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John L Stewart John L Stewart is offline
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Smile Simple Regulated PS Using 6N7 Pass Tubes

In this one the 6N7s need to be driven into grid current to get anykind of useable output current. But the stabilization factor is porportional to the pass tube mu (35) & amplifier gain. The gain is reduced a little by the 12B4 CF.

Looking back in from the output terminals the source impedance is proportional to the amplifier gain & gm of the 6N7s, so 3x whatever the 6N7s are doing at that load.

Notice it can be swiched for either C or L filter input. So at lower voltages, higher currents are possible.

Stability depends mostly on the gas tube & output sampling resistors. Altogether a passable PS for ordinary work.

Why did I use 6N7s? We had a pile of them & $$$ were short. Overtime I also used some 6A3s & 6B4Gs. Sure would not do that now!

Cheers to all, John
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John L Stewart John L Stewart is offline
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Originally Posted by John L Stewart View Post
In this one the 6N7s need to be driven into grid current to get anykind of useable output current. But the stabilization factor is porportional to the pass tube mu (35) & amplifier gain. The gain is reduced a little by the 12B4 CF.

Looking back in from the output terminals the source impedance is proportional to the amplifier gain & gm of the 6N7s, so 3x whatever the 6N7s are doing at that load.

Notice it can be swiched for either C or L filter input. So at lower voltages, higher currents are possible.

Stability depends mostly on the gas tube & output sampling resistors. Altogether a passable PS for ordinary work.

Why did I use 6N7s? We had a pile of them & $$$ were short. Overtime I also used some 6A3s & 6B4Gs. Sure would not do that now!

Cheers to all, John
Here is a somewhat improved version. The error amp is now 2-stage. The extra gain allows the filter choke to be removed. The performnce is a little better. But looks like the reference source is still an 0B2.

Up where the choke used to be on the schema see something new. The diode labelled D & its 10 microfarad cap allow the 6U8 pentode section & the 12B4 CF to run at a higher voltage than is otherwise possible in a simple cct. That ensures the 6N7s can be turned on all the way.

See at the same place on the schema the switch section S3a & a 250R, 20W resister in parallel. When the PS OP is set to the low range S3a is open. That way not as much B+ is made & the pass tubes can enjoy lower dissipation.

I've got lots more, all the way up to 4500 volts, one amp. But that one doesn't fit well in this forum!

Cheers to all, John
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patrick-turner patrick-turner is offline
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Default Simple Regulated PS Using 6N7 Pass Tubes

On Friday, 18 January 2013 11:56:25 UTC+11, John L Stewart wrote:
In this one the 6N7s need to be driven into grid current to get anykind of useable output current. But the stabilization factor is porportional to the pass tube mu (35) & amplifier gain. The gain is reduced a little by the 12B4 CF. Looking back in from the output terminals the source impedance is proportional to the amplifier gain & gm of the 6N7s, so 3x whatever the 6N7s are doing at that load. Notice it can be swiched for either C or L filter input. So at lower voltages, higher currents are possible. Stability depends mostly on the gas tube & output sampling resistors. Altogether a passable PS for ordinary work. Why did I use 6N7s? We had a pile of them & $$$ were short. Overtime I also used some 6A3s & 6B4Gs. Sure would not do that now! Cheers to all, John +-------------------------------------------------------------------+ |Filename: 6N7 Regulated Power Supply (PS) 10W 5 75 40 Contrast.jpg | |Download: http://www.audiobanter.com/attachment.php?attachmentid=325| +-------------------------------------------------------------------+ -- John L Stewart


About 12 months ago I revised a PSU bench top supply for testing KT120 tubes. I found that if you could regulate both EG2 AND Ea at +500Vdc, then 2 x KT120 could produce about 140W AB1, and KT88 about 135W, so all KT120, 90, 88 and 6550can do this although the most unhappy tube is the 6550 which has a lower Eg2 rating. The happiest tube is the KT120 which has the highest Pda rating of 60W, so they cope if RLa-a drifts low for any reason.
If for any reason the Ea and or Eg2 sags under increased DC current then you just can't get the power I just mentioned. So it pays to remember that what data sheets say is possible, may be impossible in the amp made by the average Joe Blogz, that guy who never regulates his tube amp power rails. It isn't necessary if the amp has huge PSU caps and the duty cycle of music waves means average PO 50W when maybe some peaks in the music are just beginning to clip.

