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One of the Top Solid-State CFA amp design
One of the Top Solid-State CFA amp design
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Old 21st June 2018, 05:24 AM   #731
R Dijk is offline R Dijk  Norway
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Quote:
Originally Posted by AndriyOL View Post
Q6, Q7 are MJE15035\34, with 4A Collector Current Continuous, 50W Pd.
I'll use 12-17 Ohm for R3, R4, whatever closer value I find to 70mA. There are prety big heatsinks, which are totaly cold now with current stock values. They only become little warm when PSU On witout load and the LEDs aren't working without load. This is frontend PSU from Roender's FC100 amp.
Perhaps I need to increase secondary windings to 47VAC without load, now it's 37VAC to have 50V out. Maybe it will be enough just only 45V for front end if the main amp PSU will be 40V, for example?
Thanks.
NICE!
>I think thats just fine, you have near 5V for regulation. Remember Zener diodes d7 d8 42-43V

transformer voltage * 1.42 minus diode voltage = first capasitor voltage = 37*1.42 - ( 0.6 +0.6 )= above 50v
Use 63V minimum capasitor rating.

Som will claim this is not inough. Due to variation in nett power supply for a few % you may then come close to the voltage the current sorce transistor needs (bc139 bc140) maybee 2v minimum.

Make shore the filter resistors R1 and R2 in powersupply is smal. 1 Ohm or less. (Too avoid much voltage drop)

If you use voltage doubling (not increase secondary vindings) you get just abobe 100v for first capasitor bank. that means tooo much change of components with werry litle result. For fun attached example of voltage dobbler (37*1.42*2 minus som diodes= just above 100)
Attached Images
File Type: png lazy doubler.png (85.0 KB, 108 views)

Last edited by R Dijk; 21st June 2018 at 05:41 AM.
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Old 21st June 2018, 07:16 PM   #732
mjona is offline mjona  New Zealand
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[QUOTE=AndriyOL;5468942]Because light bulb is more informative, can limit the current if something goes wrong.

Good luck with that superior attitude -if you keep doing the same things the same results will accrue.
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Old 21st June 2018, 09:02 PM   #733
AndriyOL is offline AndriyOL  Ukraine
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I never dealt with variac in such a way. I guess if I would, there will be a need for power resistors after variac, voltage meter to check the current draw. Light bulb is more simple solution against fault.

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Originally Posted by R Dijk View Post
NICE!
>I think thats just fine, you have near 5V for regulation. Remember Zener diodes d7 d8 42-43V
Do you mean when I'll have 47VAC secondary there will be 5V for regulation?
Or do you mean to leave current 37VAC secondary and use 42-43V zeners for the same output? (I exchanged 42V zeners to 50V types to raise psu' voltage)
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Last edited by AndriyOL; 21st June 2018 at 09:13 PM.
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Old 21st June 2018, 09:20 PM   #734
anatech is offline anatech  Canada
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One of the Top Solid-State CFA amp design
Hi Andriy,
The variac is by far and away the best way to power things up. You should have a built in voltmeter and ammeter (they sell digital one on Ebay for cheap). The variac will allow you to troubleshoot at reduced voltages and the equipment will act properly. I have seen cases where a light bulb in series can cause strange things to happen.

You will even get use to the sound of your variac. I use a 2A, a 3 1/2 A and a 15 ampere with add-on meters. It's the only way to fly. The only person who is happy with a light bulb tester is someone who doesn't have a variac. Or much experience and does have a variac. Use it, get used to it.

-Chris
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Old 22nd June 2018, 06:16 AM   #735
R Dijk is offline R Dijk  Norway
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Quote:
Originally Posted by AndriyOL View Post
I never dealt with variac in such a way. I guess if I would, there will be a need for power resistors after variac, voltage meter to check the current draw. Light bulb is more simple solution against fault.


Do you mean when I'll have 47VAC secondary there will be 5V for regulation?
Or do you mean to leave current 37VAC secondary and use 42-43V zeners for the same output? (I exchanged 42V zeners to 50V types to raise psu' voltage)
I mean to leave current 37VAC secondary and use 42-43V zeners for output near 45Volt.
Power supply circ:
(R1 and R2 near 1 Ohm ripple second capasitor bank, R3 and R4 current setting [ (1.8-0.6)/current sett= R3=R4 ], D7 and D8 are voltage out max setting.
voltage first capasitors 37*1.42 -1.2= near 51V without load. should give effectively near 5 volt for regulation when near 45 V out)
Have a nice modifying weekend.
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Old Yesterday, 06:41 PM   #736
AndriyOL is offline AndriyOL  Ukraine
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Originally Posted by R Dijk View Post
Have a nice modifying weekend.
Tnx. I've changed the R3, R4 to 15 Ohm. The front-end voltage isn't sag now (46.5V), but LEDs are off. I measured 1.5V on them.


