Valves in series vs in parallel

MusicMan_ZA

AVForums Grandmaster
Joined
Jul 14, 2013
Messages
2,695
Reaction score
441
Location
Cape Town
I am trying the PCB without the LED later today, but this is what I am using:

LED 3mm 12V Red (LED374)
R8.58
Red LED with internal resistor for 12V operation in standard 3mm package.
Red diffused package.
Luminous intensity 80mcd max at VF = 12V.
The cathode is the short lead.

Specifications
Peak wavelength: 625nm
Forward current at VF = 12V: 11mA
Power dissipation: 310mW
Viewing angle: 60?

-----------

I am using it in parallel, not in series.
So I assumed ( :thinking:) that the 11mA forward current won't be a problem?

 

MusicMan_ZA

AVForums Grandmaster
Joined
Jul 14, 2013
Messages
2,695
Reaction score
441
Location
Cape Town
No difference with 12V LED removed.

Will feed in the DC out from the 20A SMPS after the rectifier (to C1) next, as per
Eric's suggestion, and see what happens.
 

MusicMan_ZA

AVForums Grandmaster
Joined
Jul 14, 2013
Messages
2,695
Reaction score
441
Location
Cape Town
Definitely a problem/component on my little DIY PSU PCB.

When I feed in 12.6VDC to C1 - under load - it pushes out 0.7VDC.
When I feed in 12.6VDC to C2 - under load - it pushes out 0.7VDC.
When I feed in 12.6VDC to right before the output terminal block - under load - it pushes out 12.6VDC.
When I feed in 12.6VDC from V-out of the LM317 - under load - it pushes out 12.6VDC.
So an issue with (or my implementation of) the LM317 or the 5K trimpot.

Will replace those, and see what happens.

 

Family_Dog

AVForums Grandmaster
Staff member
Administrator
Moderator
Joined
May 17, 2006
Messages
11,941
Reaction score
973
Location
North West
The rest of the components were all brand new, specifically the caps, after the 220v was inadvertently applied to the PSU board?

Also, the PCB board used for the PSU, is it a new one, or the old one cleaned up?

Do you still have the old PCB? If so, can you compare the tracks that have been cut or made to the tracks of the new one?


-F_D
 

MusicMan_ZA

AVForums Grandmaster
Joined
Jul 14, 2013
Messages
2,695
Reaction score
441
Location
Cape Town
Family_Dog said:
Also, the PCB board used for the PSU, is it a new one, or the old one cleaned up?

Yes, new. My "fried" PCB was yellow, and the new one is green.


Family_Dog said:
The rest of the components were all brand new, specifically the caps, after the 220v was inadvertently applied to the PSU board?

Yes, all new components - every single one.


Family_Dog said:
Do you still have the old PCB? If so, can you compare the tracks that have been cut or made to the tracks of the new one?

Yes, I have it. Will compare.

I am now calling it a day, for today. Still very frustrated.

After the earlier tests (using the SMPS) I did the following this afternoon:

1. reconnected the 4 rectifier diodes I had cut for the testing.
2. removed the LM317 and replaced with another new one.
3. removed the 5K trimpot, tested (measured from 2R to 4k7 on a full turn) and refitted.
4. replaced the 2 x 120R resistors I used in series (needed 240R) with 2 x 470R in parallel - better layout.

Tested again - with no load I only got out 2.7VDC, no matter where I turned the VR to. ???

Removed the VR (suspect faulty?) and replaced with a fixed 2k2 resistor - should give me 12.7VDC out.

Tested - no load - 12.9VDC out.
Connected the 4 x valve heaters - drops to 0.7VDC.

Clearly I still have a problem, but I don't know what it is.
Tomorrow I will compare to the old PCB (that worked at first) and also
replace all 6 the 1N4007 diodes - maybe something funny going on there.




 

Family_Dog

AVForums Grandmaster
Staff member
Administrator
Moderator
Joined
May 17, 2006
Messages
11,941
Reaction score
973
Location
North West
I'm beginning to think start all over again with a fresh Veroboard, go ahead as if you're building the circuit for the very first time. Sometimes there is a "hidden" mistake that one inadvertently skips over even after checking for it numerous times. I do not think the 4k7 trimpot is a problem, but it seems highly unlikely that two different LM317 VRs could both be faulty. Having said that, I had a bad time diagnosing my Technics A5 amp some years ago (documented in the Vintage section on the forum) because the five new Protector chips were all incorrectly labelled, they were anything but overload protection chips. The fault I eventually found was a silicon diode that measured perfectly when out of circuit, no leakage evident, but in circuit it behaved completely differently and broke down, even though the voltage was only some 12v or so.

One final thing: Are you able to measure the current draw when using the SMPS before and after connecting to the pre-amp board, and is anything on the PSU perhaps getting a bit warmer than it should? As a precautionary measure, perhaps use a ?5w 12v incandescent globe such as used in car tail lights for the load. The current draw will be slightly less than 600mA but it might still give an indication of where the fault lies and whether a component heats up or not.