The circuit of my regulated +500Vdc has adjustable 50Vdc B+ steps down to 250Vdc by means of a string of zener diodes fed by resistors from the regulated output voltage. The B+ produced by HT supply PT winding and caps and diodes is adjustable by including variations from cap input to choke input plus series R to prevent pass elements overheating because of Ea x Ia product exceeding Pda ratings. Pass elements are two 6AS7 tubes with all 4 triodes paralleled which allows 250mA dc without grid current.
Driver for 6AS7 is 6BX6 gain element with its own floating 300Vdc supply referenced to the cathode so that the anode RL isn't 1M and anode current is not feeble, hence 6BX6 Gm is high and so gain is high so Rout of final product is low, despite Iout change from 20mA to 200mAdc. This floating supply comes from a transformer I had handy from junk box and performs the task of keeping any hum from main PSU from entering 6AS7 grids via the 6BX6 anode resistance which is in a divider with the high pentode Ra.

Anyway, my circuit well out performs the circuit referred to by our dear John Stewart, which follows classical 1955 thinking. Such classical thinking was in fact status quo generic thinking which could be argued was lowest common denominator but my expectations are always higher than what was good enough for 1955. I like testing junk over a wider range of Ea and Ia and with lower noise and lower Rout, so I don't regret the 2 weeks I spent sweating over my PSU which I first made in 1993.

I might add that back then I initially tried to use BU208A transistors for pass elements but after managing to fuse a few despite having quick acting over-current protection, I changed to using tube pass elements. I never figured why the BU208 failed so easily despite working below their quite high and impressive voltage ratings. I suspect I didn't have a diode across the choke to short out back EMF allowing collector voltage to soar for an instant thus causing bjt to fail. John's circuit would benefit from such a thing.. If the load current is cut off sharply, choke voltage tries to soar positively, like the anode voltage of a tube in SET amp with SE OPT - unless you have a nice big fat cap to slow it all down. But, I'd had a +400Vdc regulator with BU208 supplying 2 x 6550 in my general purpose workshop amp for years now and that has not ever failed, and B+ is much better filtered and stabilised than by any huge choke and caps could do. In fact hum at output 0.1mV and the poweramp can be used as preamp if wanted with gain = 15, 20Hz to 65kHz, at 15Vrms output, Rout = 0.5 ohms, THD 0.1%, all with this result aided by the regulated PSU with BU208. The BU108 is also not a bad bjt. But once above 500Vdc, watch out, because then things get iffy.

Patrick Turner.
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John L Stewart John L Stewart is offline
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Quote:
Originally Posted by patrick-turner View Post
On Friday, 18 January 2013 11:56:25 UTC+11, John L Stewart wrote:
In this one the 6N7s need to be driven into grid current to get anykind of useable output current. But the stabilization factor is porportional to the pass tube mu (35) & amplifier gain. The gain is reduced a little by the 12B4 CF. Looking back in from the output terminals the source impedance is proportional to the amplifier gain & gm of the 6N7s, so 3x whatever the 6N7s are doing at that load. Notice it can be swiched for either C or L filter input. So at lower voltages, higher currents are possible. Stability depends mostly on the gas tube & output sampling resistors. Altogether a passable PS for ordinary work. Why did I use 6N7s? We had a pile of them & $$$ were short. Overtime I also used some 6A3s & 6B4Gs. Sure would not do that now! Cheers to all, John +-------------------------------------------------------------------+ |Filename: 6N7 Regulated Power Supply (PS) 10W 5 75 40 Contrast.jpg | |Download: http://www.audiobanter.com/attachment.php?attachmentid=325| +-------------------------------------------------------------------+ -- John L Stewart


