Paramount II

[ducati guy]

I saw a post recently on the Paramount II prototypes and their new C4S board with soft start. Any idea if this board will be available in the near future to modify an existing Paramount? Can I ask how the soft start is implemented?

 

[Paul Joppa]

It should be pretty soon. We are in a long process to switch to the new SR-C4S boards, currently only used in the Eros but destined to appear everywhere eventually. This will probably include the 5670 driver as well, which uses the "spare" shunt reg chip to generate driver bias. That opens up the possibility of more easily trying different drivers; I hope to convert mine to 6SN7s at some point.

The time delay itself is very simple - just a 10000uF capacitor across the LEDs on the driver plate load C4S. The new board has holes for that capacitor. However, the delay allows the driver C4S to be grounded at startup through the driver tube, which exposes the transistor to excessive voltage until the startup is complete, so the regulated voltage must be reduced from 350v to 300v to protect that transistor. That in turn means the Zeners will be changed as well.

 

[jrebman]

Are there going to be any other differences in the II version?

6sn7?  That should be really nice, though the 5670 is no slouch either.

-- Jim

 

[Paul Joppa]

I'm hoping to change the power transformer terminals to solder lugs and mount the power supply board on standoffs instead of the PC pins. That should make it more possible to remove the board for inspection and/or "editing".

The 5670 will reduce gain about 5dB; the SN7 another 5dB. A lot of systems, including mine now that I have an Eros, have too much gain.

 

[Paul Birkeland]

That reduction in gain should be quite nice.  What is your proposed operating point for the 6SN7?

 

[jrebman]

If one were to purchase a paramount kit now, will the new SSC4S board be available as an upgrade to the existing kit, or would it be best to wait?

Thanks,

Jim

 

[Paul Joppa]

I want very much to make this available to existing Paramounts. We have always tried to support previous products, especially to make available any improvements we discover after the initial introduction. That's not always possible (look at the difference between Foreplay III and earlier versions for instance!) but in this case it's pretty easy.

 

[edfallon]

I wouldn't let it hold up your decision to purchase now.  The conversion is as simple as replacing the SR/C4S board as mentioned earlier and a little rewiring of the driver socket if you choose to switch to a 5670 or another tube.  I converted mine in a couple of hours and that's with no instructions to go by.  It's not really that dramatic of an upgrade anyway, more of a continuing improvement type of change.  It could be important if you want to run direct coupled mesh plate 2A3's.  The slow startup feature is nice.

 

[jrebman]

Ok, sounds good.  Ed, yes, the slow start is really what I'm most concerned about as I want to build the amp with a switch for switching cathode resistors for 45/2a3 operation as Paul and I discussed in another thread, and then also have the option of running the 2.5 v sophia mesh plate 300b in direct coupled mode as well.  My current 2a3s are shuguang Treasure series black bottles, which are out of this world good and I'm not sure they would tolerate the startup surge too well either.

-- Jim

 

[Paul Joppa]

Until the slow start board is available, I would encourage anybody to stick with the supplied EH 2A3 if using 2A3s. The direct coupled circuit is hard on some tubes at present, and yoou don't want to risk damage to expensive exotics. We know the EHs work well along with most NOS biplates and the Sovteks, and we know of a couple exotics that have problems. That leaves a few dozen others that we don't know about.

 

[Paul Joppa]

As I look more closely at the 2A3 version of Paramount, I become more aware of its touchy nature. Direct coupling always makes it tricky to get the operating points right since everything interacts with everything else. One conclusion I am coming to is that your power should be pretty close to the design value of 120vAC - no more than 5v deviation - if it is to operate as designed. This is about half the variation that can be tolerated in the other products. I may try to implement a servo or adjustable bias for the direct coupled amps in the future.

More when I know more.

 

[jrebman]

Hmmm, I think I'll look into a cheapie USB DVM and set things up for a virtual strip recorder to analyze the AC voltage variation.  I have a 2.1 KW grid-tie PV system and I really don't know how that plays with the house voltage.  On a sunny or even partly sunny day it produces all our needs and then some, but what happens as the inverter goes from pumping out excess kwh and starts drawing off the service?  Rhetorical question, of course.

-- Jim

 

[AudioDave]

Ok, sounds good.  Ed, yes, the slow start is really what I'm most concerned about as I want to build the amp with a switch for switching cathode resistors for 45/2a3 operation as Paul and I discussed in another thread, and then also have the option of running the 2.5 v sophia mesh plate 300b in direct coupled mode as well.  My current 2a3s are shuguang Treasure series black bottles, which are out of this world good and I'm not sure they would tolerate the startup surge too well either.

-- Jim

Jim,  I am also interested in using a switch on my Paramounts to switch between 2a3 and 45 tubes so I am interested in how you are going to implement this.
Thanks!
Dave

 

[jrebman]

Dave,

Paul gives the answer in this thread:

http://www.bottlehead.com/smf/index.php/topic,81.0.html

I was planning on just using a heavy duty DPDT switch (double pole so as to double the contact area), with the 4k cathode resistor string on one throw and the 6k on the other, and with the common going towhatever terminal it came from.  Of course I won't know the layout and where to position the switch until I have the kit in hand.

Hope this helps,

Jim

 

[xcortes]

Until the slow start board is available, I would encourage anybody to stick with the supplied EH 2A3 if using 2A3s.

Hi Paul.

My christmas shopping this year was mostly focused on NOS tubes. You should have looked at the security guys at the airport faces! Anyway, since it is almost impossible to get three pairs of NOS of WE 300Bs (even without discussing cost) I decided to go 2A3 for a change and get rid of the coupling caps in the process. I got three nice identical pars of 1950s double plate RCAs.

Would you recommend me to refrain from modifying the amps until I get the new circuits? My voltage always sits at 120V (I use a Power Plant) and I have CL-90 thermistors at each amp.

Thanks and Happy 2010!

 

[Grainger49]

Xavier,

Happy New Year!

The CL-90 is nice for keeping the startup voltage from hammering the rectifier circuit but, sadly, it doesn't help in Cathode stripping (Insert David Rose & Orchestra here).

If I have it right, the high voltage is applied after the heater is at its rated voltage.  It can be done the cheap way, as I would do it, by putting a properly rated switch in the B+ to the output tube.  Maybe to the B+ to the driver too, I'm not sure.

The trick here is the properly rated switch.  Looking at Mouser most are rated at 125V, all sorts of current ratings.  I found one that is rated at 250V 1A.  That current is great but still not quite enough voltage.

Here are some 250V 1A results:    http://www.mouser.com/Electromechanical/Switches/Toggle-Switches/_/N-5g2j?P=1z0x3ugZ1z0z812

By the way, I would have loved to watch the security guys looking at a bag full of tubes.  My Post Office and mail carrier both think I'm weird sending and receiving Russian Military Surplus capacitors.  Too many packages from Ukraine, I'm probably under surveillance.

 

[Paul Joppa]

Well, I'm a cautious engineer type so I would of course recommend saving the RCAs until the board is installed. But I've never actually heard of a problem with those tubes. Maybe someone else here is using them and would comment?

 

[xcortes]

Thanks Paul and Grainger.

I think that I'll install the Rubli's B+ delays that have been discussed before. Eventually, when the BH boards are available I can move Rubli's to the Paramours in the HT.

The best for 2010!