2 pc 200VA transformers are more capable then your single 300VA, wich is too smal. +/-32V rails and about 2A bias (to get 50W class A at 8ohm) is 128W dissipation pr ch. So a total of 256W dissipation+++. 18V sec will give you less power for a given load then 24V sec. But if one use 4 ohm speakers, then you might be better of with 18V sec. Lower sec voltage = higher bias current.
18V sec give you about 25W at 8ohm. While 24V sec give you about 50W at 8 ohm. That is only 3db differnece. You can gain that and alot more by changing speakers.
For +/-32V rails and 2A bias (to get 50W class A at 8ohm), you need 2x300VA or a single 600VA for a 2ch stereo amp.
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By the way. I'm using the class-A calculator at post 1426 (page 70) and with 2pair per channel, 25V rails, 0.68R emitters, 4ohm speakers and a bias voltage of 400mA I get 11W Class-A output.
Given my 2x18V 200VA transformer per channel and provided that the colling is enough, how high do you recommend me to bias?
I would like av value that lets me switch between speakers without the need to re-bias.
600mA gives me 25W class-A and a total bias of 3,53A
The total power draw would then be 88,25W
That is less than half what the transformer is rated for.
The same way 850mV still only gives 125W on the transformer and 50W Class-A at 4ohm Am I missing something?
Given my 2x18V 200VA transformer per channel and provided that the colling is enough, how high do you recommend me to bias?
I would like av value that lets me switch between speakers without the need to re-bias.
600mA gives me 25W class-A and a total bias of 3,53A
The total power draw would then be 88,25W
That is less than half what the transformer is rated for.
The same way 850mV still only gives 125W on the transformer and 50W Class-A at 4ohm Am I missing something?
Correct. mV.
Why do I need 300VA?
850mV equals 2.5A per rail, that in turn only draws 25x2.5x2 =125W and that is far below the 200VA.
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Ah, but my calculations where correct at least (I just edited to clarify).
But how can a transformer not handle half of its rated value?
That is hard to believe.
Yes, I forgot he had mono blocks.
According to the calculator, mine is 36w/ch Class A, 65w AB into 8r The devices run at about 62C and the heatsink is 57C with the fan on medium (it's a 3 speed 4" USB fan).
24v 300va transformer, 3 pairs of output transistors. The transformer does get pretty warm but not hot (<60c)
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NO. I don't think there is any shortage of suitable TO3 transistors and why skimp on buying the genuine thing from Digikey etc?
i would not trust that calculator. A singel 300VA transformer of 2x24V sec loaded that heavy will gve you under +/-30Vdc rails. and there will be some loses in the outputstage too. so you will have about 40-45W class A/B at 8ohm. And 36W class A at 8ohm indicate about 1.7A bias. That is just about 200W total dissipation for 2 ch stereo amp.
Mine ,easures 36v @ 1.5a per rail, per channel. I have 0.1f of reservoir caps per rail too which will help with transients.
Yes, you are correct. 1.5A give you 36W class A at 8ohm. 1.7A give you around 35W at 6ohm.
Your cap bank does not help anyting with voltage sag do to heavy continous load on the transformer.
36Vdc on 24Vac transformer? Then your transformer put out way more then 24V.
sec voltage x 1.414 - diode drop (0.7V typical with single bridge. or 1.4V with dual bridge). 24x1.414=33,84V before the diode drop.
Your cap bank does not help anyting with voltage sag do to heavy continous load on the transformer.
36Vdc on 24Vac transformer? Then your transformer put out way more then 24V.
sec voltage x 1.414 - diode drop (0.7V typical with single bridge. or 1.4V with dual bridge). 24x1.414=33,84V before the diode drop.
I think my transformer may be 25v, and is for 230v mains but mine is usually around 245v which comes out at about 36v.
That would raise the sec voltage with about 7-8%. that would explain a thing or two
Now, after I made the chassis for my mono blocks with heat tunnel and fans I got these sinks cut from a larger part.
The sinks are about 130x75x60mm each and 10-12mm at the base.
My plan was to use them for a class-AB amp (Greg ball gb150) but seeing the result I am starting to wonder if these are large enough for the KSA-50.
What do you guys think?
I have think angle bars available to attach the TO-3 transistors but what about the heat?
Any qualified guesses?
The sinks are about 130x75x60mm each and 10-12mm at the base.
My plan was to use them for a class-AB amp (Greg ball gb150) but seeing the result I am starting to wonder if these are large enough for the KSA-50.
What do you guys think?
I have think angle bars available to attach the TO-3 transistors but what about the heat?
Any qualified guesses?
You could do what I did on my F5...bias up the amp until your sinks are consistently around 140F (I like to use Nelson's "hot hands" method).
I think you may be ok with your heatsinks at your set bias, but unfortunately, if the sinks are not already made for TO-3 transistors, anything you build onto the heatsink will add a lot of thermal inefficiencies, reducing the overall cooling capacity of the sinks...
I think you may be ok with your heatsinks at your set bias, but unfortunately, if the sinks are not already made for TO-3 transistors, anything you build onto the heatsink will add a lot of thermal inefficiencies, reducing the overall cooling capacity of the sinks...
Way too small unless you run at low bias.
My heatsink for a pair of clones is 30cm x 12.5x12.5 with a 4" fan and TO3 cans run at about 60C & heatsink at 54C with a bias of 0.5amp per transistor for 36w (according to the calculator). With the fan turned off, the temperature shoots up to over 75C.
It would have been better to use a heatsink drilled for TO3 cans.