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Amp Builders, An OT Transformer Question - Tweed Vs Blackface

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1,871
I'm thinking about replacing an OT so and was looking at the order page on a couple of transformer sites the other day. As I read through the descriptions they are typically identified as replacements for a given amp or circuit. Alongside those are the special order winds and components offered as custom orders, let's ignore those for the moment. My question, what characteristically differs between "types" of OT? Specifically, what would you get from putting an OT identified as a blackface replacement into a tweed or vice versa. I understand that each is designed around the parameters and spec for their given circuits, but assuming that the voltages, draws, recoveries, etc. were both within an acceptable plus/minus range, what would be the difference between a tweed transformer and a blackface one? In many cases all I can see is difference in the secondary, e.g. that a tweed wants a 4 ohm speaker load and not a 4, 8, or 16 option. Are there other, basic, differences not listed in the spec; type of wire, number of or way of winding - something you amp builders already know that I can't tell from the description? In my particular case, the correvt replacement is a Mgnetic Compoenets 40-18001. If I wanted to get to get a more tweedy tone, could I do that with a different OT, or is it just a minor part of the equation?
 
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jay42

Member
Messages
7,084
The interleaving will be different. If the house is truly matching wind styles, that will make them sound a bit off in the 'wrong' application. If you want to take a 2 or 4 ohm OT and add more taps, there has to be more wire, which may alter some of the geometry. For example, the worst case would be asking for 2, 4, 8, 16 taps on a Super Reverb or tweed Bassman OT. A 2, 4, 8 or 4, 8, 16 'universal' OT in a Fender column, is more likely to be a blackface part the size of a Super Reverb or Bassman.

A couple of the tweed OTs aren't interleaved at all. I believe (don't shoot me) that original BF and SF parts are not absolutely identical.

I think you're better off taking group-grope or personal advice from someone you see eye to eye with, and not spending an inordinate amount of time on your choices. For Blackface, you can't go wrong with a resller like Dave Allen, if he has what you want. MM pricing is a hurdle, unless you know a builder with the bulk discount rate. As a winder, MM has oodles of versions. I can't help with tweed, except that Mojo generally sells Heyboer and they're perfectly good for anything. Going direct to Heyboer isn't impossible, but you have to know what you want and they prefer bulk buyers...who wouldn't?
 
Messages
1,871
Thanks Jay. That's what got me thinking. I realize of course, that different designs are going to call for different sized components and number of winds. The real "tell" though seems to be in the secondary, where you 4,8, and 16 ohm speaker taps will require a greater number of winds and as you said, different interleaving; which would essentially preclude a tweed tranny from supporting the same topology as a blackface one, right?
Thanks again, Jay, that's exactly what I wanted to know.
 
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Keyser Soze

Member
Messages
1,472
I think you are reading too much into this, or assuming that the manufacturers are putting a lot more into their products than necessary.

A transformer is, at a basic level, nothing more than a step device. It matches the load resistance of the tube(s) to the load of the speaker(s). But also allows for a wide degree of tolerance (it has to - because the true load of the speaker is frequency dependent, and this often varies substantially from speaker to speaker.)

So, as long as you 'get the numbers' within the ballpark it will function reliably and safely. Exactly how it will sound is a matter for much subjective interpretation. At that point OT swapping becomes much like speaker swapping - you won't really know until you try.

When I hear 'tweed' I tend to think lower power handling (wattage) and therefore less bass and more mid-mojo than a 'blackface', but that is a gross generalization, and may not prove out in the end.
 

Prattacaster

Member
Messages
1,369
When I hear 'tweed' I tend to think lower power handling (wattage)
I'd expect that also. The tweed OT might be spec'd for slightly lower current than the Blackface OT. The tweed deluxe was a 12w amp and the Blackface was 22w. The plate voltages were higher in the Blackface by about 50-60vdc.

I think this^^ is the difference you need to consider. If u use a Blackface PT you better use a Blackface OT. However if you use a Tweed PT then you could use either a Blackface OT or a Tweed OT safely.

I think the Blackface OT would offer a cleaner, more modern sound whereas the tweed OT would give you a vintage vibe, (a little looser bass, no ice picky highs).

