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**Kim** · 05-14-2009, 02:52 AM

Just adding to the above - I have no intentions of building 100 kilowatt guitar amps or the like. I simply want to use the research information attained in the Manual and scale it down for stuff under 10 kilowatts ( say push pull 833 triodes, or the other newer ceramic type vacuum tubes; etc.)

Designing really LARGE Power Transformers ends up as a specialist feild once you start getting over a kilowatt or so. Even more so with Audio Transformers.

So far this manual is the only Audio Transformer design material I can find on the really big stuff from covering 20hz-20khz in frequency, output impedances & voltages for standard transmitter tube operation such as those used in AM Modulators and specialist Audio equipment in industry.

With some fiddling of the figures and design parameters I cannot see why really big Hi-Fi stuff could not be designed from this manual, as it gives step by step design proceedures for practical construction of really humungous Audio Transformers.

For the serious builder - it would be far cheaper to build yourself than get a commercial winder to do the job.

I pretty well have most documents/books/articals readily attainable from the internet that are FREE on Audio Transformers ( but many links have since been lost as the websites close down ); but there are a few items that would be worthy of adding to my own collection if I can source them; such as >
'Electronic And Radio Engineering' ( By Frederick Emmons Terman ) as published in 1955, with 1078 pages; etc.

If anyone has other information on - Audio Transformer Design and/ or Construction - please email me - Thanks!

__________________
kimbalsummers@hotmail.com

**Steve Conner** · 05-14-2009, 10:27 AM

Hi Kim

I don't have any manuals on this subject, but I've researched it a lot in the past.

The main problem with high power and high voltage audio transformers is getting enough HF bandwidth. The physical size of the transformer, combined with the insulation thickness needed for high voltages, and the large number of turns needed to get the LF response, all lead to a lot of leakage inductance which limits the HF response.

The problem is bad enough that high-power amps needing to reproduce the whole frequency range tend to be designed with a lot of low-voltage tubes in parallel. For example, ten 6550s instead of two 813s. This eases design of the transformer.

Also, commercial winders tend to wimp out above a certain voltage. I once went looking for a custom transformer to make a 600W bass amp with two 4CX250Bs. The winders I asked refused to make me it, on the grounds that they weren't certified for more than 2.5kV peak (DC+signal). The guy explained that the insulation would take it fine, but they couldn't do itfor insurance reasons. (Then again, maybe he had no idea how to design the transformer and didn't want to admit it.)

In the UK, John Chambers has made some nice high-power transformers, including one that puts out 1kW RMS from four 813s, running on a 2500V B+.
Champ 1000 Watt Tube Amp

I was intrigued enough about this that I actually e-mailed him and asked what HF bandwidth he was getting. His reply: "It's for a reggae sound system, they don't care about treble, only bass"

**Kim** · 05-14-2009, 11:33 AM

Originally posted by Steve Conner View Post

Hi Kim

I don't have any manuals on this subject, but I've researched it a lot in the past.

The main problem with high power and high voltage audio transformers is getting enough HF bandwidth. The physical size of the transformer, combined with the insulation thickness needed for high voltages, and the large number of turns needed to get the LF response, all lead to a lot of leakage inductance which limits the HF response.

The problem is bad enough that high-power amps needing to reproduce the whole frequency range tend to be designed with a lot of low-voltage tubes in parallel. For example, ten 6550s instead of two 813s. This eases design of the transformer.

Also, commercial winders tend to wimp out above a certain voltage. I once went looking for a custom transformer to make a 600W bass amp with two 4CX250Bs. The winders I asked refused to make me it, on the grounds that they weren't certified for more than 2.5kV peak (DC+signal). The guy explained that the insulation would take it fine, but they couldn't do itfor insurance reasons. (Then again, maybe he had no idea how to design the transformer and didn't want to admit it.)

In the UK, John Chambers has made some nice high-power transformers, including one that puts out 1kW RMS from four 813s, running on a 2500V B+.
Champ 1000 Watt Tube Amp

I was intrigued enough about this that I actually e-mailed him and asked what HF bandwidth he was getting. His reply: "It's for a reggae sound system, they don't care about treble, only bass"

Thanks for the info. I have had exactly the same experience with transformer winders and within Australia there are less of them that really know how to wind true AUDIO than in other countries. Hence the reason I want to learn to do it myself. Unfortunately I have had a few set personal backs because of unemployment and limited income. The few who can wind Audio cringe once you get over a few hundred watts, especially if it is a one off prototype where they may fear being sued if the transformer fails.

I am already in contact with John Chambers and have exchanged a few emails in recent months. Unfortunately I am having trouble sourcing GOSS laminations in any size to make Audio Transformers; unless I pay big bux and buy it in form Asia or the USA.

You might like to look at this link > http://www.audiophool.cjb.net/Misc/3Kpdf.pdf < It's a 3,000 watt RMS audio amplifier from 1953/4.

They get around the HF response problem by winding the primary as a Bifilar winding and each alternate primary winding is criss-crossed over on itself to reduce the interwinding capacitance by half. A clever trick I have not seen utilised today, as its difficult to do.

