this subject.



Best regards,
Ming Yang

[HollowState]

Hello Ming Yang,

SPT150 power/main transformer: what is the VA rating?

This will depend on whether you power 2 channels or only 1. Since a 2A3 can run at 60mA maxium, you will want at least a 75mA current rating for one channel. Twice that for two channels on the same transformer. This is figuring 10mA more for the 6SN7.

SCH515 choke: I understand the significance of the choke, but how do i select one?? i can't seem to find any information on this choke =/

Use the above current figures as a guide. Inductance value will be somewhat of a guess with 5 to 10 Henrys being typical with about 150 ohms DC resistance.

What are the items within the dotted lines? There is one labeled N.L. a RC filter. but without ratings...and the capacitors tied to the choke, are they implied to be optional? why the dotted line huh?

The N.L. capacitor across the line is a Noise Limiting cap which has an internal resistor. They are available from makers like ERO and Wima. But you can make one with typical values of .1ufd/600V and perhaps 500 ohms. These are not critical and it can even be left out.

The dashed lines around the two capacitors indicate a dual electrolytic can type filter capacitor. Single capacitors will work just as well. They are needed and are not optional.

My output transformers:
http://singapore.rs-online.com/web/...oduct&R=2106475

For maxium power transfer, a 2A3 wants to see a 2.5/3K plate load. The transformer you chose will work but you will suffer a reduction of output power with it's 4 to 5K impedance. Also, it's maxium rating is a little low with only 40mA and 3½ watts. Some people like the sound of a lightly loaded DHT, so you might too. But you will not be able to get the maxium performance power with it. I would choose a little higher rated output transformer myself of perhaps 5 watts or more to prevent saturation on loud passages.

BTW, your English is very good. Better then some locals that grew up with it.

Victor

[Tubes4e4]

Hi,

I am a beginner trying to diy a sun audio sv-2a3 amp.

Please note this circuit has some severe driver stage related problems, see here.

Regards,

Tom Schlangen

[wmy45]

Excellent, your explaination was crystal clear! Now i have a very good picture of what to look for in future projects. Thanks!

HAHA my english is so so only lah, yours is very commendable too. I haven reveal my true powers (singlish) to you yet; a local slang unique only to singaporeans






Ming Yang