Wiring the D3A as triode - What is best?
I wired the d3a as triode, in order to use it as driver for my SE6c41c.
I did it the following way. Pin 8 (g3) to pin1 (cathode). Pin 9 (g2) with 1k to pin 7 (anode).
But I saw DHTROB use it differently (g3 to anode) and (g2 to cathode)
Anyone have experience with the d3a or any other pentode re-wired as triode?
(ps forgot to draw the grid leak resistor + I drew pin 8 to cathode as an internal wire (which it is not))
I wired the d3a as triode, in order to use it as driver for my SE6c41c.
I did it the following way. Pin 8 (g3) to pin1 (cathode). Pin 9 (g2) with 1k to pin 7 (anode).
But I saw DHTROB use it differently (g3 to anode) and (g2 to cathode)
Anyone have experience with the d3a or any other pentode re-wired as triode?
(ps forgot to draw the grid leak resistor + I drew pin 8 to cathode as an internal wire (which it is not))
An externally hosted image should be here but it was not working when we last tested it.
Mmm I should.... should I not ...only the amp weighs a ton (3channels) 3 power transformers 3 output transformers 9 chokes and 3 filament transformers !!! (And now 2 anode chokes as well)Why not try it both ways and let us know what you find.
Ok...if no-one can convince me otherwise...I'll just leave it the way I've done them.As far as I know, your connections are correct.
But I saw DHTROB use it differently (g3 to anode) and (g2 to cathode)
With 0V on the screen, you probably wouldn't be getting much current out of it at all.
I have seen schematics with the suppressor to the anode, or the cathode (with valves that have a separate suppressor pin) in triode mode, but all have the screen tied to the anode. IIRC, I've read there may or may not be some difference on where the suppressor is tied, something to do with interelectrode capacitances or something - not particularly significant.
Is this the triode-strapped D3A schematic you're referring to?
http://www.dhtrob.com/schemas/afbeeldingen/phonique_d3a.GIF
If so, look carefully. The screen is tied to the anode.
EDIT: BTW, DHTRob seems to have messed up the connection of the 0D3s, connecting 200V across them with no means of current limiting will likely end in disaster
Yes..that's the one.Is this the triode-strapped D3A schematic you're referring to
The screen is tied to the anode.
That's right. Only I have the screen connected to the cathode, hence my question which is better
[edit] just found this in the Telefunken datasheet
An externally hosted image should be here but it was not working when we last tested it.
Bas Horneman said:That's right. Only I have the screen connected to the cathode, hence my question which is better
In your schematic, the screen is connected to the anode through the screen stopper resistor...
An externally hosted image should be here but it was not working when we last tested it.
The datasheet shows the middle grid as being g2 and g3/screen as the top grid.
Hence my screen is connected to the cathode.
Nah, we're both right
The screen grid is connected to the anode, but the shielding screen is connected to the cathode (as it's connected to the same pin as the suppressor)
Damn my vague terminology
Hoping I understand this now, the question seems to be where is the best place to tie the suppressor (g3) and the shielding screen...
Well, in triode mode, I don't think it matters. So we get back to what Frank Berry said ages ago, which is try both and see what happens
The screen grid is connected to the anode, but the shielding screen is connected to the cathode (as it's connected to the same pin as the suppressor)
Damn my vague terminology
Hoping I understand this now, the question seems to be where is the best place to tie the suppressor (g3) and the shielding screen...
Well, in triode mode, I don't think it matters. So we get back to what Frank Berry said ages ago, which is try both and see what happens
Yes..thanks Jason.Well, in triode mode, I don't think it matters. So we get back to what Frank Berry said ages ago, which is try both and see what happens
From the datasheet the techspecs apparently show that the capacitance is lower with both connected to anode. But that is probably so minimal as not to matter at all.
You get a gnat's more mutual conductance if you connect g3 to a rather than k (as it happens, I made that measurementt on a D3a).
Thanks! That is great info!
How does more mutual conductance translate itself into sound?
Better detail retrieval?
Regards,
Bas
Don't tie the suppressor grid to the cathode: tie it to ground. The suppressor grid likes to be at the same DC potential of the control grid. Some people like to connect them (ex. in EL34) to the bias supply if it is a fixed bias output stage (and the bias is extremely clean). They think the tube sounds better with a suppressor much more negative than ground. I don't know... but maybe there's a max voltage allowed between anode and suppressor...
Bas Horneman said:How does more mutual conductance translate itself into sound?
Haven't a clue.
I will bypass it soon..but the funny thing is that I had the idea that the bass was better with the D3A than with the 6N1P?!
The datasheet gives 1k9 as Ri triode connected. (Or are they assuming a bypassed cathode...and does it go up that much unbypassed?) wow
Anyway...chucking the 1,9k Ri figure in the Rp box in the spreadsheet give 4Hz at -1dB...enough for me
The datasheet gives 1k9 as Ri triode connected. (Or are they assuming a bypassed cathode...and does it go up that much unbypassed?) wow
An externally hosted image should be here but it was not working when we last tested it.
Anyway...chucking the 1,9k Ri figure in the Rp box in the spreadsheet give 4Hz at -1dB...enough for me
Giaime said:They think the tube sounds better with a suppressor much more negative than ground.
Similar has been suggested to me.... but to simply connect the suppressor to ground via a correctly oriented 3.5V computer battery... i'm going to try it with EF86 (driver in EL34 SE amp under construction.
dave
With a mu of 77, the D3a will multiply any unbypassed cathode resistor by a factor of 78 (1 + mu), and add it to ra. That's a big increase...
I shall be most interested to hear what people think about playing with g3 voltages. I wouldn't have thought such a coarse grid would have much of an effect with such a small voltage, but nothing beats experiment.
I shall be most interested to hear what people think about playing with g3 voltages. I wouldn't have thought such a coarse grid would have much of an effect with such a small voltage, but nothing beats experiment.
Here some test on D3a
Hybrid Amplifier by Andrea Ciuffoli
http://www.audiodesignguide.com/Fiat/GM70d.html
Hybrid Amplifier by Andrea Ciuffoli
http://www.audiodesignguide.com/Fiat/GM70d.html
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