FP III Extended kit

Wired · 3060

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Offline Wired

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on: September 02, 2023, 05:25:56 PM
Greetings,

I have a FP III that I purchased with the Extended kit. I've been running it without the kit until now and have been very happy with its performance. I'm now building a set of OB speakers with high sensitivity horns (110dB) and am looking to tweak the FP's performace a bit. I was looking over the schematics and it looks like the two C4S upgrades can be done independently of the shunt upgrade. Is this correct? I'd like to gain the C4S advantages but don't want to add the shunt upgrade because I like the looks of the tube rectifier too much :)

Thanks!


Rick


Offline Thermioniclife

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Reply #1 on: September 02, 2023, 06:55:26 PM
The 0d3 tube is a voltage regulator not a rectifier. the preamp uses diodes for rectification. If you want to keep the 0d3 give it a try and check your voltages, and if they check ok than cool. But I can tell you that the Extended shunt regulator is an improvement. Ymmv.
If P.B. chimes in I'm sure he can give you far more insight than me.

Lee R.


Offline Paul Birkeland

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Reply #2 on: September 03, 2023, 06:36:46 AM
Yes, you can put the C4S boards in without installing the shunt regulator upgrade.  You could leave the octal socket and use a 6SN7 in the middle if you'd like to keep the look of a fatter tube in the middle, though the cement resistor in the heater power supply will likely need its value dropped a bit to trim the heater voltage back to 6V.  There are some super cool new production globe 6SN7s floating around. 

The SR power supply also drops the noise floor down a bit.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Wired

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Reply #3 on: September 03, 2023, 11:45:49 AM
The 0d3 tube is a voltage regulator not a rectifier.

Hi Lee, thanks for the catch. I meant regulator. Sometimes the fingers don't type what I mean :)

 

Rick


Offline Wired

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Reply #4 on: September 03, 2023, 12:23:53 PM
Yes, you can put the C4S boards in without installing the shunt regulator upgrade.  You could leave the octal socket and use a 6SN7 in the middle if you'd like to keep the look of a fatter tube in the middle, though the cement resistor in the heater power supply will likely need its value dropped a bit to trim the heater voltage back to 6V.  There are some super cool new production globe 6SN7s floating around. 

The SR power supply also drops the noise floor down a bit.

Paul, thanks for your reply. You make excellent points that I haven't considered before. :-[ I should have been asking these questions a decade ago lol


Rick