I´ve heard that to,the dull thing,and I thought about a CCS at the tail to
Yeah, you may bee right about that to..If I decide to go that way with a CCS loaded 6C45 will 15-20mA be enough?thats what I have to play with.
And I would be happy if someone could explain what the 15,5v at the gates on SEWA does.
Re: Geek's tube pre question
Hi Tyimo,
The cap is there to block DC that might be floating on the line. Especially of there's some SS contraption before this full of 'lytic couplers
If you have no such monster, just leave it out.
No need to put a cap after the pot, there's no DC on the wiper other than picoamps of grid charge. For safety sake, you could add a 1Meg resistor from the wiper to ground, incase the wiper does lift from age/dirt.
Or did I misundertand the question
/me need more tea
Cheers!
Hi Tyimo,
Tyimo said:
The cap is there to block DC that might be floating on the line. Especially of there's some SS contraption before this full of 'lytic couplers
If you have no such monster, just leave it out.
No need to put a cap after the pot, there's no DC on the wiper other than picoamps of grid charge. For safety sake, you could add a 1Meg resistor from the wiper to ground, incase the wiper does lift from age/dirt.
Or did I misundertand the question
/me need more tea
Cheers!
There is a way to get the performance of a Cathode follower, but with gain and extremely good linearity and a lively sound.
Take two triodes, drive the first into the seconds grid as normal. This will give a two stage with a gain which is the multiple of the firsts with the seconds. Then place a 100K resistor from the plate of the first to the plate of the second. This is called "partial feedback" or "plate to plate" feedback. It will reduce the output impedence of the second stage to a comparable figure of a CF, and will pull back the gain to a more managable level. Result will be tight strong bass and an ability to drive nearly any load you could throw at it. Use a low current triode for the front end and a high current low gain triode for the second stage. This can be achieved with a single bottle triode pentode pair such as the ECL82 or ECL86, a pair of 5687's. Make certain the output coupling cap is large 4.7uf to 10uf.
Result will be a great performing preamp with just two valves for a stereo pair.
Shoog
Take two triodes, drive the first into the seconds grid as normal. This will give a two stage with a gain which is the multiple of the firsts with the seconds. Then place a 100K resistor from the plate of the first to the plate of the second. This is called "partial feedback" or "plate to plate" feedback. It will reduce the output impedence of the second stage to a comparable figure of a CF, and will pull back the gain to a more managable level. Result will be tight strong bass and an ability to drive nearly any load you could throw at it. Use a low current triode for the front end and a high current low gain triode for the second stage. This can be achieved with a single bottle triode pentode pair such as the ECL82 or ECL86, a pair of 5687's. Make certain the output coupling cap is large 4.7uf to 10uf.
Result will be a great performing preamp with just two valves for a stereo pair.
Shoog
Shoog said:
It is a parallel feedback by voltage, reduces gain of the 1'st tube loading it by very low impedance (100K/gain of the 2'nd tube), and increases it's distortions. However, the 2'nd tube contributes more distortions, so it is not so bad. I prefer series feedback, when output from plate of the 2'nd tube goes to catode of the 1'st one.
I think your analysis of Partial feedback is very wrong headed. It is a well recognised technic which has been used by Mr Broskie in a 300B amp. It constitutes local feeback. I have used it extensively and it performs excellently, my most recent use of it was to drive an interstage phase splitting transformer with high interwinding capacitance+miller capacitance. I achieved a dramatic improvement in linearity and bandwidth by apply partial feeback. May I suggest you read the Tubecad article on the technique and come back better informed.
Shoog
Shoog said:
I think Wavebourn was correct with his short analysis. But such a technical description should not constitute a judgment, by itself, of “good” or “bad”. I think that Wavebourn’s point can be explained this way too: Think of an opamp configured as an inverting amp in the usual way, with two resistors connected to the inverting input (the “plus” input is grounded.) One resistor provides feedback from output to the inverting input; the other connects the input source to the inverting input. The feedback resistor always works to hold the inverting input at ground to match the plus input. The input resistance is therefore simply equal to the input resistor. If you reduce the input resistor to zero ohms, the input resistance also heads toward zero (with the huge gain of an opamp). Now think of your second tube as a low-gain, non-“ideal” opamp with a 100K feedback resistor from its output to its inverting input (the grid). There is no input resistor connecting the first tube stage’s plate to the grid, so the first stage plate sees a fairly low resistance load provided by the feedback around the second stage. This lower resistance will almost certainly increase the distortion of the first stage - by how much depends on several factors.
However, the configuration would also have the potential advantages of realistic gain and lowered output Z that Shoog claims. Is it worth it? Depends on the implementation and the listener, as always…
Shoog said:
Sure, my analyzis is very wrong because it is based on analyzis of the amplifier instead of analyzis of popular articles for fellow audiofools. When I try to analyze them Milton Ericson and Richard Bandler comes to mind, with their hypnotic technics to make people feel better.
First of all, speaking of tubes and amplifiers we shouls use sensory information, indirectly connecting tube geters, plate colors, and so on, with perceptions that remind good feelings and well being, for example bright sound, warm tone, smooth curves, sweet coloration, and so on... Too sweet is bad, some people hate too sweet, so your amp have to be sweet just enough, exactly for the best taste.
The best audiofool articles should of course touch strings of sexual desire and satisfactions, but it must be done the way conscious analyzis can't see all details of the suggestion.
So, suppose your first triode has soft anode (plate) output. Input of the 2'nd triode is soft and smooth as well, but when you connect anode (plate) of the 2'nd tube with anode (plate) of the first one through semi - soft resistor, this resistor makes load of the 1'st triode harder. Far the more, since the 2'st triode inverts the pase of the signal and amplifies it, it starts resisting, so when you pull your anode down it pulls it up, and when you push it up, the 2'nd tube pulls it down! It makes amplification much harder...
I would agree with both Wavebourns and Brian Becks analysis. I would say that if you were to choose a medium or low gain triode as the first stage then then the load would stay relatively high. So careful choice of valves is necissary. I have used it on a ECL82 which would suggest that the load of the first stage would be severly compromised. I implemented a split anode load to minimise this. However, subjective performance is excellent in a difficult application.
As usual its horses for courses.
I think that the plate to plate feedback is a complex dynamic compound stage which dosen't reveal all its potential to load analysis.
Shoog
As usual its horses for courses.
I think that the plate to plate feedback is a complex dynamic compound stage which dosen't reveal all its potential to load analysis.
Shoog
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.