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Title says all. Someone I know is thinking of re-tubing a restored Stereo 70. It has the original circuit, power & bias supply, 5AR4, and everything.

Will a 6L6 work OK here, or should he stick to the EL34 family? I think the primary concern is the acceptable size of the grid resistor. The GE datasheet for 6L6GC says max resistance for G1 is 100K with fixed bias. The Dynaco schematic shows a 270K part here. Of course, datasheet specifications are merely casual suggestions, right?

Ty, I ran both Winged C 6L6GCs, JJ KT77s and KT88EHs at one time or another in one of my ST70s with a VTA driver board and they all worked fine. (I had the upgraded Triode power tranny) As long as the sockets are wired for EL34s you can probably interchange ok. The EL34s need the external connection from cathode to the suppressor grid where on 6L6s and KTXXs are already connected internally. The VTA board used 270K resistors also.
Give it a try.
Mike

6L6-GC will work fine, just DON'T try 6L6 metals, G, GA or GB types. The 'GC is a whole different animal.

The Winged C (Svetlana), Sovtek and J/J 6L6GCs are very rugged tubes, I've heard reference of them being as "tough as the proverbial army boot" and they should work fine in thios application. These can last for a LONG time in most guitar amps, and they are well-rated for this kind of hard service. HiFi / Audio service is a walk in the park for these tubes Yellow_Light_Colorz_PDT_03

Just be sure that pins 1 and 8 are connected together, for each (EL34) socket, in order to connect the G3 to the cathode. THe bias voltage will have to be re-adjusted to accomodate the 6L6GCs.

HTH

/ed B

The max plate and screen dissipation of the 6L6 tube add up to 23.5W, not 33W as with the EL-34s.

http://www.nj7p.org/Tube4.php?tube=6L6

In the original Dynaco st-70 manual, 5881 tubes can be substituted for EL-34s. The max plate and screen dissipation for the 5881 tube add up to 26W.

http://tdsl.duncanamps.com/show.php?des=5881

In this amp, the 6L6GC tubes would be the best choice in the 6L6 family.

The JJ 6L6GC/5881 have a 30W max plate rating.

http://www.jj-electronic.com/index.php? ... &Itemid=11

The Russian made KT66s should also be a good alternative, along with 6L6GCs and 5881s. Stay away from the Chinese made power tubes, they are "variable" quality at best. However the Chinese 807s are pretty decent as are most of their power triodes. I've tried various "Sino" EL34s and they are OK for test or voltage regulator pass element purposes, more so than dependable quality audio power Yellow_Light_Colorz_PDT_11

As posted earlier, a year or two ago, 807s and 6BG6s will also play well in the ST70. The 807 requires a UX5 socket, and teh 6BG6 has a different octal pinout, so neither would be a "plug and pray" alternative Yellow_Light_Colorz_PDT_04 :o Some re-wiring would be required Yellow_Light_Colorz_PDT_11

/ed B