hi
On my side 6as7 in my preamp for a very very
good sound equivalent to a 300b and low zout
give a plus.
www.loginnovation.com/jeapel
if you don t like cathode follower a 6as7 + ccs
on plate and maybe 200 or 250v supply
would be a good solution
bye 🙂
On my side 6as7 in my preamp for a very very
good sound equivalent to a 300b and low zout
give a plus.
www.loginnovation.com/jeapel
if you don t like cathode follower a 6as7 + ccs
on plate and maybe 200 or 250v supply
would be a good solution
bye 🙂
Konnichiwa,
Well, early WE Datasheets specifies the 300B for DC heaters explicitly so, I think that view is highly debatable.
Sayonara
Eli Duttman said:
Well, early WE Datasheets specifies the 300B for DC heaters explicitly so, I think that view is highly debatable.
Sayonara
Konnichiwa,
Well, given that many valves exist that fit on a U4 Socket and many of these have a mu between 3 (45 which would give a gain of around 9db) and 8 (10 and derivates and 205 which would give a gain of around 18db) and most of these Valves have lowish anode impedances allowing them to drive a line output directly, why not build the thing universal.
You do not need to run the 300B at 80mA and 450V for example, a much more relaxed 180V anode voltage will work for any number of DHT Valves, including some mostly (and unjustly) ignored.
You can then add options for 20/30/40mA Anode current via CCS. I would use fixed bias, which then in combination with a suitable CCS can be used to set the Anode voltage.
For the heaters, simply (again) make them adjustable and include in the case a suitable panel meter switchable to measure Left Anode Voltage, Right Anode Voltage, Left Heater Voltage, Right Heater Voltage.
The result a simple, common cathode, line stage amplification stage. I would probably place the attenuator after the Linestage, with a 10Y or the like, you want a 10K load, all others can see lower loads with no problems, so a 10K attenuator as load after the Valve would be my choice.
Then all you need is a stock of all sorts of DHT's. With heaters up to 7.5V/1.5A you have the following linestage Valves (list may not be complete though) as options:
From the Cunningham/RCA derived series
10/10Y/VT25
26
45
71A
2A3
801A/VT62
From WE:
300B
101D
205D
The actual active circuit could look like this:
100nF PTFE input coupling Cap and 250k gridleak resistor to fixed bias with wide adjustment range.
Valve with CCS anode load.
2.2uF Output Coupling Cap (Mundorf or Audyn KP-SN would be my "starter" choice) folloowed by 10K Attenuator.
Done.
Sayonara
Bas Horneman said:
Well, given that many valves exist that fit on a U4 Socket and many of these have a mu between 3 (45 which would give a gain of around 9db) and 8 (10 and derivates and 205 which would give a gain of around 18db) and most of these Valves have lowish anode impedances allowing them to drive a line output directly, why not build the thing universal.
You do not need to run the 300B at 80mA and 450V for example, a much more relaxed 180V anode voltage will work for any number of DHT Valves, including some mostly (and unjustly) ignored.
You can then add options for 20/30/40mA Anode current via CCS. I would use fixed bias, which then in combination with a suitable CCS can be used to set the Anode voltage.
For the heaters, simply (again) make them adjustable and include in the case a suitable panel meter switchable to measure Left Anode Voltage, Right Anode Voltage, Left Heater Voltage, Right Heater Voltage.
The result a simple, common cathode, line stage amplification stage. I would probably place the attenuator after the Linestage, with a 10Y or the like, you want a 10K load, all others can see lower loads with no problems, so a 10K attenuator as load after the Valve would be my choice.
Then all you need is a stock of all sorts of DHT's. With heaters up to 7.5V/1.5A you have the following linestage Valves (list may not be complete though) as options:
From the Cunningham/RCA derived series
10/10Y/VT25
26
45
71A
2A3
801A/VT62
From WE:
300B
101D
205D
The actual active circuit could look like this:
100nF PTFE input coupling Cap and 250k gridleak resistor to fixed bias with wide adjustment range.
Valve with CCS anode load.
2.2uF Output Coupling Cap (Mundorf or Audyn KP-SN would be my "starter" choice) folloowed by 10K Attenuator.
Done.
Sayonara
Not at all a bad idea!...
Now if someone can point me to nice looking voltage meters (retro looking). I'll get going.
And maybe a good clean fixed bias (alterable) supply. (One side note...what about the voices that say cathode bias sounds better?)
😀
Konnichiwa,
I've been thinking and tinking with these ideas for a while. If you use a stepdown output transformer most of the usual suspect DHT's have no gain, forcing you to add a driver stage (like Manley does). If you end up with a parallel feed output transformer you might as well do without.
Sorry, no luck there from me, but I'd use a modern digital LCD Meter behind a nice round metal ring and switch offable backlight....
