Non parafeed Paramount

[xcortes]

Paul, I promise that this will be my last how to modify anything questions for 20013.

If I want to do the said conversion to the 300B version of a Paramount or a Parabee, would the changes be the same.

AND, for what current would you recommend that the transformer be gapped?

Thanks a lot!

Xavier

[adamct]

Sure, Xavier. And I promise I won't make any inane posts on this forum in 20014.

 

[Paul Birkeland]

If I want to do the said conversion to the 300B version of a Paramount, would the changes be the same.

Are you planning on FS-030's or TFA-204's?

[xcortes]

Ds025s all silver. Mike is building me a pair with all silver windings and 4 ohm secondaries which normally don't appear in the silver version.

Originally I was planning to build a Baby Ongaku. Later I decided to try a 300B BO (Ongaku Jr?). But it looks like the SR45 project will leave me with three spare pairs of Paramounts so probably I can just rebuild one. And I also have two pairs of ironless Parabee to rebuild so.....

My last request to Mike was to gap it for 70mA following a PJs post on the MQ forum where he auggested:

"2) You can ask Mike to make some DS-025s that are gapped for more current. You will lose some inductance and hence some deep bass, but otherwise it would retain the Baby-O basic character. Gapped for 70mA and operated at 300v at 60mA, which is a well documented 300B operating point, with very nearly the same cathode resistor - less than 2% different. You might get 7 watts. Full power DC current is 74mA, so DC overload will be similar to the Baby-O"

http://db.audioasylum.com/mhtml/m.html?forum=magnequest&n=10634&highlight=300b+baby&r=&search_url=%2Fcgi%2Fsearch.mpl%3F

Thanks

[xcortes]

OK Paul, since you're about to go for vacation I'll make it a single question and no more for the year

I'd like to replace the TFA 2004 and exo 03 in a Parabee with a ds025 gapped for 70mA. I like the idea you mentioned before of doing ultrapath: replacing the last electrolytic in the ps with a nice one and going to the cathode instead of to ground. So the big question is: what size a cap would be correct here?

Thanks !

[Paul Joppa]

The usual recommendation comes from Thorsten (used to be pretty active on the DIYtube and SET boards). If the capacitive voltage divider ultrapath/cathode bypass matches the gain of the output stage, then any noise on the power supply is cancelled by cathode injection. Hard to be exact unless you are driving a constant-impedance speaker like a Magnepan, but roughly a gain of 3 so the ultrapath is 1/2 the cathode bypass. This assumes both are large - let's say, 25uF/50uF minimum for full frequency range.

Note that this does not affect the driver sensitivity to power sully noises - a C4S will solve that, but I wanted to mention it. With a c4S's driver, this is kind of a poor-man's shunt regulator.  :^)

I'll be back by the D

[xcortes]

Awesome. Thanks a lot! I will be using the driver section from the original Paramounts that I saved when I went soft start so its sr and c4s.

Enjoy your vacation.

Xavier