Anyone care to discuss output transformers for a bit... ?

[timbertoes]

Hello... 
Curiosity killing this cat..
preface to this is:   I have not seen the wide variety of factory tube amps that many of you have.

This is about  2 OT's.  One is the 15W OT found in a Fender blues Junior. The other is Dan's Hoffmans OT for the 18W Marshall clones. The HT-6135.

What is striking to me, is that for uhm...about 20% ? power difference, the 18watter seems more than 20% increase iron, more winding window. (could be an illusion of sorts, lol)

I wonder if perhaps it is because it is multi tap down to 4ohms capable.
Or has anyone found it to be underated at 18watts? 

or is the blues junior 15watt rating a bit of spec-stretching on the part of Fender ?  lol.

[HotBluePlates]

... This is about  2 OT's.  ... The other is Dan's OT for the 18W Marshall clones. The HT-6135. ...

Got a link to compare?  I must not be on a first-name basis with Dan...

In the interim...  Transformer core size is about How Much Power, How Low (Hz), and How Low % Distortion?

So a bigger core is more power, lower, at less (OT) distortion.

[timbertoes]

Lol, I'm not on a first name basis either!

Darn, now that I put the fender back together, I wish I had taken physical measurement of the OT.
yes it's all about how much iron, and wire size thrown in. 
My first impression was I ought be able make and amp with more output power from
The heyboer 18w OT. Hehe.
Could it be the difference in steel...one has higher permability /gauss than the other.
I had always made some assumptions that "iron"
Transformers for these applications were all very similar.

[drgonzonm]

I am guessing that  Dan is Daniel Claytor, some one who posts for one of the transformer manufacturers (Mercury?). 
I looked at Hammond's website for their recommendations on replacement transformers.  1760F for the blues junior, a guitar OT, while 1750PA for the Marshall Clone, a possible bass OT.  (I compared the multitap 4-8-16, so its apples to apples.)

The 1750PA is definitely a larger transformer. 
There are differences in reflected resistance, with 8.5K for the 1750 and about 7K for the 1760. 

Had difficulty finding info on the Heyboer 18w OT. 

Which power tubes are you planning to use? 

[SnickSound]

Hello... 
Curiosity killing this cat..
preface to this is:   I have not seen the wide variety of factory tube amps that many of you have.

This is about  2 OT's.  One is the 15W OT found in a Fender blues Junior. The other is Dan's OT for the 18W Marshall clones. The HT-6135.

What is striking to me, is that for uhm...about 20% ? power difference, the 18watter seems more than 20% increase iron, more winding window. (could be an illusion of sorts, lol)

I wonder if perhaps it is because it is multi tap down to 4ohms capable.
Or has anyone found it to be underated at 18watts? 

or is the blues junior 15watt rating a bit of spec-stretching on the part of Fender ?  lol.

IIRC, the original Marshall 18W used a Hi-Fi output transformer (even has UL taps, they're just not used), it's rated for a wider frequency response.

For example, the Hammond 18W:
https://www.hammfg.com/files/parts/pdf/1750PA.pdf

VS the Hammond Blues Junior 15W:
https://www.hammfg.com/files/parts/pdf/1760F.pdf

The 18W is rated down to 30Hz instead of 75Hz on the BJr.
The 18W has a 31.83H inductance rating, compared to 27.28H on the BJr.
Interestingly, the 18W has a significantly higher DC Resistance (and according to those specs, it's imbalanced too, odd)

If you were to put a 18W Marshall OT in a BJr, you could in theory get more low end (and probably presence too) out of it, but since the primary impedance isn't the same it's not such a simple equation.
On the other hand, the BJr's OT would likely saturate at a lower volume which is one element of the whole tone equation.

[timbertoes]

good info, thanks !  I did wonder about the potential for the OT to start a bit of Saturation at full output.  The size differences just so jumped out.  I edited the Dan...it should have been Doug...lol.  Hoffman works best though :)

[drgonzonm]

I do not feel comfortable comparing Inductance between the two hammond transformers.  the biggest reason is the delta t, one transformer uses 70Hz while the other 30Hz.  formula from wiki:  v(t) = L di(dt)/dt.  I know that L the inductance should relatively constant, but my calculus, is very rusty. 

Then I do not feel so comfortable comparing impedances  with such different voltages at the center tap of the OT. 

Question for the gurus:  Is the primary impedance and therefore the secondary impedances  (Z), determined at the reference 1kHz frequency? 

[SnickSound]

I do not feel comfortable comparing Inductance between the two hammond transformers.  the biggest reason is the delta t, one transformer uses 70Hz while the other 30Hz.  formula from wiki:  v(t) = L di(dt)/dt.  I know that L the inductance should relatively constant, but my calculus, is very rusty. 

