45 Paramount

[vetmed]

IIRC one of the regular contributors around here uses 45s in his Paramounts. Since I recently changed mine over to 2A3s I wonder what would need to be changed to run 45s. TIA

Robert Lees

[Paully]

You might mean me...  Anyway, here is a post that I originally used.  Read on into it, PJ outlines the changes.

http://www.bottlehead.com/smf/index.php/topic,895.0.html

I ended up using 6800 ohms total for the resistors mentioned to get everything where I needed it.  It is really easy to accomplish and then you can see if you agree that all the fuss is worth it.  Just change two Cathode resistors per amp and wire everything back up.

[vetmed]

Thanks. I read the thread in the link, seems like an easy mod. Adding 2800 ohms to the 4000 already there should be easy


Robert Lees

[Paully]

Good point, adding another 2 - 2.8K is easy.  I replaced both 2K with resistors with 3K and then threw in another 680.  But just putting a 2.8K resistor in and leaving the ones there is even smarter.  Why didn't I think of that?

[Jim R.]

I think I'm missing something -- in the post pauly referred toabove, PJ said to replace a 4k cathode resistor with a 6K, so where did the extra 680 ohms or so come from??

Is ok to have both resistors and a jumper that can be moved to select 2a3 or 45 operation mode?

I'd be building this amp with a MQ BH6 and a all nickel TFA 2004 jr.

Then... what would things look like with a 60 ma dowdy and an exo-145 -- anything else in the circuit need changing? (assuming 45 only operation).

Thanks,

Jim
 

[johnsonad]

You may have a slightly larger voltage drop across the Dowdy. Something to verify at least.

[Jim R.]

Aaron,

Yes, but that in combination with the 5k primary of the OPT and the overall higher voltage of the paramount, the direct coupling and the SS board make me think there is going to be more to it.

If it's too much or unsafe the dowdy and exo-145 will go in the sr-45.

I have enough very nice parts to build 3 pairs of amps -- the question is do I want two 45s and a 2a3, 3 45s or 1 45 and two 2a3s. I'm going to try the best stuff in the sr-45 first and see what happens there, but the direct coupling and dc filaments of the paramount are also a very tempting possibility.

-- Jim

[johnsonad]

Don't give up on 300B's my friend. I'm a happy convert!

[Jim R.]

I'd still consider it but the largest opts I have are tfa-2004 jr.s -- one all nickel and the other m4 pinstripe. Just don't know how they'd work with the 300b power output. Already have a bh7 pair on the way.

-- Jim

[RPMac]

My ParaBee,s have TFA-2004 Jr,s nickel.

[Jim R.]

Robert,

Thanks, thatis good to know. Now I'd just have to decide whether the nickel goes with the 2a3 amps or the 300b amps, the other getting the m4 pinstripe.

-- Jim
 

[johnsonad]

Jim, maybe Mikey would give us a deal on two pair of full 2004's . You could also use an EXO-050 like I am in my 300B amps.  There are operating points for 50mA and 60mA in 5k and 3k.

[RPMac]

Maybe three pair...I've always wanted to try the 2004 on my Paraglows.

[Jim R.]

Well, I'll have to pass -- no money left, and if I did have some I'd snap up a pair of those m4/pinstripe z565s with brass ends -- I'm well set for amps, tube and SS, but I'd still love to build a scratch ppp class A 6v6 or El84 amp, with a phase splitting autoformer. Oh well, I've made my choices and things are pretty stable at this point. I just bought a mission style Morris chair for my listening room, so that kind of blew the rest of my toy budget for a good while now.

-- Jim

[RPMac]

I hear you about the Morris chair. Trying to talk my wife into one, but when I show her a Stickley, she faints.