Symasym 5.3 "AAK model" builder's thread

[AAK]

Hi George,

WIMA 2.2uF/50V at Mouser part# 505-mks22.2/50/10 are in stock and should work fine. I doubt you'll be able to hear a difference between a 3db of 3.0Hz vs. 1.5Hz. You can use them in the meantime while you wait for a 4.7uF to become available, or just leave them in.

For the 0.1uF PS caps 63V or higher is fine.

Regards,

Al

 

[Ryssen]

I´ve had no problems with the caps fitting,the only thing I had to do was to drill 2 new holes for the 0,2 ohms resistors near/between the big elyts. Maybee because I used different brand on the resistors.

 

[Colescuttle]

Thanks, Ryssen, Al and Cromodora.

I went ahead and ordered some of the 4.7uF WIMAs from Europe (I don't have room for any of the the exotic film and foils). That means in a week or so I'll have some left over, as well as some extra .1/250/5 WIMAs, if anybody needs them.

George

 

[Ryssen]

Those Wima 0,1uF are great for bypassing things..e-lyts,diods in rectifiers for example..

 

[cromodora]

About that BD139 and flying leads...

Hi Ryssen,

You'll need to mount T1 (BD139) onto one of the output transistors (U3,U4) to prevent thermal run away.

Here's a pic. I mounted T1 to U3.

Al

Al,
Is this non-negotiable?
How about a teeny heatsink.

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

 

[Sheldon]

Re: About that BD139 and flying leads...

Al,
Is this non-negotiable?
How about a teeny heatsink.

That would going in the wrong direction. You want it to track the temperature of the outputs. If you can't do that, you want it to heat up faster than the outputs. So, if anything, I'd think you'd want to insulate it.

Sheldon

 

[AAK]

Hi cromodora,

T1 has to be mounted to one of the output transistors to provide thermal tracking. Without it the output transistors will eventually self-destruct. Absolutely non-negotiable.

Best regards,

Al

 

[cromodora]

Ah! So des ne!

Will comply.

Will repeat to self..

"Thermal runway is not a heated catwalk for winter couture."

Thanks, Sheldon and Al.

 

[Ryssen]

This is what I did:

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

It is under the big transistor,I mean the BD139..

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

Probably looks wors than it is,tried to maniplate the pics to look good..

 

[Colescuttle]

Nice solution.

George

 

[Colescuttle]

I think I got a problem. (DUMMY ALERT)

My 2X18v transformers are actually producing 2x20v at the board, resulting in 27.2v DC on each rail. Is 54.4v volts pushing the envelope, and, if so, is there anything I can do short of replacing the transformers?

George

 

[Ryssen]

I think thats a little on the low side..I will use
about 2x40v DC with a 2x30vAC trafo.
The original Symasym used 2x36v DC.
Is the amp working?

 

[Colescuttle]

Hi, Ryssen.

My transformer has two 18 volt secondaries that actually each deliver 20 volts AC. Connected with a center tap, that's 40 volts AC. Rectified, I end up with 27 volts DC per rail, or 54 volts DC. I was under the impression that's what Al's circuit is designed for. Does it actually call for 50 volts DC per rail?

George

 

[Ryssen]

Yes,look at this:

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

+-50v.Total 100v I guess this is the max.

 

[RKH]

Re: Hi, Ryssen.

My transformer has two 18 volt secondaries that actually each deliver 20 volts AC. Connected with a center tap, that's 40 volts AC. Rectified, I end up with 27 volts DC per rail, or 54 volts DC. I was under the impression that's what Al's circuit is designed for. Does it actually call for 50 volts DC per rail?

George

Yours should deliver +/- 27 Volts DC. My understanding is that the AAK version is +/- 50 VDC. I cannot comment on how the SymASym will do at 27 V rails. Like Ryssen, I'm plan to run 30V transformers to give me around +/- 40 V DC.

Ryan

 

[anatech]

Hy guys,
The original SymAsym is okay a little past 35 VDC, bipolar. That's + and - 35 VDC. So you will be a little underpowered. Device dissipation and breakdown voltage of the input pair are the limiting factors.

-Chris

 

[Colescuttle]

Thanks, Guys.

I guess it's new transformer time. Oh, well.. and I was so close to finished. Anybody need a pair of new 2X115, 2X18, RFI and EFI shielded Plitrons?

 

[AAK]

Hi George,

It wouldn't sell your Plitron without trying it first, it just might work. Give it a shot and see what happens, it wont hurt anything, and it would be good to know. If it does not work I'd recommend at least 2x25VAC, and no more than 2x35VAC to keep things on the safe side. If you decide on 2x35VAC make sure your using the parts listed in my BOM specifically Q1, and Q2. And C25 - C28 need to be rated at least 63V just like the diagram in post #94.

Regards,

Al

 

[AAK]

Well after doing some simulations there's a good chance it wont work at +/- 27V rails. To make it work you'd have to change some part values to get the bias to where it needs to be. Not worth the trouble.

 

[anatech]

Hi AAK,
It will work fine at those voltages. Just a different bias possibly and lower power. I tested the 5.3's at 25 V and they worked well, later to 35 V.

I expect to buy your boards next run. It should be interesting to see what differences there are between the two.

-Chris