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6V6 triode gain increase?

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#41
andyjevans said:
The 6V6 in triode doesn't sound like a 45. It sounds like a triode strapped beam tetrode, which is what it is. A-B'd it against true triodes like 37, 76, 6P5, 6J5 and 26 and they were all audibly better. The round plate 6J5GTs sound very good - better than the flat ribbed plates. They sound like the 37 and 76, similar construction. I've been trying out all of these in my driver stage which drives an EL12 in SE. I spent some time on comparisons.
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i appreciate this. I was only basing my knowledge on what was said online.

i did build an amp which was a 76 direct coupled to a 71a which was choke loaded. this was cap coupled to a single 6B4G. I still remember to this day how awesome this sounded. low power was the issue.

question then (just an idea... throwing this out) Gain of 10, just picked a number, what would be a good DHT or other triode to drive a single mosfet as a source follower? i.e. how to get the sound of a DHT but with the power of a SS amp.
 
#42
wg_ski said:
The circuit is simple enough that if you have the tubes and coupling chokes on hand it’s time to put something on the bench and listen to what it sounds like. If it’s another 3 years till it’s finished and making music in your bedroom or living room that’s ok. Idle speculation can only go so far.
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yeah i have the tubes, i do have some ElectraPrint chokes. I have a heat sink for the mosfets. bunch of resistors, coupling caps, power supply caps etc. I jsut need to get some stuff for the power supply for the mosfet source follower.
 
#43
AudioGeek said:
i did build an amp which was a 76 direct coupled to a 71a which was choke loaded. this was cap coupled to a single 6B4G. I still remember to this day how awesome this sounded. low power was the issue.

question then (just an idea... throwing this out) Gain of 10, just picked a number, what would be a good DHT or other triode to drive a single mosfet as a source follower? i.e. how to get the sound of a DHT but with the power of a SS amp.
Click to expand...
76>71A>6B4G sounds pretty nice. That's the kind of sound to aim for. All those tubes are better than a 6V6. Only a DHT will sound like a DHT - good ones are 26, 10Y. 46 and 47 in triode not quite a true triode. 2P29L and 4P1L same. 01A is nice but needs an active load like Ale's gyrator. But a 76 is really good, mu=14. You probably know that already. Easy to do a build, resistor loaded. Won't take you long. Build it in a separate chassis and you can rotate the output section choices. That's what I do - I have a variety of drivers and 3 output stages I rotate.
 
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#44
andyjevans said:
76>71A>6B4G sounds pretty nice. That's the kind of sound to aim for. All those tubes are better than a 6V6. Only a DHT will sound like a DHT - good ones are 26, 10Y. 46 and 47 in triode not quite a true triode. 2P29L and 4P1L same. 01A is nice but needs an active load like Ale's gyrator. But a 76 is really good, mu=14. You probably know that already. Easy to do a build, resistor loaded. Won't take you long. Build it in a separate chassis and you can rotate the output section choices. That's what I do - I have a variety of drivers and 3 output stages I rotate.
Click to expand...
i agree. i just don't know right now if a resistor loaded 76 can drive a source follower mosfet. One of the reasons to look for a robust input tube.
 
#46
So I am not sure if I should start a new thread on this. After much input from all the knowledgeable folks here... I have decided to switch from the 6V6 to the 6SN7. There are a lot of varieties available for this tube. New as well as n.o.s. The 6SN7 will have a 20K (2.5x Rp) resistor load, plate voltage around 150v, bias -4v, cathode bias (LED?), 8mA. Input will be 100K. Not sure yet if I will have DC or AC on the heater. This will be cap coupled 1uF - 2.2uF depending on input impedance of the mosfet source follower. I will start here and can adjust.

The mosfet source follower will be the IRFP250. 24vdc power supply. 3A bias on the mosfet. It will be loaded with a 150mH 3A Hammond choke. This again cap coupled to speaker output. Caps will be 7800uF. Similar to the MoFo circuit that is on these forums. Input impedance of an output stage like this I have seen from 47K to 100K and above with no real impact on high frequency response. Of course the lower the better, but then the coupling cap needs to be larger to prevent bass rolloff.

I will be able to adjust the bias on the 6SN7, coupling caps, and the input impedance of the output stage to narrow down the best sound quality.

At the current 6SN7 operating point I should get about a gain of 15 out of the tube. Simulation wise its low distortion.

Power supplies will be all linear. Tube rectifier for the 6SN7 and SS for the source follower.

Need to source some large 0.5C/W heatsinks.

This is the direction I would like to go. Please let me know if there is anything glaringly wrong with this, things I need to watch for, recommendations etc. If you need a schematic I can draw one up this weekend.

I appreciate you all.

Thanks!!
 
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