D3a or 6E6P, Lundahl 1660 IT , and 300B.
Hi.
This configuration in 2 stages with interestage trasnformer, would be a good option?
Would be enough voltage swing for the 300B?
Thanks. Santiago
Hi.
This configuration in 2 stages with interestage trasnformer, would be a good option?
Would be enough voltage swing for the 300B?
Thanks. Santiago
You do have the alternative of a plate choke instead of an interstage. I have a pair of LL1660/18mA and I preferred the sound of a good plate choke with FT-2 or FT-3 coupling caps. I use 2 x 01uF in //. For example LL1668. You would save some money too.
If you are satisfied with 6-7W (depending of B+ and OPT impedance, only in A1 region) power, the IT coupled two stage amplifier would be a good solution.
D3a has enough gain to drive 300B grid even via 'Alt S' (4:4.5) connected LL1660.
The tube has enough low output impedance and IT -in this connection- has 130H inductance.
The disadvantage is the max. current (10mA) of IT, and tend to make bump at few ten kiloHertz (serial R-C snubber usually need).
I'm not a fan of LL1660, so agree with Andy, good choke and capacitor coupling is better option.
Try just the primary as a plate choke with FT-2 or FT-3 coupling caps. I prefer it that way.
Depends of Ua and OPT primary impedance.
I use +400V and 5k OPT, over the 10W ... but with FET source follower.
In A2 region the grid "eats" current, so practically at least 10mA "hard" driving necessary.
The interstage never ensures this.
santitiricco,
Yes it will work; No it will not work. It all depends . . .
D3a or 6E6P . . . are you going to use either one in pentode mode, or in triode wired mode?
What D3a / 6E6P grid bias voltage will you use?
What B+ Voltage to the interstage primary, and the DCV loss due to the primary interstage DCR times the plate current?
What is the D3a / 6E6P plate load impedance (what impedance is the interstage transformer across the audio band)?
The Western Electric 300B data sheet gives a lot of quiescent operating conditions. Here are a couple of examples:
@ 400V Plate to Filament, -91V bias . . . your driver has to swing +/- 91V, (182V peak to peak).
@ 450V Plate to Filament, -104V bias . . . your driver has to swing +/- 104V, (208V peak to peak).
As I said, it all depends.
Happy designing, building, and listening!
Yes it will work; No it will not work. It all depends . . .
D3a or 6E6P . . . are you going to use either one in pentode mode, or in triode wired mode?
What D3a / 6E6P grid bias voltage will you use?
What B+ Voltage to the interstage primary, and the DCV loss due to the primary interstage DCR times the plate current?
What is the D3a / 6E6P plate load impedance (what impedance is the interstage transformer across the audio band)?
The Western Electric 300B data sheet gives a lot of quiescent operating conditions. Here are a couple of examples:
@ 400V Plate to Filament, -91V bias . . . your driver has to swing +/- 91V, (182V peak to peak).
@ 450V Plate to Filament, -104V bias . . . your driver has to swing +/- 104V, (208V peak to peak).
As I said, it all depends.
Happy designing, building, and listening!
Andy, i found the Lundahl transformers, they are LL1671 interestage Transf.
35H would be enough for choke load for the D3a?
If i can use it for choke load, then could use FT3 capacitor to grid 300B.
35H would be enough for choke load for the D3a?
If i can use it for choke load, then could use FT3 capacitor to grid 300B.
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What is the impedance of 35H at your lowest usable frequency.
If it is approx two times the Rp of the triode connected D3a, then it will be okay.. as a minimum.
What is the Rp of the D3a in your circuit?.
As a short answer, for full range use, 35H load will be insufficient.
Consider, that 35H is at 30mA.. if you're running 15-20mA, you will have more inductance. How much more?.. build it and measure the freq response - You might find that its suitable after all.
If it is approx two times the Rp of the triode connected D3a, then it will be okay.. as a minimum.
What is the Rp of the D3a in your circuit?.
As a short answer, for full range use, 35H load will be insufficient.
Consider, that 35H is at 30mA.. if you're running 15-20mA, you will have more inductance. How much more?.. build it and measure the freq response - You might find that its suitable after all.
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35H at 20Hz is about 4k4.
D3a triode mode output impedance is 1k9.
With this impedance the low bandwidth isn't adequate.
I would use at least 60H primary inductance IT.
D3a triode mode output impedance is 1k9.
With this impedance the low bandwidth isn't adequate.
I would use at least 60H primary inductance IT.
What if you use speakers with diminished deep bass, like 2-way bookshelf speakers? You could do a calculation for 40hz rather than 20 hz, no? Here's a calculator:
https://www.translatorscafe.com/unit-converter/en-US/calculator/inductor-impedance/
I don't know how to calculate how the inductance rises as the current through the choke falls. Any suggestions?
As I wrote earlier, if the phase within the "mainstream band" change rapidly -mostly at the lower end- the quality go wrong.
