Many mains transformers have the right ratios to use as push-pull output transformers. (eg 120+120:6v)
The iron used in these transformers is not audio grade however.
What effect will this have on the frequency response?
Are Toroidal transformers any different?
Tony.
The iron used in these transformers is not audio grade however.
What effect will this have on the frequency response?
Are Toroidal transformers any different?
Tony.
Find a winder and ask him to make a toroidail transformer for you with multiple windings.
I have read a few post about toroital mains was used as an opt. The opinions were mixed. Try it if it's cheap.
I have read a few post about toroital mains was used as an opt. The opinions were mixed. Try it if it's cheap.
A lot of info in The Net.
For instance: Valves & Tubes. What use are they?. IF I wanted to build such an amp I would rather go towards parallel feed output (no magnetising current in a core).
For instance: Valves & Tubes. What use are they?. IF I wanted to build such an amp I would rather go towards parallel feed output (no magnetising current in a core).
Most mains transformers will not go to 20 KHz. Some will, but testing is the only way to find out. If the amp in question is a guitar amp, then it may just work since HiFi response to 20 KHz is not needed. When I was young and didn't know better I made quite a few guitar amps using mains transformers for output.
Now that I know better.....the last cost guitar amp I made uses a mains transformers for output. The transformer is an Antek 50 VA toroid and the amp cranks out 20 watts of good sound with a pair of UL84's.
A mains transformer will not work for SE but may be OK for P-P. Generally a toroid will have a better chance of handling the high frequencies but requires a more careful balance in DC current between the two halves of the P-P amp.
Now that I know better.....the last cost guitar amp I made uses a mains transformers for output. The transformer is an Antek 50 VA toroid and the amp cranks out 20 watts of good sound with a pair of UL84's.
A mains transformer will not work for SE but may be OK for P-P. Generally a toroid will have a better chance of handling the high frequencies but requires a more careful balance in DC current between the two halves of the P-P amp.
My commercial preamp used small toroidal power transformers as outputs. They were OK, but replacing them with Lundahl LL1674 amorphous cobalt core transformers was a big improvement.
Another thought. For your torridal PP output, use a tube with a low RP to get as high a frequency response as possible. 6080 for example comes to mind, and would work great for a class A 5watt PP amp.
You can use a mains transformer in SE, but you need a parafeed(choke or resistor) output with no DC in the output transformer.
You can use a mains transformer in SE, but you need a parafeed(choke or resistor) output with no DC in the output transformer.
There is more to an audio transformer than turns ratio and core material. Winding interleaving, for example.
Here's an example of a SE amp using a cheap Antek mains transformer. It sounds quite good, despite costing less than $200 for parts.
6V6 Lumiere
6V6 Lumiere
Yes, Shoog is an expert in this. I myself built a differential output stage(my phono and line stages are differential) with 6s19p driven by 6e6p as a cheap experiment. I used a 50VA toroidal with the 6V secondaries wired in parallel. The cathodes were AC coupled and the 4 triple cascode CCS's LED biased and made of 2 BC549's and 1 MJE340 were retuned to a negative supply of about 20V. I was lucky first time as all the sinks were matched to better than 0.5 mA. It was very easy, cost peanuts and to my delight considerably outperformed my commercial 300B SE. I would mention that I mostly listen to classical music which doesn't need much power in the bass.
First off it will not work at all for a single ended amp. It will not be able to take m much DC at all. But it can work for push-pull if you have a center tap.
What Will effect frequency response at the high end is the lack of any interleaving, not the type of iron. Power transformers don't even have the windings on the same bobbin. They are physically separate. HiFi OPTs use interwoven primary and secondaries.
But if you are over 50 your hearing might be such that maybe you don't care about what happens above 12KHz. and if this is for a guitar amp you don't need to go even that high.
At the low end, not problem. it should do full rated power at 50Hz
parafeed eliminates the DC issue. feeding a counter current through an additional winding from a high impedance can also bring you back to null.
I just measured a toroid I have here (antek AN 1T250) and even with 5ma of imbalance I still get 35hy's of primary inductance per half. That translates to 140hy end to end or 70 hy per plate. this is plenty for a PP 801A amp.
this may be true for EI and some C-core transformers, however for toroids it can be a different story. The long and narrow aspect ratio of the winding lends itself to low leakage and wide bandwidth.
for kicks I fed each winding of the above antek with a 800 ohm source into either side of the 500VCT winding and I placed 8 ohms across the 6V windings in series and grounded the Center tap (12VCT)
In this configuration, I measured -1dB @ 56Khz, -3dB was at 90Khz. -1dB on the low end was around 5hz.
an added bonus is the 120V windings are there for just under a 50% UL tap. (didn't measure that so you are on your own.)
the bad news is the 500:12 ratio represents a 14K anode to anode load. which is a bit high. There are also some 230V 200V 175V and 150V versions of this transformer (some shielded some not so be careful) but at ~$35 each, they seem worth a shot.
this is incorrect. The transformers referenced above are 100VA models which should do 80 watts at 50hz. In order to deliver 80 watts into say an 8R load you need to deliver 25V from the secondary which would require 2X the voltage drive on the primary which in the case of just about any power transformer out there would saturate it.
The output power has little to do with the core size or the VA rating but can simply be determined by taking the secondary voltage and taking that as the most voltage the device can deliver at the rated frequency. Hence a 6V secondary delivers 6V at 50/60hz It doesn't matter if it is a 10VA transformer or a 1000VA transformer since VA ratings have to do with losses and not flux density in the core.
wow that got out of hand.
dave
I'd like to challenge the idea that you cannot use mains transformers as SE output transformers. I have successfully used 240v/12v 50VA halogen downlight transformers as 5W SET output transformers. As the transformer is only passing 5W of audio, DC saturation of the core is not a problem. In addition, frequency response is more than adequate - worth trying for a cheep SET amp
Most mains transformers have very low primary inductance which will result in pathetic bass response when used with valves, even without DC magnetisation.
Power transformers and audio transformers are rated for power in a different way.
The 50W rating on a power transformer has noting to do with core saturation it has to do with what someone determines as acceptable losses (heating) at the desired operating current. Audio output transformers rate their power by the maximum AC signal at a given frequency it can handle before saturation.
since you were getting 5W, that means you needed just over half the rated secondary voltage into 8 ohms which means your AC was using 1/2 the flux of the core at line frequency. If you try to deliver 5W at 1/2 the line frequency you will be right at the edge of saturation.
As for the cores ability to handle DC, you need to be clear on the core type since C-cores are better suited to handle DC than Toroids. For EI's you have to look at how they are stacked but they typically fall somewhere in the middle.
(BTW I'm not challenging that you got sound or the quality of the sound.)
dave
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