About 12 months ago I revised a PSU bench top supply for testing KT120 tubes. I found that if you could regulate both EG2 AND Ea at +500Vdc, then 2 x KT120 could produce about 140W AB1, and KT88 about 135W, so all KT120, 90, 88 and 6550can do this although the most unhappy tube is the 6550 which has a lower Eg2 rating. The happiest tube is the KT120 which has the highest Pda rating of 60W, so they cope if RLa-a drifts low for any reason.
If for any reason the Ea and or Eg2 sags under increased DC current then you just can't get the power I just mentioned. So it pays to remember that what data sheets say is possible, may be impossible in the amp made by the average Joe Blogz, that guy who never regulates his tube amp power rails. It isn't necessary if the amp has huge PSU caps and the duty cycle of music waves means average PO 50W when maybe some peaks in the music are just beginning to clip.

The circuit of my regulated +500Vdc has adjustable 50Vdc B+ steps down to 250Vdc by means of a string of zener diodes fed by resistors from the regulated output voltage. The B+ produced by HT supply PT winding and caps and diodes is adjustable by including variations from cap input to choke input plus series R to prevent pass elements overheating because of Ea x Ia product exceeding Pda ratings. Pass elements are two 6AS7 tubes with all 4 triodes paralleled which allows 250mA dc without grid current.
Driver for 6AS7 is 6BX6 gain element with its own floating 300Vdc supply referenced to the cathode so that the anode RL isn't 1M and anode current is not feeble, hence 6BX6 Gm is high and so gain is high so Rout of final product is low, despite Iout change from 20mA to 200mAdc. This floating supply comes from a transformer I had handy from junk box and performs the task of keeping any hum from main PSU from entering 6AS7 grids via the 6BX6 anode resistance which is in a divider with the high pentode Ra.

Anyway, my circuit well out performs the circuit referred to by our dear John Stewart, which follows classical 1955 thinking. Such classical thinking was in fact status quo generic thinking which could be argued was lowest common denominator but my expectations are always higher than what was good enough for 1955. I like testing junk over a wider range of Ea and Ia and with lower noise and lower Rout, so I don't regret the 2 weeks I spent sweating over my PSU which I first made in 1993.

I might add that back then I initially tried to use BU208A transistors for pass elements but after managing to fuse a few despite having quick acting over-current protection, I changed to using tube pass elements. I never figured why the BU208 failed so easily despite working below their quite high and impressive voltage ratings. I suspect I didn't have a diode across the choke to short out back EMF allowing collector voltage to soar for an instant thus causing bjt to fail. John's circuit would benefit from such a thing.. If the load current is cut off sharply, choke voltage tries to soar positively, like the anode voltage of a tube in SET amp with SE OPT - unless you have a nice big fat cap to slow it all down. But, I'd had a +400Vdc regulator with BU208 supplying 2 x 6550 in my general purpose workshop amp for years now and that has not ever failed, and B+ is much better filtered and stabilised than by any huge choke and caps could do. In fact hum at output 0.1mV and the poweramp can be used as preamp if wanted with gain = 15, 20Hz to 65kHz, at 15Vrms output, Rout = 0.5 ohms, THD 0.1%, all with this result aided by the regulated PSU with BU208. The BU108 is also not a bad bjt. But once above 500Vdc, watch out, because then things get iffy.

Patrick Turner.
We didn’t have tubes such as the KT120 or KT 90 back in those days. But we did have 807s (lots of them), 813s & 304TH. Many of those found their way into my designs. I also used KT88s & 6550s when it made sense. By using error amplifiers of two or more stages I managed to avoid filter chokes completely.