If you use inadequate inductance as plate load (ie. impedance of inductor -at the most lower frequency- not greater 3-4 times, than tube's output impedance), the phase "go away" at the lower region.
Z=2*pi*f*L
Z at 20Hz, if inductance is 35H:
Z=2*3.14159*20*35
Z=4398 Ohm
Use 3-4 times greater (4 is recommended) load than output impedance of source.
Recommended: 4*1900= 7600 Ohm
7600=2*pi*20*L
L= 60H
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It certainly sounds like low Ri tubes have a big advantage in terms of matching with plate chokes and interstages. I'm going to pursue my idea of a 3 stage amp with 6C4C as first stage. Not sure about the middle driver tube but plenty of contenders in the 10 to 20 mu range including DHTs.
Andy, is true, low plate resistance is better for use IT or Chokes. If you are with the idea for 3 stages amp, i can tell you, are impressive.. I would like to use d3a 45 300B, but use 6E6P DR, i can not use D3a because they oscillate. But 6E6P-DR 45 300B is impressive.. They look like 20 or 30 powerful watts. And the microdetail are all.. The D3a is
Indomitable for me on this amp.
Although It's my 4th amp with 300B
Indomitable for me on this amp.
Although It's my 4th amp with 300B
I built several equipments with trioded D3a, but neither tend to oscillate, if the layout was properly designed.
"They look like 20 or 30 powerful watts"
It's not 300B amp. Even push-pull 300B capable to 20W, but SE not.
Euro21,
D3a Rp in circuit is different from data sheet.
I get 2k4.. that Rk adds.. and so does all the other stuff they dont mention.
Can post data sheet snip, but you know it already.
Cheers to all.
And still, all for naught (?) - I use 45H Hi-nickel core gapped 15mA with 10-12mA D3a.. its okay.. ;-)
Knocks my socks off 🙂 .. (I dont wear socks)..
Anymore, or ever? - hahha. (what?), socks.. (really?).. what? ..
🙂
BAN CAP - use a capacitor, practise flute insertion at band-camp.
(dont use capacitors unless you like it)
Shane
ooops
D3a Rp in circuit is different from data sheet.
I get 2k4.. that Rk adds.. and so does all the other stuff they dont mention.
Can post data sheet snip, but you know it already.
Cheers to all.
And still, all for naught (?) - I use 45H Hi-nickel core gapped 15mA with 10-12mA D3a.. its okay.. ;-)
Knocks my socks off 🙂 .. (I dont wear socks)..
Anymore, or ever? - hahha. (what?), socks.. (really?).. what? ..
🙂
BAN CAP - use a capacitor, practise flute insertion at band-camp.
(dont use capacitors unless you like it)
Shane
ooops
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Hi Shane,
Try to measure -even at 1kHz- distortion of 45H loaded D3a at 70VRMS (99V peek, 198Vpp) output level, and compare it:
Try to measure -even at 1kHz- distortion of 45H loaded D3a at 70VRMS (99V peek, 198Vpp) output level, and compare it:
Hi,
As you know, cathode at AC ground and you get Rp according to the datasheet.
But the penalty you pay for cathode at AC ground .. I guess you work it out for yourself and how you did that.. Ck, or battery in the grid circuit - all second rate IMO. Stacked supplies for low level stages, probably not. Split rail supplies - yep.. l'd like to see more.
So, if raised AC impedance cathode - higher Rp, more Lpri, more phase shift at LF, the higher the LF pole and also C of the primary.. and BW shrinks quickly from both ends.
So far as the measurements.. my application is 150mVpp to the grid, horisontal load line. If you can run it again with those parameters, great.
So far as 200Vpp levels of drive, I do understand, and each to their own, but I would use a low Cin and low mu DHT, something like 71A. Stacked supplies without cathode (fil) bypass and <2kRp. Takes an additional stage, but so long as it is a good stage, IME it sounds just as direct, okay maybe some slight loss, but more different than 'loss' but very much more effortless and less strained on peaks.
Apples for horses 🙂
As you know, cathode at AC ground and you get Rp according to the datasheet.
But the penalty you pay for cathode at AC ground .. I guess you work it out for yourself and how you did that.. Ck, or battery in the grid circuit - all second rate IMO. Stacked supplies for low level stages, probably not. Split rail supplies - yep.. l'd like to see more.
So, if raised AC impedance cathode - higher Rp, more Lpri, more phase shift at LF, the higher the LF pole and also C of the primary.. and BW shrinks quickly from both ends.
So far as the measurements.. my application is 150mVpp to the grid, horisontal load line. If you can run it again with those parameters, great.
So far as 200Vpp levels of drive, I do understand, and each to their own, but I would use a low Cin and low mu DHT, something like 71A. Stacked supplies without cathode (fil) bypass and <2kRp. Takes an additional stage, but so long as it is a good stage, IME it sounds just as direct, okay maybe some slight loss, but more different than 'loss' but very much more effortless and less strained on peaks.
Apples for horses 🙂
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