V 72 Stuff

[tony dB]

[quote author="CJ"].

The choke gets hot, the tongue expands, (yeah, baby!) , but the legs expand with the tongue.

:grin:
[/quote]

This is trannieporn at his very best

 

[CJ]

OK, I have been doing some test windings on this choke for Jenns.
You have to find the right speed. Too slow, and the wire can break do to getting hung up on the spool. A quicker speed de reels the wire better, the centripetal force tends to let the wire de spool without touching the flange.
If you go too fast, excessive centripetal force can cause the windings to expand into a sponge, you will not get as many turns on, and tensioner resonances can cause the wire to bounce around too much.

At a slow speed, I got 6800 turns on.
At medium speed, I got 7500 on there, which is perfect. At a high speed, I got about 7400 on, but there were not as neat as the medium speed layers.
DCR came out to 10.23 k, So if I use the right speed for all three sections, I will get 7500 loaded into each chamber. The dcr will come up closer to our target of 12 k also.

HEre are some more pics:

Putting on the first layers, made a new mandrel, with channels for the brealouts.
You do not want the start lead to bounce around while you are winding, you might break something, so tape it up good and tight.


http://vacuumbrain.com/The_Lab/Telefunken/Jens/choke_a.jpg

First layers:

http://vacuumbrain.com/The_Lab/Telefunken/Jens/choke_b.jpg

Air core henries are too high to believe.
The coil geometry is wreaking havoc with the meter.

http://vacuumbrain.com/The_Lab/Telefunken/Jens/choke_c.jpg

We aren't gonna mess up the lams by snapping them back in and out for measuring, but wee can put some 625 EI in there just for the heck of it.

Here's 84 Henries with a few lams installed:

http://vacuumbrain.com/The_Lab/Telefunken/Jens/choke_d.jpg

With the bobbin about 3/4 packed, we get about 180 H.
With the bobbin packe completely, we exceed the 200 H limit of the meter. So it looks like with the normal core, we will have plenty of inductance.

http://vacuumbrain.com/The_Lab/Telefunken/Jens/choke_e.jpg

OK, time to start over. This should be the final attempt for this guy.
It hurts to do this, but we want to get this thing right.


http://vacuumbrain.com/The_Lab/Telefunken/Jens/choke_f.jpg

Here is the current setup. Have not got the stepper going yet, but this works good.
Custom de-reeler, a big chunk of stainless for a wire guide, coreprene pads taped to the stainless for wire tension, the vice is mounted to a drawere slider, so I can move the wire guide back and forth as I wind.
We can wind with space between each turn for less capacitance.
A few pieces of tape should be wrapped around the chambers at 2500 and 5000 turns to tighten things up and provide a consitant winding bed.
You can see this if you look closely at pic #1, the old tape layers can be seen on the side of the bobbin.

http://vacuumbrain.com/The_Lab/Telefunken/Jens/choke_g.jpg

 

[CJ]

OK, sucess!
DCR is now 10.88 K, close enough. We can live with a little less dcr/distortion.

managed the 7500 turns on every chamber:



http://vacuumbrain.com/The_Lab/Telefunken/Jens/choke_i.jpg

Leads are soldered by wrapping the #43 onto the wire first, that way, the thin magnet wire does not melt before your eyes.
The insulation is very thin, and melts as soon as the solder hits it.

http://vacuumbrain.com/The_Lab/Telefunken/Jens/choke_h.jpg

Finished product, ready for core lacing. The extra 1000 turns I got on increased inductance by 10 percent. The Q changed quite a bit also. So those last few turns can really make a difference.

http://vacuumbrain.com/The_Lab/Telefunken/Jens/choke_k.jpg

 

[jensenmann]

:shock:
Awesome! How much work that is :shock:
I´m really impressed

 

[dissonantstring]

[quote author="jensenmann"]:shock:
Awesome! How much work that is :shock:
I´m really impressed[/quote]

holy schmoly CJ!!
i'm more than impressed. i'm in awe! :shock:
awesome thread!
-grant

 

[CJ]

Thanks for the props, I was prety impressed myself, 22,500 is a lot of 43 to hand wind without breaking.
Winding time at 750 RPM is about 30 minutes, plus taping and soldering leads.

