6CG7 / 6FQ7 socket wiring check

[Laudanum]

I may like to try my lone 6CG7/FQ7 tube for kicks since it's a simple socket rewire.  If im reading the 12AU7 and 6CG7 pinouts right all I need to do is cut the wire to seperate A4 from A5.  That will leave the wire (ground) connected at A5 but no connection at A4.  So all I need to do from there would be to connect a jumper wire from A4 to A9 (6.3vAC).  Is this correct?

Thanks.

[Jim R.]

Laudenum,

Not exactly -- you want the filament power to go to pins 4 and 5 and leave 9 unconnected.  However, if the tube has a shiield between the sections, you can ground 9 too, though I just prefer to ground pin 9 in AC terms by using a small -- .01 or so cap to ground.

HTH,

Jim

[Grainger49]

Since this is under the Crack folder and if I am reading the Crack Schematic right the connections are to pin 4 and 5 with one of those grounded.  That is a 12.6V winding directly off of the transformer.  You can't wire a 6.3V tube to work without a series resistor to shed 1/2 of the voltage.

[Laudanum]

Laudenum,

Not exactly -- you want the filament power to go to pins 4 and 5 and leave 9 unconnected.  However, if the tube has a shiield between the sections, you can ground 9 too, though I just prefer to ground pin 9 in AC terms by using a small -- .01 or so cap to ground.

HTH,

Jim

Ok so then pin 4 connects to one wire from the transformer 6.3 volt secondary and pin 5 connects to the other wire?   But if there is no shield then pin 9 goes nowhere internally inside the tube, it's just an external pin, right?   So in that case wouldnt leaving the 0 volt (gnd) wire from the transformer connected at pin 5 (A5) and then jumping from pin 9 (A9 which has 6.3v connected from the transformer) to pin 4 (A4) accomplish the same thing?   You would be connecting pin 4 and pin 5 to the transformer only you'd be doing so via a jumper from pin 9 to pin 4.  If the tube has an internal shield I couldnt do it this way but with no shield isnt it that same thing?  Im trying to make it easy to connect back which is why trying to do it this way ... assuming Im understanding this.

[Jim R.]

Laudenum,

I'm not absolutely sure that in te absence of a shield that the unused pin is just floating.  Could be, but I do remember reading somewhere that it is generally better practice to ground it with a cap.  I admit that at some level this makes no sense, or very little, and what I read didn't go into details, but I'd suppose it would be fine to hard ground pin 9 too.

I'd say just go for it, and sorry for the confusion.

-- Jim

[Laudanum]

Ok Jim, so to do this "textbook"  ... At the 6.3 volt secondary at the transformer, the 0 volt tab is grounded (at either terminal 14 or 21 if memory serves).  Wire from that tab runs to one of the heater pins of both tubes.  And wire from the 6.3 volt tab runs to the other heater pin of both tubes.  So if using the 6CG7, wire from 0v tab of that transformer secondary would be connected to one of the heater pins, say pin 5 and then wire from the 6.3V tab of the secondary would run to the other heater pin, pin 4,   correct?   So for grounding pin 9, could/would it be grounded, with capacitor, to pin 5?   If not, where is best to ground 9? 

Thanks

[Jim R.]

Yes, that's right, but I myself would probably choose something like the center terminal of the terminal strip for grounding pin 9.  Without trying it I'm not sure it would make any real difference though.

Let us know how it turns out.

-- Jim

[Laudanum]

Ok, I think got it.  Thanks for the help.

[Laudanum]

I finally got around to rewiring the socket a few days ago and trying some 6cg7/6fq7's.   I picked up a few different tubes from ebay a few weeks back.  I've been using a NOS Baldwin labeled Sylvania "chrome dome" 6SN7 for the last little while in one of those socket adaptors.  I also have some other 6SN7's that I had rolled in but the Sylvanias ended up staying without me spending a whole lot of time with the others.  Just one of those tube things where I just fell into listening with the Sylvania rather than analyzing them.  Im not very good at analyzing the sound of tubes so I just go by what makes me want to listen.   I kinda expected the 6CG7's to sound similiar because Ive read that they are basically the 9 pin equivalents of the 6SN7.  But didnt find that to be the case sonically ... not with the ones I have, compared to the Sylvania 6SN7 anyway.    The 6CG7's that I tried all seem to sound a bit rolled off in the treble and I can say the same for some of the other 6SN7's that I have as well.  Maybe "warmer" is the right term here but with some lack of detail and/or treble extension.  But the exception seems to be those chrome top sylvania 6SN7's.  They are more, maybe, vintage sounding than the 12AU7's but they dont give up the treble and overall detail that the 6CG7's and other 6SN7's (that I tried) do ... I can only speak to those tubes that I have on hand, which isnt a very big list.   I dont know which of the 6CG7/FQ7's are supposed to be the best sounding.  And I dont know which of the 6SN7's are supposed to be the best either.  But I was missing those Sylvania 6SN7's so I wired the socket back.  It's not the right time to go on an extensive 6CG7/FQ7 shopping spree right now but I'll probably try it again in the future.
Im not prepared to enlarge the hole for an octal socket either.  The socket adapter will do because the 12AU7's will be back in there at some point.  I like both the Amperex 12AU7 and these Sylvania chrome domes right now although they are quite a bit different from each other.

