Hello,
I'm embarking on an 6SN7 / KT88 ~50W PP amp. There's a lot of fantastic designs so for power side the one I've settled on requires ~500/520v B+, 480v, -80v, plus supplies of 320v and 230v for driver and phase-splitter/re-amp stages.
There is a PSU design with it, but no choke in the circuit. I would have thought a choke is very desirable to help minimise ripple. If I don't have to use a choke it will help on cost saving of course! I plan to use a torroidal transformer type: "Toroidal: Shielded, Supreme Series // 230V sec.: 400V at 250mA, 80V at 250mA and 6.3V at 6A" from Dom Audio. This is the suggested by Dom Audio.
For diodes, I plan to use STMicroelectronics STTH1210D Switching Diode, 1000V 12A, 48ns.
I have re-posted the circuits - there's no copyright and they're already posted here.
Can anyone advise please...
I'm embarking on an 6SN7 / KT88 ~50W PP amp. There's a lot of fantastic designs so for power side the one I've settled on requires ~500/520v B+, 480v, -80v, plus supplies of 320v and 230v for driver and phase-splitter/re-amp stages.
There is a PSU design with it, but no choke in the circuit. I would have thought a choke is very desirable to help minimise ripple. If I don't have to use a choke it will help on cost saving of course! I plan to use a torroidal transformer type: "Toroidal: Shielded, Supreme Series // 230V sec.: 400V at 250mA, 80V at 250mA and 6.3V at 6A" from Dom Audio. This is the suggested by Dom Audio.
For diodes, I plan to use STMicroelectronics STTH1210D Switching Diode, 1000V 12A, 48ns.
I have re-posted the circuits - there's no copyright and they're already posted here.
Can anyone advise please...
Attachments
A choke is very desirable to help obtain good sound.
It is trivial to reach acceptable ripple without a choke, just look at 90% of commercial tube amps.
Thanks for your comment... I understood that would be the case, so was surprised to see there wasn't one in the design I uploaded.
I'm presuming ideally a choke in both outputs then (not heater)?
Hammond seem a logical choice of quality and cost from what I have read/seen.
Next question is what values!! Maximum of 250mA output suggests 250mA choke or should I add some headroom to 300mA?
I'm presuming ideally a choke in both outputs then (not heater)?
Hammond seem a logical choice of quality and cost from what I have read/seen.
Next question is what values!! Maximum of 250mA output suggests 250mA choke or should I add some headroom to 300mA?
V1B should have it's filament elevated to B+/4
If it's a stereo amp then V1B should be shared with the other channel and
it's filament (only) could be raised, the other cathodes would be
close to ground anyway, thus the filament should have a ground reference,
a "hum-dinger" might be the best way.
I also agree that a chokewould be a much better way to smoothen the B+
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200mA might be enough for your needs.
$15 is a great deal.
C-14X Triad Magnetics | Inductors, Coils, Chokes | DigiKey
I do understand you on the other side of the pond.
$15 is a great deal.
C-14X Triad Magnetics | Inductors, Coils, Chokes | DigiKey
I do understand you on the other side of the pond.
150 ohms is half of the resistor ( 300 ohm) it replaces. Go for it, but by all means
try to find one in UK first!
Or, try tubetown.de :
https://www.tube-town.net/ttstore/T...mond-15x-Series/Hammond-Choke-159R::7101.html
6H 200mA 18 euros including VAT excl shipping from germany
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@Petertub - so simply replace R2 = 330R with the choke? I'd like to keep the amp as dynamic as possible so with 200mA rated choke I am restricting the rating of the T'former...
No choke for the -83v supply?
Please, all comments are appreciated - things appear contrary sometimes.
Anyone care to comment on the original design with no choke whatsoever?
No choke for the -83v supply?
Please, all comments are appreciated - things appear contrary sometimes.
Anyone care to comment on the original design with no choke whatsoever?
You want low DCR in the power supply, replacing the 330R with a 150R choke makes it more dynamic because of the lower DCR.
You aren't restricting the power transformer using a choke rated at 200mA, the 250mA rating is a maximum rating. The choke rating means that they guarantee 6H of inductance at 200mA. Go over the current and the core saturates lowering the inductance.
