[sdiy] makeshift audio output transformers

[anthony]

> Signal Transformer is indeed a brand name.
>

Aha!

[Good points snipped...]

> Also, look for any old tube gear in the pawnshop etc (if there ~is~ any)
> that you might remove output transformers from...
>

I do find a lot of old tube radios, but I find the output iron for 50C5 
tubes (what I usually find) to be less than desired for a SE EL84 amp. But 
they DO work anyway... Since I have a few to throw around I don't mind 
overworking them. Although I wouldn't want to trash one of my EL84's (my 
dear, sweet, vintage Mullard EL84's that I found in some junk in my 
basement...) in the process.

> Triad is another manufacturer to look for... they used to make audio
> output transformers.
>
> Go ahead and try your power transformers... but remember that most were
> desined for 240V max with the primaries in series.  Most guitar amps are 
> more
> like 450V ....

I wouldn't be running much more than 250V through one for a single-ended 
EL84 amp. Dunno when it comes to a push-pull, but not much more really.

The only amp I have that has voltages close to 450V, is the 6V6GT amp I've 
almost completed (as a sort of high-gain Champ or GA-5 clone) and the radio 
it's based around already had a pretty stout output tranny for it.

I may break down and buy one of those expensive 20 Watt single-ended 
trannies out there and just put all three of my EL84's in a parallel 
single-ended amp. That should be sweet and loud and very unique.

> H^) harry
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> On Mon, 14 Jan 2008 11:57:04 -0500, anthony wrote
>> I have a large number of old transaformers: power transformers and
>> audio transformers (I'm not even going to begin about the number of
>> IF transformers I have because that doesn't concern us here...).
>>
>> Anyway, I've read from time to time that power transformers can be
>> coaxed into being audio output transformers, generally with poor
>> results in the case of single-ended topology because of saturation
>> of the core by the DC flowing through the primary. BUT I have this
>> old power transformer that I'm pretty sure was the in an old
>> acoustic coupler modem and it was definitely being used in the
>> capacity of its power transformer (since the mains wires were run
>> straight up to it...); but the point is that it has a serious airgap
>> just like a small 5-7Watt output transformer. The DC resistance is
>> about the same as that for the somewhat stout single-ended output
>> transformer in the Wards Airline Radio 6V6GT amp that I mentioned
>> making here. The secondary is center tapped so I'd have options for
>> speakers. It's been my experience that with small amps you can use
>> just about anything with close to the correct values. I used a tiny
>> crappy output transformer with no visible gap that was actually
>> originally used in a solid state audio amp
>> (using high voltage transistors) that ran from a tap on the flyback -
>>  and it sounded OK. A little farty when you tried to run bass
>> through it, but it worked.
>>
>> But my real interest at moment is using power transformers with dual
>> primaries or those split-core "signal transformers" is amplifiers
>> with push-pull topologies. Probably this is just a stop-gap until I
>> can afford the Hammon1609 that I WANT to use in my 2xEL84, 100%
>> Class A, 10 Watt, Push-Pull amp. But I have several tranformers for
>> 120V/240V service just depending on how the primaries are connected.
>> I assumed if you got the right ends, and connected the two points in
>> the center as the center tap, you should be able to use it in a push-
>> pull amp. If there's a danger in damaging tubes, I can use my
>> 6AQ5A's as guinea pigs (although I really hope I don't fry one).
>> Seemingly lackluster 6AQ5's seem to really shine when you use them
>> in push-pull amps - some say even moreso in triode mode. But the
>> other amp I intend to use 6AQ5's (4 of them to be exact) is going to
>> be more of a Class AB1 as opposed to the 2xEL84 amp that I want to
>> run Class A.
>>
>> I guess in the end there's no substitute for serious iron in an amp,
>> but I am not shooting for hi-fi here. These are going to be amps for
>> guitars and monosynths. I guess I'm curious about what is crucially
>> different about a transformer, intended as a power transformer that
>> can be configured to work like an audio output transformer and the
>> actual center-tapped, push-pull audio transformer. My guess is that
>> more care is given to giving in the right impedance at the right
>> frequency response.
>>
>> And then there are those split-bobbin transformers that I've pulled
>> out of gear in which they are clearly being used as power
>> transformers and plain as say it says "Signal Transformer" on it. My
>> guess is that this is just a brand name, but is it? Do these have
>> audio possibilities? If so, the ones I have probably couldn't handle
>> that much power anyway.
>>
>> Or can anybody direct me to a push-pull transformer that is better
>> than a Hammonnd 125E and cheaper than a 1609? I don't need the
>> ultralinear tap. I do OK finding decent single-ended iron for 5 Watt
>> amps, so I'm mostly on the look-out for a few good push-pull models
>> with power handling capabilities rangeing from 10 Watts to 50 Watts.
>> I actually think that I can have better luck on eBay with the higher
>> powered ones than the little 10 Watt push-pull I want to make. Maybe
>> I could put a Bandmaster transformer in the small amp and just make
>> sure I connect higher impedance speakers.
>>
>> cheers,
>> Anthony
>>
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>
>
> Harry Bissell & Nora Abdullah 4eva
>
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