I have been following and reviewing several new and old threads regarding SE 300b amps. Thanks to all the new and more experienced posters for all their input, thoughts and ideas.
I am going to fish for more opinion here, regarding input tubes.
I have seen many different input/driver tubes used in different configurations. The following is a quickly acquired list: (in no order)
717A
ECC81
CV4024
6sn7
5687WB
5842
D3a
437A
El34
6EM7
5691
6C45P1
EL84
2A3
Any others?
And what are some wonderful thoughts on these? Strengths, weaknesses?
I would like to stay away from transformer coupling, although the pluses and minuses of that might be interesting too.
Also, what are opinions of what a 300b tube wants? High voltage swing, high current, low impedance, etc. and what might get us there.
Thanks!
I am going to fish for more opinion here, regarding input tubes.
I have seen many different input/driver tubes used in different configurations. The following is a quickly acquired list: (in no order)
717A
ECC81
CV4024
6sn7
5687WB
5842
D3a
437A
El34
6EM7
5691
6C45P1
EL84
2A3
Any others?
And what are some wonderful thoughts on these? Strengths, weaknesses?
I would like to stay away from transformer coupling, although the pluses and minuses of that might be interesting too.
Also, what are opinions of what a 300b tube wants? High voltage swing, high current, low impedance, etc. and what might get us there.
Thanks!
Opinions? I guess those old tube manufacturers wasted their time publishing datasheets. I guess I'll have to chuck all the tube design handbooks I bought too.
In all seriousness, your list is deeply flawed. You are just throwing out tube types, irregardless of whether they were used for multiple stage, single stage, or hybrid stage driver circuits. To what end?
Last edited:
Well, yes. I am just throwing out tube types. These are tubes I have seen used in 300b SE designs.
I am seeking opinions on why one might choose one over the other. This could include multiple, single or hybrid stages. Do they sound better, are they easier to implement, require multiple stages or a pre-amp, and so on.
I am not looking for anyone to tell me which tube to use, just what different people have been drawn towards and why.
I guess "opinions" on what a 300b needs for input is not the right term. What are idea input parameters for a 300b (current, Vp-p, etc.)?
By the way, I am seeking thoughts, insight and meaningful discussion. Not criticism. Keep that for yourself.
I am seeking opinions on why one might choose one over the other. This could include multiple, single or hybrid stages. Do they sound better, are they easier to implement, require multiple stages or a pre-amp, and so on.
I am not looking for anyone to tell me which tube to use, just what different people have been drawn towards and why.
I guess "opinions" on what a 300b needs for input is not the right term. What are idea input parameters for a 300b (current, Vp-p, etc.)?
By the way, I am seeking thoughts, insight and meaningful discussion. Not criticism. Keep that for yourself.
From what I understand, the 300B wants to be driven by a stage with low output impedance. Some paging around in Morgan Jones would yield some ideas for topologies along with the tube characteristics that are desirable for those topologies. Why not start there?
This may not be a single-stage solution. A gain stage (common cathode) followed by a cathode follower is - as far as I can deduce from forum trawling - a common solution. For myself, I plan to use a 6J5 (because I have them) as a gain stage and another one as a follower. I might use a MOSFET as a source follower - like George (tubelab) does in his Tubelab SE. I figured I'd experiment and play for a while.
~Tom
This may not be a single-stage solution. A gain stage (common cathode) followed by a cathode follower is - as far as I can deduce from forum trawling - a common solution. For myself, I plan to use a 6J5 (because I have them) as a gain stage and another one as a follower. I might use a MOSFET as a source follower - like George (tubelab) does in his Tubelab SE. I figured I'd experiment and play for a while.
~Tom
i agree, but not the same sounding! beware - E180F is softer and more harmonically rich. E280F has a bit harder sound and more gain and you have to take that into serious account when you design your amp to avoid input/driver stage saturating the amp too early with too much amplification.
generally i don't think i've heard a better sounding driver than properly implemented E180F but i should be quiet about it, the tube is still cheap.
you don't need to drive it triode stripped, some people like a bit more bounce you get from a pentode driver.
my experience comes from 2A3, 6B4G, 300B and 10Y amps and E180F is brilliant in all of them. leaves a definitive stamp of claritiy and harmonical richness and minimizes the influence of the power tube (though soundwise my preference remains 10Y/801A - though not in a shishido IIT A2 circuit).
Thanks! Looks cool and interesting. Would there be significant modifications for a 300b output? Seems they should be quite similar if not the same.
jrenkin, I think your driver choice should be based on the following questions:
What voltage swing do I need in order to drive the 300B to the required level?
What input signal level do I have, hence what gain do I need to achieve from the driver?
What driver output impedance do I need in order to drive the input / Miller capacitance of the 300B?
How easy are the tubes to obtain, and at what cost?
Don't listen to subjective opinion about driver 'sound quality' because that's just nonsense. Tubes have characteristics that you must manipulate to achieve your desired results; they do not come with an inherent sound quality.
: )
What voltage swing do I need in order to drive the 300B to the required level?
What input signal level do I have, hence what gain do I need to achieve from the driver?
What driver output impedance do I need in order to drive the input / Miller capacitance of the 300B?
How easy are the tubes to obtain, and at what cost?
Don't listen to subjective opinion about driver 'sound quality' because that's just nonsense. Tubes have characteristics that you must manipulate to achieve your desired results; they do not come with an inherent sound quality.
: )
I beg to differ from the last post - all my experience tells me tubes have a disctinct sound quality, and that DHT tubes sound generally better than indirectly heated ones. I would use a 31, 71a, 46 or 10Y as a driver, and 26 or 01a as an input tube.
I've been through so many combinations I couldn't list them all, and those are my conclusions which I stand by!
andy
I've been through so many combinations I couldn't list them all, and those are my conclusions which I stand by!
andy
To get the 300B to really sing, you need to drive it into deep A1 or even A2. To do that without a interstage transformer, you need a driver with a low plate resistance. My favorite is a 45, then 2A3. If you can stand not using a DHT (I can't) you can use a 6BX7 (low Rp) or even a triode connected 6W6gt (plate Rp almost matches the 45). I agree with the input tubes, I use a 26 but tried many including a 1H4. When driven with the 45 the input tube controls the overall "color" of the amp. The front end needs its own power supply and (shunt) regulator. I perfer tubes, so use 2, 0D3.
Haven't used them in this application yet but these tetrodes when run triode-connected take serious current without generating reams of high frequency distortion components, unlike say a 6C45 which I've found isn't much good over 10 ma. My current preamp is a 6e6p-dr driving a 10K:600 SE OPT parafeed and it measures and sounds wonderful. Be aware they can be microphonic.
Good questions I have been struggling with. Maybe you can answer a few dumb questions for me.
1. How do I determine the input swing needed to drive a tube? Is it just determined by the bias voltage?
2. How do I determine the driver output impedance and what the output tube likes? I don't seem to understand how the output impedance and Miller capacitance interact.
3. I am thinking of a similar circuit to the Tubelab SE with a 300b and input with the 5842 for first run and trying to modify the front end later with an E180F to see which I like better (or trying any number of the possibilities in this thread). I can't seem to figure out what George is biasing the 300b at by his extensive description. Am I just being dense?
Thanks for your help and all the interesting input in this thread!
Thanks!
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.