By the time I joined HP in 1965 most regulated PS were SS. To get around the potential failure problems, pre-regulators using phase controlled SCRs was common. I’ve not built a tube based regulator since then. And for high voltages used in photomultipliers there are some nice hybrid designs.

All my higher powered designs had separate +ve & -ve rails for the error amplifiers. I also did several large supplies where the current needed to be regulated. Voltage & current regulators are not much different. But if you see a 4-quadrant regulator it may seem familiar. Just another name for a power Op-Amp. They can Sink or Source current, something needed with active loads.

Best common tube reference is the 85A2. But for ordinary applications all the others, 0A2, 0B2, Etc work quite well. I found HV Zeners tend to drift as they warm up.

A single pentode error amp will also drift, all caused by the heater temperature changes as the line moves around. But again, OK for ordinary work. A diff amp for the 1st stage is a good cure for that. But adds to the complexity.

One oddity we see is in the example given in the RCA tube manual is their placement of the equalization resistors in the plates of the 6AS7. They should be in the cathodes where they will have (1 + mu) times the effectiveness. Perhaps designed by someone barely out of school.

The transistor failure in the regulated PS Patrick tried was most likely caused by something called, ’Second Breakdown’. I will leave it to the curious to look that up. It is well known that a transistor is a better fuse than a real fuse. I noticed that early on!

My personal regulated PS is something I built more than 55 years ago. It still uses the 25 Hz Hammond iron I had previously used in a PA based on an 815 running Class AB2. It made a lot of music at many parties. I junked the amp & built my regulator. It has a catcher diode so that while running in the choke input mode, the turnoff transient does not cause problems.

Best way to switch a tube regulator on/off is on the AC secondary of the HT transformer. Like always, easier to switch AC than the DC you are making. Much easier on the switch. But never had a switch fail, whether on AC or DC.

These days N-Channel MOS-Fets make a lot of sense. If a lot of power, then a preregulator to keep the lid on things. All somewhat more complicated but a lot more efficient & stable.

Monday morning quarterbacks are everywhere. We did what we could with the devices available to us at the time. For me it was a break to work in the Physics lab at U of T. By interning there I got a PEng out of it. And a lot of common sense too!

Having designed & built something like 40 regulated PS & a lot of other stuff, My thoughts, anyway. John
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GRe GRe is offline
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Default Simple Regulated PS Using 6N7 Pass Tubes


"John L Stewart" wrote in message
...

In this one the 6N7s need to be driven into grid current to get anykind
of useable output current. But the stabilization factor is porportional
to the pass tube mu (35) & amplifier gain. The gain is reduced a little
by the 12B4 CF.

Looking back in from the output terminals the source impedance is
proportional to the amplifier gain & gm of the 6N7s, so 3x whatever the
6N7s are doing at that load.

Notice it can be swiched for either C or L filter input. So at lower
voltages, higher currents are possible.

Stability depends mostly on the gas tube & output sampling resistors.
Altogether a passable PS for ordinary work.

Why did I use 6N7s? We had a pile of them & $$$ were short. Overtime I
also used some 6A3s & 6B4Gs. Sure would not do that now!

Cheers to all, John


+-------------------------------------------------------------------+
|Filename: 6N7 Regulated Power Supply (PS) 10W 5 75 40 Contrast.jpg |
|Download: http://www.audiobanter.com/attachment.php?attachmentid=325|
+-------------------------------------------------------------------+



--
John L Stewart


Another simple regulated PS.

In a LM117HV/217HV/317HV data sheet I found an application for this
regulator in combination with a series regulator triode.
Can't find the app on the web, hence the drawing, the original is
in the National Semiconductor Voltage Reg. Handbook 1981/p.10-22.


