Toroidal PT prim 230V sec 270V 0.08A - 14V 2A - Suggestion for use ?

[kagliostro]

Some time ago I bought 3 of these transformers

Toroidal PT prim 230V sec 270V 0.08A - 14V 2A

https://www.musikding.de/Toroidal-transformer-230V-270V-14V

one was intended for a preamp in a U1 rack, the others I ordered to have them available

Councils about a small amplifier using one of this ?

Many Thanks

Franco

[uki]

Hi Franco !

On this video the amp have a toroidal PT check this out, maybe not what you looking for but may give you some ideas !

I think the schematic for the amp is available online,

Also RobRob have a champ version with toroidal PT
https://robrobinette.com/Champ_Micro.htm (scroll down)

[kagliostro]

Ciao UKI

Thanks for answering

Looking to the image of the amp on the movie you linked I doubt that my 0.08A of current disposable for B+ will be enough to feed those Power Tubes

My "problem" isn't the fact that the PT is Toroidal, the concerning is about voltage and current disposables

Franco

[uki]

Did you look at the micro champ ? Does it still too much?

[tubeswell]

Did you look at the micro champ ? Does it still too much?

I think Kagliostro in more concerned about how to use the 14V winding on his PT

[uki]

I think Kagliostro in more concerned about how to use the 14V winding on his PT

It is possible to regulate it to the desired voltage ?

[vibrolax]

You could power push pull 6K6GT's (filaments in series) with 2 or 3 ECC83's.  Maybe need a small value ballast resistor to drop the filament voltage a bit.

[tubeswell]

You could power push pull 6K6GT's (filaments in series) with 2 or 3 ECC83's.

Kirchoff's current law requires that all current entering and exiting a node must sum to zero. 6K6s have 400mA heaters. 12AX7s are 300mA in 6.6Vac mode or 150mA in 12.6Vac mode. So getting them in series is trickier than just stringing them in a line.

[tubeswell]

Suggestion  for 14VAC heater winding - Untried and may be pushing the capability of the winding to supply the needed overall DC voltage, but it illustrates the need to ensure that the total current for any component in series is the same (Will depend upon how good the PT's load regulation is  - and there may need to be more filtering between the filaments etc. and as for the ‘low resistance resistor’ in the PS filter; 0.9V/0.9A = 1R, so the ability of this to filter out ripple is probably non-existent*, but it all serves to underline the difficulty in using the 14V winding. Another option could be to use a 14VAC:6.3VAC bucking transformer with an appropriate V.A rating. Or, if you’re going to go there, a separate 6.3 VAC Heater PT.)


*f= 1/(2Pi.R.C)
=> 1/[(44/7x1x0.0044) = 36Hz

[kagliostro]

Hi Friends, Thanks

About the micro champ the spec on that transformer show an HT of 200V, my PT Is 270V (too much for that project)

The Heather winding Is 14V AC and my intention is to use preamp tubes that can be connected for 12.6V heaters and use a pair of small Power tubes

connecting filaments in series or a single tube that has 12,6v heaters

To tame the 14V to 12,6V I want to use a simple resistor

The concern Is to find a 12,6v Power tube or a 6,3V tube to be used in PP or PSE without exceding the 80mA disposable and compatibile with the 270V x 1.4 (SS rectifier obviously)

Thanks

Franco

[sluckey]

Here are two 6GW8 amps that could use that PT...

     http://sluckeyamps.com/PeeWee/PeeWee.pdf
     http://sluckeyamps.com/lil_maggie/Magnatone_M2.pdf

There are several 6BM8 schematics by tubenit and geezer in some of the other forum categories. Take a look.

[kagliostro]

Grazie Steve

I didn't considered the 6GW8 because my 270V AC x 1,4 will result in 378V DC, too high

but I was thinking to a SS rectify, with an EZ81 the voltage will drop a bit (and may be enough)

Your project remembered me I've the rectifier and 2 or 4 14GW8 tubes

---

Meanwile, thinkin to tubes I've, I was thinking to a 12ax7 (or two) setted for 12.6V and a 1625 that is a 12.6V tube

and to solve the problem to have around 250V DC for G2 I was thinking to a VVR setted for that voltage

but near for sure I miss the 10-15 W - 4.2K SE OT required

---

Again Many Thanks

Franco

EDIT:

BTW, just when I finished to write I noticed a paper bag behind the PC monitor, what inside ?