I laced it back up and found it to be 300 henries at 1 k hz on the Gen Rad bridge, which usually measures way low compared to most meters, due to the 1000 hz oscilator inside. Q went up to 12. So, plenty of henries, good to know the lams are still crankin.

Since this is going out to someone other than myself, I decided I better hi-pot it just in case.
I had the nerve for 1000 volts D.C. thats all. I'm satisfied it won't break.
Don't want to push my luck.

Going to bolt this baby back onto the transformer plate and wire it up.

http://vacuumbrain.com/The_Lab/Telefunken/Jens/choke_hipot.jpg

 

[tony dB]

do you need an European distributor? :green:

CJ, what you're doing is just over awesome!

 

[CJ]

Thanks, Tony, but you can have all of the V module work you like.
I used to think that Ollie was making a killing on restoring these modules, now I think he's the one getting killed!

For me, this is like a kid in a candy shop, getting to explore these historic wonders.

Anyway, the hardest part is over, now I just gotta assemble this guy and wire up the new filter caps.

More pics,

You have to take off the pilot lamp and hum trimmer mounting bracket to get the choke back in there:
http://vacuumbrain.com/The_Lab/Telefunken/Jens/choke_o.jpg

Terminal plated soldered, brackets removed..

http://vacuumbrain.com/The_Lab/Telefunken/Jens/choke_p.jpg

I was thinking of asking Jens about putting in a gain pot instead of the heater trimmer.
That way you could maybe go from a stock V72 to a V72 EMI, which had the feedback resistor tweaked for more gain.
A pot on the front panel could be cool.
The wire wound pot is toast anyway, so maybe trim the hum with fixed resistors, then use the bracket for a feedbak tweak pot.

http://vacuumbrain.com/The_Lab/Telefunken/Jens/choke_q.jpg

Packed up tight!

Maybe some voodoo coupling between the output core and the choke?

http://vacuumbrain.com/The_Lab/Telefunken/Jens/choke_s.jpg

 

[guavatone]

Uh...

WOW!
n
i
c
e
:green:

 

[CJ]

Working on the prw supply now.
The pwr supply board has had every drop of resin evaporated from it, due to being in a hot enviroment, maybe switched on 24/7 during it's lifetime. Two of the caps were completely dead. When I tried to drill a holein the old board, it snapped like a dry twig in a stiff desert wind.

But I had some spare permali laying around, twice the thickness, which is good, because the original V 72 board is only 1/16 thick, in order to alow the 8uf/450 volt caps to fit in there. The ground leads are pressed right up against the chassis compartment, and there is minimum clearance between the pwr supply resistors and the top of the chassis.

Newer filter caps are smaller, so I can get away with beefing up the board.
Stock supply was five 8/450's .
We can improve that greatly with todays caps, but must not alter the sound any, so we will increas C on the first two caps, then drop back down to about 10 or 12 uf.

Why not burn a pc board?
No way!
That would look so politically incorrect in a V module, I don't even want to visualize it. We want more beef than a thin copper trace holding our B+ out of harms way, right?
Anyways, here are some shots.

I traced out the old board onto the new with an exacto knife. This way I don't have to use the digi readout on the mill, which takes a little longer.

The new board after the milling machine.
Good thing to change out the board, if it breaks on the way back to Germany, then you have B+ wires a danglin round.
We don't want to kill Jenns, right?

Looks like the original, ehh Sunny Jim?

 

[guavatone]

Good one CJ. A While back Ollie(i think) told me he wouldn't go higher than 10uF on those PS caps. -I couldn't see why, but I didn't feel like questioning God.

