Author Topic: It looks for me as stupid schematic (Oldtimers welcome!)  (Read 5998 times)

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Online T3sl4co1l

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #25 on: October 03, 2019, 03:08:19 pm »
The capacitors are laughably oversized, more a liability than any electrical benefit.  It won't handle a short for very long but I think it will actually survive one momentarily.

Yeah, it'll perform better -- not to mention be cheaper to make -- with a zener.  Less bias current needed, too.

Tim
« Last Edit: October 03, 2019, 03:09:58 pm by T3sl4co1l »
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Offline schmitt trigger

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #26 on: October 03, 2019, 03:34:52 pm »
One aesthetic advantage of the 0A2 tube vs a zener diode, is that they have that gorgeous glow that only a gas discharge produces. For those of us which look into the aesthetic looks of tubes, it is beautiful.

On the other hand, the breakdown voltage changes with ambient illumination. And parallel capacitance should be limited to less than 0.1uF, otherwise the tube will start motorboating. These characteristics are described in the linked datasheet.
Plus they are significantly more expensive.
 

Offline SiliconWizard

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #27 on: October 03, 2019, 04:04:24 pm »
On the other hand, the breakdown voltage changes with ambient illumination.

Ahah yeah, that's part of their charm. Like they also have a "microphonic" behavior. They are susceptible to vibration and shock.
 

Offline 001Topic starter

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #28 on: October 03, 2019, 05:07:45 pm »
On the other hand, the breakdown voltage changes with ambient illumination.

Ahah yeah, that's part of their charm. Like they also have a "microphonic" behavior. They are susceptible to vibration and shock.

Very strange design for REGULATOR circuit  :-//
 

Offline floobydust

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #29 on: October 03, 2019, 06:30:17 pm »
We don't know the requirements for voltage and especially output current.
For audio applications, these are HV regulators to get of line and load variations, and absolute voltage is not critical. 1% regulation at 400V is 4V so 396V or 404V is not a problem. I find low noise is harder to get.

Don't tell anyone but I've used 0B2, 12AX7 and 6LC/6550 and no drama there. About 550VDC input and 350VDC output to over 300mA. I had the parts lying around decades ago and thought it would be fun to learn as a teenager.  Otherwise I use a simple BJT and zener with CCS for low current loads, say under 50mA.
OP's circuit is missing a dedicated (floating on high side) filament winding for the pass tubes, which is an extra expense.

These HV regulator threads always end up in a flame war of solid-state verses vacuum tube (pass device) because people want unrealistic output currents in a $5 circuit with a handful of parts. Solid-state HV regulators in the few hundred mA league need many parts, SOA and current-limiting to be tough and reliable. They are dangerous to develop on the workbench and unforgiving of mistakes. There is no simple circuit out there that is 100% solid-state. Sorry but that fantasy has to end, so we end up with these hybrid designs.
 
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Offline 001Topic starter

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #30 on: October 03, 2019, 07:38:07 pm »
Thank You for detailed answer

Can You post schematics  You told (and built)?
 

Offline 001Topic starter

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #31 on: October 03, 2019, 07:40:50 pm »
They are dangerous to develop on the workbench and unforgiving of mistakes. There is no simple circuit out there that is 100% solid-state. Sorry but that fantasy has to end, so we end up with these hybrid designs.

That the right way to use pass tube with solidstate driver circuit?
 

Offline Yansi

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #32 on: October 03, 2019, 09:25:33 pm »
Follow here, some nice article about twoob power supplies: http://www.angelfire.com/electronic/funwithtubes/bench_psu.html

I almost got a thirst to cobble up some of these supplies and compare and test their performances against each other.
 
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Offline techman-001

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #33 on: October 04, 2019, 01:13:00 am »
T3sl4co1l - "No current limiting (aside from the impedance of the poor tube itself), and it'll explode if ever you should accidentally short the output."

As I said, I made that supply 40 years ago and I'm still waiting for the 6BX7 tube to explode, maybe in 50 years.:-DD I've never ever seen a tube explode but I have seen some tube plates glow bright red.

