The nicest sounding SE output tube is the one I use 
I actually use a GU50 pentode on about 45mA with 430V plate and 250V G2. However this is in a tight feedback loop with it's driver so I suspect not much of it's signature can be heard, especially as (as a pentode) it's an extremely fast and easy to drive tube.
It manages to fill a medium sized living room with wonderful sound with 87dB/watt speakers too - i.e. it's pretty powerful, but no idea of the actual power (estimates welcome!)
I'm going to build a PP amp using the same driver/output tube combo too, although maybe experimenting with a Schade with a loaded SRPP and a mixing resistor - mixing with the Schade resistor into the GU50 grid.
I actually use a GU50 pentode on about 45mA with 430V plate and 250V G2. However this is in a tight feedback loop with it's driver so I suspect not much of it's signature can be heard, especially as (as a pentode) it's an extremely fast and easy to drive tube.
It manages to fill a medium sized living room with wonderful sound with 87dB/watt speakers too - i.e. it's pretty powerful, but no idea of the actual power (estimates welcome!)
I'm going to build a PP amp using the same driver/output tube combo too, although maybe experimenting with a Schade with a loaded SRPP and a mixing resistor - mixing with the Schade resistor into the GU50 grid.
The nicest sounding SE output tube is the one I use
I actually use a GU50 pentode on about 45mA with 430V plate and 250V G2. However this is in a tight feedback loop with it's driver so I suspect not much of it's signature can be heard, especially as (as a pentode) it's an extremely fast and easy to drive tube.
It manages to fill a medium sized living room with wonderful sound with 87dB/watt speakers too - i.e. it's pretty powerful, but no idea of the actual power (estimates welcome!)
I'm going to build a PP amp using the same driver/output tube combo too, although maybe experimenting with a Schade with a loaded SRPP and a mixing resistor - mixing with the Schade resistor into the GU50 grid.
I was just wanted to ask in this topic is some one tried a GU50.
Did you also tried in a Triode strapped mode ? Thats what im curious for.
Yes I did try it like that first, it sounded pretty good but the topology is so different now (and more powerful) it's difficult to say if it was the triode mode.
One benefit of triode mode is the impedance is lower, which you have to synthesize with a pentode. IME a low impedance driving the OPT makes a big improvement in quality.
I own an Audio Mirror amp that uses a pair of 6as7/6080 tubes per channel. That's 4 triodes paralleled for each side. I gotta say it's one impressive amp. A useable power output for regular speakers, really natural sound, and the tubes are cheap! This is the only SE 6as7 amp I have ever heard, I have also heard them in OTL applications and they do quite well there too. Since this is a DIY place, I'll say that it is my understanding that the 6as7 doesn't give you many options for topology if you want to run them SE. They also have a very low mu, so the gain has to come from somewhere other than the output stage. Give them a try, they are plenty cheap...
I have 2 allready... and i was thinking about a simple SE amp. One tube per channel. Might work well
Ditto for the 6S4A - plus it is so easy to use. IDH, 8V bias but only one watt. I'm too chicken to muck around with my vintage 2A3s etc even if they'd probably sound better
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Greenvalve,
What is the B+ and the bias voltage on the 826? Also, what load does it see from the IT?
Thanks,
John
Sorry no idea about the OPTs, it was a re-built FU50 Sweet Peach which used the GU50s in triode strapped mode.
With the new SEP configuration I haven't really managed to clip it I don't think, the power seems immense but it can logically only be around 10W or so.
I only have a scope, so I do a lot of listening once the scope shows no oscillations and a reasonable frequency response. It's great for thumping bass and subtle vocals and strings - quite surprised how capable it is. The key is a very (Very) tight feedback loop from GU50 plate to driver cathode. I.e. feedback is a 22uF capacitor in series with a 27k resistor direct from GU50 plate, into the cathode of a 6N2p SRPP circuit with 1k resistors. This gives the GU50 the energetic _drive_ for the OPT and is the only feedback in the amplifier.
What's that then - any pics?
Couldn't seem to find it on Google so it must be very old!
Yep. Tubes/Valves the US Army left behind in Europe after WW-II. Valves have dates like May and June 1942. Pics ASAP.
I prefer RCA's mid-range. Have a pair of G.E. GL-211 too.
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