I ordered my OPTs from Torotrans, but those are for instrument amps.
You need to convert the ratios into something that a mains winder can understand - ie voltages.
For 5k/8 I use a secondary voltage of 9v. I suppose for 2.5k you would need 6.3V, but do run the calculations yourself.
There are two main issues with using toroids as OPTs. One is DC balance, which has to be accounted for in circuit design. The second is lack of primary inductance, which has to be addressed in the speaker or you will get poor bass response.
Of course if your design has high bandwidth you can probably get away correcting this with feedback, but you lose a bit of the tube's operating power. Check out the Baby Huey design, it is designed to work with low inductance OPTs by employing shunt feedback and running the input stage off the output transformer, neat design.
The transformers cost me about 800 for 60VA unit, which should be good for power output up to about 15W. The bigger ones, meant for HIFI use, have excellent frequency characteristics specially at HF, very clean output. Those are 120VA and should be good for 30 to 40 watts. They cost a little less than twice the earlier ones, but have not been used apart from a basic test. The primary inductance is about 1H and 1.5H, so we'll see how that works out in practice.
BTW Delta transformers are used by a manufacturer here in India. Therefore they will have some ready products. I've heard those amps and am totally not impressed, bit you might be all right with a little less performance. I am also not sure if it was the amp design that was flawed or the OPTs, I'm guessing both were to blame.
You need to convert the ratios into something that a mains winder can understand - ie voltages.
For 5k/8 I use a secondary voltage of 9v. I suppose for 2.5k you would need 6.3V, but do run the calculations yourself.
There are two main issues with using toroids as OPTs. One is DC balance, which has to be accounted for in circuit design. The second is lack of primary inductance, which has to be addressed in the speaker or you will get poor bass response.
Of course if your design has high bandwidth you can probably get away correcting this with feedback, but you lose a bit of the tube's operating power. Check out the Baby Huey design, it is designed to work with low inductance OPTs by employing shunt feedback and running the input stage off the output transformer, neat design.
The transformers cost me about 800 for 60VA unit, which should be good for power output up to about 15W. The bigger ones, meant for HIFI use, have excellent frequency characteristics specially at HF, very clean output. Those are 120VA and should be good for 30 to 40 watts. They cost a little less than twice the earlier ones, but have not been used apart from a basic test. The primary inductance is about 1H and 1.5H, so we'll see how that works out in practice.
BTW Delta transformers are used by a manufacturer here in India. Therefore they will have some ready products. I've heard those amps and am totally not impressed, bit you might be all right with a little less performance. I am also not sure if it was the amp design that was flawed or the OPTs, I'm guessing both were to blame.
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Thanks for the awesome help Sangram. It does make a lot of sense speaking to the winders in terms of voltages. Will do that next time i try to buy them off the street.
Feedback adjustment was something i was trying not to deal with given the my noob level
.
Will also check out torotrans - they are in pune so reachable.
Thanks so much again
Feedback adjustment was something i was trying not to deal with given the my noob level
. Will also check out torotrans - they are in pune so reachable
.Thanks so much again
At the cost of repetition, do note that the conversion ratio is squared for impedance and direct proportion for voltage, so a 2500:8 impedance ratio is actually 12.6V (I use 13V for 5000:16, which is the exact same ratio).
When ordering from Torotrans you can ask them to wind secondary winding first, this is said to mildly increase bandwidth. Also if your winding is more than 50VA you should ideally ask for two or more secondary windings which you can then parallel/series the way you want.
Also tapping is not an issue. You can get 50% UL taps if the primary windings are separated, or if you are winding the whole thing as one center-tapped primary, then you can design the tap wherever you like. Same for secondaries, this will give you some flexibility. A 9V winding corresponds to 5k:8 and a 6.3V to 5k:4.
Remember to oversize the core 4x (3x is acceptable) for best results.
Good Luck!
When ordering from Torotrans you can ask them to wind secondary winding first, this is said to mildly increase bandwidth. Also if your winding is more than 50VA you should ideally ask for two or more secondary windings which you can then parallel/series the way you want.
Also tapping is not an issue. You can get 50% UL taps if the primary windings are separated, or if you are winding the whole thing as one center-tapped primary, then you can design the tap wherever you like. Same for secondaries, this will give you some flexibility. A 9V winding corresponds to 5k:8 and a 6.3V to 5k:4.
Remember to oversize the core 4x (3x is acceptable) for best results.
Good Luck!
Its a *lot* more complicated than that.
You need to divide the primary and secondary into multiple sections and interleave them.
Telling the winding guy voltages will not work, you have to design the transformer down to the last detail and tell the guy how many turns of what gauge to wind on each layer.
I wish I could say something about selection of core material, but the last time I checked the market only one grade of silicon steel was available in retail quantity.
Different core types - R-Core, tape wound core - these are things we can only dream about.
This books is a good starting point: http://www.dissident-audio.com/Transfos/Papers/Wolpert_Audio_Xfmr_Design_Manual.pdf
Not toroids, they don't have bobbin wound layers. You can get good coupling between windings and very high bandwidth out of even an ordinary mains toroid.
