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

[galyons]

One amp is done!!  Now I always thought that PB was perfect!!  Well, he is not!!  He clearly stated, earlier in the thread, that I would see bias rise from 2.5V to 6.0V on the B3 of the 6CG7.  Not so! It is only 5.999V on my meter.    (I won't mention that the closest to the 3.5K resistor, (on the added LM431), I could get was 3.47K ohms!)

So the changes to the bias voltage were spot on!  I did get close to 12v on the other cathode, B8. That is double the approximately 6V in the manual, but seems to follow doubling the bias voltage on C3?

Hard to judge the sonic effect, too soon and only mono. BUT, it sounds really nice, smoother, perhaps a little bit better HF extension.  This is with an EH gold 300B.  Will try my "good" non test 300B's after all is sorted.

Big plus, my system really likes the reduced gain.  I will have to rework the resistors in my FP3X potentiometer circuit.  So initial report....Yeah man!

The change to 6SN7/7N7/6CG7 works!!  As a matter of fact, it works very well!  Thanks PB & PJ!!  PB is helping me on an issue with amp 2, but hope to be back to 300B stereo quite soon. 

Cheers,
Geary

[Paul Birkeland]

I'm glad to hear that you have one up and running, now you have a good reference point. 

The 12V on the regulator Kreg is just where the cathode sits with the regulated B+ and the regulator triode drawing off the extra current provided by the "A" side C4S.  Very, very generally speaking, more voltage gain=less voltage here, and less voltage gain=less cathode voltage.  The voltage at that point must be above ~3V for the regulator to work, and once it's over about 30 volts, the regulator will pop, so there is a nice range of functionality.

[galyons]

I have had about three weeks of listening to the Paramounts with PB's driver tube bias mod to run 6CG7/6SN7/7N7 tubes.  I am quite happy with the sound.  I am currently using 6CG7's  because that was the simplest, most expeditious route to getting the amps running.  Bear in mind that this is NOT a comparison to V1.1 with 5760 Softstart.  I haven't heard that configuration. My goals were to lower driver stage gain and use 6SN7ish tubes.  Mission accomplished!

I have compared this configuration to my Paramour 2A3's and 45's.   The 45's are tricked out with MQ BCP-15 plate chokes and EXO-045 Nickel parafeed OPT's.  The 2A3's have BCP-15's and Altec Lansing OPT's.  The Paramounts are stock iron.  All of the amps are capped with PIO and Teflon caps in the signal stages.  The 45's have been my prime amps for awhile.  The mid range is magical with a palpable presence that is simply eerie.  The Paramounts get close to the midrange while besting the 45's in low and high frequency extension.  The 2A3's  were closer to the Paramounts but were bested across all subjective parameters. 

My speakers are a reworked '60's 3 way horn system with 102dB/1W/1m sensitivity.  Preamp is an FP3 Extended with 6cg7's.  I could easily live with any of the three amps, but the Paramounts, with the more "ballsy" sound, really make the speakers shine with a broader array of musical genre's than the 45's.   I listen to mostly jazz, blues, female vocals and classical.   The Paramounts get the job done very  well on all genres, where the 45's were challenged with big orchestral classical and some of the higher energy blues recordings.  I have been listening to Shuguang 50 Year Treasure black bottles and Russian Genelex Gold Lion 300B's.  Hard to say which I like better.  Either set sounds damn fine with only rather subtle differences.

The reduced gain is really a blessing.  I was never getting past about 6 clicks, out of 24, on my stepped attenuators.  Listening range now is 10-14 clicks with real steps getting there! Now I may even be able to eliminate the dropping resistors before the selector switch.  The system just "likes" the newly reduced gain MUCH better!!

So now, as is ALWAYS the problem, I am now dreaming of MQ iron upgrades for the Paramounts!!!  But next step is to tear the amps apart, anodize the top plate, paint the PT's and generally clean up some rather dodgy cosmetics. That will be the switch over point for the octal/loktal tubes.  Until then, I am a happy listener!!

My thanks to PB & PJ for helping me get this done!!! (And the Queen, too!)

Cheers,
Geary

[Paul Birkeland]

Hello Geary,

Do bear in mind that those resistors in the foreplay keep the input impedance reasonable.

If you remove them, you will need to replace the stock level controls with new ones (50-100K)

[galyons]

Thanks Paul.  I am running 100K attenuators and have 200k's as the dropping resistors. Never really been comfortable with this configuration, but it worked to get the gain down to somewhat usable.  The attenuators are 0-75dB, so should be fine without the dropping resistors. (?)

Cheers,
Geary

[Paul Birkeland]

Ah, good, yeah, you may find that you no longer need them.

[Jim R.]

So, how much different would these changes be in order to use the 6cg7 in the paramount 1.1 with soft start?  Amps are not built yet, but SS boards are. If this is doable without major surgery to the SS board, then can I also assume that the 6sn7 will also work in much the same way?

Thanks,

Jim

[johnsonad]

The 6sn7 is a drop in with a converter. I bought a pair off of ePay and didn't need to change a thing. Set the bias the same as you would for the 5670 at 175v.

[Jim R.]

Thanks Aaron,

Since I haven't eeven drilled the top plate yet, it's just as easy to drill for an octal socket. Also easier for me to solder to. But this is great information.

Thanks,

Jim

[johnsonad]

It you haven't heard the 5670, please give it a try. I've got a stash of them if you don't want to try and track them all down. If the 5670 doesn't cut it for you and if you can spare 6dB in gain then I would recommend trying the 6SN7. I've had the Paramounts with 12at7's and 5670's. For my system the 6sn7 was a better fit.

The spacers that come with the soft start kit will give you room to start with a 9 pin socket and later change to an 8 pin if you like. You are smart to over drill in the beginning. The socket is an easy rewire and I wouldn't lose too much sleep over that.

[Jim R.]

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