Just finished building up a 10 watt PP valve amplifier chassis.
Uses back to back power transformers for heaters and HVAC.
Uses a power transformer for output transformer and sounds very good.
Uses back to back power transformers for heaters and HVAC.
Uses a power transformer for output transformer and sounds very good.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I'd ground the black lead of the output winding, even if you don't use overall feedback.
I just wired the screens to B+ through 220R resistors.
If you look at the picture you will see 220R resistors soldered on the pcb transformer connector to B+.
I managed to get sound out of this Toroid Transformer for audio: Output ~12V/1A; In ~100/110/115/120/220/230/240V | eBay Plenty of taps for UL of your liking but I hold myself not to do so. I substituted Hammond 125D for this. I don't regret it! I'm with Nigel for back to back power transformers and mains toroids as OPT.
power tubes do not last long with wrong rp
with sound card and PC and dummy load
check linearity
download RTA to check odd harmonics
download ARTA check thd
play bansury raga bach cello not rap
you will see
the money you save with cheap toroids you go to buy many tubes
its a nonsense
a low cost transistor hifi amp + tubes with only heather for the look
and a blue led on the bottom cheap and better sound
with sound card and PC and dummy load
check linearity
download RTA to check odd harmonics
download ARTA check thd
play bansury raga bach cello not rap
you will see
the money you save with cheap toroids you go to buy many tubes
its a nonsense
a low cost transistor hifi amp + tubes with only heather for the look
and a blue led on the bottom cheap and better sound
I plan to build a EL84 push pull amplifier very similar to this one, and I am wondering what kind of result could be expected from a modified toroidal isolating transformer used as output transformer. My plan is to start with the RS components stock number 1176060, a 200VA toroidal transformer with 110mm diameter and 4 identical windings, nominally two 115V primary and two 115v secondary. I will use all four windings in series as primary winding to increase inductance, and wrap around the transformer an additional center tapped winding as secondary. This isolating transformer has the same size of the Toroidy TTG-EL84PP, and the current price is 15 euro lower (+ VAT + shipping). My goal is to get about the same performance of the Toroidy transformer, but with the ability to customize the secondary to my speaker exact impedence and save about 50 euro over the transformer pair.
Here are some back-of-the envelope preliminary calculations. Am I missing something? When the primary is energized at 230V, with no load on the secondary, I have measured 2,75V from 10 turns of wire wrapped around the core. With a trivial proportion, this means that each winding should have about 836 turns. Connecting all 4 windings in series gives a 3345 turns primary. It should reflect 8000 ohms from the 4+4 ohm secondary, this means a 1:31 winding ratio with a center tap. The 106 turns of the secondary will be made with 53 turns of enameled copper wire wouund from two spools in parallel. Each turn will need about 16cm of wire, so two 10m spools will be enough: it should be possible to have them shaped to go trough the center of the donut with ease.
Here are some back-of-the envelope preliminary calculations. Am I missing something? When the primary is energized at 230V, with no load on the secondary, I have measured 2,75V from 10 turns of wire wrapped around the core. With a trivial proportion, this means that each winding should have about 836 turns. Connecting all 4 windings in series gives a 3345 turns primary. It should reflect 8000 ohms from the 4+4 ohm secondary, this means a 1:31 winding ratio with a center tap. The 106 turns of the secondary will be made with 53 turns of enameled copper wire wouund from two spools in parallel. Each turn will need about 16cm of wire, so two 10m spools will be enough: it should be possible to have them shaped to go trough the center of the donut with ease.
Many of us have used toroidal PT as OPT with excellent results. I've built 7 amps with this technique with -3db of ~125kHz (sine). Square waves are cleaner than using my Hammond 1650N, too. Granted, I wouldn't use them for a 100W amp, but for up to about 30W they are an excellent alternative. In my 7 amps, I've saved over $1500 so far, and the Triad models I use don't even need fancy biasing. Individual bias adjustments realize excellent DC balance, and at 1W output it's within 1db 6Hz - 50kHz.
As you are no doubt aware, many different load impedances work well with tubes, so long as they are in a reasonable range. If you do the math correctly to choose a suitable load impedance, and verify that it is going to be suitable for your application, it is no different than choosing any other audio grade transformer.
Saying you will ruin tubes and calling it all "nonsense" is absurd and downright rude. This isn't just some random part from a junkbox. Some of us have been successfully using Toroids correctly in this manner for years, with excellent linearity and performance.
Step out of your box and open your mind.
My recent EL86 amplifier uses Antek Toroids for power and output, and the Toroid I have chosen for output is the AS-0505, with the secondaries in series for 10 volts, the impedance is 4232 ohms anode to anode, so it presents 2100~ ohms per pentode. Looking at the datasheet we see that this is a good load for output power and distortion, in comparison to the usual 1500R per tube that one often sees recommended for these tubes... Since many speakers have a dip in impedance at some points lower in the frequency response, a smidge higher impedance can help to keep the tubes happy. This isn't a junkbox part, its actually chosen to present an optimum load to the output stage. No "nonsense" here.
This same transformer would be a fantastic choice for parallel EL84 or 6V6 outputs as well.
I think a lot of the negative response to Toroids is based on a lack of understanding of how these things operate, coupled with the "it's different so it can't possibly work" mentality that is so persistent in the tube world these days. That, and the whole "much parasitic capacitance” argument that is practically a non-issue when actually using them in an output stage. Pretty much everyone I've seen that finally sat and measured one and built an amplifier with them has been very pleased, and they sound wonderful. Flat frequency response across the audio band, tight coupling for fantastic "micro detail" that will rival even a massively overbuilt DHT SE rig, and great, tight, accurate bass. What's not to like?
This same transformer would be a fantastic choice for parallel EL84 or 6V6 outputs as well.
I think a lot of the negative response to Toroids is based on a lack of understanding of how these things operate, coupled with the "it's different so it can't possibly work" mentality that is so persistent in the tube world these days. That, and the whole "much parasitic capacitance” argument that is practically a non-issue when actually using them in an output stage. Pretty much everyone I've seen that finally sat and measured one and built an amplifier with them has been very pleased, and they sound wonderful. Flat frequency response across the audio band, tight coupling for fantastic "micro detail" that will rival even a massively overbuilt DHT SE rig, and great, tight, accurate bass. What's not to like?
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Thanks, Jazbo. I'm still learning how to figure out load line calculations for a PP output stage. Right now I'm just sticking to "typical operation" in the datasheet, but I'd like to learn how to design a class B amp. I'd like to know how much power I can make if i beat the crap out of a pair of 6P1P tubes, distortion be damned. 
I have Broskies' PP calculator but it only handles triodes.
I have Broskies' PP calculator but it only handles triodes.