But I am making many assumptions here as to how they are spec'ing their OT's. I could very easily be wrong about the tonal implications.
 

SatelliteAmps

Member
Messages
6,170
I think you are reading too much into this, or assuming that the manufacturers are putting a lot more into their products than necessary.

A transformer is, at a basic level, nothing more than a step device. It matches the load resistance of the tube(s) to the load of the speaker(s). But also allows for a wide degree of tolerance (it has to - because the true load of the speaker is frequency dependent, and this often varies substantially from speaker to speaker.)

So, as long as you 'get the numbers' within the ballpark it will function reliably and safely. Exactly how it will sound is a matter for much subjective interpretation. At that point OT swapping becomes much like speaker swapping - you won't really know until you try.

When I hear 'tweed' I tend to think lower power handling (wattage) and therefore less bass and more mid-mojo than a 'blackface', but that is a gross generalization, and may not prove out in the end.


An output transformer is actually quite a difficult device to get right. It's not just a matter of getting the number in the ballpark. At it's most basic explanation, yes, it is how you described it, but if you are talking about getting a specific tone out of something it is very different. Interleaving, wire size, air gap (if it has one), impedance, resistance, etc. all make a huge difference in the final product. Manufacturers have to put a lot of work into getting something right. A lot more than most people give them credit for.

Most companies have off the shelf transformers that will work in specific situations, but very few are true clones of an original (even when they might say that they are). If a company is saying there is a replacement, that just means that the numbers are close in it's most general sense.

For instance, if you were talking about upgrading a Princeton output transformer, you would find that every maker that is after the guitar amp market has a replacement for a tweed (single ended) and a blackface (push pull). Each has a single secondary or a multiple secondary option. If you actually measure each makers transformer, they all measure different, and for at least the tweed version, no one makes an actual clone of an original.

As for the one the OP is looking at, the 40-18001 from Magnetic Components, that is a general purpose replacement transformer. In basic terms, that means they already had an output transformer that was close to what the end result was wanted on a Super Reverb type output transformer. That means it had about the right resistance, and the right wattage, but that is it. It wasn't sonically designed to be an upgrade, or even a replacement to a Super OT. It is something that will function. In some cases these types of transformers can sound as good, or sometimes better than originals. Sometimes they don't.

As for the differences, the ones that Magnetic is referencing are not the same spec's even to each other (they reference 022871 (Bassman) and 022855 (Concert)). The 022871 is a 40 watt transformer with a 4Ω secondary. The 022855 is a 50 watt transformer with a 2Ω secondary. Both have a 4K primary. This is where general numbers don't work, and what is being grossly misleading. A 4K primary into a 2Ω secondary means a ratio of roughly 44:1. A 4K primary into a 4Ω secondary means a ratio of 31:1. This is the ratio between the primary and secondary wires. This is a HUGE difference between how the two will sound.


The Magnetic Components is a 60 watt transformer with a 4, 8, and 16Ω secondary (on the 16Ω tap your ratio is 16:1, on the 4Ω it is 33:1). Now, if you needed to replace a Concert's output transformer, and you got this generic replacement, you wouldn't even be able to get the correct impedance match to make it work (no 2Ω output), but the company says it is a replacement/upgrade for the amp.

If you truly want to upgrade your amp's transformer, make sure the upgrade will work properly. Call the company (or email) to find out if the transformer is truly meant for the amp you are putting it in, or if it is just a general replacement. If it is a clone, ask them specifically what transformer they used as a clone.

Will most 50 watt style output transformers work in Bassman? Yes. They will function. Will they sound like a tweed Bassman? Most likely no. Blackface Bassman? Depends on which Bassman we are talking about, but most likely no.
 

Jerry Glass

Member
Messages
870
Are there other, basic, differences not listed in the spec; type of wire, number of or way of winding - something you amp builders already know that I can't tell from the description?
Most transformer manufacturers use wire with a polyurethane single build insulation across the board. One thing that is not in the spec for any transformer is the magnetic steel grade...and this can vary quite a bit from design to design. A less efficient coupling will result in bandwidth compression as output levels increase while a low loss core may remain full frequiency.