Vin----+
|
|
===
V1 --- -----------------+
O |
| |
| 40V Zener |
o-------Z|---------o
| |
| LM117HV |
| +-------+ |
| | | |
o-----+Vi Vo+-----o------o---Vout
| | ADJ | | |
| +---+---+ | |
| | | |
| o--[600]--+ |
.1µ === | === 1µ
| | |
| +--[50K]--+ |
| | |
| | |
GND --- --- ---

I find the circuit inspiring enough to give it a try in combination
with 6AS7/6080, which I have around doing nothing, for a bench PSU.
However, at relative high Va-k and low Ia the LM117 input to output
difference may not suffice to keep Vg negative enough for this tube.
In that case the circuit either calls for a higher µ tube or for a
tracking pre-regulator that doubles or triples the max. in-/output
difference. Personal stock dictates, sort of, the latter solution.
BTW, I don't know why in the original app. the Zener is "limited"
to 40V, the max. input to output difference for an LMx17HV is 60V.

Below my first thoughts (tripler).


Vin----+
|
|
===
V1 --- --------------------------------+
O |
| |
| Max. 120V Zener |
o--------------Z|-----------------o
| |
| |
o---[Rx2]---o---[ R ]--------------o
| | |
| | LMx17HV |
| === +-------+ |
| c // \ e | | |
o---------- v-----+Vi Vo+-----o------o---Vout
| | ADJ | | |
| NPN-darlington +---+---+ | |
| | | |
| +--[POT]--o--[600]--+ |
.1µ === | | === 1µ
| | | |
| | +--[ R ]--+ |
| | | bleeder |
| | | |
GND --- --- --- ---

Other and complementary idea's welcome.

Regards,
Gio.

P.s.
News client: use courier font to read the schematic.
Web based: copy & paste into WORD and set to courier.









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John L Stewart John L Stewart is offline
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Quote:
Originally Posted by GRe View Post
"John L Stewart" wrote in message
...

In this one the 6N7s need to be driven into grid current to get anykind
of useable output current. But the stabilization factor is porportional
to the pass tube mu (35) & amplifier gain. The gain is reduced a little
by the 12B4 CF.

Looking back in from the output terminals the source impedance is
proportional to the amplifier gain & gm of the 6N7s, so 3x whatever the
6N7s are doing at that load.

Notice it can be swiched for either C or L filter input. So at lower
voltages, higher currents are possible.

Stability depends mostly on the gas tube & output sampling resistors.
Altogether a passable PS for ordinary work.

Why did I use 6N7s? We had a pile of them & $$$ were short. Overtime I
also used some 6A3s & 6B4Gs. Sure would not do that now!

Cheers to all, John


+-------------------------------------------------------------------+
|Filename: 6N7 Regulated Power Supply (PS) 10W 5 75 40 Contrast.jpg |
|Download: http://www.audiobanter.com/attachment.php?attachmentid=325|
+-------------------------------------------------------------------+



--
John L Stewart


Another simple regulated PS.

In a LM117HV/217HV/317HV data sheet I found an application for this
regulator in combination with a series regulator triode.
Can't find the app on the web, hence the drawing, the original is
in the National Semiconductor Voltage Reg. Handbook 1981/p.10-22.


Vin----+
|
|
===
V1 --- -----------------+
O |
| |
| 40V Zener |
o-------Z|---------o
| |
| LM117HV |
| +-------+ |
| | | |
o-----+Vi Vo+-----o------o---Vout
| | ADJ | | |
| +---+---+ | |
| | | |
| o--[600]--+ |
.1µ === | === 1µ
| | |
| +--[50K]--+ |
| | |
| | |
GND --- --- ---

I find the circuit inspiring enough to give it a try in combination
with 6AS7/6080, which I have around doing nothing, for a bench PSU.
However, at relative high Va-k and low Ia the LM117 input to output
difference may not suffice to keep Vg negative enough for this tube.
In that case the circuit either calls for a higher µ tube or for a
tracking pre-regulator that doubles or triples the max. in-/output
difference. Personal stock dictates, sort of, the latter solution.
BTW, I don't know why in the original app. the Zener is "limited"
to 40V, the max. input to output difference for an LMx17HV is 60V.