After looking at Chambers multitube outputs for high power I am more favourable to his approach than using two big tubes - as much as two big tube look impressive and more expensive and fragile, most of the time.

The reasons in favour are primarily having lower and henec safer B+ rails of high current rating ( hence more reliable ) with lots of cheaper tubes in parallel. Also lower drive swing is required and far less chance of flash over on O/C primaries, which in parellel operation can drive very LOW Z windings and hence deliver better high frequency response; just to name few ideas.

I have zillion Military 807 NOS tubes I want to use in this multitube configuration and its the only way to get "cheap costing" watts to compete with solid state designs.

**Steve Conner** · 05-14-2009, 12:02 PM

Transformer laminations are a b*tch to buy. Your best bet is usually to salvage them from old transformers. I recently had a lucky find, a 2kVA transformer made with two 1kVA cut core sets. It was scrapped due to shorted turns, but after a little persuading with a hammer and blowtorch, it came right apart!

scopeboy's l33t photo blog

Each core would be good for about 500W of audio down to 25Hz.

Also, I notice that the 3kW amp you linked is only specified to work from 400-3000Hz.

**Kim** · 05-14-2009, 10:47 PM

Originally posted by Steve Conner View Post

Transformer laminations are a b*tch to buy. Your best bet is usually to salvage them from old transformers. I recently had a lucky find, a 2kVA transformer made with two 1kVA cut core sets. It was scrapped due to shorted turns, but after a little persuading with a hammer and blowtorch, it came right apart!

scopeboy's l33t photo blog

Each core would be good for about 500W of audio down to 25Hz.

Also, I notice that the 3kW amp you linked is only specified to work from 400-3000Hz.

True Steve, the 3 KW Amps HF response is limited to mid frequencies. But realistically, it would be quite possible to design such to extend to 20 khz.
The US military document "High Voltage, High Power Audio Design Manual" I talk about at the beginning of this thread, shows how to design audio amplifier transformers for modulators and large amplifiers up to 20 khz and as high as 350 KW output - so it must be practically possible to do such.

Alternatives to this approach would be using a biamped system, with dedicated narrow band transformers for part of the audio spectrum only, useing active filtering networks. In this way you could design the output transformer for a more efficient narrow bandwidth, with a dedicated no compromise winding design, maybe even using a ferrite core on the real high frequency end.
I have found from my own experience that a biamped system is far more superior to a single wide band amplifier which does everything from 20 hz- 20 khz. The speakers are then dedicated to the band they work in, as is the coupling components and phase response and transformer design. The negative side of such an approach is the added cost and the need for many amplifiers to carry the bandwidth of the music source creating acoustic doppler and non-linear phasing issues.

If you have to resolve yourself to one really big amp with all frequencies passing through it - use many pairs of output tubes in pushpull parrallel to reduce the plate impedance and hence the effects of winding capacitance and leakage inductance. But again use cheaply available easy to source tubes such as 6CM5, 807, etc and run them towards the lower end of their plate dissipation to get increased life from the tubes.

[ For example 10x 807 in pp parrallel can deliver 600watts @ 750 volts (verses 2x 813 which can give about 600 watts at 2.5 KV) but running the same 10 x 807 at a lower B+ rating of 500 volts to get 40 watts a pair ( 200 watts in total ) will allow them to last for many, many, years longer; and useing a much lower plate load Z as compared to 2 x 813.]

Good you found some nice C-cores. They should clean up OK. Now how are you going to find out their characteristics without a magnetic gauss meter for testing laminations ? Are the cores GOSS steel, or something like garden variety Lycore-150; etc ? Unless you know for sure what the core is, (hence one can design around it), I find salvage to be limited and maybe even a waste of time, unless you can reverse engineer the transformer.

If it's a power transformer you have, a far better chance of reusing it for another power transformer, as frequency response is not such an issue. If its an unknown transformer - then it MAY BE useless without proper testing.

Kimbal

**Enzo** · 05-15-2009, 01:10 AM

The US military document "High Voltage, High Power Audio Design Manual" I talk about at the beginning of this thread, shows how to design audio amplifier transformers for modulators and large amplifiers up to 20 khz and as high as 350 KW output - so it must be practically possible to do such.

"Practical" is not usually a major concern of the military. They want something and they want it for some purpose, then they get it done, but that isn;t the same thing as practical.

**Kim** · 05-15-2009, 01:44 AM

Originally posted by Enzo View Post

"Practical" is not usually a major concern of the military. They want something and they want it for some purpose, then they get it done, but that isn't the same thing as practical.

Let me rephrase my last post comment and say "it's technically possible to build such". Saying it is "practical" is poor choice of words for the homebrew DIY.

**Enzo** · 05-15-2009, 03:39 AM

Hi Kim, welcome to the forum.

I wasn;t really criticising, I was musing on the mental image.

**Steve Conner** · 05-15-2009, 10:52 AM

Hi all

Those 350kW military setups might go up to 20kHz, but I know without even looking that the same power amp won't go down to 20Hz too. And yes, the military's idea of practical is not the same as ours, detonating hydrogen bombs in space is just another day at the office for them.

