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Iron

Dswankey

Dswankey

Lunatic Member
I've noticed the term "Nice Iron", "look at that Iron" etc; with regards to pics of tube amp nudies here and in another forum.

So here is my tube noobie question, what are people referring to when they reference Iron? Just curious as I feel liking learning something new today.

TIA
 
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@Jaymanaa,

Thanks for clarafication and if I may ask another question are transformers in the "bigger the better" or the "more the merrier"conversation? again I'm a newbie to tube's so if this question is silly I apologize.
 
Generally the size of the transformer is indicative of its power handling capabilities, or of its bandwidth; both properties are directly proportional to the size of the transformer, normally.
 
Ok one more question, Is the transformer in the upper left of this picture?

attachment.php
 
Usually bigger the better. In tube amps you've got transformers (iron) in three different uses.... Power transformer (aka PT) - almost always 1 per amp, and commonly but not always the biggest on the chassis. Output transfomers (aka OPTs) - one per channel, and depending on the amp design it would be a Single-Ended OPT or a Push-Pull OPT - and there is a difference. Filter Chokes - sometimes none, sometimes several, they are used mainly in the power supply to filter, ie quite down, the DC voltage supply.

In your picture the PT is in the upper left. The OPTs (push-pull) are on the lower right. Those are good sized P-P OPTs :yes:
 
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Not always, like most things audio, there are compromises. As a rule of thumb, larger transformers are better for low frequencies and can sacrifice higher frequencies. Smaller transformers normally work very well into the higher frequencies (some out to 50-60 khz). For Hi-Fidelity we of course want the best of both worlds, so very smart people came up with winding techniques that could deliver both. Generally speaking for an example; a large output transformers may have some "bundled" groups of smaller windings to extend the high frequency abilities. Magical recipes abound, hidden in dark wet caves and guarded by fire breathing dragons.:D Actual most of the outputs that were worth a darn have already been unwound and reverse engineered for new production. Some are better than others at this type thing, but I like everything I've ever tried from Heyboer, and Triodes Dynaco remakes. Just very general, but I hope it helps.
 
Dswankey said:
Ok one more question, Is the transformer in the upper left of this picture?

attachment.php
Click to expand...

There are three transformers in the photo. The power transformer is the one at top left. The PT turns AC at line voltage into high voltage for the B+ that does the heavy lifting in a tube circuit, filament voltage that lights the tubes' filaments to boil electrons off the cathodes to let the tubes do their work, and also may include a 'bias supply' winding for a "fixed bias" circuit design.

The matched pair of transformers on the bottom center and right of the chassis are the output transformers. These OPTs match the high voltage on the plates of the output tubes (at high impedance) to a lower voltage, higher current output for the low impedance speaker "load" for each of the two stereo channels. The design, construction, and materials used in the OPTs is critical to their bandwidth, linearity, and distortion levels. Good iron ain't cheap! :-)

EDIT: In case you didn't know, the output tubes are the pairs of tubes to the left of each OPT - one pair of tubes per channel; one "pushes", and one "pulls", i.e., one tube in each pair is responsible for amplifying half of the music waveform for the pair's channel. The tube just below the PT in the photo is the amp's HV rectifier, which takes the high voltage from the PT's "B+" winding and rectifies it to pulsed DC. That pulsed DC is smoothed or "filtered" using either capacitors (sections of one or both of the grey cylinders top center in the amp) and/or a "choke" (a coil of wire, sort of like half of a transfomer) and "adjusted" with resistors to provide the final, very pure B+ DC. Sometimes the filaments are rectified to DC, too, to minimize "hum" in the amp, and a fixed bias amp will also have a rectifier and filter network for that, too.

EDIT: PS, a solid state amp will also have a power transfomer, and in older ss amps, it will look a lot like the PT in a tube amp. The purpose of the PT in a ss amp is ususally to lower the AC mains voltage for rectification and filtering as described above for the various circuits and functions in the ss amp. Transistors, (very) generally speaking, do their work at lower voltages than vacuum tubes.

