6SN7 Driver in Paramount 1.0 (Original with 12AT7)

[jrebman]

I still plan to use the 5670 2c51 in my Paramour II 45. I have plenty of them too, including a NOS matched pair of Bendix Eclipse 2c51s.
The only ones I don't have are early 50s WE 396s and the siemens/ericsson 1950s black plate, gold pin 2c51s.

I'm also playing a hunch, based on experience, that the 6sn7s will play nicer with my speakers for my taste.

WAlso, nothing is set in stone yet, and it really depends on how the break-in on the speakers goes -- they're very, very nice, but also very articulate and detailed yet  they are also good at showing the character of the gear in front of them, so a warmer, more lush front end will sound very much like that with these speakers and likewise, sterile, an anylytical front end will sound that way at the speakers. That may seem obvious, but these tend to be more faithful to the source than any other speaker I've owned.

-- Jim

 

[galyons]

Nearly 2 years now of listening to my Paramount 1.0 300b with 6CG7 mod.  PB did say give it awhile before the major surgery of going to 8 pin tubes.  The amps sounded so fine I damn near decided to stay with the 6GC7's.    My MQ iron pusher forced me into another purchase for my Paramount 45 build, (EXO-145 Nickel and Dowdy chokes built to match), that I figured I better get the conversion done on the old Girls. 

The first amp was a royal b!#ch.  In detaching the boards and the physical stress rewiring and/or moving wires, I managed to break a wire inside the insulation. Then in testing/diagnosing, managed to short and blow an LED! :-(.  Found the issue running continuity checks on all of the wires.  So pretty much replaced most of the wires, the 220 ohm grid stoppers and, of course, the sockets.  (I bought some Teflon Loktal sockets from the UK, nasty itsy bitsy wiring eyes! Definitely made it far more challenging!)  The second amp was a breeze! Go figger!

Threw in a pair of 1943 Philco 7N7's.  Pulled my Paramour II 45's, (which never fail to please!), and put the Paramount's back into the system...

Wow! The improvement was not subtle and that was streaming our local Jazz station via Touch.  I won't go into all of the flowery verbosity.  For right now let's just say everything is better, sweeter, more real.  I need to listen more seriously and spin some of my warhorse vinyl and tapes.  But for now, my impression is that  this exercise was well worth the effort.

A big thanks to  the PJ and PB for their patience and support. Special kudos to PB for  figuring the driver board changes required. I could never have pulled this off with out the extra effort of these wizards!  Now to try to wipe the grin off of my face before bed!!

I'll listen for a couple of weeks or so than close this odyssey.

Cheers,
Geary

 

[galyons]

I'll listen for a couple of weeks or so then close this odyssey.

Short and sweet.  Changing to the 8 pin Loctal 7N7 from 9 pin Noval tubes is the single biggest improvement in all of the incessant tweaking that I have done to these amps.  Both ends of the sonic spectrum were increased and improved.  It was literally like I had EQ'd to extend the bass and treble.  I spent a great  deal of time sorting the treble response on my EV Sentry IV-A's, with abundant mentoring by a life long EV engineer.  This tube switch made another quantum improvement in the tweeter's response.

All of the typical audiophile subjective performance categories got a Big A+.  Better timbre, imaging and sound-stage.  Vocals are simply scary in their palpable presence.  The leading edges of transients are shockingly realistic.

Would  I have gotten the same reward, for the effort, with Octal 6SN7's?  Probably, but, IMO, only with the big bucks, close to unobtainable selections.  The Loktal 7N7's, with the highly desirable construction variations, are dirt cheap in comparison!! (I will repeat my long term bias here, I have always found the Octal/Loctal  equivalent to Novals to be much more to my taste! Crack, Foreplay EXT.  Of course YMMV!)  One caveat, I use a line stage, (Smash w/UP).  If you are not running a line stage/preamp, you may find the loss of input sensitivity a problem.

PB made a suggestion early in this process and I now wholeheartedly concur, do the soft start upgrade first.  Get the amps running as v1.1. It greatly simplifies the process.  Listen to the 9 pin tubes of your choice, then take a leap of faith and try the 6SN7 or 7N7.  (You can cheat and try a 6SN7 adapter, but I have never been a fan!)  The Paramount chassis already will accommodate the Octal/Loctal bases, (just remove the adapter plate!).  Thank you PJ for the prescience!!! You can always go back!!! 

Now time to build my Paramount 1.1 45's!!!  Wanna guess the driver tubes? ;=)

Cheers,
Geary

 

[johnsonad]

One step closer my friend. When you get that itch again, buy a couple of 7n7, 6SN7 converters and shoot me a PM. I'll send you a few pair of 6SN7's to try out.  The differences between brands is not small and may yet improve on what greatness you have already achieved.

My next experiment is a 6J5 for the shunt reg side and a 2C22 for the gain stage.  I've got a feeling that the tungsol round plates I'm already using will still top it but it's worth experimenting with

 

[galyons]

One step closer my friend. When you get that itch again, buy a couple of 7n7, 6SN7 converters and shoot me a PM. I'll send you a few pair of 6SN7's to try out.  The differences between brands is not small and may yet improve on what greatness you have already achieved.

