Do you think you the amp would benefit from regulation of he driver stage?
Yes, that point has been in the back of my mind from the start The effect of the series reg, is it means the conditions the second choke sees are more affected by the output stage than if there was no reg, so there is certainly a case to try one.
Just lazy I guess.
Actually, teh other reason is I was trying to talk myself out of a SS reg, and there isn't enough headroom for a valve one, and again, I wanted to try and keep the thing reasnably simple.
I think I want to try and get a handle on what it soulds like as it stands first, so hopefully some better OP TX's are the first target. Then I may be able to hear better what effect regulating the driver stage has.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
i've been thinking of using a seperate reg for the front end of my choke loaded 76-45 for some time. i've been thinking how nice it would be to get rid of the dropper and decoupling cap between driver and 45. the big thing for me is lack of space (it's getting pretty crowded in my small room, hot too ) to try another valve based one. the SS MJ one looks interesting but i get a mental block with SS. I have most of the components to try one and just may have room to squeeze one in
I've got them working fine, and regulating OK, but I'm still trying to get them quiet enough. I think I'm there, this morning in fact, I suspect there wasn't enough bias current on the reg.
Anyway what I have learnt so far...
1) the resistor on the collector of the MJE 340 that baiases the zener needs to be a biggie wattage-wise.
2) make sure the sense pin on the reg is set to pass at least 5mA and the same for the zener.
3) The resistor on the sense pin needs to to be a biggish wattage as well. Look at his diagram that uses 47k, not the one with the 200k sense resistor. I think that was one of my problems, of course more current needs a bigger resistor.
4) Make the 47R current limit resistor 1/2 watt as well, in case you do short to ground or draw too much current.
5) Watch the blummin scope probe, they hate shorting to ground. I have one that doesn't work anymore as a result of that. Despite all the protection circuitry. If they do blow whilst your experimenting then replace the MJE340 and the reg together as if one's gone west they take the other out and if you replace one when the other's gone you just break the new one again.
6) Use chuffin big heatsinks! They get toasty.
I have a spice model that will help set the operating points, resistances etc. Can post it, if you want.
cheers,
-- Andrew
Last edited by Andrew on Sun Aug 19, 2007 2:13 pm, edited 2 times in total.
Figure 5.48 is pretty close to where I am now. The one to ignore is figure 5.44. I need to get my other reg working again then compare the lower bias one I built based upon Fig 5.44 with the one I have now.
My only problem is, I now need some big-ish wattage 47k resistors to get started again.
Let me know if you can see any hum on the output, my scope only has a 50mA sensitivity so I'm struggling to see anything now on a dummy load.
If I can fix the other one and cobble to together some 47K-ish @ high-ish wattage then I'll wire the both up and try the listening test.
They look quite attractive, low voltage drop, wide range of operation, no need for seperate heaters etc, low component count and offer the potential for high peformance, the downside, at the moment is that I haven't been able to get them quiet enough, but I suspect its me rather than the circuit.
abit off topic but how hot do 6c33c tend to run in normal useage? i've been toying with the idea of using a regulator based around one for a 2a3 amp i'm working.
Hi, Toby.i as you are in west yorks, you are welcome to come over (Halifax) and see how hot they get. Its hot, but workable, once you don't have cathode caps adding heat its not too bad.
I too, have thought they would do a good job as a regulator for a 2a3/300b amp, the regulator in this amp, is happy controlling 300ma with about 170v drop across the reg, so the same sort of current at (say) 350v shoudn't be a problem. Maybe you would have to delay B+ to allow it to get going, to avoid having too much voltage across the valve at startup.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
thats a very kind offer- i'm only ten minutes down the road in sowerby bridge. i'll send you a PM once i get the chassis back from the metalshop and know how much space i've got to play with.
Fine, let me know when you want to call in. I used to live in Sowerby Bridge (we ran the Puzzle Hall Inn 1990-1994). We are now on the other side of Halifax, between Halifax and Queensbury.
Out of interest, how did you find this place, I only ask as its nice to have another valve head in the area, and you have missed several local (ish) get-togethers.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
i think i googled a term that came up (might have been 845 amplifier or similar). the puzzel is a great little place. a touch on the small side when there is a live band playing!
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) to try another valve based one. the SS MJ one looks interesting but i get a mental block with SS. I have most of the components to try one and just may have room to squeeze one in 