Tim,
Bret'll probably be asleep in his Kangaroo pouch at the moment
Your driver and output stage looks just like those fitted to British TV's in the mid to late 60's.
People would complain how bad the sound was, but that was mainly due to a small speaker and puny output transformer.
Cheers,
Bret'll probably be asleep in his Kangaroo pouch at the moment
Your driver and output stage looks just like those fitted to British TV's in the mid to late 60's.
People would complain how bad the sound was, but that was mainly due to a small speaker and puny output transformer.
And what do you mean to imply by that?
Cheers,
Sch3mat1c said:From what I've seen, the Asylum is even worse than this place...
Tim
As a newcomer, I am delighted (so far) by the absence of stupid posts about the shapes of getters, date codes, "smooth plates" and all that rubbish.
The standard of discussion is much better here.
The thread on the 6SL7/2A3 project has so much fascinating information from Brett and others that I feel that I should print the lot for study.
The downside of all this is the fact that I am spending far too much time reading.
7N7
Attachments
![smoking[1].gif](/community/data/attachments/5/5220-46dec24870e74de2504939340612d0c2.jpg){kind=small}
Sch3mat1c said:
Oh. So if I wanted to scare some logic into some people I should've gone to the Asylum instead?
(Wonder how they would feel about my RadioShank 1/2W 5% carbon film resistors...)
Tim
Funny stuff "Logic" everyone (or almost everyone) seems to have their own; this can be seen on almost any thread.As for the carbon resistors, well I suppose they belong in the components department.
For myself I wouldn't use them - not because I can "hear" them, but because they are noisier than the cheap metal film ones that I use (I can't hear the "noise" either, but I am happy that it's not there!!)
I would never pay say, £2 for a single resistor just because it has Holco or some other fancy name written on it. The only time I would pay any extra would be for 0.1% items for some precision application, e.g. RIAA.
7N7
...slew rate....did someone say slew rate??
Tim,
Your driver stage runs just over the current required to prevent slew rate limiying into your chosen output tube...
Some of us beleive that say doubling the current would improve your amplifier still further . . . care to try it and report back...
Of course if you don't hear any difference it must be because your other equipment is too poor, your OPT is crap, you have cloth ears or your lying
seriously, please try this and report back. I really don't know if it would make a difference with your output stage but I have found it makes a difference with 2A3 based output stages...
ciao
James
Tim,
Your driver stage runs just over the current required to prevent slew rate limiying into your chosen output tube...
Some of us beleive that say doubling the current would improve your amplifier still further . . . care to try it and report back...
Of course if you don't hear any difference it must be because your other equipment is too poor, your OPT is crap, you have cloth ears or your lying seriously, please try this and report back. I really don't know if it would make a difference with your output stage but I have found it makes a difference with 2A3 based output stages...
ciao
James
Re: ...slew rate....did someone say slew rate??
Really?
[Figurin']
Lesse, rumor has it Dmitry's 6SL7 has 1/5 as much rate as neccessary. 2A3 has 17pF Cgp and 8pf Cgk; I forget which is multiplied by our good friend Miller, but I think it's Cgp, with Cgk simply added on top. [Checks ARRL handbook] Formula is Cin = Cgk + Cgp * (A+1).
Data shows amplification is 2, i.e. for 45V input, 90V is seen on the plate, so Cgp is multiplied by 3, for 51, making a total of 59pF input.
Now, I'm not sure how slew rate is figured, but I'm guessing it's the T = RC response of the circuit. In this case, a 120k supply resistor and 60pF, for 7.2µS per 63%(?) of voltage change...but how much change...
Oh yeah. Voltage supply is 300V, so if it were 'uncapped' (by the 6SL7 and 2A3 grid diode), it would take 7.2µS to go from zero to 190V (63% of 300V).
That means that a sine wave of at least 130kHz, and 190Vp could fit in here...yet if his stage begins to be limited at 10kHz, I must be missing something here.
Ok. I'm not done figuring yet.
If his is slew-limited at 10kHz full signal, and takes 45V drive, and mine takes about half as much drive, uses the same driver current (in fact it ought to be less, 220k vs. 120k), and my 6L6 amplifies about 10 times, then its input capacitance must be 12 times lower than 2A3's. Data sheet shows Cgp = .6pF, and Cin = 10. So total Cin for my circuit is about 16pF, only 5 times, not 12 times lower.