Then I do not feel so comfortable comparing impedances  with such different voltages at the center tap of the OT. 

Question for the gurus:  Is the primary impedance and therefore the secondary impedances  (Z), determined at the reference 1kHz frequency?

From the datasheets above, the quoted inductance figures appear to be rated at their respective lowest rated frequency (70Hz vs 30Hz)

Also of note, the rated frequency response is within 1dB of the reference. Meaning the smaller BJr OT doesn't necessarily fall off below 70Hz, but it drops by more than 1dB compared to the reference.

[timbertoes]

Hammond and others may use anything from really nice equipment to an ancient Gen-Rad bridge to measure the Inductance :)
FWIW, One place I visited used a DC coupled Crown HIFi amp to test transformers!

[HotBluePlates]

I do not feel comfortable comparing Inductance between the two hammond transformers.  the biggest reason is the delta t, one transformer uses 70Hz while the other 30Hz.  formula from wiki:  v(t) = L di(dt)/dt.  ...

Red Herring.  Forget all that mess.

For example, the Hammond 18W:
https://www.hammfg.com/files/parts/pdf/1750PA.pdf

VS the Hammond Blues Junior 15W:
https://www.hammfg.com/files/parts/pdf/1760F.pdf

Compare the dimensions of the cores for those 2 transformers.  Which one is bigger?

Now look at each transformer's rated power, and lowest rated frequency (for full output power).  Which transformer goes lower, at higher power throughput?

[HotBluePlates]

Question for the gurus:  Is the primary impedance and therefore the secondary impedances  (Z), determined at the reference 1kHz frequency?

Doesn't matter; any frequency within the pass-band.  That's because it is dependent on turns ratio, not inductance.

We've said the same thing for years, but it hasn't clicked yet.

From the datasheets above, the quoted inductance figures appear to be rated at their respective lowest rated frequency (70Hz vs 30Hz)

Doesn't matter.

Inductance can be measured with any frequency, because a frequency is applied and the resulting reactance (X_L, in Ohms) is measured.  It's then either a math function in a digital meter, or an issue of calibration in an analog dial, as to how the measured Inductance is indicated.

Inductive Reactance:
X_L = 2*π*f*L
f = Frequency in Hz
L = Inductance in Henries

If one meter uses a test frequency of 100Hz, but another uses a test frequency of 10kHz, the difference is the expected reactance in the test circuit.  A 10H inductance looks like 6283Ω of inductive reactance in the 100Hz tester, but 628.8kΩ of inductive reactance in the 10kHz tester.

A simple test circuit places an inductance in series with a rheostat, applies a.c. at a known frequency across the series circuit, and adjusts the rheostat resistance until equal a.c. voltages are measured across the rheostat & the inductance.  Inductive Reactance is then equal to the rheostat resistance.  Inductance is the calculated from  L = 2*π*f*X_L, since X_L and the test frequency are known quantities.

If there are any standard test frequencies (for an expected range of reactances), it's to allow easy comparison to a convenient standard (often a resistance) during measurement.

For transformer design, the transformer's primary inductance must support the lowest frequency to be used.  But that inductance doesn't tell you whether you have a 1w transformer or a 100w transformer.  Power at that low frequency is about how much flux the core can support, and more power requires more core material.

[drgonzonm]

HBP,

Your KIS method is more appropriate for this discussion than applying the equations for practical transformers found in chapter 5 of RDH-4.

after all,  we don't have rudimentary data on transformers found in the initial postings of this thread. 

Someone (namely me), confused the issue by referencing an upgraded transformer the blues junior and a replacement transformer for 18w Marshall. 

At the best, any calculations are qualitative at the best, and the ideal transformer equations provide sufficient information for discussion.

Bottom line, The 18w transformer is probably not underrated.  as wire size in the transformer is likely the limiting factor on power. 

After reviewing chapter 5 in RDH-4, the stated 1kHz is important in reporting the voltage ratios. 

[HotBluePlates]

What is striking to me, is that for uhm...about 20% ? power difference, the 18watter seems more than 20% increase iron ... Or has anyone found it to be underated at 18watts?  or is the blues junior 15watt rating a bit of spec-stretching on the part of Fender ?  lol.

Mark Baier (of Victoria Amps) pointed out some time ago that Fender solved an issue with under-power-capable speakers in their tweed amps by using smaller-cored OT's.

Bass requires the most power & most speaker cone excursion.  It also requires big OT cores to pass all the power of the bass notes to the speaker.  And an OT rated to pass full power down to 20Hz has a much bigger, heavier core than an OT rated for the same power but only down to 100Hz.