 

[jensenmann]

Good thing to change out the board, if it breaks on the way back to Germany, then you have B+ wires a danglin round.
We don't want to kill Jenns, right?

That´s a pretty good idea :wink:
Regarding the EMI-mod you mentioned before, I´d be comfortable with that. It surely is a nice option between the other V72s. If you want to do it, CJ, go ahead. :green: :thumb:

(this thread makes me really hot for those thingies)

 

[CJ]

The 10 uf limit might be because of the power transformer.
I have to study the pwr trans section of Grossner.

Interesting to note that this is one of the few tube supplies I have seen with a full wave bridge for the B+.
A Selenium bridge is a hassle, no?

I figured out why, there is about 1 square inch of air space in those modules.
The bridge compared to a full wave ct arangement means a smaller power trans, which is needed to fit in that box.

 

[dissonantstring]

hey CJ,
i think i mentioned to you at Andy's that my friend replaced the selenium rectifiers in his ampex pres because they supposedly fail upredictably (and release toxic stuff when they do). i think his was a half wave for the DC filament supply, but he used 1N5401's for the replacement.
have fun at AES!
-grant

 

[CJ]

Thanks Grant!
I will have to knock the voltage down a bit, since therer is going to be less drop with the solid state rectifiers.

AES should be fun. I wonder if Tony of Stepehn Paul is going to be there.
I have not heard a word on that mic.

 

[dissonantstring]

CJ,
let us know if you find out anything about the Stephen Paul Mic.
i think PMI represents them, but nothing about any release date.
-grant

 

[CJ]

This is a hi potter:

It is good to 5000 volts, ac or dc, as I just found out.
I snapped the pic at 4.5 kv, then forgot to turn it off before grabbing the lead to hook up the victim.
Don't use the hi potter if you are hi on pot. :grin:
But, current is limited to 500 microamperes, or about half a mil, in tech lingo, so I barley even felt it. The leakage light usually comes on just before the "terminal" light.
If can do no destroy testing, but I don't trust anything after the leak lite comes on.

Here is a vintage V72 pwr trans.
Luckily, it has seen better days and a couple of the coils are open, which is good for me, if yo catch my drift.
:green:

I always wantede to know if the white coats really knew their stuff, so here goes nutin. I will rewind this baby with Nomex and modern wire, so it will be good for at least another hundread years, or until Jenns croaks, which is a disytinct possibillity the way I am going, or whichever comes last. :razz:

It comes in a mu can for low static, lined with a piece of paper so the lams don't short at the ends.

http://vacuumbrain.com/The_Lab/TA/Telefunken/Jens/v72_hipot_b.jpg


Set it up:

Voltage, up, up up , up up up up, up up...
it's hard to get good British plugs, ya know.

Sombitch made it all the way to 3 KV AC!
Going from ground to any terminal.
Term to term had the same 3 kv.

Pretty good, since the insl must be aged to toast by now.
The White Coats in the XFMR Dept get an A+.

Now the fun part, checking out all the carbon tracking inside this bad boy.
Whopeee!

FYI: Every xfmr you buy should have a hipot stamp somewhere on the core or elsewhere. By law in the US at least.

 

[jensenmann]

:grin: :thumb: :thumb: :thumb:

 

[dissonantstring]

i love this thread. it always makes me smile...not only because i want to build a V72, but because Jens is willing to sacrifice stuff and CJ is more than willing to "break it down" in everyway possible! :green:
wheeeeeeee!! CJ please be careful. i know you're very experienced in the HV stuff, but still... 4.5KV AC at any amps scares me!:shock:
we need our uncle CJ!
-grant

p.s. hey jens, your woman has moved from toobies to paulies! :grin:

 

[CJ]

Actually, it felt good getting zapped.
In fact, now I am walking around work, charging people by the KW for a good ZAAAAAPPPPPP!
.