You can see the PT in an early 1970s Kenwood KT-88 stereo receiver in the top right of the chassis in the photo below:

DSC_1654.jpg
 
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Dswankey -- "Iron" is a generic term that can refer to the power transformer (PT) which ultimately takes the AC line voltage and then transforms it into all the different voltages necessary to power the amplifier, or the output transformer (OPT), which couples the high voltage low current signal from the output tubes to the low voltage high current demands of the speaker. It is a bit of a misnomer, in that the transformer's lamination's are actually made out of steel. But still, the tradition to call it "iron" continues.

Regarding PTs, usually the bigger the better, implying that it will have ample capability to power the amplifier properly under all signal conditions, and that it will do so without getting excessively hot over long periods of operation.

For OPTs, an understanding of general transformer size versus the rated power of the unit is even more important, as it can give a strong indication of the amplifier's ability to deliver as much low frequency power, as it can in the mid range frequencies. Small economic units will have small OPTs for their power rating, indicating their ability to deliver very much of their power at low frequencies is very limited.

In the end, it is all relevant, as one set of transformers may be well capable and even overrated for one application, whereas they could be severely undersize for another.

Name brand also commands attention. Names like Peerless, Acrosound, and Chicago virtually guarantee a high quality transformer for the application at hand.

As you become familiar with various units of different manufacturers and power ratings, you will begin to calibrate yourself to what looks like a great set of transformers for a given amplifier, and what is equipped with "get by" iron.

I hope this helps!

Dave

Wow, I see that mhardy and others already handled this question superbly!
 
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To everyone who posted and shared their knowledge I thank you very much!!!!, I learned a lot today and I do appreciate it. As I said it's at the shop and I'll be getting her back soon. I'll chime in when she's home and hooked up to a pair of speakers. I'm looking forward to it.
 
Is it Radio Shack or Lafayette, or other? Looks mid-1960s Japanese. The big iron makes me think of a Lafayette LR-224 or similar; the R/S amps tended to have rather meagre output iron.

LRELA-224A1966.jpg
 
As mentioned it's the output transforms that really make a tube amp, so you want the best you can afford.

Looks like you have good hefty iron there for EL84/6BQ5 tubes.

Newer designs include C-cores and doubles C- cores (they can be half the wt. of a comparable EI core like in the above pic's) They are said to have sonic advantages too. Popular in Europe.

There are also the Toroids (look like donuts with exposed Cu. wire). A rather rare type is the R core more popular in Asia etc. Again sonic improvements are claimed.

Enjoy your new amp when you get it and I'll mention it in case you don't know it , don't run it without a load (speakers or big 16 ohm 25W + resistors) or you risk the output transformers. Also if the sound changes or lowers in volume investigate further as you again risk the transformers.

Best of luck with it!

Randy
 
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FWIW, Lafayette was my initial thought as well. 224 (or a rebranded 224) I think is right on.

Good post in this thread. I wonder if it's the heat or that there's just been a bit of a lull on AK lately and people are hungry to correspond. :scratch2:
 
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That little add on RCA deal with what looks like speaker is the dead give away as to what it is. Looks like it was a bad home mod, but was factory. I had one on my bench not long ago, but I'll be damned if I can remember what it was.
 
Another mention for the less conventional designs, but there are such things as tranformerless amps, both power and output. Not having a power transformer is dangerous because it provides no isolation from the power line. Often one side of the line cord is tied to the chassis. You find this in cheaper radios and console stereos and stuff thats more or less not worth owning.

Not having output transformers is simply unusual. No real danger there, but sometimes it ends up using strange high impedance speakers or a lot of tubes wired in a certain manner to get the impedance down low. Running into these is unlikely, but Phillips Norelco had some radios in the late 50s that used this design, along with an 800 ohm speaker to make it work.
 
mhardy6647 said:
Is it Radio Shack or Lafayette, or other? Looks mid-1960s Japanese. The big iron makes me think of a Lafayette LR-224 or similar; the R/S amps tended to have rather meagre output iron.

LRELA-224A1966.jpg
Click to expand...

It's the Lafayette LA-224A (Japan), you actually hooked me up with the image posted above via email awhile back, thanks again by the way for doing that.
 
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