New c core
« on: December 22, 2018, 03:12:21 PM »
Finally after one seller never sent the items out and refunded me ,another seller sold me these and they arrived ,in probably the last post before Christmas .
Nice quality items,  matched pair for both primary and secondary inductance  and resistance , the sectionalising and lay of the wires is very neat ,single ended 3500 ohm to 4,8  ,they will be perfect for my next project headphone amplifier with spring reverb drive  . I have nice set of 6V6's in mind for it   but I wonder if 6K6 is better or how it differs .
I got them for about 90 euros the pair including shipping by regular postal delivery service ,

https://www.ebay.ie/itm/253839557010
« Last Edit: December 22, 2018, 03:43:01 PM by Tubetec »


CJ

Re: New c core
« Reply #1 on: December 22, 2018, 05:03:30 PM »
Nice!
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

Gene Pink

Re: New c core
« Reply #2 on: December 22, 2018, 08:18:03 PM »
Nice quality items,  matched pair for both primary and secondary inductance  and resistance....
Make sure you keep that giant radiator hose clamp good and tight. Otherwise it'll leak flux out all over the place, run across your bench and down your leg, making a real mess, everywhere. 

That stuff is hard to clean up

 ;D ;D

Gene


JohnRoberts

Re: New c core
« Reply #3 on: December 22, 2018, 08:21:21 PM »
Make sure you keep that giant radiator hose clamp good and tight. Otherwise it'll leak flux out all over the place, run across your bench and down your leg, making a real mess, everywhere. 

That stuff is hard to clean up

 ;D ;D

Gene
Hose clamp, screw clamp, transformer clamp... what's the diff?

JR
John Roberts
http://circularscience.com
Tune it, or don't play it...

Re: New c core
« Reply #4 on: December 22, 2018, 08:24:32 PM »
https://www.youtube.com/watch?v=biPhaIkjW6Y

Lemon song live  seems to fit

Re: New c core
« Reply #5 on: December 22, 2018, 08:36:24 PM »
The manufacture  only supplied  a jubilee clip ,but theres a special type of bolt clamp I might try and find ,any over torqueing the bolt on a jubilee clip and it fails , a proper bolted clamp would be much better .

alexc

Re: New c core
« Reply #6 on: December 23, 2018, 12:01:10 AM »
I did some compare of good nos 6v6 and 6k6 in both a pp 'deluxe' style amp and an se 'champ' style too.

In pp, the 6V6 was the clear standout ...  for bass response  ..  especially in triode mode where the 6K6 has a higher rp. The higher power ratings of the 6V6 were also most at home in this pp config.

In se, it was less compelling  ...  my 'champ' setup uses a 'magnetic components' output traffo  - like the original, it is small and lightweight - like from an old time kitchen table radio  :)  - it can't take much level or bass before it futzes out hopelessly.

SO - the 6K6 was better than the 6V6 in this app, where the extra power and bass response don't help any .. at all.  A case of being better matched to the op traffo and some sweeter for it.

...

I kept the av7 / 6k6  in the champ se  ...  and went to the strongest 6V6 I could for the pp   ... in this case JJ 6V6S which I really really like.

I am a great fan of 6V6 in general and the 6K6 is an interesting cut-down version that can find real application in lower power builds.

Mind you, I got a few 6K6 when they were throwing them away; they probably be quite exe by now ...  the 'black glass' thing.
I ping therefore I am

Re: New c core
« Reply #7 on: December 23, 2018, 12:37:43 AM »
Thanks Alex ,
Id probably need to make a driver stage if I used any larger a tube , with the small power tube I can drive it directly from studio level outputs . 6V6 will do the job I think , 6L6 would probably be overkill for my application .I intend to side chain the reverb tanks off the main output through a wirewound pot attenuator and switchable light bulb limiter ,  I'm wondering what would be  a sensible ohmage for the tanks , I have 4 and 8 0hm windings on the transformer ,some tanks have 4 or 8 ohm input  impedences, or would I be better off not loading the outputs and make the drive coils something like 40-80 ohms 