You will have to calculate the exact quiescent current draw for the amp but it's probably ~150mA which is less than both choke and Transformer max current draw.
You aren't restricting the power transformer using a choke rated at 200mA, the 250mA rating is a maximum rating. The choke rating means that they guarantee 6H of inductance at 200mA. Go over the current and the core saturates lowering the inductance.
You will have to calculate the exact quiescent current draw for the amp but it's probably ~150mA which is less than both choke and Transformer max current draw.
> No choke for the -83v supply?
No.
Bias supply ripple nearly cancels in push-pull.
Bias ripple here is further reduced by the 100K+0.22uFd grid networks.
It is very low current (7mA).
You are starting with well-excess voltage. You can afford to lose some in an R-C filter.
At this power level, a "large" cap is not a budget breaker.
And this plan features a full-wave bridge.
In The Old Days, we used half-wave bias rectifier and smaller caps, got fine sound.
No.
Bias supply ripple nearly cancels in push-pull.
Bias ripple here is further reduced by the 100K+0.22uFd grid networks.
It is very low current (7mA).
You are starting with well-excess voltage. You can afford to lose some in an R-C filter.
At this power level, a "large" cap is not a budget breaker.
And this plan features a full-wave bridge.
In The Old Days, we used half-wave bias rectifier and smaller caps, got fine sound.
Folks - thanks for the replies, I feel like I'm making some headroom now....
I'm gathering the parts together, so have purchased a bundle of 1W and 2W metal film +/-1% resistors from EBay plus I've scored some .22uF polypropylene 5% 630v non-inductive axial capacitors from the same place at an excellent price.
The rectifier diodes are probably way over the top but the cost was good and they are fast recovery at 48nS. I can experiment here, especially for the Bias supply.
For experimentation I've managed to get hold of NOS 6N8S/6SN7 and cheap-ish KT88. When I'm happy with the results maybe I'll try some PSVANE UK-6SN7 and KT88
I have an idea to monitor key voltage and current values using an Arduino or Raspberry Pi and sensors, then connect to my wi-fi to enable remote monitoring. But I get ahead of myself... best build it first!!
I'm gathering the parts together, so have purchased a bundle of 1W and 2W metal film +/-1% resistors from EBay plus I've scored some .22uF polypropylene 5% 630v non-inductive axial capacitors from the same place at an excellent price.
The rectifier diodes are probably way over the top but the cost was good and they are fast recovery at 48nS. I can experiment here, especially for the Bias supply.
For experimentation I've managed to get hold of NOS 6N8S/6SN7 and cheap-ish KT88. When I'm happy with the results maybe I'll try some PSVANE UK-6SN7 and KT88
I have an idea to monitor key voltage and current values using an Arduino or Raspberry Pi and sensors, then connect to my wi-fi to enable remote monitoring. But I get ahead of myself... best build it first!!
I am also busy building a valve amp (Mullard 5-20 variant).
Also look here, UK site, good products.
BluebellAudio
Where is Dom Audio, I do not find a website?
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Yes, replace 330ohm with a choke.
Leaving out a choke saves money and weight, but needs a lot more capacitor to
get decent level of hum. Include a choke and you can use less caps for same
level of hum.
Bias circuit normally draws so little power that one or two small caps will
filter out all remaining hum.
...slip of the fingers... it's Don Audio:
https://www.don-audio.com
I have no affiliation with them, but have experienced great service.
@Petertub... thanks for your comments. Looking at the power supply circuit I have uploaded, if I were to include a choke as recommended what value of electrolytic would you suggest for C3 and C4? Would C1 and C2 remain the same?
560uF electrolytics at around 400v can be pretty expensive from my searches!
560uF electrolytics at around 400v can be pretty expensive from my searches!
I would try 50 - 100 uF in both places, and you don't need serial connections
as 500V is available ( JJ makes them for instanse, tubetown.de:
https://www.tube-town.net/ttstore/Capacitors/JJ-Electronics/JJ-Cap-axial:::31_36_170.html
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