76 in the Paramount

[Paully]

As usual Grainger and I are looking for something to do.  On the old board I had asked about converting the Paramount to 76 to drive the 45.  I was told I would have to add another triode which may be quite a squeeze.  I have the soft start boards.  The 2C4 was suggested and could possibly use half of a 12at7 since I have so many.  Just musing, would there be any other major concerns I should worry over?  It sounds like quite a project and something that could be a lot of fun.

[Grainger49]

We are thinking about a 45 output tube and a capacitor coupling between the driver and the 45.  I figure that changes some of the parameters so I thought to mention it.

[2wo]

Are you already running the 45 with the stock tube? I forget what it is, 5670?...John

[Grainger49]

He has a 45 output and soft start board (stock 5670) driver.  This question is concerning a scratch stereo 45 build.

[Paul Birkeland]

You could likely squeeze in a pair of 0A2's to perform the task of regulating without the need for eating up filament current (or needing the zener string).

[John Roman]

Any progress on the 76?

[Paully]

I bought a pair of driver boards for a scratch build.  We are going to build a tube rectified 45 amp with the Magnequest chokes and transformers.  It seemed a shame to leave the original Paramount transformers lying around when the Paramounts have a 300B power supply waiting for them.  So I converted the Paramounts back to 300B and we will should get around to the scratch build around Christmas.  The plan is to build some monoblocks using the 5670 as the regulator, a 76 as a driver, and a 45 as the output tube.  If there is room underneath I will get the Bottlehead filament chokes as well.  Not certain yet but thinking about an 866A Mercury rectifier.  Have been reading about those starting to have flaking problems due to their age that can cause internal arcing, but it is still tempting.  Not sure what rectifier we will settle on but we are working it out.

[2wo]

Try AC on the 45's. My SR-45 has very little hum...John

[Paully]

We have been going back and forth on that.  With my Altecs being so efficient I was concerned about putting AC on the filaments.  The Paramounts sound pretty good with DC!  I suppose we could leave space for rectification but try AC to start.

[2wo]

Yea, with the Altec's I see your point. Tough call...John

[Paully]

I assume in the end we will just go DC on the filaments.  But I reserve the right to change my mind.  Often.