80W into 4 Ohms with a pair of EL34

by j beede Sat Mar 26, 2011 2:26 pm

j beede: Posts : 473
Join date : 2011-02-07
Location : California

Post n°1

80W into 4 Ohms with a pair of EL34

by j beede Sat Mar 26, 2011 2:26 pm

I think the venerable ST-70 is good for may 20-35W per channel into an 8Ohm load, 20-20KHz, <1% distortion. Is that about right? I've got a 15 year old stereo amp, push-pull pair of EL34 running in UL mode that measures ~80W/ch into 4 Ohms and still has the original factory supplied "fake" Mullards (Russia) in place. It has a quad of 12at7 in the front end. I don't own a ST-70, what will a stock ST-70 measure when driving 4 Ohms? What about a modern ST-70 ( e.g. VTA-70)? The OTs are highly regarded on the ST-70 so the bottleneck must be the PT?
...j

by **Bob Latino** Sat Mar 26, 2011 7:06 pm

Bob Latino

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Post n°2

Re: 80W into 4 Ohms with a pair of EL34

by Bob Latino Sat Mar 26, 2011 7:06 pm

Yes - the original ST-70 with the stock circuit is good for about 20 to 25 watts per channel with > the stock power transformer and the stock 90 uF of DC power storage. A VTA ST-70 with an upgraded power transformer and 500+ uF of DC power storage will do 45 watts over most of the audio band in ultralinear mode and over 20 watts in triode mode without clipping. Below is a test link done by one VTA ST-70 kit builder who has the proper test equipment.

Testing the VTA ST-70 amp kit

Bob

by Sled108 Sat Mar 26, 2011 10:02 pm

Sled108

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Join date : 2010-02-03

Post n°3

Re: 80W into 4 Ohms with a pair of EL34

by Sled108 Sat Mar 26, 2011 10:02 pm

Hey Bob...Any idea what my Frankin-70 puts out with a S/S Regulation, PA-060 PT, Mucho Caps and KT77's @ 50mA into 60 Watt Edcor OT's with 4 Speakers @ 6 Ohms on the 8 Ohm Taps? Just wondering, because it really Rattles the Plaster..