There is both a primary fuse and a 10 ohm resistor as protection in case you missed that. I also stated I wanted to build a supply out of parts I had in my junk box and I didn't intend to make a complicated supply that would have all the bells and whistles that my programmable precision bench supplies have today. You should be pleased I even put meters on the supply!  8)

That's a really nice schematic, it took me back 40 years ago as well.

I've never seen a tube explode either and I've run them with red hot anodes for hours, I've had then bright blue inside and sparks flying everywhere (from massively positive grids) before they burnt out.

Tubes are incredibly rugged, far more so than semiconductors.

I've seen a few TV CRT's IMPLODE ......... after I threw a brick at them  :clap:
 
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Offline floobydust

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #34 on: October 05, 2019, 05:54:35 am »
Can You post schematics  You told (and built)?

You'll have to decide if you want to use vacuum tubes or solid-state, or a mix of both.

Here are scans of classic, all-tube voltage regulator circuits from some GE and RCA databooks I have.
I used the GE circuit with an extra RC filter after the VR tube to filter noise, as gas tubes are noisier than zeners.
The RCA one has 0.1% load and line regulation with 0-225mA. The Compactron circuit is very cheap using a neon lamp as the reference.

The architecture is very basic and anything can replaced by solid-state components. It's whatever you like. Add some op-amps if you want better performance and more parts and have lots of money.

The hardest part is the pass transistor or mosfet, if you use one. They need a lot of protection for high voltage linear use.
If your load has big capacitance 100's of uF like some audio circuits use, it will blow the transistor/mosfet on power up. Too much inrush current for too long.
 
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Offline Yansi

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #35 on: October 05, 2019, 09:47:09 am »
R1 in the first schematic above is not placed the best. Shall be going from the cathode of the pass tube, not anode. This way, you can get better regulation.

In the second schematic you can get rid of OB3 completely, not necessary as you can reference cathode of 6SJ7 to the output minus terminal and the bottom of the feedback divider to the negative reference voltage.
« Last Edit: October 05, 2019, 09:52:19 am by Yansi »
 
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Offline 001Topic starter

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #36 on: October 05, 2019, 10:06:10 am »
Can You post schematics  You told (and built)?

Here are scans of classic, all-tube voltage regulator circuits from some GE and RCA databooks I have.

Thanx You a lot! Great work  :-+ :-+ :-+ :-+

R1 in the first schematic above is not placed the best. Shall be going from the cathode of the pass tube, not anode. This way, you can get better regulation. 

Hahah No way because it is variable REGULATOR
 

Offline Yansi

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #37 on: October 05, 2019, 01:45:26 pm »
Hahaha, don't be silly. Couple days ago you did not have even slightest understanding how the circuit works.  Now trying to be smart, but still no, you have to learn more and harder.

Variable or not, the reference still can be supplied from the output. It all depends on many things.
 
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Offline floobydust

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #38 on: October 05, 2019, 08:04:58 pm »
In the second schematic, note the 6SJ7 screen is also regulated by the 0B3. This is favorable for better PSRR and line regulation.

In the first (Compactron) schematic, which is bare bones cheap, placing the VR tube at the output can add instability as an NE-2's dynamic impedance is not zero. Have to look if the VR ends up in-phase or out-of-phase with the pass tube, as far unexpected feedback in these circuits. I'm used to the VR tube being at the raw DC side, I thought it was to save 10's mA off the pass tube's load in the case of the big 0B2, 0B3.

Testing these circuits is a PITA, I used to use a scrap bin big 814 tetrode connected to a signal generator as a load. The workbench looked like Frankenstein's lab lol.
« Last Edit: October 05, 2019, 08:59:11 pm by floobydust »
 
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Offline 001Topic starter

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #39 on: October 06, 2019, 03:37:23 pm »

Variable or not, the reference still can be supplied from the output.
Don`t be  @#^&&% please

This is favorable for better PSRR and line regulation.

Thanx a lot for Your posting  :-+
Is it good idea to replace  ONLY diver tube (6AU6/6SJ7 etc)  with some transistor(s)? What the way to do it right?
 

