Bottlehead Forum

Bottlehead Kits => Legacy Kit Products => Topic started by: Jim R. on June 29, 2013, 09:59:58 AM

Title: Does the PT2 have enough juice for a shunt regulated driver stage?
Post by: Jim R. on June 29, 2013, 09:59:58 AM

As I'm looking over the assortment of parts and iron I have I came across a combination that I wasn't sure if it would work or not... a pair of paramour IIs in 2a3 mode and using the paramount v1.1 driver board for a shunt regulated driver stage.  Everything else the same -- RC coupled, AC filaments, etc.  And I could go with standard MQ BH5-ni OPT and BH6 chokes, or could go with nickel tfa-2004 jr and dowdy chokes gapped for 60mA.

Any reason why this wouldn't work, or should I just put all the eggs in the Paramount 2a3 and leave it at that?

-- Jim

Title: Re: Does the PT2 have enough juice for a shunt regulated driver stage?
Post by: Paul Joppa on June 29, 2013, 12:04:28 PM

Yes it does. The original Paramour I was limited to 55mA (50mA for the 2A3, 4mA for the driver,, and 1mA for the C4S bias). When I specified the transformer for the Paramour II I asked for at least 60mA capability, for exactly that reason.

Title: Re: Does the PT2 have enough juice for a shunt regulated driver stage?
Post by: Jim R. on June 29, 2013, 01:30:40 PM

Well then, I don't see any reason that I shouldn't take advantage of that future planning you did. ;-)

Though I suppose it will be configured somewhat differently than the 2a3 paramount considering the direct connection, or maybe that's not part of the calculation.

Thanks,

Jim

Title: Re: Does the PT2 have enough juice for a shunt regulated driver stage?
Post by: Paul Birkeland on June 30, 2013, 07:20:34 AM

Quote from: Jim R. on June 29, 2013, 01:30:40 PM

Though I suppose it will be configured somewhat differently than the 2a3 paramount considering the direct connection, or maybe that's not part of the calculation.

Yes, somewhat differently.  Depending on which manual you have (soft start or classic 12AT7), you will want to drop the regulated voltage down to something closer to 280V, which isn't all that tough to do.

-PB

Title: Re: Does the PT2 have enough juice for a shunt regulated driver stage?
Post by: Jim R. on June 30, 2013, 08:54:08 AM

Thanks, PB -- that sounds straightforward enough.

-- Jim

Title: Re: Does the PT2 have enough juice for a shunt regulated driver stage?
Post by: Paul Joppa on June 30, 2013, 02:54:13 PM

It is not necessary to change the regulated voltage - the PSU provides 380v, giving an 80v compliance margin for the 300v regulated.

Title: Re: Does the PT2 have enough juice for a shunt regulated driver stage?
Post by: Paul Birkeland on June 30, 2013, 05:16:47 PM

Quote from: Paul Joppa on June 30, 2013, 02:54:13 PM

It is not necessary to change the regulated voltage - the PSU provides 380v, giving an 80v compliance margin for the 300v regulated.

I see 320V on the schematic. 

Title: Re: Does the PT2 have enough juice for a shunt regulated driver stage?
Post by: Paul Joppa on June 30, 2013, 06:52:15 PM

Oh yeah, I forgot it was designed around the Speco which had to be grounded. Using better transformers, I would move the signal ground to the negative PSU point, as in the Stereomour, and pick up the extra 60 volts. More headroom for the driver that way. Replace the 1.1K bias resistor with 1.2K, also as in Stereomour.

Title: Re: Does the PT2 have enough juice for a shunt regulated driver stage?
Post by: Jim R. on July 01, 2013, 05:41:57 AM

Thanks again Pauls.  I'm liking this idea more and more. I always really liked the sound of the Paramour IIs and hoping this will make it just that much more enjoyable.

Thanks,

Jim

Title: Re: Does the PT2 have enough juice for a shunt regulated driver stage?
Post by: Jim R. on July 02, 2013, 11:58:58 AM

I guess it's official now -- I ordered the soft start kit, a new box of iron from MQ is here, and my new workbench for my garage shop will be here friday afternoon.  Then it's time to setup the new drill press and get to making the copper top plates.

-- Jim