Audio transformer for small tube projects?

[snapper]

Hello everyone
Conrad has a small audio transformer that, according to reviews from various buyers,
it can be used as an audio transformer for small tube projects.
I'm just wondering how best to connect it to an EL84SE amplifier!?

https://www.conrad.com/en/p/elma-tt...-1-25-2-5-5-0-10-v-content-1-pc-s-516104.html

the photo on the conrad site gives you eye cancer

 

[6A3sUMMER]

Only 10V on the primary?
Not a [power] output transformer.

 

[stevenrotterdam]

For SE you need to cut the welds. But maybe it is made badly enough so you have not too much saturation

 

[jjasniew]

The transformer I think means Watts. I'd guess it's too small for "SE" application, plus I've read those types dont lend themselves very well to such. It's because of the quiescent current, which is balanced in a PP, but not SE.

 

[stevenrotterdam]

And the technical description of Conrad is BS.

 

[20to20]

I'm just wondering how best to connect it to an EL84SE amplifier!?

This transformer is for a 100v distribution system. It's not for use as an amp OPT. It goes with each speaker as a step down transformer and the power of the speaker.

 

[Tubelab_com]

The key words here are given on the website.

"100 V audio frequency transformer ....... This text is machine translated."

When some form of "machine translation" is used, AI breaks down to AS, Artificial Stupidity.

This is a typical line matching transformer for a 100 volt audio distribution line. They can be used in low powered PUSH PULL tube amps as OPT's. They are pretty useless in SE.

I am using a $6 "70 volt 10 Watt line matching transformer" for the OPT in a push pull guitar amp that makes 4 watts. It works good for that purpose. Experiments with more power or frequencies outside the 82 Hz to 5 KHz range of a typical electric guitar proved that it would not be suitable.

https://www.parts-express.com/70V-10W-Line-Matching-Transformer-300-040?quantity=1

The technical description looks like a poorly translated MSDS (Material Safety Data Sheet).

 

[ratbagp]

I used them in SE parafeed amps. There is more information in the following.

https://audioratbag.blogspot.com/2012/02/829b-lightbulb-amplifier.html

Actually, the most interesting part of the amp was using lightbulbs. They sound better than ordinary resistors.

ray

 

[b_force]

The 70V/100V line audio transformer work fine for small power output transformers, but only in push-pull configuration.

They have no air gap, so are not suitable for single ended operation, or maybe just a few mA at most.

I have the exact same ELA/Conrad transformer here and they aren't so bad actually.
I can look up some specs.

Instead of going for a single ended EL84, you could also go for PP EL91, EL95 or 6AK6

 

[stocktrader200]

Probably not good s SE transformer. As a p-p transformer 70v audio transformers work great above 50 hz. 100v line transformers may be better yet.

 

[ratbagp]

In a parafeed topology, you can also wire them as autoformers which I preferred. Being small, they are excellent for high frequencies and there were rumours that some of the Radio Shack versions had nickel laminations.

The disadvantage is that for a plate load you need a plate choke (which can be expensive) with the normal B+ or a resistor with double the B+. For experimental purposes, the resistor / double B+ is the cheaper option.

Bottlehead uses parafeed topology in their amplifiers.
https://bottlehead.com/

ray

 

[wg_ski]

I’m not too sure about that particular transformer. I read the spec sheet, and it lists the winding count. Looks like they tried to compensate for copper losses when setting up the ratios, and there is no configuration that is properly CENTER tapped. 25 turns off - which will be a problem with DC balance. You’re better off using a “cheaper” one that doesn’t change the turns ratio to compensate losses (it just lives with them).

 

[Fuling]

I’m not too sure about that particular transformer. I read the spec sheet, and it lists the winding count. Looks like they tried to compensate for copper losses when setting up the ratios, and there is no configuration that is properly CENTER tapped. 25 turns off - which will be a problem with DC balance. You’re better off using a “cheaper” one that doesn’t change the turns ratio to compensate losses (it just lives with them).

Sounds similar to a small 100V transformer (Monacor, IIRC) I bought a few years ago to use in a flea power guitar amp. Something like 800 turns on one half of the primary and 825 on the other. More suitable PP transformers can be had for just a little more money at Ask Jan First (Germany) and Piemme Transformatori (Italy).