But what happens if you attempt to push full (mid-band) rated power through that 100Hz OT, but down at 20 or 40Hz?  The OT core isn't big enough to sustain all the flux necessary, and it saturates rather than pass all the power applied to the primary.  Compared to the signal on the primary, the secondary's output to the speaker is compressed and actually has higher harmonics not unlike tube distortion.

Now think about Marshall amp evolution...  Marshall amps were right there with Rock all the way.  And as the style of the day moved to heavier distortion, Marshall preamp trimmed more bass.  Distorted bass fundamentals generate midrange harmonics that beat against the midrange fundamental notes being played.  Rolling off the bottom octave of the guitar clears up the distorted sound, but your ear doesn't miss the fundamentals much because the harmonics of the note are still there.

This is also the basis of a Treble Booster pedal (though that also assumes a distorted amp is being pushed by the Treble Booster to prevent the sound from being harsh).  See a demonstration at ~8:54 of the video below.

Other than the tweed Twin and Bassman (actually intended for bass players when produced), original Fender OT's up to the early 60's look mighty puny.

In the blackface amps, Fender had the Concert, Bassman, Bandmaster, Vibrolux, Tremolux, Pro and Super, all with 2x6L6 output stages.  What is the difference between them (other than speakers)?  The OT's are different sizes...  IIRC, the Bassman and Super Reverb had the biggest OT's, while the Bandmaster, Tremolux, Vibrolux and Pro Reverb all shared the same smaller OT.  I know my Pro Reverb isn't as loud at the same setting as the Super Reverb I used to own, and that is probably because the   OT core is smaller than the Super Reverb's OT.  It's not all the speakers (though that plays a role as well).

KISS, because it's not all Guru Smoke...

https://www.youtube.com/watch?v=Wzs2g1nz4JQ?t=8m54s

[timbertoes]

Thank you, that is a very educational reply !

[PRR]

> Marshall preamp trimmed more bass.  ... Rolling off the bottom octave of the guitar clears up the distorted sound, but your ear doesn't miss the fundamentals much...

Also bass players were beginning to get enough Watts and Inches to fill the two bottom octaves, making "full" reproduction of guitar bottom unnecessary.

1965: John Entwistle (The Who), JTM45 and two 4x12" cabinets; within a year the amps and cabinets doubled in size/power, quickly followed by Marshall Major, Sound City, and Sunn bass power. This peaked in the early 1970s when the Dead had 26,000+ Watts power and three semitrailers of speaker, maybe 1/3rd of all that for bass.

[drgonzonm]

KIS used rather than KISS, in many realms the last S many times means stu....

Couple of thoughts,
1.  the ampeg 8x10 is a distorted bass amp, not a true bass amp, check out the specs
2.  Leo used 4x10's on the 5_6 series because the 15" speakers would not handle the low end very well
3.  Bass amps are designed for a greater frequency response than guitar amps, (Zimmerman). 
4.  You need more watts on the low end to equal the loudness toward the middle. 
5.  Guitars filtered at 100Hz sound tinny.  (A few mixing board have 100Hz filters to reduce popping on microphones, and this is first place to look if the guitar sounds tinny. 

[HotBluePlates]

...
5.  Guitars filtered at 100Hz sound tinny.  (A few mixing board have 100Hz filters to reduce popping on microphones, and this is first place to look if the guitar sounds tinny.

Everything changes when moving from "guitar playing alone" to "guitar in a mix".  What sounds lush alone usually sounds muddy and obscures other instruments in a mix.

A guitar might sound tinny when everything below 1kilo-Hz is cut, but that is exactly what gets do to most rhythm acoustic guitars in a multi-piece band.  There, the acoustic is expected to fill a similar space as the drummer's hi-hat, convey rhythm, but not cloud the meat of the sound provided by the bass, kick drum, electric guitar/keyboard, and singer's voice.

Most electric guitars within a band track will have much of 250Hz and below stripped out, at least compared to what the player might like sitting & playing solo.  This equates to the lower notes of the bottom 3 strings of the guitar, where most guitars have enough to too-much energy.

A good producer will direct the guitarist on which sound/pickup/EQ (from the amp) they want to hear when everyone plays as a group laying basic tracks.  But most of the time, the rules for recording guitars are

• Make it Louder
• Make it Brighter
• Make it Louder & Brighter

The above works best when you start with an instrument/amp that already has all the meat and all the harmonics you could ever want, and you're just shaping what makes it through to the final sound.  Like a block of marble being sculpted, you can cut away unneeded bits, but it doesn't work nearly as well to add a missing piece to a instrument's sound.

[You'll need good headphones to listen to the Youtube video; computer speakers won't reproduce the bass in the discussed track.]



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