My next experiment is a 6J5 for the shunt reg side and a 2C22 for the gain stage.  I've got a feeling that the tungsol round plates I'm already using will still top it but it's worth experimenting with

Thanks Aaron!!  Gotta get the Paramount v1.1 45 build done first!  There are so many really great 6SN7 iterations available. I ran Golden Tube Audio SE40's for years.  They are PSE 6L6GC amps with 6SN7 drivers.  Changes in the driver 6SN7's were not subtle!!

I really like 6J5's.  I rebuilt an early Foreplay with them.  IMHO, it was pretty damn nice sounding!! I am not  familiar with the 2C22. The top contacts on the 2C22 might present granddaughter & cat problems!!! 

Once the new Paramount 45's are built, I will probably rebuild the Paramount 300B's as V1.1 with TFA 2004 Jr.  nickel pinstripe OPT's, PS choke and Dowdy plate choke.  The choke selections will really depends on how I like the sound of the Paramount 45's with the huge iron!!

I keep telling myself that will be the end of my power amp odyssey.  I kid myself too much!!  :

Cheers,
Geary

 

[Brillo]

Hi all.  I just completed the swap to 6sn7 drivers on v1.1 Paramounts with the soft-start board.  I get a strange resistance reading on B2 (previously B4) of 279K ohms versus 130K.  On start-up, I get 355v on B5 (previously B6), and the two LEDs on the left side of the board (those further away from the trim pot) are dim. I double checked wiring and everything is correct according to my translations, but I missed a re-solder on U18, which I've corrected. 

I must have fried something on the board.  I didn't get smoke, or smell, but heard a very slight sizzle which, at the time, I thought was some loose hardware or wire clippings sliding as I tilted the plate to flip the power switch.  Anyway, thoughts on troubleshooting?

 

[Paul Joppa]

Voltages would tell us a lot, especially those on 6SN7 pins 1-2-3-4-5-6. You may have to unscrew the C4S board and tilt it out of the way. If you can, photos or the socket and both sides of the board would also help. Does the 6SN7 heater glow?

 

[Brillo]

I will take more measurements this weekend Paul. While not all things are equal since the swap, the manual suggested shutting down immediately if voltages on B5 where above 350vdc. So that's what I did after running for about 60 seconds. Then I went back to check resistances. I'll take photos, and hopefully get them posted to this string.

Chris

 

[Paul Joppa]

355v is close enough to 350v. This is the voltage set by the Zener string, before the regulator circuit kicks in.  There are 5 Zener diodes, 68v each, for 340v. The diodes are said to be +/-5%, so 324 to 357 would indicate they are functioning correctly.

The regulated voltage will be about 300v, so if you still have 355v after 60 seconds, the regulator is probably not working. Tube pin voltages will help figure out why that is the case.

 

[galyons]

PJ,
Thanks for being so supportive of the 6SN7 driver conversion!!!  I love mine, (7N7) and, to my ears, it is really worth the extra effort!!!

Cheers,
Geary

 

[Brillo]

It was a steady 355v for that brief period, but I'll watch more closely tonight and report back. I'll echo Geary and say thanks for supporting me with this customization. I know I'm outside the fence a bit.

 

[Brillo]

Start-up voltage does not decrease, but climbs slowly.  Heaters do not glow.  LEDs don't light.  Voltages are as follows:
B1: 350v
B2: 350v
B3: 0v
B4: 0v
B5:350v
B6: 0v

Not sure if I did this correctly, but I've tried to attach my photos and the pinout translation table.

 

[Paul Joppa]

The pin numbering appears to be incorrect.

 

[Brillo]

Pin numbering is incorrect in the translation table, the top-plate, or the wiring?  The top plate was labeled during the original build, prior to the soft-start install, and doesn't describe the current wiring.

It might be a little hard to see in the slightly blurry photo, but the keyhole is shown, splitting the difference between the standoffs, and pin 1 is to the lower right with the 220ohm resistor going to L20.  Sequence goes counter clockwise from there.

If my translation table is incorrect, then there ya go.

 

[Paul Joppa]

Pins are numbered clockwise as seen from the bottom. The 220 ohm resistor in the picture is soldered to pin 8, not pin 1. I assume the heater does not glow, because it appears the heater wires are soldered to pins 1 and 2, not to 7 and 8.

 

[Brillo]

Wow.  I'm embarrassed.  Sorry for the bonehead error, and for consuming your time needlessly.  I'll correct and report back.  Hopefully I didn't do permanent damage to the board.

I will say that the PCB that came with the tube socket mislead me.  Not sure why it would be labeled as it is.  Lesson learned.

Chris

 

[Doc B]

I just worked on an amp with a nine pin aftermarket socket that was numbered like that as well. It's useless unless it is marked top and bottom.

 

[Brillo]

It sure is useless. I've used 9 and 4 pin versions of these sockets, with and without the PCB, and haven't had this problem before. It's my bad though. Hopefully this string will keep others from making a similar mistake. 

 

[Brillo]

Well, permanent damage has been done.  No voltage on B1-B6, and no LEDs light.  Filaments on 300B glow, but that's the only sign of life. 

 

[galyons]

Well, permanent damage has been done.  No voltage on B1-B6, and no LEDs light.  Filaments on 300B glow, but that's the only sign of life.

No....permanent repairable damage has been done! Hang in there!!!

Cheers,
Geary