Paramount Soft Start Upgrade
Firstly the new driver PC board has a soft start function (and yes, this kit includes two boards, one for each monoblock). This delays the B+ to the plate of the driver tube for about 30 seconds at startup. I should note here that once fired up, the amp will need to sit for about 20 minutes after you turn it off for the circuit to “reset” itself and function with the soft start. This was added in response to a user who was using some exotic 2A3s in the direct coupled 2A3 version of original Paramount and experiencing those 2A3s arcing at startup when hit with the driver plate supply B+ before the filament could heat up. This new soft start circuit resolves that issue, assuming that the user takes care to wait the specified time before restarting. This should not be an issue in the cap coupled 300B version. However the soft start may be useful in extending the lifetime of other tubes as well.
Secondly, the zener diode string has been beefed up. The original string worked fine unless you goofed something up in the build that overstressed it. The new string is much more tolerant of errant solder joints, miswires, etc. The circuit has been stress tested by Doc B. inadvertent-, uh, personally.
The MJE5731As on the new PC board now sport heat sinks to extend their reliability as well.
One of the most noticeable changes is that we have gone to a 5670/2C51/WE396A tube as the driver. Why? Partly because a lot of folks found that the 12AT7 had to much gain in their system which led to hair trigger volume controls and a bit more transmission of the noise floor from front end equipment than they liked. The 5670 has a mu of 33 as opposed to the mu of 60 of the 12AT7. The 5670 is also a very sweet sounding, particularly linear tube, that we feel is step up sonically from the typical 12AT7. There’s enough variety of brands to make tube rolling interesting and it is not prohibitively expensive. Even if you are running your Paramount in 300B mode like Doc does, you may find the 5670 a most compelling reason to upgrade your Paramounts to the new setup.
Impressions
“Last night I finished installing the Paramount soft start retrofit kit. As usual the excellent instruction manual made the retrofit an easy build. But, because of all the modifications that I have made to my Paramount the build was a little more complicated, actually a real pain in the ass. A stock Paramount would not be difficult at all.
Put the Paramounts (300B version) back into the system this morning, I had forgotten what a wonderful amp the Paramount is, and that in the right amp the 300B is an excellent sounding tube. I have been playing around with several amps (4) with the 45 power tube. Thought I had found the ideal sounding power tube, but after listening this morning to the Paramounts with the soft start retrofit installed has made me rethink my previous assumptions.
Now the fun begins, listening and tube rolling. Highly Recommended upgrade, one of the best “bang for the buck” that I have encountered in audio.”