Valves in series vs in parallel

[MusicMan_ZA]

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

Only goes to 15 VDC, but I will use that.

 

[Family_Dog]

OK, output voltage will be a bit lower but should be substantially higher than 0.7v. observe the amperage as well.


-F_D

 

[handsome]

Your LM317 seems to regulate without a load but stops working when loaded. The 240R resistor presents a 5mA load. With your multimeter measuring the voltage output of 317, add a 1k resistor across the output does the voltage change? If not then put just one valve in its socket and measure if voltage does not change much add another valve. You are trying to see what the LM317 is doing.

I will hazard a guess though that because 4x different 317 boards AND 4x different 317s are all giving the same problem?..you are wiring up the LM317 incorrectly

 

[Family_Dog]

I get that feeling too, but yet it used to work up until the time 220v AC was applied incorrectly. One really needs to get this in one's own grubby hands to sort it out - but I'm sure the solution will present itself sooner than later.


-F_D

 

[handsome]

You are dropping >12V across the 317 at 600mA that would be 7.5 watts of heat - way too much for that tiny heatsink your 317?s thermal protection could be shutting it down - does the 317 get hot? Touch it. Does the voltage briefly reach 12.6V and then drop to 0.7V? Clip your multimeter to the output and try no load then the 1k resistor then 1x valve etc and watch the multimter reading

 

[handsome]

The valves do not seem to be at fault 12.6V across them gets you 600mA through them, as it should be. There is enough DCV (well too much really ) going into the regulator. The transformer has the current capacity. So that leaves the circuit. Looking at the 317 from the front pins are from left adj, out, in. Wiring up vero board is always confusing and a bitch?..

 

[MusicMan_ZA]

Thanks Gents.
Did a lot more tests today.

1. 12.6VDC from 25A SMPS into Phono PCB - all 100%, valve heaters glow reassuringly, VDC measures 12.6 and current measures 0.597A (just under the 600mA I expected from 4 x 12xx7 heaters in series) at point of entry into Phono board.

2. My transformer 220VAC/18VAC into a dummy load easily provided 12.6VDC at 1 Amp (and I only need 600mA).

3. All my boards could not supply 12.6VDC at 0.6A into a dummy load (DL set to ask for 600mA).

4. Connecting the SMPS to C1 of my latest board (i.e. bypassing the 4 x 1N4007 rectifier diodes) produced 12.6VDC out,
no load, but dropped to 0.7VDC when a load is connected (both the dummy load and the actual Phono board).

5. my deduction: the problem is not with the phono board and the 4 x 12xx7 valves, nor with the 220/18VAC transformer, but
with my voltage regulation PCB.

6. VR PCB is on a new perfboard with all new components, so probably not a dodgy component.

7. Am I wiring the LM 317T correctly? I think so. I have checked this 10 times.
Looking at it from the front (the face with the writing on it)
I am connecting V-in to the third (right-most) (3) leg, taking V-out from the middle leg (2), and using the first (left-most)
leg (1) as Adjust to the 5k trimpot (actually, to the center of the 240R resistor and the trimpot set to about 2k2).

8. Just in case I was wiring the 5k trimpot (R2) incorrectly, I removed it, and fitted a 2k2 resistor - in theory, this
should then give me 12,7VDC out of the LM317 with R1 being a 240R. Not - I still only got 0.7VDC.

I know I must be doing something wrong, but I just don't yet know what it is!

I will keep on keeping on...

Again, thanks for all the thoughts and help!

 

[Family_Dog]

I think Handsome raised a good point - are you using a heat sink at all on the LM317? It might well be going into protection. I wanted to mention this earlier as well, but I'm sure I read somewhere you did mention that it did work correctly for a while, until the unfortunate incident with the 220v.

If no heatsink, try fabricate one using aluminium or whatever, U-shaped if possible, mount it to the metal part of the LM317 and see what happens. Alternatively, as mentioned above, try running it with just one valve in (i.e. 150mA) and test again.


-F_D

 

[handsome]

Put a resistor of 10R or more between your bridge diodes and C1 (it will have to be about 10W) you want to try drop the voltage going into the LM317 to about 15-16V, this will minimise the heat the 317 will generate and, if it solves then you need either a bigger heatsink or a lower input DCV.

 

[MusicMan_ZA]

Put a resistor of 10R or more between your bridge diodes and C1 (it will have to be about 10W) you want to try drop the voltage going into the LM317 to about 15-16V, this will minimise the heat the 317 will generate and, if it solves then you need either a bigger heatsink or a lower input DCV.

I understand the point of feeding the LM317 with "too high" DC, and only sending 12.6VDC out and thus generating heat that could cause the LM317 to shut down.

But when I do this:

"4. Connecting the SMPS to C1 of my latest board (i.e. bypassing the 4 x 1N4007 rectifier diodes) produced 12.6VDC out,
no load, but dropped to 0.7VDC when a load is connected (both the dummy load and the actual Phono board)."

