Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Paramount => Topic started by: xcortes on July 26, 2013, 08:29:08 PM
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What changes in addition to removing the plate choke and parafeed cap would be recommended to modify a Paramount (2A3 soft start) to series feed? I am in the process of getting a DS 025 transformer. Thanks
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Paramour or Paramount? In either case I would measure the DC resistance of the choke and the primary of the DS 025 and see if this makes a significant difference to the plate voltage.
Robert Lees
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Paramount. Corrected the original post.
I don't have the 025s yet. Mike will build me a very special and unique pair. In any case the difference from the plate choke I don't think will be much more volts and the soft start driver provide for adjustable voltage so dialing up is easy. But do I have to do something with, for example, the ps caps?
Thanks
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Give us the details on that iron my friend!
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You do not HAVE to make any other changes.
But for the best sonics, I would do the following:
1) replace the 270-ohm power resistor in the power supply, with a filter choke such as the good old C7-X. For you Xavier, see if you can find one of the made-in-Mexico Triad ones!
2) For the last PSU capacitor, replace the two electrolytics with a 630-v film capacitor of 20uF or greater, and take the negative end to the hum pot center terminal (the effective cathode connection) rather than to ground. This capacitor carries the signal current, and thus has a similar effect to that of the parafeed capacitor.
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@ Aaron: the all silver version of the QS 025 doesn't have 4 ohm taps so Mike will build me an all silver pair with 4 ohm secondaries.
@Paul I already have MQ filter chokes BMC8 I think so point A has bee taken care of. As for point B let's see if I uderstood correctly. I take out the two last filter caps (270uF) and install the new one from the + rail to the hum pot. And make it a nice one. Am i right?
Thanks a lot Paul.
Ps I'm at the storage facility leasing some space for the big horns, Karlsons etc. Didn't knew how big and sunny my living room is. Now the three pair of Paramounts will be different: one pair Ni tfa 2004, the second Co pinstripes 2004 jrs and the third series feed silver primaries and secondaries. Each game has different types of fun. Let's see for how long I can survive without the big sound.
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Keep us updated as to which set of amps matches those WE's best!
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...I take out the two last filter caps (270uF) and install the new one from the + rail to the hum pot. And make it a nice one. Am i right?
You're right. Should be interesting! :^)
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3 Pairs 3
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Don't let go of those 2004's without letting me know please! (Not as if you will :))
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Nope. No intentions to let them go. With these two pairs I have everything to build (rebuild) two pairs of Parabees for the Quads.
I' also keeping the three pairs of tl404s. The day I get back to horns it will be with a revenge: sr45s.
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I hope that you don't mind me inviting myself for visit at some point Xavier! I really would love to hear your system! You always have a place to stay in San Diego!
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Right now I don't have a system :)
But you're welcome any day. We have a guests' room and now that I rented some storage it may even come with a useable shower!
If things go well I hope to start renting a place in Coronado next year. I used to go to SD several times a year when my girlfriend (now wife) lived there. And subsequently for many years until my inlaws moved to Mexico about three years ago. Most of my BH kits and MQ iron went to their Chula Vista house.
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Xavier,
I would imagine with that many tubes removed your living room is not only larger but cooler.
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Paul,
I've been studying your suggestion and I learned that what you suggest is an ultrapath topology. Thanks for the lesson!
BTW, would the change be the same for a 300B Paramount? How about a Parabee?
Thanks!
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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
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Sure, Xavier. And I promise I won't make any inane posts on this forum in 20014.
;D
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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?
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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
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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 !
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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
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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