Offline schmitt trigger

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #40 on: October 08, 2019, 01:17:38 am »
floobydust:

Thanks for this particular RCA schematic you attached.
I have the exact same RCA receiving valve manual RC-29, but in Spanish. Published by Editorial Arbo from Argentina, @ 1974.

Although the very first page indicates that this is an authorized version from RCA Corporation, Electronic Components, Harrison NJ, the book has a serious omission:
The project 29-22 Series-type stabilized voltage supply (Fuente de Alimentacion estabilizada tipo serie) does not include a schematic! Seriously!

It is the only topic in the whole book which is missing an attached image or schematic.
Other than that, the Spanish description and parts list is wholly accurate, word by word.

Back in my tube experimenting days of the mid 1970s, I remember reading the circuit description and being enticed to build it, but then becoming frustrated that without a schematic I wouldn't be able to do so.

Roughly 45 years later, I finally see what the schematic looks like.

Thanks!
 
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Offline Yansi

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #41 on: October 08, 2019, 12:11:45 pm »
Why R1 in the anodes?  That should have been in the cathodes...  :o
... to provide negative feedback for dividing current evenly between the twoobs.
« Last Edit: October 08, 2019, 12:13:49 pm by Yansi »
 

Offline 001Topic starter

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #42 on: October 10, 2019, 03:47:55 pm »


Roughly 45 years later, I finally see what the schematic looks like.
 

Can You tell what minimal and maximal output voltages achieved with this strange potentiometer R9?
 

Online T3sl4co1l

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #43 on: October 10, 2019, 11:48:17 pm »
Well, not less than 80V, where it will oscillate.  But that would require a larger value than is shown.  Adjustable range looks to be around 180V to Vin (unregulated).

Tim
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Offline 001Topic starter

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #44 on: October 11, 2019, 12:26:50 pm »
  Adjustable range looks to be around 180V to Vin (unregulated).
 

Thanx a lot!

But is it real Vin (unregulated)? It means zero voltage drop at pass tube, izn`t it?
 

Offline schmitt trigger

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #45 on: October 11, 2019, 01:18:44 pm »
It would be at Vin's valley voltage, plus some saturation plate saturation voltage.

However, if Vin is very well filtered thanks to a Pi-filter, the valley voltage should be very close to the average voltage.

As I mentioned previously, this is a project that I've wanted to build for 45 years...... I might give it a try.
 
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Online T3sl4co1l

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #46 on: October 11, 2019, 11:17:37 pm »
Yes, it would be saturated high and not regulating.

Somewhat less than Vin, it will be in regulation, at least up to some current.  The dropout voltage varies with load, of course.

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Offline 001Topic starter

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #47 on: October 12, 2019, 08:54:26 am »
Thanx

The strange thing about tube regulators is tetrode mode.
Why 6L6 is used as tetrode if anode voltage (Anode to Catode) may be LOWER than second screen voltage (2nd screen to catode)?
Triode mode benefit is lower Ri, isn`t it?
 

Offline Yansi

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #48 on: October 12, 2019, 09:37:50 am »
Did you read the article I have posted, didn't you?


 

Offline 001Topic starter

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Re: It looks for me as stupid schematic (Oldtimers welcome!)
« Reply #49 on: October 12, 2019, 09:42:34 am »
Did you read the article I have posted, didn't you?

Yours link is about common transistor line regulators, not teterodes, isn`t it?

So I read this. But why heathkit use 6l6 as tetrode?

Quote
It is a given among engineers that when the pass tubes are connected as pentodes the regulation is better than when they are connected as triodes. However, my initial attempts to prove this by the numbers taken from the curves met with failure. I tried comparing the gain of the pass tubes as a cathode follower which yielded only a small percent difference. Same went for the transconductance, 5 millimhos for the triode and 6 for the pentode. I did not use tube manual numbers but picked values from the graphs as close as possible to the actual operating point.
« Last Edit: October 12, 2019, 09:47:45 am by 001 »
 


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