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 Post subject: Output transformers in series?
PostPosted: Dec Fri 27, 2019 11:10 pm 
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I need an output transformer for push-pull 50C5 tubes.
In my boxes I found two Hammond 125A transformers, which are push-pull but rated for only 2 Watts. My plan then is to connect them in series making sure they are in phase, and using the common connection of the primaries for the primary center tap.
Does anyone think or know that this won't work?
I haven't found a reference to this being done but know it has been tried some time in the long history of tube audio.

With regards to the secondaries, I imagine they will also be connected in series. But what would be the consequence if each secondary drove a different speaker? Any thoughts on this appreciated, nothing built yet, still hunting for parts and doing the cerebral exercises. :lol:

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 Post subject: Re: Output transformers in series?
PostPosted: Dec Fri 27, 2019 11:25 pm 
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If the secondaries were driving separate speakers, then you would have two separate singled ended class AB stages with all the associated distortion such an arraignment would produce. Secondaries in parallel or series would effectively couple some of the energy from one transformer to the other, with a limited improvement in distortion. Best method would probably be to just parallel everything up. Primaries in parallel, secondaries in parallel.


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 Post subject: Re: Output transformers in series?
PostPosted: Dec Sat 28, 2019 2:10 am 
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I get that about the secondaries, bad idea to use two speakers.

My goal is to increase the power rating, and for that would need series connections, no?

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 Post subject: Re: Output transformers in series?
PostPosted: Dec Sat 28, 2019 3:48 am 
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No. Parallel still gets you twice the amount of iron and copper.


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 Post subject: Re: Output transformers in series?
PostPosted: Dec Sat 28, 2019 9:34 am 
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If you connect the primaries in series, the magnetic field from the DC plate current of one tube won't cancel the field from the DC current of the second tube. The result will be more or less saturation of the cores depending on the design of the transformers. The likely effect will be reduced bass response.

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 Post subject: Re: Output transformers in series?
PostPosted: Dec Sat 28, 2019 11:13 pm 
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OK, and thanks for the education. 8)

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 Post subject: Re: Output transformers in series?
PostPosted: Dec Sat 28, 2019 11:28 pm 
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Your best bet would be to connect them in parallel. That'll get you a doubling of power (need to double the secondary impedance taps too) but that's not without it's downsides as well. The big one is it'll cut the primary inductance in half, reducing the native bass response (which isn't stellar to begin with).


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 Post subject: Re: Output transformers in series?
PostPosted: Dec Sun 29, 2019 1:13 am 
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They are rated 3 watts. How much do you expect to get out of 50c5 in push pull anyway? 1 will be fine.


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 Post subject: Re: Output transformers in series?
PostPosted: Dec Sun 29, 2019 8:21 pm 
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n3uvt wrote:
They are rated 3 watts. How much do you expect to get out of 50c5 in push pull anyway? 1 will be fine.
You are correct, the box I found them in says 2 Watts, and they are tiny, but spec sheet says 3 Watts.
This makes sense too, as I was wondering what tubes these were designed for.
Push-pull 50C5s with a boosted B+, I think the output may be a little higher than 3, altho only at max volume.
I'll try a single but will monitor the temperature.

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 Post subject: Re: Output transformers in series?
PostPosted: Dec Mon 30, 2019 2:54 am 
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westcoastjohn wrote:
n3uvt wrote:
They are rated 3 watts. How much do you expect to get out of 50c5 in push pull anyway? 1 will be fine.
You are correct, the box I found them in says 2 Watts, and they are tiny, but spec sheet says 3 Watts.
This makes sense too, as I was wondering what tubes these were designed for.
Push-pull 50C5s with a boosted B+, I think the output may be a little higher than 3, altho only at max volume.
I'll try a single but will monitor the temperature.
Audio 'power' can be misleading and the average power level of music for a given volume is WAY lower than people think. Take a 100 Watt amp, for example. The average power at 'max volume' is only about 1 Watt. What takes the 'power', so to speak, are transient peaks. But transient peaks are, well, transient, which means they fall towards the high(er) frequency spectrum (and why they don't contribute much to the average power even though they take 100 Watt for the millisecond they're there).

Why does that matter? Because a transformer's power rating is what it can handle (before saturation) at the lowest frequency but they can handle more power as the frequency increases.

So your "3 watt" only has to handle to the bass and there's more than 3 Watt capability to handle the rest, which is where the transients are.

Btw, the audio transformer's power rating has nothing to do with heat. It's the max power it can handle before it begins to distort due to core saturation.

Having said that, I've never fully understood Hammonds spec sheets on the things. I mean, they give Henries and power for a 'universal' transformer with multple taps that should change the Henries and power depending on which are used, but they don't say what their rating is based on.


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 Post subject: Re: Output transformers in series?
PostPosted: Dec Mon 30, 2019 2:59 am 
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They also state the freq is 150hz for that transformer, so not much bass but i am assuming it's for a 50c5 table radio?


