Paramount Magnaquest Iron Upgrade

[Steve_in_NV]

I found the instructions to upgrade the Paramour iron but I am unable to find the same for Paramount, does such an animal exist?  Thank you for any direction.

[Paul Joppa]

I don't think there are any instructions, but it's real easy - replace the stock iron with the Magnequest iron.  :^)  <-- OK, so it's not entirely obvious!

I'm going from memory here since I don't at the moment have a set to look at, but I think here are the details:

Plate choke has two terminals, one of which is marked with a dot. Mike says "the dot is hot" meaning it goes to the plate of the output tube (pin 2) where the signal is. The other terminal goes to the high voltage power supply. Really, all you should have to do is unsolder the wires from the stock choke and re-solder them onto the Magnequest part.

The same goes for the output transformer primary; the dot goes to the parafeed cap and the other terminal goes to the middle terminal of the hum pot. The secondary is marked "c - 8 - 16" and C is the black output binding post. The wire from the red binding post goes to 8 or 16 depending on what impedance your speakers are.

[Grainger49]

I understand his confusion.  The Paramour upgrade took the plate choke and put it in the power supply.  Sort of a waste not, want not situation.

I'm glad you explained further because when you said, "the dot is hot," I would have thought that the dot went to the higher voltage point, to the supply not the plate.  Can you explain why the plate is considered the "hot?"

[Paul Joppa]

The dot marks the start of the winding, nearest the core. Because there is either a bobbin or a thick paper layer on which the coil is wound, the capacitance to the core (which is normally grounded) is both small and reliable. So this is the part that should have the greatest signal voltage. The finish of a winding, without the dot, is at the outside of the coil and can capacitively couple to the rest of the circuit. So it ought naturally be at AC ground potential, shielding the higher signal voltages from either picking up hum and noise, or from coupling to sensitive parts of the rest of the circuit.

Note the similarity to the rule for capacitors, in which the outer foil side should be connected to the lowest impedance, which is ground for power supply capacitors, or (usually) the source rather than the load for caps in the direct signal path.

[Grainger49]

Paul, thanks for the information.  I get it now.  I am familiar with dotted transformers but didn't know that the dot indicated the core.

[Steve_in_NV]

Thanks for the reply I'm going to order a set (nickle).  Also, same Paramount just different question, you indicated in a previous post about replacing the existing parafeed capacitor (3.3uF) to a 5.6uF if upgrading iron, is this correct?
 

[Paul Joppa]

Yes, 5.6 is closer to the "theoretical optimum". The realistic optimum is roughly anywhere from 3uF to 12uF, it's not extremely sensitive. That theoretical optimum is for resistive loads, since it's hard to generalize about speaker impedance in the bass - so I would listen to the upgrade with the original caps as well as with the larger ones, so you can hear the difference yourself, with your speakers, and in your room. Remember to allow for some break-in time when installing new caps and/or transformers.

For what it's worth, I bought  some 5.0uF Auricaps from pxX recently for my own Paramounts (with stock iron), and I like them.

[johnsonad]

Hi Paul.  Would you care to comment futher on the Auricaps?  I've got a pair on the way for either the Paramounts or another project.  I've also got some KBG's (6uF) I'm considering once I figure out how to mount the things....

[Paul Joppa]

Not really much to say beyond the usual "the Auricaps do a better job of getting out of the way of the music" compared to the stock Solens. They are quite a bit larger, so a good creative mounting scheme would be better than my underslung truck-nuts approach (I always do the simplest method without cutting leads for the first shot!) I'll find a better mounting scheme when I switch to 6SN7 drivers.

The sad fact is, I like to do circuit design and I am not that excited about component swapping, even though it makes a big difference. So I generally take the advice of Doc B or the Forum denizens on component choices, and if I feel the need of a sonic change I'll adjust the circuit values first.

I'll admit that I've been unpleasantly surprised a time or two with this approach, and have once or twice had to rip out well-regarded components!

[johnsonad]

Hi Paul.  I went ahead and put in a pair of 6uF KBG PIO caps for the parafeed and .113uF SSG-1 silver mica coupling caps yesterday.  They still aren't mounted well but that will come in time.  They have been burning in using sweeps and pink noise for 24 hours or so and I'm very impressed with them over the stock caps.

I do have a question in regards to sizing the parafeed cap.  You wrote anywhere between 3.3uF and 10uF with between 5-6uF optimal.  The bass with these new caps is unreal, almost as if a sub woofer is being used in the room (Altec Model 19 speakers and a 13' x 17' x 8' room).  Does increasing the size of this cap have a proportional effect on the bass response?  If so and if I find the bass to be too much (lord help me!), should I decrease the parafeed cap some?  I'll play around with it and tune to ear but I'm curious how this all works.

Thanks,

Aaron

[Grainger49]

Aaron,

PJ has posted a number of cap sizing posts in the last 14 hours.  Call up his profile and click on his recent posts, at the bottom, to find an explanation that there is a design center value and from one half to double that number works and should be tried for suiting your taste.  He also smiles and says he stands by his 3.3uF value.  Paul says it more eloquently and with more explanation than I do.

I will bet the newly found bass is the result of the oiler, which I really like, rather than the value. Though I don't think the motor start/run caps have the tightest bass.  I use them in power supplies often.  But calculations, and an ensuing Bodie plot (graph of frequency response), show that doubling the value should yield a flat bass response an octave lower.

Just remember, if you change the cap composition and value at the same time you don't know which of those made the change in the sound you hear.

[johnsonad]

Thanks for your post.  I've got a pair of 4uF KBG's on their way and will give them a run in when they arrive.  The Paramounts with the stock caps had decent bass, on par with other amps I've got around though the mid range was not quite there.  It might have been the change to an oiler but whatever did it, the bass is present.  It could be a little tighter but I've never had much tighter from these speakers.  The crossovers are probably ready for a rebuild but I'm not in a hurry. 

[Paul Joppa]

For the Paramount, varying the cap value has an effect only on the deepest sub-bass, around 15-20Hz. You won't hear that effect unless you have unusual hearing and a really unusual speaker system and listening room. What you are more likely to hear is the interaction of the plate choke/parafeed cap/output transformer/tube distortion/speaker impedance fluctuations/room acoustics - and a few other more minor effects. Because of the widely varying nature of the last two effects, that becomes hard to predict. In terms of measured frequency response above 30Hz, i.e. anything musically important, changing the cap in the range I am talking of will have nearly zero effect.

[johnsonad]

Thanks again Paul. No super hearing here...  The caps have calmed down with another 20 hours or so of break in.  I was worried there for a minute

I'm really impressed by the sound so far!  Next up is to order some iron from Mikey but with the amps sounding this good I'm in no hurry.

[johnsonad]

Well with another 80 hours or so of burn in the bass is gone, nearly all of it.  Hmmm, I hope it comes back at some point though this is probably close to the finial sound.  Anybody know how long these oilers take to break in?