2 x 5879, 1 x 5725, some anti vibration 7 pin and 9 pin sockets plus ....... 2 x PCL86 tubes 

[thetragichero]

guess i never scanned my schematic but my every week church amp used a 216vac/120ma 12vac/800ma toroidal power transformer purchased pretty cheap from ebay. if you can get the filament voltage down to 12v (big horkin resistor?) this used 12au6 12ax7(12v filaments) and 2x6v6 (power tube filaments in series to make 12v). very simple, vox-ish (12ax7 long tail pair). treble control vox cut, bass control rotary switch to select between cathode bypass capacitors on the gain stage... felt like that gave more tonal variation than switching coupling capacitors)
anyway i love trying to figure out what i can build with oddball/salvaged transformers

[vibrolax]

You could power push pull 6K6GT's (filaments in series) with 2 or 3 ECC83's.

Kirchoff's current law requires that all current entering and exiting a node must sum to zero. 6K6s have 400mA heaters. 12AX7s are 300mA in 6.6Vac mode or 150mA in 12.6Vac mode. So getting them in series is trickier than just stringing them in a line.

I omitted that the ECC8x filaments should be connected in parallel.  As you pointed out, filaments connected in series must draw the same current.

[glass54]

Hi Franco,
I have done a number of preamps using Toroidal transformers (my preference  )
They have usually been 240VAC and Heaters at 12.5V-15VAC for secondaries. I usually split the Heater series dropping resistor into 2 halves if required (one in each leg) so I get a nice heater "centretap" (pair of 100R 1W resistors to ground) and I use SS Rectifier and 3 RC sections to get around 300V to 320V DC for the ECC8x (12A-7) Tubes.  Has worked well for me BUT it was Preamps.
My main concern is if you want to have a small power amp included, you only have something in the order of 50 to 60mA DC maximum available. I an not familiar with suitable low current power tubes (apart from 12AT7 as used for Rev Driver), but some others may be able to guide you.
Regards
Mirek

[kagliostro]

Many Thanks Friends

Franco

[capdestroyer]

I think Kagliostro in more concerned about how to use the 14V winding on his PT

I know this thread is two years old but I registered after seeing this and wanted to give a simple solution to anyone that is going to use a similar Transformer:

Using a half-wave rectifier (a single diode) without a smoothing capacitor would convert the 14V to about 6.1-6.3V. It's not the best way but it's a simple solution. It will however lower the available current to half. After powering the filaments and measuring again the voltage you can decide if you need to add a small smoothing capacitor, starting with 0.1-0.47uF

[Merlin]

I know this thread is two years old but I registered after seeing this and wanted to give a simple solution to anyone that is going to use a similar Transformer:

Using a half-wave rectifier (a single diode) without a smoothing capacitor would convert the 14V to about 6.1-6.3V. It's not the best way but it's a simple solution.

Unfortunately, if it has to supply more than a couple of mA, a half-wave rectifier will saturate the transformer.

[capdestroyer]

Unfortunately, if it has to supply more than a couple of mA, a half-wave rectifier will saturate the transformer.

even if that's a possibility, if someone has already bought the transformer it's not a bad idea to try it and see where he gets from there. After all it's just a diode... no cost, no circuit, no wasted time.

[kagliostro]

The easy way is to use an in series resistor

or, if no math must be involved, just use 4 diodes, in series two by two and connected in antiparallel

This way each diode drop around 0.7V (2 in series 1.4V) and the 12.6V for heaters are obtained

Then use 12.6V tubes or 6.3V tubes in  series

Those transformers were probably planned for a preamp, but with a bit of application they can be used for low  Power amps

Franco