mc-240 tubes

[jackbean]

mc-240 lists a 6L6 GC original output tube what/how does a 6L6 GB tube compare to it ? reason being i have all good original tubes in my 240 and would like to preserve them
thanks
john

 

[ron-c]

John,

The GB tube will fail in a properly operating 240. The GB is not rated for the 440 volts of the 240 and will arc over. You can use 6L6GC or 7027A output tubes.

Ron-C

 

[jackbean]

thanks ron, wasn't sure but thought i'd ask here my 240 was redone by ryan @audio classics and is all original (tube wise)i'd like to listen and preserve history at the same time

 

[ron-c]

The 6L6GC is rated for 500 volts and 30 watts plate dissapation where the earlier versions are 360 volts and 19 max plate watts.

Ron-C

 

[dewickt]

6L6, 6L6G, and 6L6GB are Design Center at 360V, the design maximum is not given in my RCA handbook while the GC is given as 500V and same design center.
The 50W1 used 6L6G at 420V and the MC30 used 1614/6L6 at 440V, with these amps you would be safe with any of the 6L6 verities. The MC40/240 used the 6L6GC with 470V on the screen, here is where a GC should only be used !! You would be asking for problems with the earlier type tube, a good arc over can take out an output transformer and $500+ for a rewind can make one think twice about experimenting.

 

[ron-c]

The 6L6Gc was on the scene in the early 50s. A hot rod response to the new Tungsol 6550 for sure. I have seen documentation from 1952 on the MC60 running the 6550s even though the records show the amp was not out until 1954 or 1955.
Of course we are using transistors today that will not find wide spread use for many years like the new Ong/Motorola Thermo Track device in the MC2KW.

Ron-C

 

[radioactive]

The 50W1 used 6L6G at 420V and the MC30 used 1614/6L6 at 440V, with these amps you would be safe with any of the 6L6 verities

actually all the mc30's ive seen all call for the 1614 which has a design center value of 550v.using a 6l6 be it g or gb which only have a design center value of 360 or a plain old 6l6(metal)good for 375volts is not going to be doing the tubes much good running at 440volts in my opinion.i would therefore only recommend the 6l6gc in the mc30's or 7027.with so many currently available 6l6gc's i wouldnt even bother with the g's or gb's unless i was in a jam.
chris

 

[dewickt]

I agree, the SED winged C are a good example of why I stay with new tubes, put them in 4 MC240's so far and all have tested at the 1% THD point (just start of clipping) at 52+ watts, to me this would be the only way to go.
While doing some quick research on the topic of 6L6 I ran into one I have never seen '6L6GX' rated at 500V as listed in my P.H. Brans' Vade-Mecum .

 

[Number 9]

I'm surprised nobody has brought this up, but a lot of the "tube rolling" advocates out there, claim that other tubes sound better. For example, on AA, Klipsch and the Steve Hoffman forums, other supposedly "highly recoomended NOS tubes" mentioned include:
WE350B
Mullard EL37
GEC KT66

All of the above are expensive. Interestingly, someone with a very good ear is Steve Hoffman (the disk mastering guru), and he basically recommends a good ol' GE 6l6GC.

 

[Audible Nectar]

I'm running RCA 6L6GC's in my 30's now, tried a matched quad of tested Valve Art KT66's and thought they were a step back in the 30's. Heard them in other amps with very good results. Got a matched quad on loan of GEC KT66 smoked glass, gonna roll them in over the weekend and see what I think of these. Gotta hunch I'm a 6L6 kinda guy in these amps though....but the GEC's should give a better clue as to whether the KT66 is my ultimate choice here.

Kinda funny about preferences, though.....know an MC30 owner who prefers the Valve Arts over his RCA blackplates.....go figure.

 

[ron-c]

The 7027A is a drop in on the MC240 but the MC30s are not wired for these. The 6l6GC is the most popular guitar amp tube so all should be safe with continuing to use these in their MC30s.
Ron-C