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We've been kicking around the best way to go about making up a kit of parts for the fully shunt regulated mod for Paramour IIs with the MQ iron upgrade. I'd like to keep the cost as low as possible on this one, and one way to do that is to reduce our labor. The biggest consumer of my time on this kind of thing is writing a manual. Since this is a pretty advanced circuit and I suspect we not not sell hundreds of them, I have decided to offer it as a kit of parts plus a schematic and a photo or two of the mod installed on my own Paramour IIs. If the community is up for supporting each other on the installation so that I don't have to spend a week writing and photographing "Disconnect the red wire from terminal 11. Install a 158K ohm 1/2 watt resistor as shown in the photo" etc., etc. I can put out this kit of parts for two shunt regulated/C4S PC boards, new cathode resistors for the 45 tubes, two 6CM7 tubes and a bit of extra wire for $99.This will be a "production run", that is, I will do a limited number of kits based on how many orders I receive by Friday.
One critical thing to note here is that the 6CM7 driver has lower gain than the 12AT7 used in the stock circuit. So you will find that you need to turn up the level controls on your Foreplay a few notches after the installation. If you are using another preamp besides the Foreplay be sure that you have enough headroom (i.e. clicks above your typical level setting) left on your volume control to drive the less sensitive amp. Figure that you will need to be able to set the level 6dB higher to be on the safe side.
The question has already come about if this kit can be fit into older versions of Paramour. This is a better topic of discussion for here on the forum than for me to address with an individual. That way we all benefit from the sharing of information. PJ has summed up the necessities pretty well in the linked post.
Edits: 06/05/07
Hi Doc,
Why all the talk about expensive 45s? Is it possible to make a shunt regulated 2a3 upgrade kit? Would it make sense?
-Brian
how about for those of us who don't currently have the paramour 's , will you offer this 45 upgrade along with the magnequest opt's in a special 45 s.r. mag. paramour kit ? wouldn't it be better if optimized exclusively for 45 tubes with a 5 k primary opt and higher gain so we can use it in a passive system ? if yes sign me up .
I don't know yet if or when we will offer a special 45 kit. That was the original intent when we started to look at the design many months ago, and this shunt reg conversion is being done to test the market potential for more 45 projects.
PJ has explained why the gain of this circuit is what it is. There aren't any good choices for a higher gain tube that can properly drive the 45 grid and also work as a shunt regulator for the whole amp. So to make a change to a higher gain driver we're talking about separate tubes, which means a chassis redesign. If we're going to go to that trouble there may be other changes to consider as well. For example I'd like to do a direct coupled version with an actively loaded 45. For that we would need a new power supply and a fair amount of time spent prototyping.
FWIW I haven't found passive controls to be optimal always. I've had a couple of instances where owners of very high end, high resolution systems have asked me to install a Foreplay III based gain stage at their passive control in order to correct sonic deficiencies they were experiencing.
I originally used the S&B passively with no Foreplay...after 2 weeks I swithched back to the FP with sweet whispers. Decided to stay with FP active but as you know; I now use it as a vol attenuation control with zero resistors.
Another occasion; heard G Pimm's with Slagel TVC - found it too dry and methodic. My 3 cents ( inflation : ) )
OK, looks like 10 or 12 takers at this point. I will go ahead and order enough parts for those folks and a few more for stragglers. I should be able to have it all together late next week and I can put up a temporary order button on the website.
Paul sent this to me yesterday - a harvest of various Paramour 45 conversion schemes including a rough guide to wiring changes for a PII upgrade to SR45 -
Non-shunt regulated 45 conversions:
To replace the 2A3 with a Type 45 tube in the Paramour, two changes are needed. The plate voltage must be reduced, and the cathode bias resistor must be increased.
For the Paramour II, these changes are documented in the manual. For the iron upgrade, they are documented in the installation instructions posted on the web site.
For the older Paramour, here are the changes:
Cathode bias resistor
The cathode bias resistor is changed from 1200 ohms to 1600 ohms.
High voltage power supply
In all cases, it is worthwhile to connect the signal ground to chassis ground. Run a short piece of wire from B1, B2, or B3 to the center tab of the 5-tab terminal strip at the driver socket – this is the T-strip that was added for the C4S upgrade. If you have the iron upgrade, don't solder the terminal strip end yet...
For the stock iron, the rest is simple – just replace the 270 ohm 5 watt resistor in the power supply with 1600 ohms, 10 watts.
If you have done the iron upgrade, and have already replaced the 270 ohm 5 watt resistor with the former plate choke (10 henry, 270 ohms DC) then you will need to add another 1300 ohms 10 watt resistor and a 47uF/450v capacitor. Disconnect the plate choke wire from T15, and re-attach it to the empty second terminal on the driver T-strip – the one between the end used by the C4S and the middle terminal, which is now ground. Don't solder yet, there are two more things to go here! Now run a 1300 ohm 10 watt resistor from T15 to this second terminal – it will parallel the 15K that goes to the C4S, but connects to the adjacent terminal. Now add a 47uF/450v cap, with the positive lead to the second T-strip terminal and the negative lead to the middle terminal. Solder both terminals.