Measuring the characteristics of a transformer core is easy. All you need is a signal generator, a power amp, an op-amp, and a scope with an X-Y mode, and you can draw the B-H loop on the scope screen.

I imagine the cores I salvaged will be some grade of grain-oriented steel anyway. They're made by winding steel ribbon onto a mandrel, gluing it up and sawing the resulting lump in half, so it's very easy for the maker to use GOSS and have the grains properly oriented. (E-I laminations are a nightmare to make from GOSS, because they're punched from a sheet: the grains can't be properly oriented with respect to the magnetic field everywhere.)

On the 4hv forum, which I help to moderate, one of our members recently trash-picked a 2.5kW vacuum tube amp that was used to drive a shaker table. The OPT is so big, it's a separate unit that needs a forklift to move it! (And it's a Partridge!) See the pics here:

4hv.org: Forums / General Chatting / Whats the most useful item you've salvaged?

You may want to join this forum if you're interested in extreme levels of power and voltage

**Kim** · 05-16-2009, 01:32 AM

Originally posted by Steve Conner View Post

Hi all

Those 350kW military setups might go up to 20kHz, but I know without even looking that the same power amp won't go down to 20Hz too. And yes, the military's idea of practical is not the same as ours, detonating hydrogen bombs in space is just another day at the office for them.

Measuring the characteristics of a transformer core is easy. All you need is a signal generator, a power amp, an op-amp, and a scope with an X-Y mode, and you can draw the B-H loop on the scope screen.

I imagine the cores I salvaged will be some grade of grain-oriented steel anyway. They're made by winding steel ribbon onto a mandrel, gluing it up and sawing the resulting lump in half, so it's very easy for the maker to use GOSS and have the grains properly oriented. (E-I laminations are a nightmare to make from GOSS, because they're punched from a sheet: the grains can't be properly oriented with respect to the magnetic field everywhere.)

On the 4hv forum, which I help to moderate, one of our members recently trash-picked a 2.5kW vacuum tube amp that was used to drive a shaker table. The OPT is so big, it's a separate unit that needs a forklift to move it! (And it's a Partridge!) See the pics here:

4hv.org: Forums / General Chatting / Whats the most useful item you've salvaged?

You may want to join this forum if you're interested in extreme levels of power and voltage

Thanks Steve, I will sign up to the other forum as well.

Its good to see you got a large Amp to play with. I heard years ago of a similar vibration tester using a 10 KW solid state amp driving a steel plate for vibration testing. I doubt the HF response would be great but it would make a good bass Sub.

As for the Military manual, until I actually see what it has in it; we are only assuming that it is "this or that". I do agree the Military are a bit over the top with their specialist technologies, but there are some things one can learn from their research - and I am not refering to making bombs or partical beam weapons. You may well be right; but in my case, its more the research data and proceedures I am interested in. As I said in a previous post I am not wanting to build a 100 Kw guitar amp, but take the design principles and scale them down to audio stuff from 1kw to 10kw range.

I had years ago some 35 watt Tube PA amps using a pair of STC 5B255M (basically an 807 Locktal ) tubes, attained from a military auction; which had very nice OIL filled Output and Power Transformers and fairly rugged construction. Yes an overkill for a 35 watt tube amp.

Please email me a sketch of how you test your Iron core BH loop with a scope and power amp. If you have any circuits I would be interested in looking at such. I have good scope and power amp, so all I need is the Op amp stage. I could build a test jig.

Cheers again;
Kimbal

**Old Tele man** · 05-18-2009, 04:22 AM

...and with "Military" also tags along the phrase "...cost is no object."

**R.G.** · 05-31-2009, 02:07 PM

To get ruler-flat response from 100+ KW transformers is technically quite simple. All you need to do is insulate the primary wire by spiral-rolling US$100 notes around the wire as you wind it. :

Most commercial winders will be only too glad to help you apply this technique once they figure out the technology.

**Steve Conner** · 05-31-2009, 09:51 PM

Please excuse the cross-pimpage:

4hv.org: Forums / General Science and Electronics / Coercive force of a Slinky?

In this thread on 4hv.org, "Klugesmith" demonstrates the exact method I was talking about, by drawing the B-H curve of a slinky, among other things.

He mentions a "fluxmeter" which is basically an integrator. Since I don't own one of these, I'd have made my own integrator from an op-amp.

RG: The $100 note method works great, but how come the contractors always want so many more $100 notes than it actually takes to do the job?

**R.G.** · 06-01-2009, 01:04 PM

Originally posted by Steve Conner View Post

RG: The $100 note method works great, but how come the contractors always want so many more $100 notes than it actually takes to do the job?

Well, as they'll explain to you, no real physical process is 100% efficient. There is always a percentage of $100 bills that have pinhole defects, or serrated edges which can cause corona emission, unfortunate overlap angles of the security threads, and so on. In fact, I suspect a really good contractor would require you to give them a substantial materials-test sample ahead of time so they could investigate and figure out what the fallout rate will be.

In any large technical organization, there are individuals whose job titles vary, but whose real work is "technical explainer". These are the guys who can smooth-talk skilled and experienced professionals in the field into grinning agreement. They are worth their weight in platinum in the bid process.

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