The 6SL7GT valve & It's variants - MY ADVENTURES!

[da2222]

Phew dodged a bullet!

Not necessarily... It may well be compatible in your setup

[Wakefield Turntables]

PT XVI - RCA Red base 5691


rca red base 5691.jpg

Sometime ago I heard about the RCA redbase 5691. There's plenty of information on the internet about them. They are perhaps the ultimate variant of the 6SL7 valve with many improvements over standard 6SL7'S. I liked this valve so much I had the Croft pre-amp modded to specifically run from them and I still have the flexibility to run all the old 6SL7 and GT / GTY variants as well. This valve put quite simply is the best thing I've ever heard in my Croft Pre-amp. Even though I have a pair of Bendix Red Base 6591 which I used for quite a while until they went tits up and then I got the RCA's. They are the same spec wise but the RCA's just seem better, it's probably down to them being a strong tested pair. They are very holographic and ideal for Jazz they have a midrange that beats anything that I've heard before. Vocals are also life like. Overall I think these are probably not going to be bettered, but I'll try!! I've still not heard Mullard ECC35's or the Melz 5 hole variants. So, these are now my new reference valves. Here's how things look now with the shoot out results.


1. RCA 5691 (Red Base) 9.75/10
2. Bendix 5691 (Red Base) 9.75/10
3. Tung Sol 6S7GT (Black Bottle) 9.6/10
4. Tung Sol 6SL7GT (Orange base) 9.5/10
5. Mullard 6SL7GT (Black base) 9.25/10
6. Ken Rad 6SL7GT (Black Base) VT229 9.25/10
7. Tung Sol 6SL7GT VT229 (Black bottle) 9.1/10
8. General Electric GSL7GT (Black base 1970's) 8.75 / 10
9. Slyvania 6SL7GT black base 7/10
10. Brimar 6SL7GT (black base) 6.25/10
11. Reflektor black base 70's version 5/10

Until next time.

[da2222]

The RCA red base 5691 is indeed an excellent tube- I used these for some months till finding and settling on the smoked glass Tung Sol 6U7 gty. I find the latter more rounded and 'ballsy' and not quite as dry sounding

[Wakefield Turntables]

PT XVII - RCA "coin" base 6SL7GT

MbsIGD.jpg

I'd never even heard of this one until Marco bought a pair. I decided to follow suit and see if they could usurp my 5691 reference valves. The "coin" base is very well made and dates from the 1970's. It's an extremely articulate valve. It demonstrates excellent timbrel decay and female vocals sound amazing. This valve produces a very well defined and powerful bass and it demonstrates amazing insight into recordings. It's a great valve and one that I'd quite happily live with but it does have it's issues. It produces a muted top end treble and looses out some of the clarity and precision of the 5691 I noticed this on the production of rim shots that were less well defined. I also noticed that this valve had no "air". Notes hang around in the soundstage with the 5691's this was not apparent with the "coin" base RCA's. I'd also say that the 5691 has a tad more delicacy than the "coin" base. Overall a great valve, the 5691 is still king of the tower. I'm going to give this one a 9.6 it's not as good as the Tung-sol black bottle so it can sit in the No 4 position.

1. RCA 5691 (Red Base) 9.75/10
2. Bendix 5691 (Red Base) 9.75/10
3. Tung Sol 6S7GT (Black Bottle) 9.6/10
4. RCA 6SL7GT (Coin base" 9.6/10
5. Tung Sol 6SL7GT (Orange base) 9.5/10
6. Mullard 6SL7GT (Black base) 9.25/10
7. Ken Rad 6SL7GT (Black Base) VT229 9.25/10
8. Tung Sol 6SL7GT VT229 (Black bottle) 9.1/10
9. General Electric GSL7GT (Black base 1970's) 8.75 / 10
10. Slyvania 6SL7GT black base 7/10
11. Brimar 6SL7GT (black base) 6.25/10
12. Reflektor black base 70's version 5/10

Next time around I will be looking at a very special 6SL7 variant the Black Bottle Tung-Sol 6SU7GTY from the 1950's.

s-l1601.jpg

s-l1600.jpg

Until next time....

[Filterlab]

I certainly agree with your top placing. Superb valves.

[Wakefield Turntables]

I certainly agree with your top placing. Superb valves.

Yep they are superb, maybe the 6SULGTY's will beat them, we shall have to see.

[Filterlab]

Be interested to read your findings.

[Wakefield Turntables]

I've got big expectations now that Marco bigged 'em up.

[Wakefield Turntables]

6SU7GTY - Have landed today from US of A, I shall be installing these over the next few days for evaluation.

[Wakefield Turntables]

Just out of interest I found this on a website and thought it might be useful for those of you that dabble with these valves. THIS IS NOT MY TEXT!



