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ETI 477 resurrected but with problems.
ETI 477 resurrected but with problems.
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Old 11th December 2018, 06:14 AM   #31
arthur is online now arthur
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Join Date: Oct 2001
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ETI 477 resurrected but with problems.
Default ta 477 kit

see attached
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Old 11th December 2018, 06:27 AM   #32
Ian Finch is offline Ian Finch  Australia
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Location: Coffs Harbour, NSW
On Semi's KSC3503/KSA1381 have been the go-to CRT driver transistors here for many years. If SMD is OK, BF720-722 are Nexperia and Infineon's SOT223 versions of the original Philips and Siemens BF469/470. Their wide collector tabs provide for some essential cooling but perhaps not enough for ETI477, where the VAS normally runs very hot.
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Old 11th December 2018, 07:01 AM   #33
Leinster Lad is offline Leinster Lad  Australia
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Quote:
Originally Posted by Ian Finch View Post
On Semi's KSC3503/KSA1381 have been the go-to CRT driver transistors here for many years. If SMD is OK, BF720-722 are Nexperia and Infineon's SOT223 versions of the original Philips and Siemens BF469/470. Their wide collector tabs provide for some essential cooling but perhaps not enough for ETI477, where the VAS normally runs very hot.

Thanks for the info Ian.
Would these be direct "drop in" replacements for the BF's ??


Also, I notice that the 2SC3505 and the KSC3505 are noted on the data sheets as the same.
Is this correct or is there actually a difference ??
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Old 11th December 2018, 07:20 AM   #34
RM is offline RM  Norway
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Join Date: Apr 2005
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Tran, not re.

Snigger.

R
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Old 11th December 2018, 07:25 AM   #35
Leinster Lad is offline Leinster Lad  Australia
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Join Date: Jun 2013
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Quote:
Originally Posted by arthur View Post
see attached

Thanks Arthur, I can see a few component changes in your schematic.


A couple of quick questions please.


The position of R16 and C5 are reversed and the voltage of C5 reduced from 25v to 16v in your schematic. Is there a reason for this ?


C6 (10pF) has been increased to 12pF in your circuit. (NFB)



Cap C14 on the base/collector of Q6 is increased from 220pF to 470pF in your circuit. Is this to stop oscillations ?


Gate drive resistors increased to 470 ohm
Gate clamp zeners increased from 12v to 13v .
Diodes changed to 4148's

C3 on the input leg has been changed from 330pF to 470pF.

C10 and C11 increased from 47nF to 68nF.
Values at output zobel(?) changed



I would be very appreciative if you could take the time to explain to me the reason why these values have been changed.
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Old 11th December 2018, 07:39 AM   #36
arthur is online now arthur
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Join Date: Oct 2001
Location: .
ETI 477 resurrected but with problems.
I can't explain as this was not changed by me
This was the kit from a hong kong electroinc company
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Old 11th December 2018, 08:32 AM   #37
Leinster Lad is offline Leinster Lad  Australia
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Join Date: Jun 2013
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Quote:
Originally Posted by arthur View Post
I can't explain as this was not changed by me
This was the kit from a hong kong electroinc company

Okay, thanks
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Old 11th December 2018, 08:48 AM   #38
RM is offline RM  Norway
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Join Date: Apr 2005
Location: Buskerud
Tran, not re.

Snigger.

R
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Old 11th December 2018, 09:36 AM   #39
manic mechanic is offline manic mechanic  Germany
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Join Date: Nov 2018
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I built six of the Tilbrook amps in 1982 for a 3 way active unit. The design was published in Germany in elrad magazine in 81. It took me quite a while to cure a wild oscillation of each and every amp - R29 in the kits didn´t look like but was wire wound. Replacement solved the issue once and for all.

Regarding replacement of the BF´s, there obviously is NOS of a GDR/CSSR-equivalent for the BF 470 (Tesla KF 470) available here for peanuts:

https://www.pollin.de/p/pnp-transistor-tesla-kf470-131455
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Old 11th December 2018, 11:10 AM   #40
schillg11 is offline schillg11  Germany
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Join Date: Dec 2011
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I also built the Elrad PowerMosfet from 1981 and solved the oscillating , with 5 x 1 Ohm resistors in parallel, later when dig out again with 0.22 Ohm Metal band resistors (MPC-71) for the source resistors of each MOSFET. It's still running and remaind me at the former HITACHI HMA-7500.
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