I have 6n1p driving 300b and a direct coupled 6n1p/2a3. I listen to a 3b7/2a3 all DHT.
Did you ever get the 4p1l/2a3 direct coupled playing? That’s where I want to go. With my 6a3 preamp.
Did you ever get the 4p1l/2a3 direct coupled playing? That’s where I want to go. With my 6a3 preamp.
I asked the question because you could try a sleeper like the 49. With 120mA filament current you will not burn more than 3.2 VA for filament bias and 250V would be enough to run at 135V plate voltage + 20-24V bias (for 6 mA anode current approx) and 15K plate resistance. If you cathode bias the 300B then RC coupling will be ok as a starter.
However, you will need another input gain stage as mu is just over 4.
But if you like it you could then go with IT coupling and use the 90V wasted on plate resistor to make a mini-Loftin-White driver with a small DHT pentode DC coupled to the 49.
The 49 is tougher than datasheet suggests. And just like the 46 is also very linear in triode mode. I believe specs were cautious because as it was meant mostly for PA use. I can run it at 150-160V (triode of course) without troubles if more voltage drive is necessary. At this plate voltage with IT and enough inductance you can get up 150Vpp easily at low distortion (basically 2H and very little else).
Just to do something different...but use "new" 49s for this if you should go for it!😀
Easy to find at modest price.
I have no type 49 tubes. I can see they're cheap in the USA but with shipping and import taxes they won't be cheap in the UK. Plus if I went down that road I'd need to buy a handful to experiment with and have backup. It doesn't seem to have fired up DHT users since prices remain low.
Have you or anyone else used it? Does it sound as good as the 46 - I have some of those?
Have you or anyone else used it? Does it sound as good as the 46 - I have some of those?
I've abandoned the 4P1L for now, though I have plenty. I find the sound rather thin in the midrange and it can develop a slight edge which puts me off. The 26 is nice and smooth, though it doesn't have 4P1L's virtues of low Rp and high current. 01A is much better sounding if it can be used, and 10Y is similarly good sounding. I may pull out the 2P29L again and give it a listen. 12A as well. You should consider these alternatives. You can put decent current through a 2P29L.
The 6N1P is definitely going to be tried as a 2 stage option.
I've used the 4P1L as output in PSE and as a driver. In PSE it served me for many years since it had just about enough gain for me to use a DHT to drive it, like 10Y. I think that disguised its shortcomings. But I and others found that a 4P1L driving a 4P1L had a kind of edginess which was unacceptable. And a rather thin midrange, lacking body and richness. The sound was just not quite right.
I think there's something inherently not quite right about the 4P1L, though there's much that's good about it. It needs plenty of current - at least 25mA and the more the better. Frustratingly, it's nearly a perfect solution for using a DHT, except it isn't quite. 10Y, 01A, 26, 46 and outputs like 2a3 and 300b are all better sounding. It can probably be optimised in various ways, or combined with other tubes that balance out its defects, but I don't think it will ever be perfect.
I can tell where to buy in EU at modest price which is where I bought my lot of 20. And yes is extremely similar to the 46, just lower power level. It has not fired up probably because most people do not know that is as linear as a 45 or 46, probably do not realize that specs are cautious and can be a nice driver in many applications. Very flexible: RC coupled, IT coupled and DC coupled....at the price of low mu. But that low mu for a DHT should already sound like linear, don't you think so?😉😀
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Yes, played with 49 several years ago and still have a stash of them.
The low mu calls for a SUT at the input or a preamp. I could get about 0.08% at 160Vpp so it’s extremely linear. Great valve!
Cheers
Ale
The low mu calls for a SUT at the input or a preamp. I could get about 0.08% at 160Vpp so it’s extremely linear. Great valve!
Cheers
Ale
LoL...I just told him in pm Ale about your measurement of plate curves and low distortion driver....
Yes remember our collaboration exploring that tube, feels like it was ages ago!
Hope you’re keeping well and safe
Ale
Hope you’re keeping well and safe
Ale
Hi Friends.
2 days ago I finished this amp.
I haven't measured it yet.
But it does sound promising.
First impression is that subjectively it appears to have many W.
Not just 7W or 8W.
I am testing it with Bowers & Wilkins 602 speakers, with 89dB W, and less than 5 ohms at some frequencies.
In some cases the resistance values are approximate.
2 days ago I finished this amp.
I haven't measured it yet.
But it does sound promising.
First impression is that subjectively it appears to have many W.
Not just 7W or 8W.
I am testing it with Bowers & Wilkins 602 speakers, with 89dB W, and less than 5 ohms at some frequencies.
In some cases the resistance values are approximate.
Attachments
Two remarks:
The - voltages should be + voltages;
Copper losses of the OPT (primary 145 ohm; secondary 0,5 ohm) are a bit more than what I'd like to see in a 300B SE amp with this hiqh quality input / driver.
The - voltages should be + voltages;
Copper losses of the OPT (primary 145 ohm; secondary 0,5 ohm) are a bit more than what I'd like to see in a 300B SE amp with this hiqh quality input / driver.
You know that I live in Argentina, it is difficult to import things comfortably for us, and this Lundahl transformers are a luxury for us.
But of course I understand your position.
And I appreciate your comment.
Thanks
But of course I understand your position.
And I appreciate your comment.
Thanks
Hello daanve,
What negative effects, other than slight loss of efficiency, do the copper losses cause? I'm curious, here, because my OPTs have a slightly higher primary DCR of 160 ohm.
Also, what would you consider to be an acceptable primary and secondary DCR?
Thanks!
Regards,
John
@ John:
It also depends on application.
With the 3k:8 impedance ratio of the LL1664 output transformer the output impedance of the amplifier is already highish (around 2 ohm); then the additional 0,5 ohm of secondary DCR...damping factor around 3 for an 8 ohm load.
Now the secondary load is really important, in other words the loudspeaker efficiency and impedance must seriously taken into account to get the combination work well.
For a higher quality output transformer I'd suggest to stay at or below 10% of tube Ra, so preferably max. 80 ohm primary DCR; secondary DCR 0,3 ohm or lower.
I know it asks for a bigger piece of "iron", but it pays off.
It also depends on application.
With the 3k:8 impedance ratio of the LL1664 output transformer the output impedance of the amplifier is already highish (around 2 ohm); then the additional 0,5 ohm of secondary DCR...damping factor around 3 for an 8 ohm load.
Now the secondary load is really important, in other words the loudspeaker efficiency and impedance must seriously taken into account to get the combination work well.
For a higher quality output transformer I'd suggest to stay at or below 10% of tube Ra, so preferably max. 80 ohm primary DCR; secondary DCR 0,3 ohm or lower.
I know it asks for a bigger piece of "iron", but it pays off.