 

[Paul Joppa]

In a parafeed topology, you can also wire them as autoformers which I preferred. Being small, they are excellent for high frequencies and there were rumours that some of the Radio Shack versions had nickel laminations.

The disadvantage is that for a plate load you need a plate choke (which can be expensive) with the normal B+ or a resistor with double the B+. For experimental purposes, the resistor / double B+ is the cheaper option.

Bottlehead uses parafeed topology in their amplifiers.
https://bottlehead.com/

ray

Hi Ray - it's been a few decades, but I remember the meeting I attended where we met - that was a great group!

My first design for Bottlehead (the original Paramour) used a 70-volt line transformer in parafeed. and a 10-henry filter choke. The design objective was a cheap 2A3 amp - I think those parts cost about $4 and $8 respectively at the time. Hammond made a custom power transformer for us, and you could get Chinese 2A3s for $11. It worked pretty well, for what it was. The same basic circuit is still in production, though the iron has gone through many iterations. We used the same transformers in the first stereo version of the Single Ended eXperimenter's amp, on a different tap.

These days, many of these transformers are smaller than the one in this thread and probably can't handle the bass. Hammond made an 8-watt unit that is a bit bigger and might perform better, though I haven't measured it.

 

[ratbagp]

Yes, it was a lot of fun. From memory, I got a lot of information from Bottlehead.

ray

 

[b_force]

Unless you already own a EL84 and a good choke, price wise and space wise SE parafeed doesn't make sense to compared to a simple PP.
To me personally.

 

[Michael C]

Its a no go. Not worth the candle.mr hashimoto would be apalld.

 

[wg_ski]

Sounds similar to a small 100V transformer (Monacor, IIRC) I bought a few years ago to use in a flea power guitar amp. Something like 800 turns on one half of the primary and 825 on the other. More suitable PP transformers can be had for just a little more money at Ask Jan First (Germany) and Piemme Transformatori (Italy).

It‘s not “just a little more money” - paying a premium for a line transformer then using it as an OPT just doesn’t make any sense. THE reason to use them is being able to get one for $6. A cheap Chinese one of course, and they are more likely to just have the round figures winding ratios which give less accuracy on the power taps in the real world. But at 5 (and under) watts, who cares? The $6.4 question is how did they do it on the one that PE is selling now? Last ones of these I got were from MCM, decades ago. And I was using them for what they are supposed to be used for, not this.

A $20 solution exists - it’s called a 50 VA Antek power toroid. They work VERY well. But if you really want/need to cheap out when you only need single digits push pull watts it’s nice to be able to get something “appropriate”.

 

[volkswagenvan]

Cheap Output Transformers https://www.ozvalveamps.org/optrans.htm
​

 

[Tubelab_com]

We used the same transformers in the first stereo version of the Single Ended eXperimenter's amp, on a different tap.

Twenty some years ago a friend brought me an SE amp kit to finish. It used a vertical output transformer from a TV set with a 6DN7 or 6EM7 tube. I believe it was called a SEX amp.

A $20 solution exists - it’s called a 50 VA Antek power toroid. They work VERY well. But if you really want/need to cheap out when you only need single digits push pull watts it’s nice to be able to get something “appropriate”.

Back in 2011 there was the Hundred Buck Amp Challenge which is now a sticky in the instruments and amps forum. The idea was to make the best possible guitar amp for less than $100 in total parts cost. This does require some creative transformer sourcing. I made two amps, one that just squeezed in at $99.something and it DID use a 50 VA Antek toroid for the OPT. The other amp was an absolute minimum cost amp that came in in the $45 range with a Triad N-68X for the power transformer and the Parts Express 300-040 for the OPT. The Triad was under $15 and the PE unit $4 at the time. After the challenge was over, I rebuilt the little amp adding a few low cost parts and still use it today.

During the rebuild I decided to see what the PE transformer could do, and I did manage to squeeze almost 10 watts through it by raising the B+ from 165 to 330 volts. Those little transformers were not meant to eat the voltage that they will see in a cranked guitar amp running on 330 volts into a speaker at resonance, so I went with the 4 watt setup.

Tomorrow, my wife will not be home. I recently built a new guitar speaker cabinet, and I just got a new guitar, so the little 4 watt amp will see some serious abuse. I might plug a bass into it....that will "test" the little PE transformer.