Balanced - Cascoded F5

[NYCOne]

I was fairly far along with my Cascoded F5, and I was in the midst of my Balanced F5 when I realized a trivial change could transform one of my projects to a Balanced Cascoded F5.

I completed the transformation on one channel tonight. The transformed board is not as pretty as I'd hoped, but I'll make a set of custom boards if I like the outcome. Believe it or not, I literally ran out of wire during the build, so testing will have to wait until tomorrow.

On another note, I was also the recipient of a kind gift - mica insulators (thanks to TB). Now my heat sink measurements should be better.

In any case, I hope the outcome is as good as the excitement I have in building the project.

[Melon Head]

It is good to see someone making progress.
What voltages have you decided to go with?

[Melon Head]

Originally Posted by Melon Head

What voltages have you decided to go with?

I wouldn't have thought that this was a particularly difficult question to answer. Particularly in light of the fact that you were complaining about other people not answering your questions, I find this rather strange behaviour.

Even a "I don't know" would have sufficed.

I have lost all sympathy.

[NYCOne]

Melon,

I know you're eager to see where this goes, so am I. I think you need to realize I have kids, my weekends are not my own. I haven't checked this thread until this minute because I haven't had anything new to add.

On one of your points: the difference between me and the folks I am not impressed with is - I will answer any question I can to the fullest extent possible, the others met out information like rationed food in wartime.

Finally, I haven't decided on any voltage yet. I've converted the board and have one channel ready for testing. I have two toroids at the moment - 18V and 26V, I'll try them both.

I hope to get time tonight to press on, but weekends are for the kids. Patience, I think I've gone from design to built channel and ready to test in something like 10 days. Give me a day or two to find time to fire up the beast!

Originally Posted by Melon Head

I wouldn't have thought that this was a particularly difficult question to answer. Particularly in light of the fact that you were complaining about other people not answering your questions, I find this rather strange behavior.

Even a "I don't know" would have sufficed.

I have lost all sympathy.

[Melon Head]

Originally Posted by NYCOne

Melon,

I know you're eager to see where this goes, so am I. I think you need to realize I have kids, my weekends are not my own.

I hope to get time tonight to press on, but weekends are for the kids. Patience, I think I've gone from design to built channel and ready to test in something like 10 days. Give me a day or two to find time to fire up the beast!

Having children myself I understand your predicament completely.
No problem

[NYCOne]

I finally had a chance to try the beast. It lives!

I used my stock F5 toroid 18V 400VA for 22.4V rails (measured).

I had an interesting time biasing. I'd made the mistake (the last time I do such) of buying trimmers from Tayda. They sent 100K trimmers instead of the 5K ordered. Now I didn't know if the spaghetti mix of cross connections was correct, and every time I turned a trimmer, Pow! - amps would flow like Niagara Falls. I kept thinking I'd made a connection mistake.

In the end, I checked the trimmers - they were 100K which accounted for the wild changes with each turn. Luckily I had some 2Ks around.

The next adventure was again my fault. Another forum member had recommended grounding the "X" for the initial bias. I tried this and couldn't get stability between on-off cycles. I un-grounded the "X" and the circuit was rock solid.

I biased to 2.6A for each side of the circuit (like the stock F5) making the Balanced side 5.2A. This is too much for my Conrads - they settled in at 30C above room temperature.

I cut the bias to 4A for the channel and got 26C above room temperature. Still a little high.

Tomorrow brings sound. I'm hopeful for a nice outcome. In the end I have to make some choices about voltage bias and heat-sink size. I think I'd have gone with bigger sinks if I knew I was going a Balanced Cascoded F5.

Ironically, this is the circuit I proposed a few times in the forum when I first started out (except for the cascoding).

[Melon Head]

As someone mentioned in one of the other threads, I think you are calculating the bias wrong.
I think you have 2A not 4A.

By the way, 26 degrees above ambient is fine.

[AndrewT]

Originally Posted by NYCOne

I biased to 2.6A for each side of the circuit (like the stock F5) making the Balanced side 5.2A.
I cut the bias to 4A for the channel

this cannot be right.
The bias for a standard F5 is 1.3A, not 2.6A

I suspect you have not read that other thread yet!

[Tea-Bag]

I would think if your gonna cascode, then might as well spike up the rail voltage.
I've got a BA2 cascoded in the works with 12 outputs per channel. Still waiting for some parts to come.

I am watching your threads here to wait for some sonic results of the cascoding and higher voltage input.

One can't be too eager. I've got a kid too, who is sick this weekend, so science project's stop. Good luck.

Btw, I like the cheaper Vishay T64 pots, as the resistance is printed clearly on it.

Good luck.

[Russellc]

Originally Posted by Tea-Bag

I would think if your gonna cascode, then might as well spike up the rail voltage.
I've got a BA2 cascoded in the works with 12 outputs per channel. Still waiting for some parts to come.



Good luck.

I hope you document that build, i would like to do one similarly as well.

Russellc