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 Post subject: Re: Output transformers in series?
PostPosted: Dec Mon 30, 2019 6:19 am 
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Flipperhome wrote:
Audio 'power' can be misleading and the average power level of music for a given volume is WAY lower than people think. Take a 100 Watt amp, for example. The average power at 'max volume' is only about 1 Watt.

I watt output is only about as loud as a garbage disposal or alarm clock. I watt is not my normal listening level, I have blown the 5 amp output fuses in my 200 watt amps a few times. :)

DM


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 Post subject: Re: Output transformers in series?
PostPosted: Dec Tue 31, 2019 2:54 am 
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devilsmist wrote:
Flipperhome wrote:
Audio 'power' can be misleading and the average power level of music for a given volume is WAY lower than people think. Take a 100 Watt amp, for example. The average power at 'max volume' is only about 1 Watt.

I watt output is only about as loud as a garbage disposal or alarm clock. I watt is not my normal listening level, I have blown the 5 amp output fuses in my 200 watt amps a few times. :)

DM
The actual 'loudness' would depend on the speaker(s), no?

n3uvt wrote:
They also state the freq is 150hz for that transformer, so not much bass but i am assuming it's for a 50c5 table radio?
Right, strictly a low-fi sound system. I'm building a left channel powered speaker to add to a mono system that uses an 8 inch speaker. No tweeters, no woofer, altho could add those.
I have two 8" speakers from a 1970's transistor guitar amp. They are very efficient at low power.

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Last edited by westcoastjohn on Dec Tue 31, 2019 5:16 am, edited 1 time in total.

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 Post subject: Re: Output transformers in series?
PostPosted: Dec Tue 31, 2019 5:14 am 
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devilsmist wrote:
Flipperhome wrote:
Audio 'power' can be misleading and the average power level of music for a given volume is WAY lower than people think. Take a 100 Watt amp, for example. The average power at 'max volume' is only about 1 Watt.

I watt output is only about as loud as a garbage disposal or alarm clock. I watt is not my normal listening level, I have blown the 5 amp output fuses in my 200 watt amps a few times. :)

DM

Then you have a very, VERY, loud garbage disposal and alarm clock.

This is one of the great myths of audio amplifiers that when you have them up 'loud' you are using the full wattage of the amp when, in fact, the average power out is quite low. The transient PEAKS are high, but the average power is low.

It get complicated because a myriad of factors come onto play (such as speaker SPL) but, as a rule of thumb, I was basing that on no clipping (clipping will make the amp 'sound' artificially 'loud' because the harmonics created are 'hurtful' to your ears and simulate 'loud') and the classic transient peak music spec of 20 dB. From there it's simple math. 20 dB is a 100 to 1 power ratio so If the amp is 100 Watt then the average power out is 1 Watt. Another interesting fact is that Increasing the amp to 200 Watt only increases the average loudness level by 3dB, which is barely noticeable.

It's rather obvious, when you think about it, why this happens. First, there's the 'attack' phase of any instrument's note, immediately followed by sustain and then decay. The attack is a 'peak' that is much higher than the sustain. Then there's the matter of having a myriad of frequencies (it's 'music', after all) which will, occasionally, reach their sine wave peaks all at the same time (and other times be at various other mixes). When they all sum they sum to a 'peak' needing that much power to handle them. The rest of the time, however, that power is not needed.

One of the complicating factors is that some 'rock' music is highly compressed (with a corresponding lack of dynamic range) so that it 'sounds' louder (which was the entire point of compressing it) so the transient peaks are as low as 10dB (it varies depending on the release) which means the average power level can be increased and since CD are relative to 0dB (usually -3 dB for practicality's sake) that means the song will 'sound' louder at the same volume level. 10 dB is, perception wise, about twice as 'loud' and corresponds to 10 Watt, which is still only 1/10th of 'max power'.

The peak vs average power is also why tube amps sound 'louder' than a SS amp of the same wattage. By their nature tubes clip 'softly', meaning one is able to drive them deeper into clipping than solid state before they 'sound' bad. Tube amps, in effect, naturally do a mild 'on the spot' peak compression, which allows then to be driven to a higher average power level.


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 Post subject: Re: Output transformers in series?
PostPosted: Dec Tue 31, 2019 5:23 am 
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This transformer will do just what you need.

https://www.tubesandmore.com/products/t ... output-8-w

I used one when I converted my Hallicrafters S-41W to push pull 35L6 and it sounds a lot like a console radio when an external speaker is connected.


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 Post subject: Re: Output transformers in series?
PostPosted: Feb Sat 01, 2020 1:34 am 
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Location: Powell River BC Canada
You could connect the transformers in series or parallel fed through a capacitor
driven by two output tubes in series (totem pole stack).

I once had to do something like that to re speaker a Philips .

The Philips had an 800 ohm speaker. and used EL86 tubes.

The only other thing I remember about that place I worked at,
is a customer gifted me a bottle of wine for some job.

Left it on my bench. Boss came in on weekend and drank it.

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