However, DC is a massive problem because of the untapped core, and also the primary inductance. If you are able to counter that in your design, you can get decent results. Better than a potshot with the low quality cores available in India and used by EI manufacturers.
I do agree that a properly wound transformer will be the way to go, but sources for such are non existent. Also, asking a local winder to do this is akin to asking a baboon to do algebra. In the absence of better options, one should choose the lesser evil. For me, that was the toroid. If it failed, at least I could use it as a transformer.
However, DC is a massive problem because of the untapped core, and also the primary inductance. If you are able to counter that in your design, you can get decent results. Better than a potshot with the low quality cores available in India and used by EI manufacturers.
I do agree that a properly wound transformer will be the way to go, but sources for such are non existent. Also, asking a local winder to do this is akin to asking a baboon to do algebra. In the absence of better options, one should choose the lesser evil. For me, that was the toroid. If it failed, at least I could use it as a transformer.
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try Menda- 7,1st flr , (above Laxmi book depot)Solanki Sadan,Shivaji path, Thane 25367458, I went for power Tx about 10 yrs back. Don't know if they are still in business. I also saw Philips auth dealer(ahead of Lamington PO) selling audio tx for false ceiling mounted spk. or Tomson transformers under Grant Rd bridge. Hope this helps.
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Check out Kothari electronics. However, I think the supply of desirable low-noise audio JFETs like the 2sk170 is pretty tight. You will probably get industrial and measurement-quality stuff like J310, J175, J176, etc., but no low-noise audio. Low-noise p-channel is unobtainium except on EBay and elsewhere.
The old BFW10/11 are easily available at almost any place such as Vishal, tho relatively expensive (abt Rs 10, if I recall right). These were the jfets of choice for many audio projects in the old Wireless World mag., but can easily work at RF too. Since many audio opamps such as TL072 or LF353 have jfet inputs, I guess use of discrete jfets for audio fell off. Also finding matched pairs is an impossible but necessary task if you are shooting for dc coupled application such as for a scope preamp. Far easier to use use a modern hi-performance opamp.
vkj
vkj
True. I recently bought 10 BC546 transistors from Ceepee, who in the past has been reliable. But I was disappointed to find that they were fake. I guess the bad printing on the case shd have warned me (looked like BEL make). I had to throw them all out.
Similarly some power Mosfets I bought from Vishal turned out to be fakes. In this case CeePee had good ones! Im guessing even these guys dont know if what they are selling fakes or not.
The best source for reliable parts in Amar. Hes been around for > 40 years! More expensive but 100% genuine. But he wont entertain small purchases. Also I doubt he will have audio components.
Nowadays Im finding the biggest obstacle to any project is sourcing reliable components.
vkj
It's about Rs.65 to Rs.125, depending on availability. The Rs.30 fakes are probably remarked NEC UPC1238 or ST TDA2030 chipamps, which are nice chips in their own right, but just can't handle higher rails and power.
You may want to pick up and hoard the authentic TDA2030A and TDA2050 chipamps while they're still available at reasonable prices - the latter has been discontinued last year by ST.
BC546 is a commodity part - the generic ones from NXP, BEL, CDIL, KEC, On Semi should all work well. IIRC, the NXP ones from China (silver face with black lettering) are widely available and shouldn't be more than Rs.1 to 2 each - they should meet all specs and work well.
If you can work with 45V Vceo transistors, you can substitute BC547 or 2sc1815 for the BC546. I pay about Rs.2.50 each for authentic Toshiba 2sc1815-GR, 3.5x higher than the Rs.0.70 that I paid for some 2sc1815-Y a few years ago, but no regrets. There's also plenty of authentic 2sc1959-Y available for Re.1 each, and I've stockpiled a couple of hundred - they're fine upto 30V Vce. That dealer has some 10,000+ pieces, so they aren't going to run out soon.
BTW, BEL made and/or makes a bunch of small-signal transistors with reversed or alternate pinouts. You may have got one of those.
Worst case, if you need the 65V Vceo of the BC546 and can't find any, just go with the BC639 - DC beta is lower at ~100..120, but that's fine in many applications. Just take care with the BCE pinout.
BTW, On Semi is discontinuing virtually all their current production TO-92 BJTs and FETs. There are second sources for most, but if you plan to use them in the future, it's best to stock up in the next few months.
http://www.onsemi.com/pub/docs/pcn/PD20685.pdf
The useful ones that I use frequently are the BC5xx series, BC327/328, BC639/640, BF423, J310, 2N4401/4403, 2N5401/5551 and a few others. Most of these are also available from Fairchild, NXP and KEC, so no immediate problem foreseen. However, the drop in demand for TO-92 devices will affect all manufacturers and other lines will also eventually be closed or consolidated.
http://www.onsemi.com/pub/docs/pcn/PD20685.pdf
The useful ones that I use frequently are the BC5xx series, BC327/328, BC639/640, BF423, J310, 2N4401/4403, 2N5401/5551 and a few others. Most of these are also available from Fairchild, NXP and KEC, so no immediate problem foreseen. However, the drop in demand for TO-92 devices will affect all manufacturers and other lines will also eventually be closed or consolidated.