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Favorite 6CG7

ab0ez

ab0ez

AB0EZ
If you all have read any of my posts about various amp rebuilds, mods and custom builds you know that I'm a big fan of the 6CG7 dual triode tube. I can't decide which I like better: The Sylvania black plates, or the RCA gray plate clear tops. Both sound excellent, but have slightly different tonal qualities. The RCAs MIGHT be just a tad quieter. So what's your favorite?

Jim, AB0EZ
 
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ab0ez said:
If you all have read any of my posts about various amp rebuilds, mods and custom builds you know that I'm a big fan of the 6CG7 dual triode tube. I can't decide which I like better: The Sylvania black plates, or the RCA gray plate clear tops. Both sound excellent, but have slightly different tonal qualities. The RCAs MIGHT be just a tad quieter. So what's your favorite?

Jim, AB0EZ
Click to expand...

Is there a tonal difference between 6CG7 and 6FQ7? I have an RCA amp (RS177H) that uses those. Are Sylvania and RCA the only companies that made 6CG7s or are those your top preferences?
 
Kingfisher said:
Is there a tonal difference between 6CG7 and 6FQ7? I have an RCA amp (RS177H) that uses those. Are Sylvania and RCA the only companies that made 6CG7s or are those your top preferences?
Click to expand...

Those are just my preferences in the amps I have built, thus far. Tung Sol, Amperex, Raytheon, Westinghouse, Matsushita, GE and probably others also made 6CG7s.

The 6FQ7 and 6CG7 pretty much differ only, from what I have been able to tell, by a couple of inter-electrode capacitance figures. Yes, there are tonal differences between those two tube types, just as there are between the two 6CG7s I prefer to use. Fun stuff and great tubes!
 
You are using the ones with the plate in between the sections right?:yes: Cleartops or blacks is my favorites too. Ever try any of the shorter 6GU7s?
 
Yeah, I should have mentioned I prefer the ones with the shield between the two triode sections. I've got a couple of the 6GU7's but haven't tried them yet. I have looked at the specs and they look for all intents and purposes like a slightly de-rated 6CG7.
 
ab0ez said:
Those are just my preferences in the amps I have built, thus far. Tung Sol, Amperex, Raytheon, Westinghouse, Matsushita, GE and probably others also made 6CG7s.
Click to expand...

I've got some "Made in Gt Britain" labeled ones that I think are Brimar....

Here's some of my stash of these tubes. Wish they were worth as much as 12AX7's....:D


02955c6e.jpg
 
I'm partial to the RCA charcoal colored plates, not the shiny black plate but the
duller "flat black" ones, other wise I've got a couple Amperex that are quite nice.

Depending where these are used there are a lot of tubes with the same style of
pinout an may sub, in certain circuits I've used 6DJ8 through 6bk7/bq7/bz7 even.
(and of'course the 6GU7 should sub pretty much anywhere an 6CG7 is used)
 
Kegger said:
I'm partial to the RCA charcoal colored plates, not the shiny black plate but the
duller "flat black" ones, other wise I've got a couple Amperex that are quite nice.

Depending where these are used there are a lot of tubes with the same style of
pinout an may sub, in certain circuits I've used 6DJ8 through 6bk7/bq7/bz7 even.
(and of'course the 6GU7 should sub pretty much anywhere an 6CG7 is used)
Click to expand...

I like the same RCA flat black 6CG7's. I changed out the 12AU7's on my Heathkit W5M's with 6CG7's and I tried everything available. Always came back to the RCA's. Second in line were the Jan Sylvania's with green lettering. Can't remember the Syl's plate color.
 
Kegger said:
I'm partial to the RCA charcoal colored plates, not the shiny black plate but the
duller "flat black" ones, other wise I've got a couple Amperex that are quite nice.

Depending where these are used there are a lot of tubes with the same style of
pinout an may sub, in certain circuits I've used 6DJ8 through 6bk7/bq7/bz7 even.
(and of'course the 6GU7 should sub pretty much anywhere an 6CG7 is used)
Click to expand...

Is a 7308 also a direct sub???....:scratch2:

Also, how doers a 6GU7 differ from a 6CG7? Gain only or are there current or other differences?
 
Just a quick an dirty type of description,

Call the 6CG7 an 7k plate resistance tube.

The 6GU7 call it a 5k plate resistance tube.

6CG7 call it a 20mu/gain tube.

6GU7 call it a 17mu/gain tube.

So the 6GU7 has a little lower plate resistance an gain, in most circuits the
difference is so small you'd never know there was one or the other in there.

-----------

The 7308 call it a 2.5k plate resistance tube.

7308 call it a 33mu/gain tube.

------------------

Now in "some" circuits all these tubes will work. (some good fit, others not)

That 6GU7 and 6CG7 are so close that most any circuit where one was built
for the other would sub with no problem. (the 6GU7 is a 9AJ pin-out 12BH7)
(6CG7 is the 9pin equivalent to the 6SN7, and "similar" to 9a pin-out 12AU7)

The 7308 is basically a sooped up 6DJ8, should work anywhere an 6DJ8 does.

With any swaps one should be aware of the circuit and piece the tubes going
into to determine if its a good fit, gain, voltage and current both heater an B+
should be looked at, if it is an phase splitter are the loads proper for that tube.
Saying tubes are an generic swap could lead to troubles, you should Know that
certain tube is a decent swap for your given circuit, not difficult to figure it out. :)
 
hey-Hey!!!,
Another similar tube( roughly) is the Russian 6H6Pi. heater current is near 1A and for a CCS-ed LTP stage y'all can plug-an-play nearly anything with the same pinout. The 6H6Pi is near 5687 in terms of mu and gm, and can do a better job at driving than the 6CG7.
cheers,
Douglas
 
PakProtector said:
hey-Hey!!!,
Another similar tube( roughly) is the Russian 6H6Pi. heater current is near 1A and for a CCS-ed LTP stage y'all can plug-an-play nearly anything with the same pinout. The 6H6Pi is near 5687 in terms of mu and gm, and can do a better job at driving than the 6CG7.
cheers,
Douglas
Click to expand...

That's pretty interesting Douglas. I will definitely have to check that one out.

Jim, AB0EZ
 
Just to cover all bases, the 6H6Pi is the same tube as the 6N6P that we've discussed
in the past, they are very beefy, good tubes and cheap to boot, I've got my stash. :)
 
Kegger said:
Just to cover all bases, the 6H6Pi is the same tube as the 6N6P that we've discussed
in the past, they are very beefy, good tubes and cheap to boot, I've got my stash. :)
Click to expand...

Another nice quality ov those tubes is their sections are well matched. Not quite so well as GE 5-Star 5687, but a close second...:)
cheers,
Douglas
 
I built a stereo tube amp using a 12BH7, 6CG7, EL84's. I was surprised to find that my bass improved when I changed out the 6CG7 tube for an Amperex 6CG7 (short grey plates made in Holland). In this circuit I am using it as the phase splitter (concertina). I was using a clear top RCA with grey plates. Before that I was using a Black Plate RCA.
 
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