Please try monitor the DV voltage as well as DC current consumption if you have, you will need two DMMS for this.

-F_D
 

MusicMan_ZA

AVForums Grandmaster
Joined
Jul 14, 2013
Messages
2,695
Reaction score
441
Location
Cape Town
Family_Dog said:
I had a bad time diagnosing my Technics A5 amp some years ago (documented in the Vintage section on the forum) because the five new Protector chips were all incorrectly labelled, they were anything but overload protection chips. The fault I eventually found was a silicon diode that measured perfectly when out of circuit, no leakage evident, but in circuit it behaved completely differently and broke down, even though the voltage was only some 12v or so.

-F_D

Was that the time you temporarily changed your name to F_D = Frustrated_Dog?  :BWAHAHAH:

Yes, the current draw when using the SMPS is 0.6A at 12.6VDC.

I will start again - there is no way this thing is getting the better of me.
But it is hurting my pride, and my pocket  :sd: and costing me valuable time.

Thanks for all the help!  :thumbs:


 

Family_Dog

AVForums Grandmaster
Staff member
Administrator
Moderator
Joined
May 17, 2006
Messages
11,941
Reaction score
973
Location
North West
I was very much a Frustrated Dog with that Technics, as every time i figured I had it right, it would behave for anything between 2-3 hours and 2-3 days before acting up again. My Barber said I have a healthy mop of hair on my head, I need never worry about going bald. Well, after tearing my hair out and racking my grey matter for evenings at that time, at least he prophesied correctly as I still have a healthy mop of hair. I spent many hours on that A5 but in the end it was all worth it and it performs happily to this day!    :dop:


-F_D
 
 

fredeb

AVForums Grandmaster
Joined
Mar 29, 2012
Messages
3,485
Reaction score
528
Location
Somerset West
MusicMan_ZA said:
Variable-Power-Supply-using-LM317-600x245.jpg

Orientation of trimpot incorrect on this schematic , try like so :

lm317-voltage-regulator-circuit.png


If I remember correctly , one of the caps should be a Tantalium cap , check LM317 datasheet


https://www.ti.com/lit/ds/symlink/lm317.pdf?ts=1651348322525&ref_url=https%253A%252F%252Fwww.google.com%252F






 

handsome

AVForums Super Veteran
Joined
Jan 23, 2009
Messages
1,359
Reaction score
356
The trimpot must be wired as a rheostat or variable resistor in other words the wiper must be connected to one of the other terminals. You need to work in blocks, too many changes just confuse the issue.
Build the rectifier diodes and C1 then test with your transformer.
Add LM317, trimpot and R1 and then test - R1 can be a 1/4W resistor of any value from 100R to 470R - the less parts the better (the value of 240R is designed to draw 5mA from the LM317 - below this value of current the LM317 will not regulate properly but in a constant draw circuit like valve heaters you will always draw more than 5mA).
If it works then connect to your valve heaters - and if that works then add the extra diodes, capacitors and LED.
If when you connect the valves (full load current) your voltage drops, then check the voltage on C1 in this condition if it too has dropped then something is pulling too much current. Check your LM317 is tightly connected to your heatsink and use some thermal paste - high temps will trigger the 317?s thermal protection. Check its heatsink is not inadvertently connected to something else in circuit.
If all else fails ping me I can sell you a smart-looking adjustable heater PCB with extra filtering and a mute delay designed especially for valve preamps - I sold one to [member=13623]fredeb[/member] a while back - it?s cheap, it works and if i say so myself it looks good  :spam:
 

MusicMan_ZA

AVForums Grandmaster
Joined
Jul 14, 2013
Messages
2,695
Reaction score
441
Location
Cape Town
handsome said:
If all else fails ping me I can sell you a smart-looking adjustable heater PCB with extra filtering and a mute delay designed especially for valve preamps - I sold one to [member=13623]fredeb[/member] a while back - it?s cheap, it works and if i say so myself it looks good  :spam:

Thanks for the offer - I may yet take you up on it. How about a pic?

However, not now: I am building this because I need it, but also because I need to be building things and struggle with them and then solve them and then feel good about achieving something.

Please don't think my frustrated grumbling is moaning and complaining - it is not!  :pleasant:
 

Family_Dog

AVForums Grandmaster
Staff member
Administrator
Moderator
Joined
May 17, 2006
Messages
11,941
Reaction score
973
Location
North West
Johan, follow the steps as details by Handsome, that will be a good way to diagnosing the problem.


-F_D
 

Family_Dog

AVForums Grandmaster
Staff member
Administrator
Moderator
Joined
May 17, 2006
Messages
11,941
Reaction score
973
Location
North West
Johan, follow the steps as details by Handsome, that will be a good way to diagnosing the problem. I'm also wondering whether the heatsink is not shorting out somewhere, check that out carefully.


