• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

120mA traffo sufficient for 2A3?

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#21
I was highly skeptical of the Hammond "document" because it did not jibe with my own experience as a specifier/user and former seller of power transformers. I'm glad PRR asked question and confirmed my misgivings.

I do like their chokes and small filament transformers in some applications, but generally go elsewhere for plate power and output transformers. (Heyboer, Edcor, Monolith Magnetics, Antek)
 
#22
My take on what the Hammond guy said would be that he was being sarcastic. I would seriously doubt that someone that has been building and selling transformers for as long they have would have something like that up on their site that they just found on the Internet and put their name on it. And then further post that their transformers are conservatively designed and can be run full wave bridge or full wave C.T.

Do they like having their transformers fail?
 
#23
DF96 said:
I think Hammond admitted (to PRR?) ....
Click to expand...

Sadly, the email had the usual corporate NDA footer. While probably not intentional, I have my own uses for NDAs and don't like to break them without strong reason.

You may write to Hammond and get an answer of your own.

The dubiousness of that chart should be obvious to anybody who knows power and looks at every entry. If not, then nevermind.
 
#24
NDAs should only be used for genuine trade secrets, and only with the prior agreement of the recipient. Simply adding an NDA paragraph to the end of every email would be silly, but corporate lawyers can be silly. On the other hand, it is generally regarded as good manners not to publish the content of a private email unless there is an overwhelming public interest reason.

As the page concerned is publicly available on their website, and people quote it as authoritative, I think it is legitimate to alert others to the fact that Hammond admit to not being the authors and have not checked it for accuracy. It would have been better if they simply linked to it with a disclaimer; this would also avoid any possible copyright infringement.
 
#25
LJT said:
Question is simple:
Will a transformer rated for 250v 120mA be sufficient for powering a stereo SET 2A3 set amp. <snip>
Click to expand...
for your amp take Hammond 302AX if you use tube rectifier.
its perfect and no need anything more.
if you want good amplifier main power transformer its first thing
here everybody throw up on Hammond but i thankyou thems,
no Hammond no diy or very little diy
i get good transformers a good price in 48 Heures
 
#26
Getting hold of a different mains transformer is my conclution as well. Although I was planning to use solid state rectifier, I will have a good look at the 302AX.

I feal that what has been under debate in this thread is more related to the document linked on their web-page, rather than the quality of their products.

It is a pitty that the contents of the paper apparently had insufficient quality check before publishing. A summary of use like that would be really nice (as long as the contents can be trusted). The mistake is worsened by the fact that it is published it with their own company logo on the document footer.
 
#27
Nothing wrong with Hammond's guide as a way to select one of their transformers, though it's only a starting point. Many other variables, too much for a single page. Simulate your circuit or live with the compromises of an "almost right" transformer. In a commercial product, it might take several custom prototypes to get the best mix of cost, weight, and performance and hobbyists don't have that luxury.

I have found many military and industrial transformers that can handle much more than the rated current marked on the housing - they were designed for a lower temperature rise than commercial parts (or just designed to fit a space that was larger than necessary). High volume parts will not have any more copper or iron or temperature margin than necessary.
 
#28
I built a pair of 6550 monoblocks with one Hammond 278CX in each.

You'd think that at roughly 2x what I needed per amp that the 278CX would be happy, but each amp hums loudly. The 278CX seems to be quiet until you ask for more than 100mA of HV current from it. This is with a 3.5A load on the 6A heater winding.

I should make a video...
 
#30
The problem starts with the fact that the core of Hammond 278CX is hardly (apparently not) capable of delivering over 450 watt secondary power (the slightly larger European standard EI120 is good for 466 watt secondary power with the best quality iron (M6 - 0.35 mm).
For EI120 in the thickest version the core excitation is some 1.7 T with 466 watt secondary power capability; this is about the limit before risk of core saturation.
So, when (but I doubt it) the Hammond has 0.35 mm M6 iron, the core excitation is most likely the main cause of hum. Pulling less secondary power does not help as the problem is already at the primary side.
 
#33
audiowize said:
I built a pair of 6550 monoblocks with one Hammond 278CX in each.

You'd think that at roughly 2x what I needed per amp that the 278CX would be happy, but each amp hums loudly. The 278CX seems to be quiet until you ask for more than 100mA of HV current from it. This is with a 3.5A load on the 6A heater winding.

I should make a video...
Click to expand...

I can confirm that other 278 series transformers can also be noisy. (X) I used some in a project some years back and they buzzed like angry bees at more than 30% of rated current. Part of the solution was to put them on sandwich mounts which greatly reduced the coupling to the chassis.

Some 278X/CX are silent, but there seems to have been variable QC in the past. I no longer use these in anything.

The 378CX series is an entirely different animal and virtually silent in reasonable application.

Heyboer will build entirely custom transformers to your specifications for not a whole lot more money in most cases if more than one piece is involved and they are completely silent IMVLE.
 
#35
No. It's even a bit smaller than EI120.
EI150 is much larger; that one (largest version), with high quality steel, can deliver over 900 watt secondary power.
Actually, a 900 watt EI150 core would be an excellent choice for a 450 watt transformer like these Hammonds.
With this substantial core a transformer can be made with low (sub 1T) core excitation, and all other parameters can be optimized.
This way any discussion on differences between sound quality of EI, toroidal and c-core power supply transformers is completely meaningless!
(This last remark refers to Power transformer (advise needed))
It's all about choices and economics.
 
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#37
#40
OK - advice needed on rectification.
I now have at hand one Hammond 302AX transformer and 2 pcs 158Q drossels for my planned 2A3 build.
For the planned amp I am contemplating using fixed bias. My original plan was to use UF4007 rectification, however I suspect that this solution will result in a B+ that is to high remembering that 2A3 has max anode voltage 300V

What approximate B+ voltage would I have using sand vs tube rectification?
What rectifier tube would you folks recommend?
 
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