As a side note, I think I read somewhere that using 6SN7's with the adaptor can have a tendency to cause some hum or noise to be apparent.  Im not finding this to be the case at all.  With Speedball installed, there has been no noise at all with any of the tubes I have tried including the 6SN7 with the socket adapter.  No hum, buzz, hiss, rush, nada.  I was very happy about that.      

[Lee Hankins]

The 6CG7 and 6SN7 are electrically equivalent, this does not mean they sound the same, they do not.  I discovered this years ago when I changed my FP III to 6CG7 tubes.  The 6CG7 seems to be another one of the tubes that has very little sound variation between brands.  Some say that the RCA 6FQ7 clear top is the best sounding tube in this family.  I have not found any sound difference between the RCA clear top 6FQ7 and the earlier RCA 6CG7's, the earlier 6CG7's to me sound better than any 6FQ7.  In general I believe that the 6SN7 family sounds better than the 6CG7/6FQ7 family of tubes.

The better (IMHO) sounding 6SN7 tubes are 1: Tung-Sol round plates; 2: Tie, RCA VT-231 and Sylvania JAN-CHS-6SN7WGT; 3: Raytheon
VT-231;  4: KenRad VT-231 5: Sylvania 6SN7GT Tall Boy (Bottom Getter).  These 6 tubes are usually a the top in most 6SN7 list, just not in the same order.

I have found that in my Crack the RCA VT-231 sounds better than the round Plate Tung-Sol's (my Tung-Sol's are showing their age).

Hope you find this information helpful.

Lee Hankins

[Laudanum]

Very helpful Lee, thanks.  That explains why I prefer the 6SN7's.   I have both RCA clear top 6CG7's as well as the top getter version.  I dont think I heard any real difference between the two either.

I wonder if the Sylvania "Chrome Dome" is sonically similiar, atleast in terms of general character, to the Sylvania JAN that you mention.  I dont have a slew of 6SN7's, no Tungsols, no KenRad's.  I have some GE's, RCA's, a USA Amperex, a couple others I believe and then the Baldwin labeled Sylvania Chrome's. Then there is this unlabeled brown base tube with Chrome Top that looks kinda like the Sylvanias with some exceptions.  I should say that, eventhough there is no brand label, I immediately thought it was a Sylvania because it is actually quite a bit different structrually.  The brown base tube is a WGTA and has an extra support rod.  The plate structure is different.  It only has the type labeling, on the side.   The Baldwin labeled tubes are GTB's.  The two types sound very similiar and are the best sounding of the 6SN7's that I have and really good sounding tubes in my opinion.  I have to spend more time with the brown base tube but after brief listening last night, it might be a little better than the Baldwin labeled tubes but they are very similiar.  I cant detail the differences as of yet, I need to spend some time with it.

I know that the chrome domes do seem to be pretty popular and can be found for not much money (on the bay) but some sellers want a lot for them.  I got the Baldwin pair for around 16 bucks I think.  5 of the others sold in a lot for cheap, the brown base was among them.  It appears to be NOS and the Baldwins are definitely NOS.

Im curious about this brown base tube.  It is a rather short bottle like the Baldwin labeled chrome domes. Heavy, symmetrical top flashing extending about 1/3 way down the tube, like the chrome domes.  The only marking is on the side ... 6SN7 over WGTA in fairly small print.  Then underneath that in smaller font is 5744A over 312B over USA.  Also, the top mica supports to the glass are metal rods, L-shaped that extend downward and touch the glass rather than the typical points at the edges of the mica spacers.  I cant see the getter structure or whether or not there is an additional mica spacer at the top because of the heavy flashing at the top of the tube.  The tubes feels like it may be a little heavier in the hand.  Im assuming it's a ruggedized tube and browsing the Tube World site, it looks structurally  identical to the Sylvania JAN brown base tubes (short bottle) including the plate structure.  But many of those look alike.  Im assuming that it is one of the JAN Sylvania tubes but have no idea which vintage or specific one.  The labeleing is unlike any I have seen in pictures.  Im assuming some has worn off.    Camera is having a mind of it's own so a picture is probably out but I'll try and get one up.   In any event, I think that I stole this one in that tube lot purchase. It may not be one of the top 6 6SN7's but based on the $25 (from memory) with shipping that I paid for the lot of 5 tubes this one was amongst, I got a pretty nice tube for 5 bucks.

 Any ideas or thoughts on specifics of this tube and on the "standard"  chrome domes I mentioned,  if you have tried them?

Thanks

[Lee Hankins]

Your tube is a Sylvania WGTA tube made in the 44 week of 1957, most 6SN7 tubes with brown bases are Sylvania, I have seen Tung-Sol brown base tube, but they were not the round plate version.  The tube made with your described top mica were made in the 50's to early 60's.  The difference being that the earlier tubes (like your 1957) had the flashing extending down the side of the tube and with taller brown bases, about .2" taller than the brown based tubed made in the 60's.    I have 1955 and 59 tubes with the taller base all JAN, and 62+ that I own all have the shorter base, the earlier WGT tubes have the shorter brown base.   Internal structures seems to be identical in all WGTA top getter tubes, earlier GT were usually bottom getter tubes with different structures, the WGT and the WGTB tubes had a different internal structure.   

These Sylvania tubes are excellent sounding, just not up to the standard of the ones mentioned earlier.

[Laudanum]

Thanks Lee, great info.  I guess then it was indeed a steal at $5 (averaging the cost of the 5 tube lot it was in).   I'll give it a good listen to compare against the Baldwin labeled chrome top Ive been listening to.

Thanks again.