abbey road d enfer

Re: New c core
« Reply #8 on: December 23, 2018, 05:07:59 AM »
Thanks Alex ,
Id probably need to make a driver stage if I used any larger a tube , with the small power tube I can drive it directly from studio level outputs . 6V6 will do the job I think , 6L6 would probably be overkill for my application .I intend to side chain the reverb tanks off the main output through a wirewound pot attenuator and switchable light bulb limiter ,  I'm wondering what would be  a sensible ohmage for the tanks , I have 4 and 8 0hm windings on the transformer ,some tanks have 4 or 8 ohm input  impedences, or would I be better off not loading the outputs and make the drive coils something like 40-80 ohms
What nominal power do you expect? A 6V6 with 0dBu input at the grid would have an output level of about 10Vrms into 3.4k, so a power of about 30mW, which is enough to drive headphones but not enough if it needs to be shared with the input transducer of the Accutronics tank.
Basically, you'll need more power to drive the tank than the headphones.
Maybe you should consider using a more sensitive tube. An EL84 would be twice as much sensitive, but still the output would not leave much headroom.
You need to define more parameters such as B+ voltage, expected output power...
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

CJ

Re: New c core
« Reply #9 on: December 23, 2018, 07:31:03 AM »
we used stainless steel banding strap on those C cores,   1/2" for the small ones, 3/4" for the big pulse transformers with the $2000 dollar Arnold cores, mating surfaces had a mirror finish, sometimes we would have to send those cores back because pulse transformers are very touchy when it comes to the core,

be careful with the cut ends, they are mu metal sharp.  we used to make core lacing tools out of the strap, you cut about a 6" chunk, round one end like a butter knife, put a slight edge on it, tape the other end with glass cloth tape from the winders stash, now you can go to town on a big three phase core by spreading the 3 x 3 legs to stuff the I bars,  Three phase transformers have two different length I bars , a big chunk for the middle T, and smaller chunks for going from the sides to the center leg. this is because you have three coils sitting on those legs, so the two different I bars had to be cut perfect otherwise you would have rough edges on the side of the core, or the middle bar would not mate up well with the outer legs, so you lay out a 1 lam thick core on a big table and put your sample cuts together to check the gaps.

you can use more than one strap per core, you can get crimpers for cheap on evilbay, but the stainless strap will cost ya,
« Last Edit: December 23, 2018, 07:48:48 AM by CJ »
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html


Re: New c core
« Reply #10 on: December 23, 2018, 12:43:53 PM »
Thanks Abbey ,
I did realise the EL84 was probably better suited to the job alright with a gain of almost 20 .Maybe a ht of around 220-250 volts 5 watts pentode connection . I can easily rewind or modify the drive/pickup  coils to any impedence ,  two tanks per channel

I need to draw things up on paper for clarity , will post sketch soon .

alexc

Re: New c core
« Reply #11 on: December 24, 2018, 11:36:10 PM »
I've been tempted by some eby sino moderate priced .. double-c core amorphous (with copper frame).

No idea now good they might be  ...   and even   what's what  ...   in the rarefied world of esoteric transformer construction, but it seems like an affordable inroad to try   ...  to 'dip one's beak' as it were.   :)

Something like 240us or so all up for a pair  ..   You can see them if search transformer -> amorphous

If they would work out to be useful, one could 'can them up'  ... there are some interesting cans on eby too. No idea on what kind of 'metal' they are using, hopefully it would have some iron. Perhaps nesting a couple with some potting compound and what not ...  could be interesting.

I've been looking for a reason to have a go at some direct-heat tubes in a low-power amp context  ..  some 6s4s octals (15W plates) in parallel se, for example.  A pair together is like a 6L6.

These traffos are prolly good for 60mA or so, I would think (on perousal of spec). They say 22H primary inductance.



« Last Edit: December 24, 2018, 11:43:26 PM by alexc »
I ping therefore I am

Re: New c core
« Reply #12 on: December 26, 2018, 07:58:37 AM »
I found a few now selling core materials , one Bulgarian source on Ebay seems to have sillicon steel cut cores ,with pressboard former included , anywhere from about 13 euros up depending on size . They look as rough as a badgers proverbials  ,is it just looks like a large 0 shaped chunk of cast steel cut in two , I see a material thickness of .3mm does this mean its a strip wound core ?