Easy, rectifiy the same voltage as for the HT, add some capacitors in series to the rectifiers to drop the voltage and the use a multiple RC cell filter chain onto 10K multiturn Trmimmers (you get nice panel mount hardware for them). If you use 4 - 6 RC Cells (even just 1K/22u) you knock any noise flat as a pancake.
This is a by far too simplified argument. If well implemented both have their own sets of advantages and much will depend upon what you want. For a linestage I have tried both several times (before giving up and going passive) and I found that fixed bias is reliably MUCH better, even when comparing to BG cathode bypass cap's and all that.
Sayonara
Bas Horneman said:
I've been thinking and tinking with these ideas for a while. If you use a stepdown output transformer most of the usual suspect DHT's have no gain, forcing you to add a driver stage (like Manley does). If you end up with a parallel feed output transformer you might as well do without.
Bas Horneman said:
Sorry, no luck there from me, but I'd use a modern digital LCD Meter behind a nice round metal ring and switch offable backlight....
Bas Horneman said:
Easy, rectifiy the same voltage as for the HT, add some capacitors in series to the rectifiers to drop the voltage and the use a multiple RC cell filter chain onto 10K multiturn Trmimmers (you get nice panel mount hardware for them). If you use 4 - 6 RC Cells (even just 1K/22u) you knock any noise flat as a pancake.
Bas Horneman said:
This is a by far too simplified argument. If well implemented both have their own sets of advantages and much will depend upon what you want. For a linestage I have tried both several times (before giving up and going passive) and I found that fixed bias is reliably MUCH better, even when comparing to BG cathode bypass cap's and all that.
Sayonara
Don't I need a seperate transformer so I can make a negative bias? (Putting up the positive rail of the second supply on the earth of the first supply ) so I end up with a negative supply?
Ah yes. Tis al coming back to me now...(Boy do I feel like Mike Schutte now...(actually am starting to look like him as well))
http://www.diyaudio.com/forums/showthread.php?s=&threadid=45740&highlight=
I use 150v B+ on my RCA 842 line out.
John
why not?
I am in! I think I will start with a passive preamp based on the S&B 102TX an later on I can add an active stage based on a parafeed push-pull of 2A3.
What do you think of the schematics I think to follow??!! I still need to work on it but your impressions would be very welcome.
Gianluca
I am in! I think I will start with a passive preamp based on the S&B 102TX an later on I can add an active stage based on a parafeed push-pull of 2A3.
What do you think of the schematics I think to follow??!! I still need to work on it but your impressions would be very welcome.
Gianluca
Attachments
Like a Raven, only better 🙂 But why the SS PS? Btw, the 'ultrapath' cap in Raven changes the sound for the better IME.
I wonder if the TX102 won't be happier driven by a capable driver rather than being left to the mercy of whatever source is plugged in. Of course this means further complications and there is nothing minimalist about the approach.
Mama mia 😉 😉
SS PS ... well just to stay simple and to give the hexfreds a try but yes changing the PS would be straightforward. I noticed I missed a cap in the RC!!
Source ... I just bought on e-bay a Tascam CD-R for 250eur ... happily waiting for it. I will had a source selector anyway and probably a +6db selector for the TX102
Like a Raven ... yes indeed. I like Push-Pull
Caps ... I am not a part picker but I fear I will need to test different caps
???DC (current) heater???
I am not going to series connect the heaters: I think the best thing to do is to have a separate supply (probably just the last current regulator) feeding each of the valve so each channel should have a bridge + CLC + V regulator + 2 parallel current regulator
Anything wrong???
gluca
SS PS ... well just to stay simple and to give the hexfreds a try but yes changing the PS would be straightforward. I noticed I missed a cap in the RC!!
Source ... I just bought on e-bay a Tascam CD-R for 250eur ... happily waiting for it. I will had a source selector anyway and probably a +6db selector for the TX102
Like a Raven ... yes indeed. I like Push-Pull
Caps ... I am not a part picker but I fear I will need to test different caps
???DC (current) heater???
I am not going to series connect the heaters: I think the best thing to do is to have a separate supply (probably just the last current regulator) feeding each of the valve so each channel should have a bridge + CLC + V regulator + 2 parallel current regulator
Anything wrong???
gluca
Hi Gianluca,
I saw that preamp when I was looking for an example of the 300B preamps on the net..I'm just not too keen on the gain stage of the preamp...with the 6sl7 and all...
Nice preamp though huh🙂
Regards,
Bas
I saw that preamp when I was looking for an example of the 300B preamps on the net..I'm just not too keen on the gain stage of the preamp...with the 6sl7 and all...
Nice preamp though huh🙂
Regards,
Bas
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