Shunt regulated 45 conversions
To replace the 2A3 with a shunt-regulated Type 45 tube in the Paramour, you must have the current PT-2 power transformer, not the older Hammond one. The new one has solder terminals, the Hammond has leads with colored insulation.
The 45 operates at a lower plate voltage and a higher current than in the stock 45 version of Paramour, so the voltages and resistances are not the same. This article only covers conversion from 2A3 to shunt-regulated 45 operation.
Cathode bias resistor
The cathode bias resistor is changed from 1200 ohms to 1300 ohms.
High voltage power supply
The high voltage power supply remains the same. Check the voltage, which should be around 380v at T15. If it's less than 340v, the shunt regulator voltage will have to be reduced to allow some compliance for the upper current source – asking fro help on the Bottlehead forum is the main resource if you can't figure it out yourself. If it's more than 380v, then a larger heat sink may be needed – again, ask on the forum if you need help.
Shunt regulated driver
These are merely sketchy notes.
Basically, you will rip out all the driver socket connections and re-do it like the shunt-reg mod described for the Paramour II.
The input from the RCA jack goes to pin 7 of the new 6CM7 driver, through a 220 ohm carbon comp grid stopper resistor; the 249K or 270K grid leak at the RCA remains in place.
The 6v heater supply goes to B4 and B5, with the center tap to ground at or near the B socket.
The power supply positive is at T15 and goes to the shunt reg board.
The driver output is at B6, and goes to T17.
On the boards that you will supply. What will the C4S currents and the regulator current set to?
thanks
C4S on top of the shunt reg passes 60mA
The shunt reg dumps 12.9mA
The C4S on the driver passes 3.6mA
nt
please add me on the list....thanks
Please include me.
Alonzo
nt
Boo
Doc...I would be interested, but not right now. I need to do a little more research on the mod to my amps to determine if I can understand the schematics enough since I have the original paramours. Thanks for the opportunity though....BH's efforts are greatly appreciated.
Hey Doc,
In light of PJ's post re: modifying older Paramours for the 45 shunt reg mod - would you be willing to offer PT-2's along with the shunt reg kit?
I think I'm in either way - I can possibly source an adequate PT - or is the PT-2 the special dual secondary model?
I'm in.
Gary
Vinyl and Film Forever
Are you OK with people buying the kit to experiment with it for different circuits than the Paramour? I'm thinking of a shunt regulated direct coupled 71A amp. If the answer is yes please count me in.
On a related question. Since the first C4s of the mod is set for a largish amount of current. Do you use some type of heatsink?
xavier
Question I:Sure, you can do anthing you want with the parts. We won't be able to offer any detailed support about what you would need to change to make the kit work in other applications, so it will probably be worth it to study the articles on shunt regulation in the July 1999 issue of Tube CAD journal and the original C4S manual. Most parts in the kit would stay the same for different applications, except for most of the resistors supplied in the kit and perhaps the shunt regulator bypass capacitor whose value is selected depending upon the regulated voltage chosen. In the case of a direct coupled shunt regulated amp where voltages can get pretty high you need to keep the voltage limit of 375V across the MJE5731A in mind.
Question II:
The MJE5731A can handle 2 watts maximum dissipation without a heatsink. Any more than that and an appropriate heat sink needs to be used. You would need to calculate the current and voltage across the MJE5731As to determine the power dissipation in a different application. In the case of the SR45 the MJE5731A that is in the C4S load on top of the shunt regulator is dissipating about 3W and hence modest heat sinks will be included with the kit.
I like this approach as it gets back to the basics and promotes learning. Hopefully the instructions would include some theory on how the resistors etc. were sized, limitations of the parts etc. so that adapting the upgrade kit to other incarnations of the Paramour can be readily figured out by an advanced self-taught amateur. Something along the lines of the original C4S manual. As much fun as this mod sounds, I am not ready myself to jump right in as the Paramours are my current main amplifiers and I fear that my current 92-93 dB speakers (Triangle Celius 202) might sound a bit anemic with 45 tubes. Now if I could get my hands on a pair of Lamhorns (I am about as likely to convince my wife of the wisdom of such a purchase as I would be convincing her of the wisdom of buying a Porsche).... When I do build new main amps this mod kit will probably follow shortly thereafter though.
The instructions will be a photo and a schematic. Writing a bunch of general instructions for how hybrid shunt regs work and how to adapt the board for a lot of different uses would take even more time than shooting the photos and writing step by step instructions. But all is not lost as discussion of the theory and working up solutions for the few who want to modify the circuit is exactly what the forum is supposed to be for. The tools are in place to save us all time and money, waiting to be taken advantage of.
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