-F_D
 

handsome

AVForums Super Veteran
Joined
Jan 23, 2009
Messages
1,359
Reaction score
356
This is what a board looks like:







Its is the exact same LM317 adjustable regulator circuit like your with 2x additions:

1. It has a balanced filter on the input - this drastically reduces noise but requires a slightly higher input voltage (you can determine that by the size of the resistors you choose to use) plus it isolates the earth return. You can skip this filter completely by soldering two short wires to the board - I would not though. The filter simply cleans up the voltage going into the LM317

2.  It has a delay circuit included. You can set the delay to the length of time that suits you with the value of a capacitor. You connect a relay to the delay output and when the heater supply is switched on after the delay time the relay will be triggered. I set the delay to 60 seconds and connect the relay to the output of the preamplifier. When I turn my preamplifier its output is muted (connected to earth) for 60 seconds while the preamplifier warms up. This protects whatever the preamp is connected to. Capacitor-coupled valve preamps (almost all of them) will put a nasty high voltage (more half the HT voltage) on their outputs when warming up and this usually destroys whatever they are connected to - I killed an expensive sound card this way.

The only "snags" are that the board has a silkscreen error on it - there are two "Mute LED" connections - one is for the Mute LED the other is for the mute relay itself and the "Mute Switch" connection does not work - however adding a mute switch can be done it just requires a switch!

I will also give you complete instructions and a comprehensive parts list.

You can have the board(s) for whatever [member=13623]fredeb[/member] paid for them - but I cannot remember what that was so please [member=13623]fredeb[/member] keep me honest here and tell us what you paid.

And whilst I am spamming away here below is a High Voltage Power Supply  PCB I use for my preamps. This circuit will put out up to 350V at up to ~100mA and it is very, very quiet - noise was measured as just over 1uV RMS at 20Hz to 20kHz unweighted - that's better than -100dBV.  I have 3x of these for sale again [member=13623]fredeb[/member] will kepp me honest on pricing here.





You are quite right to build and solve yourself - but trust me all valve amps need heater supplies and having a simple, quiet plug-n-play solution makes building and thinking about the important parts of your designs far easier! Ditto the HT PSU.
 

fredeb

AVForums Grandmaster
Joined
Mar 29, 2012
Messages
3,485
Reaction score
528
Location
Somerset West
I went back and checked our personal messages , which contain no prices , I can't check my whatsapp because I changed phones ..... and I can't remember what you charged  :???:

It may have been R200/ bare pcb , and comprehensive instructions were included .


 

MusicMan_ZA

AVForums Grandmaster
Joined
Jul 14, 2013
Messages
2,695
Reaction score
441
Location
Cape Town
Update, for those who are not bone-tired of this thread! :)

I built the 4th voltage regulation DIY PCB today.
It is the one of the far right. The other 3 all give the same problem, on at least 4 different transformers.

279708477_2193480837469560_8985689523824624488_n.jpg


New board, all new components, not looking at the previous attempts, just building, step-by-step, from the schematic
I posted before.

1. After the 4 x 1N4007 rectifier diodes and the 2200uF C1, I measure 18.2VAC in and 24.4VDC out.
2. After C2 (0.33uF WIMA) and the LM317 fitted (only V-in and V-out connected, no Adjust yet) I measure 24.21VDC out.
3. After the LM317T Adjust leg connected to the dividing point between the 240R resistor and the 5K pot, adjust to 12.6VDC out.
4. Connect to load (4 x 12ax7 valve heaters in series) - measure 0.7VDC out. Same problem as before...

279733249_2193480914136219_6013882780001465659_n.jpg


Before the load is connected.

279727021_2193480870802890_325488838061344685_n.jpg


This is the transformer I am using for this test: 18VAC out, 40VA Texaco Alarm system transformer.

Then, as a sanity check, I connected the SMPS again, directly to the Phono board (it is a 15VDC/25Amp unit).

The VDC out, load connected:

279828017_2193481144136196_4992333378812514729_n.jpg


279563336_2193481227469521_5940047128717687679_n.jpg


And the current, load connected:

279692501_2193481017469542_227245093645307270_n.jpg


No idea what is going on here. But tomorrow is another day!




 

Family_Dog

AVForums Grandmaster
Staff member
Administrator
Moderator
Joined
May 17, 2006
Messages
11,941
Reaction score
973
Location
North West
OK, now connect the SMPS output directly to the first filter cap after the first 1N4007 bank of diodes - observe polarity. Set it to 18v and measure everything as before. Report back :)


-F_D
 

MusicMan_ZA

AVForums Grandmaster
Joined
Jul 14, 2013
Messages
2,695
Reaction score
441
Location
Cape Town
Family_Dog said:
OK, now connect the SMPS output directly to the first filter cap after the first 1N4007 bank of diodes - observe polarity. Set it to 18v and measure everything as before. Report back :)


-F_D

Roger, Wilco.
 
Top