Hammond 290-series Guitar amp PTs

[prosounddaryl]

Hi Daryl

What you wrote here says you did not understand the description of the output transformer:

" If I can provide a reflected impedance load that the supply side wants to "See", why would a higher quality piece of copper and Iron give you less performance?"

The first part of the assumption is incorrect inasmuch as the OT has a centre-tap to feed power to the tube plates and your line ATs do not. You cannot use what is essentially a single-ended transformer designed for zero standing-DC as a replacement for a real push-pull transformer.

The second part of your statement has nothing to do with anything I stated. Guitar amps are not about fidelity per se; rather, they are about tone creation. For some players fidelity is improved tone, where others find such a change contrary to what they want. There is no right and wrong there.

Computers and guitar amps both have resistors and capacitors but they are wildly different devices. The same goes for line transformers and tube output transformers - apples and oranges. TUT volumes 2,4,5,6 have explanations about how output transformers function and how to specify them.

In a push-pull circuit, each tube only amplifies half the signal, working on its own end of the OT primary with CT tied to B+. The signal is "added together" within the OT. While one tube works the other rests but both ends of the transformer are magnetically in parallel so thew working tube does not see half the end-to-end impedance but one-quarter. The secondary is designed to match the speaker. OTs come in all power ranges and with narrow or wide frequency response. B+ can be hundreds of volts and the end-to-end voltage approaches twice the B+ value. OTs are designed for this environment.

On the other hand, line distribution transformers like you have are designed to match an amplifier speaker output to a 70V line, or to match the 70V line to a speaker load. Neither side can tolerate DC current or voltage. To reflect an impedance of k-ohms would require a very nonstandard speaker and everything else about the transformer is truly inadequate for the goal of replacing a real tube amp output transformer. As far as that application goes, your ATs are the wrong device. Why not use them to distribute sound through your house? The point of the high-voltage distribution is to allow the use of thin and inexpensive wire.

Have fun

Thanks for your reply, Kevin. Would you mind terribly providing me with the info on where I can read the info on "An easy change to make to the PA is to increase the feedback loop values by a factor of ten. Gain remains the same but the tone will be more dynamic." I believe this is the sort of tonal changes I was looking for.

And again, understanding the mission of this forum is to be as respectful as possible, I'll be brief and if you are curious to hear more I'd be happy to explain.

My business used to be in providing large scale speech and music systems in large acreage events. I doubt very much there are many more people who have designed and successfully implemented 140V distributed systems of this type than I, using 11 gauge wire, and 2 x Altec 2200 series amps in a push/pull arrangement for 1150 watts @8 ohms, (times x number of racks of this arrangement) and large format EV devices at the receiving end. I've hooked up numerous transformers using a real impedance bridge and other tools available to provide foreground music over miles, and actually used some of these components for the delay rings at Kenny Loggings Closing Ceremonies at Mile High Stadium in Denver, CO for the 1995 US OLympic Fest.

I am not writing any of this as braggadocio, I am explaining why I profoundly disagree with the statement these systems are designed to get away with thin wire and only as background music. My real life experience states this just is not correct.

I'll leave my comments about this issue at that, unless you are interested in hearing some of the very neat and creative things I've done in past. Once again, offered with respect.

And if you could point me in the right direction to increase the feedback loop by a factor of 10, I would be appreciative. Thanks very much.