Below my first thoughts (tripler).


Vin----+
|
|
===
V1 --- --------------------------------+
O |
| |
| Max. 120V Zener |
o--------------Z|-----------------o
| |
| |
o---[Rx2]---o---[ R ]--------------o
| | |
| | LMx17HV |
| === +-------+ |
| c // \ e | | |
o---------- v-----+Vi Vo+-----o------o---Vout
| | ADJ | | |
| NPN-darlington +---+---+ | |
| | | |
| +--[POT]--o--[600]--+ |
.1µ === | | === 1µ
| | | |
| | +--[ R ]--+ |
| | | bleeder |
| | | |
GND --- --- --- ---

Other and complementary idea's welcome.

Regards,
Gio.

P.s.
News client: use courier font to read the schematic.
Web based: copy & paste into WORD and set to courier.
I tried that cut & paste to WORD & then Courier but no luck. What am I
missing?

There are some hybrid cascode circuits combining power triodes with N-Channel Fets. The Fet is connected into the cathode cct of the triode in such a way that it controls the triode bias. I did some simulations a few years ago for a reg PS that looked promising. I'll dig something out & post it later.

Cheers, John
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John L Stewart John L Stewart is offline
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Location: Toronto
Posts: 301
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Quote:
Originally Posted by John L Stewart View Post
In this one the 6N7s need to be driven into grid current to get anykind of useable output current. But the stabilization factor is porportional to the pass tube mu (35) & amplifier gain. The gain is reduced a little by the 12B4 CF.

Looking back in from the output terminals the source impedance is proportional to the amplifier gain & gm of the 6N7s, so 3x whatever the 6N7s are doing at that load.

Notice it can be swiched for either C or L filter input. So at lower voltages, higher currents are possible.

Stability depends mostly on the gas tube & output sampling resistors. Altogether a passable PS for ordinary work.

Why did I use 6N7s? We had a pile of them & $$$ were short. Overtime I also used some 6A3s & 6B4Gs. Sure would not do that now!

Cheers to all, John
Here is my dayly driver at home since 1955. And it does have protection for switch off while choke input connected as Patrick T had pointed out. Not very sophisticated at all, but very reliable. No problems in all that time!

OK for most of my needs, anyway!!

Power Supply Parts List for 200-400 Volt Power Supply

C1, C2 20 microF, 600wvdc
C3, C4 10 microF, 450 wvdc
C5 330 nF, 630 v
C6 10 microF, 600 wvdc
C7 50 nF, 600 v

R1 to R4 680K
R5 2K, 10 W WW
R6 5K, 10 W WW
R7 4.7K, 10 W WW
R8 560K, 2 W
R9, R10, R22 68 K, 2 W
R11 1M
R12 330K
R13 47K
R14, R15, R18 1K
R16, R17 39R
R19 270K
R20 141K (Three 47K, 2 W in series)
R21 47K, 2 W
R23 390K, 2 W
R24 10R

D1 to D5 1N4007

L1 Hammond 10-200X, 10H, 200 mA, Use Hammond 193J

P1 20K Pot

S1 SPST ON-OFF
S2 DPST DC Standby
S3 SPDT L or C Input to filter
S4 SPST Output Voltage Range

T1 Hammond 275X, 400-0-400 @ 135 ma using cap input filter
6.6 vac ct @ 5 amps & 5 vac ct @ 3 amps
T2 Hammond 23376 (a special), 6.3 vac, 4 Amps
Use Hammond 167N
T3 Hammond 167B, 6.3 vac, 0.3 amp
Use Hammond 166F6

V1 5AR4/GZ34 or 5V4G/GA or SSR from New Sensor
V2 6080/6AS7G
V3 6AU6
V4 0D3/VR150
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