I feed the LM317 with 12.6VDC and I "adjust" the LM317 to supply 12.6VDC so that means there is no reason to heat up and shut down? Yet, even in this case, my no-load supply of 12.6VDC drops to 0.7VDC when I connect the 600mA load?

Of course I agree that for the final implementation, once it works, I will need a decent size heatsink that meets the requirements - not trying to debate that at all.

Thanks again for all the advice.  :thumbs:

 

[Family_Dog]

You need ?3v higher input voltage than output voltage for the LM317, try setting the SMPS to 16v, check for 12.6v after the VR, then insert only one valve in the pre-amp. Report back


-F_D

 

[MusicMan_ZA]

We are having a full day of consistent (and much needed) rain down here in Durbanville, so the
workshop (patio table outside) is closed "due to the weather".

More work tomorrow, or Sunday.

 

[MusicMan_ZA]

So, to break out of the Groundhog Day loop I found myself in, I threw away the first schematic
I kept on building and building, and got together the components (and a new board) to build
this version (as suggested by Ari - thanks!):

It went quickly, and the finished product looks like this:

I connected up the 21VAC-out transformer, adjusted the output DC to 12.6, and connected the load.

This is what I got:

And, it works! Why? I don't know. What is different? Not too sure. Am I happy? Yes!

After a while the new, and slightly bigger, heatsink got quite warm, so I swopped in another transformer that
delivers 12.7VAC before rectification.

This still supplied the current that I needed, set to 12.5VDC under load, and after a couple of hours was only
slightly warm (not hot).

So I think (and hope) I have cracked this.
However, it is not good not knowing what went wrong with all the other attempts.
I will keep the second-last unit, and re-visit the trouble shooting in a little while.
But, for now, I am on track again!

Thanks for all the help.

 

[Family_Dog]

Glad you came right, Johan! Yet if I compare the two schematics, they appear to be essentially the same.Somewhere there was an unknown glitch, would have been good to find out just what.

Great stuff, now what's the next project?  :angel:


-F_D

 

[MusicMan_ZA]

Great stuff, now what's the next project?  :angel:

There is still lots to be done on this phono pre-amp, but after this, in no particular order:
- dismantle my AVO VCM 163 to clean the roller selector switches
- build a 49:1 unun
- build a ZS6BKW antenna
- restore a few turntables
- clean a few (lots of) records
- test a few valves
- fix the paint/re-spray my Leak Stereo 20
- restore a few turntables
- build a few plinths
- have a few turntable lids made up
- restore my Dr. Carey valve mono blocks
- start work on my AKAI M8 mono blocks
- fix up a broken Yaesu FT901DM
- build an antenna tuner
- restore my QUAD FM and Mono tuners
- cosmetically restore my Leak Sandwich 600 speakers
- follow orders and do some handyman work around the house
- xxx

...and my car is about 10 washes behind! Never a dull moment over here
(just many frustrating ones)

 

[Family_Dog]

This reads very much like my own "to do" list, with the exception of building a ZS6BKW antenna. I was mates with ZS6BKH, a local radio ham here in Klerksdorp whose stepson is also a forum member here (Hi Robert!). Working with two-way radios every single day of my life (we sell them!) I decided to rather branch out to Audio instead of RF.

I do not yet have any Leak equipment, always wanted to purchase some but somehow I was never an ardent Leak fan, I preferred Quad. Charles here on this forum introduced me to the sonic qualities of Leak some years ago but I have never had an opportunity to purchase any of Harold's fine wares.

Turntables... I decided to get rid of all those that I had other than a few Garrard 301s, a 401, a 4HF (nostalgia - takes me back to my school days) and a Thorens TD150, B&O 1000/1200 series, Technics SP10 and a Denon DP-60L.

I really have no room for any more equipment so have been pretty good not buying everything I fell in love with - Vintage Gear rules forever!  :dop:


-F_D

 

[handsome]

[member=14924]MusicMan_ZA[/member] no doubt you are relieved....

 

[MusicMan_ZA]

[member=14924]MusicMan_ZA[/member] no doubt you are relieved....

I am very happy that I now have a working solution.
I am not so happy not understanding why my previous attempts did not work,
as I still can't see an obvious issue (and yet there must be one).

Thanks again for everyone's help and advice!

 

[johan.pretorius]

There is still lots to be done on this phono pre-amp, but after this, in no particular order:

... snip ...

- follow orders and do some handyman work around the house
- xxx

Don't want to hi-jack your thread, but my project list is getting out of hand as well:

- clean and service a number of cassette decks
- build an adjustable shelf for HiFi gear
- fix up a stripped Garrard 301
- build a plinth or two
- complete a granadilla arbor/treliis (lockdown project)
- build a new kennel for the dog
- restore a Thorens TD124/II
- and bit more on topic, find a suitable valve amplifier for a DIY project

Might be a good idea to start a new thread on the topic of ever expanding project lists... Details of abandoned projects would be a fun read as well