someone can explain me why filament supply of cascode's stage are inverted ? The botton 6922 tube is powered by elevating voltge at 125 volts and the upper at 12 v. it nay be normaly inverted or not ?
Thanks for explaination
Thanks for explaination
If it is PH3, the elevation is only for V3 ( one half for each channel) that is a cathode follower and not vor V1 and V2 They have the filament in series.
one section of V1 and V2 have the catode at around the 55 Vdc so under the limit of 6922
one section of V1 and V2 have the catode at around the 55 Vdc so under the limit of 6922
Ciao Walter, ci conosciamo da un po' ma è da tanto che non ci vediamo.
mi riferivo al pre Audio Research Sp 10, stadio phono. Se guardi lo schema, il secondo stadio è un cascode di 6922 con le sezioni di entrambi i triodi in parallelo. Lo stadio è collegato ad un catodo follower di 6922 in parallelo.
Questa tipologia di circuito è stato inventato da William Johnson (brevetto EP 0 210 155 A2) ed è stato invitato sullo stadio fono dell'Sp 10.
Ora, in uno stadio cascode, di norma, la valvola bassa è accesa con filamento riferito a massa, mentre la valvola alta ha il filamento sollevato a, in questo caso, 125 V.
ionvece nello schema Audio Research Sp 10 notiamo, nella sezione di alimentazione che l'alimentazione dei filamenti bassi è flottante e non ancorata a massa ma, soprattutto, che i tubi cascode sono accesi all'inverso, cioè la valvola bassa a +125 V da massa con il suo catodo a +0,68 v mentre la valvola superiore ha il flottante da 12,6 volt. Non era logico il contrario? Perché non dovrebbe ronzare?
Grazie Walter. Antonio
mi riferivo al pre Audio Research Sp 10, stadio phono. Se guardi lo schema, il secondo stadio è un cascode di 6922 con le sezioni di entrambi i triodi in parallelo. Lo stadio è collegato ad un catodo follower di 6922 in parallelo.
Questa tipologia di circuito è stato inventato da William Johnson (brevetto EP 0 210 155 A2) ed è stato invitato sullo stadio fono dell'Sp 10.
Ora, in uno stadio cascode, di norma, la valvola bassa è accesa con filamento riferito a massa, mentre la valvola alta ha il filamento sollevato a, in questo caso, 125 V.
ionvece nello schema Audio Research Sp 10 notiamo, nella sezione di alimentazione che l'alimentazione dei filamenti bassi è flottante e non ancorata a massa ma, soprattutto, che i tubi cascode sono accesi all'inverso, cioè la valvola bassa a +125 V da massa con il suo catodo a +0,68 v mentre la valvola superiore ha il flottante da 12,6 volt. Non era logico il contrario? Perché non dovrebbe ronzare?
Grazie Walter. Antonio
Thank You for saying which "Audio Research phono stage".
Link would be nice too:
https://audioresearch.com/wp-content/uploads/2021/08/SP10_Manual_Schem.pdf
Snippet:
There is also a computer-drawn diagram but it seems to be copied from the 1982 hand-drawings.
Yes, the lower heater is shown biased-up at +122V, while the upper is near Common.
Also odd: the upper cathode follows a +32V grid, so is +35V to +40V, so does not need a hundred volt bias.
I would be dubious about this until an expert appears or a known-good example is on the bench. It may just be a drawing error on this too-complicated preamp.
Hi, thank you for your replay
this is the last schematic by official manual.
the typology of the circuit derives from the invention of william Johnson who describes the identical amplification stage, composed of a 6922 in a cascode configuration coupled directly to a cathode follower. the cathode voltage divider supplies the +38V voltage to the upper cascode triode grids. The cathode is at +40V. certainly there is a reason but the ignition of the filaments is reversed and the filament of the low valves is floating.
On this topic it should be noted that the 6922 triode has a VKf of +/- 200 volts, therefore the inversion should have no effect on the circuit functioning but what is strange is the lower cascode triode whose cathode is at +0.68V and its filament raised to +122V.
Why?, What goal do they want to achieve? Also, the voltage of the "low" filaments is floating, i.e. not anchored to the "common" and this doesn't lead to hum?
Thanks for your contribution
this is the last schematic by official manual.
the typology of the circuit derives from the invention of william Johnson who describes the identical amplification stage, composed of a 6922 in a cascode configuration coupled directly to a cathode follower. the cathode voltage divider supplies the +38V voltage to the upper cascode triode grids. The cathode is at +40V. certainly there is a reason but the ignition of the filaments is reversed and the filament of the low valves is floating.
On this topic it should be noted that the 6922 triode has a VKf of +/- 200 volts, therefore the inversion should have no effect on the circuit functioning but what is strange is the lower cascode triode whose cathode is at +0.68V and its filament raised to +122V.
Why?, What goal do they want to achieve? Also, the voltage of the "low" filaments is floating, i.e. not anchored to the "common" and this doesn't lead to hum?
Thanks for your contribution
Attachments
I suppose an error on details on schematic about tubes label
V5 (6) is V3 (4)
The others seeme to be fine as labeled
At that time the AR used the 6DJ8 not the 6922 so the Vkf is less than 200 volt max, quite same for 6922 that are more robust
Walter
V5 (6) is V3 (4)
The others seeme to be fine as labeled
At that time the AR used the 6DJ8 not the 6922 so the Vkf is less than 200 volt max, quite same for 6922 that are more robust
Walter
I too had thought of an AR error but someone in the world would have noticed it sooner or later. However, in the previous pages of the manual, the previous version is also shown, the diagram of which is drawn by hand and shows the same situation. In any case, why is the ignition of the low valve filament floating? I can assume it's to not "lean" the negative side of the filament to the common