Shall we finilize the schematic of the amplifier? Any thoughts about R Dijk input stage?
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Last edited by AndriyOL; Yesterday at 06:43 PM.
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Old Yesterday, 08:50 PM   #737
R Dijk is offline R Dijk  Norway
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ssahp.png

Quote:
Originally Posted by AndriyOL View Post
Tnx. I've changed the R3, R4 to 15 Ohm. The front-end voltage isn't sag now (46.5V), but LEDs are off. I measured 1.5V on them.

Shall we finilize the schematic of the amplifier? Any thoughts about R Dijk input stage?
Les of means current regulating transistor is not yet putting out calculated current, but somthing like (1.5volt led -0.6 volt base emitter / 15 Ohm resistanc =60 mA thats just within dynamic ragne and peak no or near zero current for shunt regulation... well if you want a tuch more and light reduse R6 and R7. that is base current for current sorce transistors. reduse somthig like 20% if 10k use 8k ( or multiply by 0.8 if u like that bether ). new output 1.8V LED-0.6v base collector/ 15= 1.2/15 = near 80mA wich makes shore shunt transistors in powersupply output is never of. Some consider this safe side, others BULLSH|T. Remember its still one very important thing here: Its you that is making amplifier NOT everybody else. you want light or not its as simple as that.

finalize ? me ? ive let mee learn that this is a LazyCat construction. I belive he simply love CFA configuration.

I gave one example of one way for stabilizing the construction when driving "heavy capasitive load". And i had a comment or to about transistors for input stage.

2sa979 2sc2240 is cheap value for money transistors. excellent replacement for what you say you are using. But by now you must have become doctor in repairing pcb's ??! Remember cleaning is werry werry werry werry important for performance so you dont make unwanted capacitors and make the construction unnessesearrrrrry dangerous.

Mid sommer sun at its highest and grilling is a must IF possiblle.
Still Nice weekend.

This attached should work. C3, C5 and C12 is stabilizing for bad load. Here is a print screen.

Last edited by R Dijk; Yesterday at 08:55 PM.
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Old Yesterday, 09:36 PM   #738
AndriyOL is offline AndriyOL  Ukraine
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Quote:
Originally Posted by R Dijk View Post
well if you want a tuch more and light reduse R6 and R7

Remember its still one werry important thing here: Its you that is making amplifier NOT everybody else.

finalize ? me ?

2sa979 2sc2240 is cheap value for money transistors. exelent replacement for what you say you are using. But by now you must have become doctor in repearing pcb's ??!
I guess you meant R5, R6

Before we agreed here that the amp is made for comunity, not only for me. Some contribute to design, I'll make a layout.

Sorry, I wrote it in the same post. I asked about finilizing the amp for all contributors, this wasn't addressed especially to you, but you already have taken a part in this.
Which input bjts can you offer as better than these - 2sa970 2sc2240? I'm using these transistors. Why do you think I have to become a doctor? Because I'm making many mods?

Enjoy your weekend!)
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Last edited by AndriyOL; Yesterday at 09:44 PM.
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Old Yesterday, 11:03 PM   #739
R Dijk is offline R Dijk  Norway
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Yea i ment R 5 and R 6.

2sa997 and its complement. for lower voltage bc550 bc560. here there is a variation slightly dependent on manufakturer slight regarding noise and current gain grup... witch one where for the porpose of...
slightly rugher for voltage 2N 5401 2N5551 but hav in mind they'r not the best regarding noise. The typical driver for mos and somtime vas stage 2sa1145 2sc2705 may bee hard to trace ( fake on the marked says this forum. 1w 200Mhz 150 volt . It enjoys a lot of voltage.... so on...... but i dont remember the full catalog .... I know many others have good transistor knowledge.
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Old Today, 05:46 AM   #740
AndriyOL is offline AndriyOL  Ukraine
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Fujitsu 2sa997 are very low Vce, 2sa1145 has low beta, not suitable for purpose. 2sa970/2sc2240 are better than others. As I know the only higher grade alternative could be Sanyo transistors from 90-th 2sa872, 2sa893 which are the most unobtainable.
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