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PP CFB toroidy OPT

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LKA

LKA

Member
Joined 2014
Hi,

I'm building my second VT power amplifier (designing first). It consists of
- two OPS boards
- two DRIVER boards
- 6.3VDC PSU (DRIVER heaters)
- AC power control board
- 5V/12V PSU
- 120VA transformer for heaters
- 200VA transformer for HT and bias PSUs
- two toroidal CFB OPTs from toroidy.pl
- metal chassis
Maybe there will be also
- one analog meter for bias setting
- remote control board (on/off, volume)

Almost all components are ready. I'm about to design DRIVER board and I want to know your opinion. There are two DC coupled LTPs supported by CCS and powered by mosfet regulators. First stage E88CC, second stage E88CC or ECC99, heaters have configurable jumpers. Regards NFB, you can have global or/and local "Schade" feedback.

PP1-DRIVER-v1.3.JPG
 
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M

multi

R.I.P.
Joined 2011
6550 cathode feadback

I have two toroidal CFB OPTs from toroidy.pl for 6550 /KT88.
I hope to use the attached circuits Still to decide which one} capable of 180 volts RMS into 47k load {47K is max for current 6550 and KT88 tubes} using the 5687. A toroid power transformer and solid state rectifiers
 

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G

gregt

Member
Joined 2012
Nice design. I built a CFB amp using Toroidy CFB transformers and they worked well, but did have an initial issue with instability at low frequency. (High frequency was fine). I initally suspected power supply but on testing observed slight more phase shift a 10 Hz that I was expecting. I solved problem by using Normal Koren design concepts and instead of global feedback to the first stage I changed to feedback to the drivers.
 
G

gregt

Member
Joined 2012
See thread PP amp with Toriody Transformers and 7591A
Note that schematic changed on post 28. Samples of output into 8 ohms parrelled with 1uf. I like the look of your design...but I choose the 7591a tube as this is easier to drive given that the use of CFB the drive requirements double.
 
G

gregt

Member
Joined 2012
My understanding is that Toriodal transformers are more sensitive to DC imbalance in the output pair. John Broskie (Tubecad) proposed a Cross-Refenced Auto Bias Circuit in his thread "Blumlein’s garter circuit revisited"

I will try this in my next design (also using Toriody transformers)
 
Lingwendil

Lingwendil

Member
Joined 2008
gregt said:
My understanding is that Toriodal transformers are more sensitive to DC imbalance in the output pair. John Broskie (Tubecad) proposed a Cross-Refenced Auto Bias Circuit in his thread "Blumlein’s garter circuit revisited"

I will try this in my next design (also using Toriody transformers)
Click to expand...

Garter bias works very well, and I use it a great deal. I like it enough that my Flea amp uses it, and to be designing a PCB for it with EL84/86 types- 6N2P/6CW5 design with toroidal outputs
 
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