lukas

Fonia Cenrit People United
« on: December 19, 2017, 11:37:35 AM »
Fonia Cenrit is Polish manufacture( i think this is very worth attention pre...i don't have, i listen old polish records i believe they from this preamp  ). I redrawn circuit from  what i found on web, but oryginal schematic is very bad quality,  if someone have information about(or even Fonia tubes Prea) or have this stuff, and can check correctly value, and tracking in my schematics, i will be happy.


lukas

Re: Fonia Cenrit People United
« Reply #1 on: February 01, 2021, 05:33:33 PM »
Correct version schematics of the Fonia WAB31a ... run and checked. Works ok.

abbey road d enfer

Re: Fonia Cenrit People United
« Reply #2 on: February 01, 2021, 05:51:36 PM »
Interesting schemo. ECC81 in the input stage is a tad surprizing.
I hope the rotary switch is MBB; if not gain change would not be very quiet!
« Last Edit: February 02, 2021, 02:53:07 AM by abbey road d enfer »
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

shabtek

Re: Fonia Cenrit People United
« Reply #3 on: February 01, 2021, 08:21:02 PM »
 first switch is doing a few things; altering bias of v1 would require MBB , also feedback from tertiary winding is varied with this same switch.

curious what the merits are of the v2 topology
"really fine players do not use stomp boxes or master volume, they match the amp to the room and turn it up to 11.  Stevie Ray, BB King, Albert King, Duane Allman, Dicky Betts, Louis Armstrong"
   -CJ

abbey road d enfer

Re: Fonia Cenrit People United
« Reply #4 on: February 02, 2021, 02:59:55 AM »
first switch is doing a few things; altering bias of v1 would require MBB
I don't think this switch has anything on bias.

Quote
, also feedback from tertiary winding is varied with this same switch.
That's what it is here for.
I was concerned with the grid becoming floating between positions if the switch is BBM.

Quote
curious what the merits are of the v2 topology
Just a way to get (almost) balanced drive without a PI. Works well enough for a class A push-pull.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

ruffrecords

Re: Fonia Cenrit People United
« Reply #5 on: February 02, 2021, 04:34:38 AM »
The gain switch is interesting. It appears to alter the open loop gain in step with the closed loop gain. This means the amount of feedback is kept more or less constant which considerably simplifies maintaining stability over a wide gain range.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

lukas

Re: Fonia Cenrit People United
« Reply #6 on: February 03, 2021, 06:49:45 AM »
Ecc81 its not the best tube on the first stage, but this is communist time... less everything...if i good remember Polish tube manufecture(...Philips Licence) made the tubes like ecc82-83 but in very small quantities. Ecc81(Ecc82, and Ecc83 too) taken form RFT, and Tesla companies, but Fonia decide to Ecc81...something...
All amplification stages, including the output transformer,
are subject to negative feedback with a value independent of rotary adjustable gain switch...Quotation from Fonia Manual.
I gave the original Fonia TK-15-005 output transformer (very good fraquency response...permalloy EI60 24mm stack), the input Lundahl 7903 ratio1: 8.
Grayhill switch without MBB i think - AJN (N - non shorting if i correctly reading)...my friend testing on the studio, and i don't tell me enything about  the pop's on them...

shabtek

Re: Fonia Cenrit People United
« Reply #7 on: February 03, 2021, 09:24:20 AM »
as drawn the transformer 'cold' end and electrostatic shield will are switched , the grid would me momentarily open or unbiased (I think is the word) when switching  BBM/ non-shorting...
"really fine players do not use stomp boxes or master volume, they match the amp to the room and turn it up to 11.  Stevie Ray, BB King, Albert King, Duane Allman, Dicky Betts, Louis Armstrong"
   -CJ