Double / Dual C-Core Output Transformer Pressboard Silicon Steel Alloy  :ebay

I also note from CJ's files, tripple nested sheilding on some of high spec old transformers , I recall Abbey saying he did for a while sell shielding cans , what are the secrets here ,can I start off with a cheap and cheerfull Chinese iron can transformer shield and add extra layers of screen internally , would buying two steel cans one fitting inside the other then adding an extra mu metal shield be worth it ?I also see aluminium cans I presume these are purely for asthetic purposes as they wont have much screening value magnetically.   

abbey road d enfer

Re: New c core
« Reply #13 on: December 26, 2018, 10:46:47 AM »
I found a few now selling core materials , one Bulgarian source on Ebay seems to have sillicon steel cut cores ,with pressboard former included , anywhere from about 13 euros up depending on size . They look as rough as a badgers proverbials  ,is it just looks like a large 0 shaped chunk of cast steel cut in two , I see a material thickness of .3mm does this mean its a strip wound core ?
That's how dual-C cores are usually made. A solid core would be too lossy.

Quote
I also note from CJ's files, tripple nested sheilding on some of high spec old transformers , I recall Abbey saying he did for a while sell shielding cans , what are the secrets here
No secrets here, layered shielding is more efficient than solid shield. That's because some of the flux is reflected at the boundary, instead of being transmitted.

Quote
  ,can I start off with a cheap and cheerfull Chinese iron can transformer shield and add extra layers of screen internally , would buying two steel cans one fitting inside the other then adding an extra mu metal shield be worth it ?
That would certainly work.

Quote
I also see aluminium cans I presume these are purely for asthetic purposes as they wont have much screening value magnetically.
Correct.
« Last Edit: December 26, 2018, 11:07:36 AM by abbey road d enfer »
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

Re: New c core
« Reply #14 on: December 26, 2018, 01:31:21 PM »
Thanks Abbey , and thanks CJ for the core clamping info earlier too .

I had seen a few other made up c core transformers too , I think those ones you saw were the work of 'James'  Transformer of Taiwan  Alex  .

alexc

Re: New c core
« Reply #15 on: December 28, 2018, 09:49:03 PM »
Ahhh. Righto.  Those guys (James of Taiwan) know how to make really good traffos to a price point and with the nice can too.

These amorphous types  look good to me, and obviously quite a few sold.

...

I bought a couple of cheap  vintage traffos with a crazy spec (50ohm:100K) just for the quality of the canning.

I plan to go 'CJ' on their a**es, and re-fill them with another traffo with some flying leads and potting goop.

..  like Lundahl or Haufe :)  ...  each of which are a pain to re-use because of the 'pcb pinout' format  but perform quite well. With proper shielding they do a lot better!

For the money, it works out well  ...  and I can have a try at some winding of bobbins for some tutorial value.
I ping therefore I am

abbey road d enfer

Re: New c core
« Reply #16 on: December 29, 2018, 03:23:09 AM »
I bought a couple of cheap  vintage traffos with a crazy spec (50ohm:100K)
You have to put these specs in regard with the intended BW.
Typically, a 100k winding is 2.2 times the number of turns of a 20k winding, everything else being equal. So the stray capacitance and leakage inductance will be higher, which results in a much lower HF roll-off frequency.
Just the same, shifting up the LF roll-off allows decreasing the number of turns for a given target impedance.
In the 40's and early 50's PA systems were expected to cover about 60Hz-6kHz; that makes building tra,nsformers much easier.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.


 

Related Topics

  Subject / Started by Replies Last post
3 Replies
1681 Views
Last post September 23, 2004, 04:07:17 PM
by CJ
14 Replies
5645 Views
Last post February 11, 2005, 01:35:17 PM
by [email protected]
3 Replies
1102 Views
Last post October 25, 2005, 04:31:11 PM
by mnats
70 Replies
30266 Views
Last post August 23, 2009, 12:04:42 PM
by leswatts