Ok. I'm off my
.
[/Figurin']
Tim (doesn't know much about slew other than ~= rise time)
James D. said:
Really?
[Figurin']
Lesse, rumor has it Dmitry's 6SL7 has 1/5 as much rate as neccessary. 2A3 has 17pF Cgp and 8pf Cgk; I forget which is multiplied by our good friend Miller, but I think it's Cgp, with Cgk simply added on top. [Checks ARRL handbook] Formula is Cin = Cgk + Cgp * (A+1).
Data shows amplification is 2, i.e. for 45V input, 90V is seen on the plate, so Cgp is multiplied by 3, for 51, making a total of 59pF input.
Now, I'm not sure how slew rate is figured, but I'm guessing it's the T = RC response of the circuit. In this case, a 120k supply resistor and 60pF, for 7.2µS per 63%(?) of voltage change...but how much change...
Oh yeah. Voltage supply is 300V, so if it were 'uncapped' (by the 6SL7 and 2A3 grid diode), it would take 7.2µS to go from zero to 190V (63% of 300V).
That means that a sine wave of at least 130kHz, and 190Vp could fit in here...yet if his stage begins to be limited at 10kHz, I must be missing something here.
Ok. I'm not done figuring yet.
If his is slew-limited at 10kHz full signal, and takes 45V drive, and mine takes about half as much drive, uses the same driver current (in fact it ought to be less, 220k vs. 120k), and my 6L6 amplifies about 10 times, then its input capacitance must be 12 times lower than 2A3's. Data sheet shows Cgp = .6pF, and Cin = 10. So total Cin for my circuit is about 16pF, only 5 times, not 12 times lower.
Ok. I'm off my
.[/Figurin']
Tim (doesn't know much about slew other than ~= rise time)
7N7 said:
As for the g2 supply, perhaps you are lucky with your electricity supply?
Here in London I have seen it vary between 226v and 241v
It is supposed to be 230v!
---------------------------------------------------------------------------------
The now pan-european specifications for the power utility is:
230v+5%, -10%. i.e. from 207V to 241.5V. (this is so, as to be in line with the highest voltage of the previous regulations which were 220V +/- 10%, i.e.from 198V to 242V). So, don't plan to move from where you live!
Regards
George
Hi Choky
I just go for whatever my gut feels like...this time it pulled for 220k and I drew on whatever operating point looked best...namely, 1k cathode bias
Suppose I could add a doubler for +600V for the tube, but the 269AX is already pretty stressed as-is (FWB across the 250VCT makes 330V, and I'm drawing about 70mA, which equates to 140mA if it were FWCT, so I'm 40% over max yet it still passes the 10 second finger test!). Could add another hole ... if I transplanted it into another chassis...
Or maybe rip out the PT and shove it in another chassis...then I'd have room to rectify the heaters and get DC and waste even more VARs heating the transformer....what else...oh, use some oil caps instead of those rusty ol' aluminum 'lytics...heck, make 'em 1/4" aluminiuminum sheets suspended in air by hardened 4130 chrome-moly aircraft-grade steel supports, at 1/4" spacing that'd need what, maybe only a few thousand for the same 50uF?
Tim (this style is somewhat familiar if you know Shiva on RAT...)
I just go for whatever my gut feels like...this time it pulled for 220k and I drew on whatever operating point looked best...namely, 1k cathode bias
Suppose I could add a doubler for +600V for the tube, but the 269AX is already pretty stressed as-is (FWB across the 250VCT makes 330V, and I'm drawing about 70mA, which equates to 140mA if it were FWCT, so I'm 40% over max
yet it still passes the 10 second finger test!). Could add another hole ... if I transplanted it into another chassis...Or maybe rip out the PT and shove it in another chassis...then I'd have room to rectify the heaters and get DC and waste even more VARs heating the transformer....what else...oh, use some oil caps instead of those rusty ol' aluminum 'lytics...heck, make 'em 1/4" aluminiuminum sheets suspended in air by hardened 4130 chrome-moly aircraft-grade steel supports, at 1/4" spacing that'd need what, maybe only a few thousand for the same 50uF?
Tim (this style is somewhat familiar if you know Shiva on RAT...)
to high current drivers.
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