The 6SL7 is a high-mu twin triode in an octal based glass package. To my knowledge, there were not any metal shell versions made. Each triode section operates as a

class-A amplifier. This tube has much higher mu than it's cousin, the 6SN7. It's factor is 70, whereas the 6SN7 is only 20, therefore these two tubes are not

interchangeable. There is still a good population of hi-fi and musical instrument amps using this tube in the preamp stage out there, and these tubes are still

available. The 6SL7 was never as popular as the 6SN7---due to the 6SN7's widespread use in television chassis design---so this tube does not turn up as often whenever

vintage tubes are being sold. It is, in the proper circuit, a wonderful sounding tube, and audiophiles would do well to try the NOS vintage 6SL7 tubes before buying

anything currently made today.

These tubes come in glass packages, and have envelope sizes similar to the 6SN7 family. GE usually used a short glass shell, RCA used the medium, and Sylvania,

Westinghouse, and Raytheon often used the "tall boy" style. There are many variations among brands, and even within brands. Here is a summary of what is most often

available:

6SL7GT / G:
This is the standard version of this tube produced by most USA makers. Nearly all have a pair of cylindrical plates, usually mounted low in the tube. Early versions

have an RF shield sprayed on inside the glass (greyglass), and then since about 1952 were made of clearglass. RCA used the famous blackplates and a bottom getter, as

did early Sylvania. In the 1950s, Sylvania went to a top getter, called chrome tops, and used both a short and a tall boy style. General Electric used a short glass

envelope, bright nickel plates, and a side mounted getter. They also made tubes for other brands. Whenever you see the bright plates, even in tall boy glass with

bottom getters they were most likely made by GE. Ken Rad tubes are just like GE. Early Tung Sol tubes looked like RCA, but later went to small grey rectangular plates

that looked like tiny 6SN7 GE plates. Tubes made after 1975 used the coin or wafer base. These are all great vintage tubes.

5691:
This is the "industrial" version of the 6SL7, and has premium qualifications. These include a long life heater, extra thick mica spacers, extra support rods, and often

a low loss micanol base. RCA made these in their famous "red base" line, identified by their red marbled micanol base. Other brands sold a 5691 with brown or black

bases, but virtually all were made by RCA. The early versions have dull blackplates and the old circle RCA logo on the base and/or the top of the tube. Later versions

have greyplates, and the modern RCA logo in orange on the redbase. Both sound and perform identically. Since the greyplates are usually easier to find, they are

usually priced lower, giving a great opportunity to own a real 5691 at a savings. These tubes are great, and last a long time. They have also nearly disappeared. Their

high price is justified by their high quality and demand in the market. The military versions of the 6SL7 are often just as good, so don't despair if you can't find

5691 tubes!

ECC35:
A very rare European type of 6SL7. Philips are what are mostly seen, if rarely. The Holland made versions are similar in size to the "tall boy" USA types. These

usually have high-mounted cylindrical plates, and brown micanol bases. These are sweet and rare versions of the 6SL7, and are plug and play compatible with any 6SL7 or

5691 type tube. Some say they have all the best attributes of the 5691, with better richness and vocal clarity. Very hard to find in the USA, and worth grabbing

whenever you can find them!

JAN 6SL7GT, JAN 6SL7WGT, VT229:
These are the military versions of these tubes. The Joint Army-Navy used the term "JAN", sometimes (but not always!) with the letters WGT, and / or (but again, not

always!) with the designation of VT229. A true military tube will always be marked "JAN". They may or may not have listings such as "WGT", which is mil spec

ruggedized; or VT229, which is the military type number of this tube. A common belief is that VT229 tubes are better than JAN or WGT types. Not true! These ARE ALL THE

SAME TUBES. They may or may not have brown micanol bases. All have extra support rods and mica, and are very rugged tubes that sound wonderful. The RCA, Sylvania, Ken

Rad, and Tung Sol JAN blackbase tubes look much like their civilian counterparts. JAN Sylvania, Tung Sol, GE, and RCA also made versions with brown bases, mostly with

short glass envelopes. The JAN Sylvania have a light marbled base, and the plates inside are very short black cylinders. These milspec versions are an endangered

species, and stocks may be wiped out when the 5691 series of tubes vanish. Prices are on the way up because of this.

6SU7GTY / 6188:
This is a premium version made by Tung Sol, possibly made by them for other brands as well, as GE lists it in their own "Essential Characteristics" book. It has a

brown micanol base and the triode sections are factory matched. Sometimes the tube is listed by the industrial number of 6198, some military types list both numbers on

the tube, and yet some don't use the industrial number. It's the same tube regardless. These are great 6SL7 substitutes said to sound sweet, but are rare.