If I wanted to get to get a more tweedy tone, could I do that with a different OT, or is it just a minor part of the equation?
Personally, I think the OT would be the last thing I'd turn to if I wanted a more tweed like response; the power supply is where I'd start.
 

HipKitty

Gold Supporting Member
Messages
2,674
An output transformer is actually quite a difficult device to get right. It's not just a matter of getting the number in the ballpark. At it's most basic explanation, yes, it is how you described it, but if you are talking about getting a specific tone out of something it is very different. Interleaving, wire size, air gap (if it has one), impedance, resistance, etc. all make a huge difference in the final product. Manufacturers have to put a lot of work into getting something right. A lot more than most people give them credit for.

Most companies have off the shelf transformers that will work in specific situations, but very few are true clones of an original (even when they might say that they are). If a company is saying there is a replacement, that just means that the numbers are close in it's most general sense.

For instance, if you were talking about upgrading a Princeton output transformer, you would find that every maker that is after the guitar amp market has a replacement for a tweed (single ended) and a blackface (push pull). Each has a single secondary or a multiple secondary option. If you actually measure each makers transformer, they all measure different, and for at least the tweed version, no one makes an actual clone of an original.

As for the one the OP is looking at, the 40-18001 from Magnetic Components, that is a general purpose replacement transformer. In basic terms, that means they already had an output transformer that was close to what the end result was wanted on a Super Reverb type output transformer. That means it had about the right resistance, and the right wattage, but that is it. It wasn't sonically designed to be an upgrade, or even a replacement to a Super OT. It is something that will function. In some cases these types of transformers can sound as good, or sometimes better than originals. Sometimes they don't.

As for the differences, the ones that Magnetic is referencing are not the same spec's even to each other (they reference 022871 (Bassman) and 022855 (Concert)). The 022871 is a 40 watt transformer with a 4Ω secondary. The 022855 is a 50 watt transformer with a 2Ω secondary. Both have a 4K primary. This is where general numbers don't work, and what is being grossly misleading. A 4K primary into a 2Ω secondary means a ratio of roughly 44:1. A 4K primary into a 4Ω secondary means a ratio of 31:1. This is the ratio between the primary and secondary wires. This is a HUGE difference between how the two will sound.


The Magnetic Components is a 60 watt transformer with a 4, 8, and 16Ω secondary (on the 16Ω tap your ratio is 16:1, on the 4Ω it is 33:1). Now, if you needed to replace a Concert's output transformer, and you got this generic replacement, you wouldn't even be able to get the correct impedance match to make it work (no 2Ω output), but the company says it is a replacement/upgrade for the amp.

If you truly want to upgrade your amp's transformer, make sure the upgrade will work properly. Call the company (or email) to find out if the transformer is truly meant for the amp you are putting it in, or if it is just a general replacement. If it is a clone, ask them specifically what transformer they used as a clone.

Will most 50 watt style output transformers work in Bassman? Yes. They will function. Will they sound like a tweed Bassman? Most likely no. Blackface Bassman? Depends on which Bassman we are talking about, but most likely no.

Well said Adam!

I could only add that product marketing from the after market transformer companies certainly hasn't made (true) understanding of transformer make-up, design and application clear by any means.
 

Che_Guitarra

Member
Messages
4,165
I want to revive this thread.

I've got a much loved DIY brownface Princeton and I want to benefit it with a 20W 'deluxe' OT upgrade. I'm not expecting a drastic change, rather an incremental improvement in sought areas. Anyway, this upgrade is well discussed and I don't wish to rekindle an argument about it here.


What I want to know is this - my brownface circuit falls between the tweed and blackface eras so i'm wondering which direction (or which OT variant) I should opt for when I switch out? I had been looking at an Allen/Heyboer T020, but it only has a 8Ω tap - I want at least 4/8Ω compatibility.

I currently use a Classictone 40-18045 (8.5K Z primary) OT. I'd like to stick with Classictone, thus my options are their tweed deluxe 20-18022 (8.0K Z) or the deluxe reverb 40-18002 (6.8K Z) OT. The Allen T020 has a 6.6K impedence.


Which style OT do you think would best suit a brownface Princeton?
 






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