Rerurn to Romy the Cat's Site

Romy the Cat wrote:

Because GM70 can work in A2 class the ML3 has a very powerful high current-capable second stage (I do not know it they are 4 parallel 6H30 of some kind of composite follower) to be able to handle the GM70’s grid current.

http://blog.stereophile.com/fsi2008/040708lamm/

“The ML3 Signature runs a single Russian GM70 directly heated output tube (introduced in 1948, the year I was born) with 1200V on the plate to give 28 watts into 8 ohms. The GM70 is driven by four paralleled 6N30P "Super Tubes," with a single 12AX7 as the input stage. The choke-smoothed power supply in a separate chassis uses four 12AX3 diode tubes as a bridge rectifier to derive the high-voltage rail for the output tube, with another two 12AX3 tubes supplying DC to the front-end tubes.”

Ok, now we know the true voltage on the GM70’s plate.  My initial presumption was that Lamm drives GM70 at low voltage and needs 4 tubes in the driver stage to gel with grid current in class A2. If John Atkinson is correct and Lamm LM3’s GM70 sits at 1200V then it will hardly ever go into A2 and the amp should have around 35, though Lamm was always very conservative with his power rating. The only question remains open is way he needed to pile up 4 parallel capacitance coupled tubes if he uses 1200V in the output’s anode. The first stage in ML3 is lifted on feedback, like in ML2.  The second stage would not swing close AC voltage to approach the GM70’ grid (at 1200V in plate is will be let say minus 200V). So why Lamm need the current build up in the driver stage? Go figure…

Rerurn to Romy the Cat's Site