Introduction/Question: Multipurpose OT/PT for amp prototyping?

[Axeplyr]

Hi, my first post. My name is John, and I'm an Ampcoholic.

I'm getting ready to get into amp building. I've spent considerable time reading up on the subject, and I'm getting ready to build something resembling a 5F1/5F2A Champ/Princeton. It's easy enough to identify a whole bunch of compatible PT's and OT's that will do the job. However, I am leaning forward to my next project - a 5E3 type - and realized I can probably buy these transformers carefully and slightly overspec'd, thus preventing me from having to rebuy when I decide to tweak/redesign for potentially push-pull EL84/6V6 or single tube SE EL-34/6L6 designs.

So, I've narrowed down a couple of potential transformers:

PT: 370EX
OT: 125ESE

Both are significantly overspec'd to the Champ circuit and the Tweed Deluxe circuit. I spent considerable time looking for transformers that people used in a variety of different projects.

The 370EX PT is has 275-0-275/125mA, 5v/3A and 6.3v/4A secondaries, which according to my research should handle a single EL-34. In addition, it should work fine with a single 6L6, two 6V6's, two EL-84's, a single 6V6, or single EL-84.

the Hammond 125ESE is being used in amp projects utilizing a single EL-34, 6L6, or a KT66 in an single-ended config.


I picked these because they seem to be usable for a variety of circuits. However, I get conflicting info on the 125ESE; it's optimized for single-ended class A, yet some seem to indicate they've used them for class A/B push-pull.

These are the types of things I'm concerned about. I'd really like to be able to buy a single set of transformers and get alot of flexibility.

My questions are:

1. Will these transformers sound good in a Champ/Princeton circuit?

2. Will the 125ESE transformer (designed for single-ended operation) sound OK in a push-pull dual 6V6 or dual EL-84 circuit?

Part of the problem is I live in Australia, where these transformers aren't $50 each! They're $150 to $300 each. So I'd like to buy a single set and have max tweakability!

Anyone tried this? Are there better transformers for what I'm trying to do, and can handle everything from SE 6V6/EL84 to push-pull 6V6/EL84 and up to a single tube SE 6L6/EL34/KT66 design? Or should I resign myself to buying multiple transformers?

Thanks!

[Paul P]

Welcome John. I'm a newbie like yourself and have gone through just about
the same thought process. I'm building an amp that will hopefully give me
the flexibility in configuration you're talking about.

However, I'd say it's far from certain that this will work well. I've read the
opinion that an overpowered amp will sound sterile, much like using metal film
resistors is supposed to do. I'm going to prove this to myself by maybe
building the most sterile amp in existence. But then I'm going to change
things bit by bit until it sounds good (even if I have to rebuild the whole
thing, which isn't impossible given I'm going with a non-standard chassis
layout). At least by then I'll know what works and what doesn't. There's
too much information on the net to be able to come to a conclusion before
building something.

I believe conventional wisdom is to start small and then grow to bigger things
as your experience deepens. Start by building a Champ and then go on
to something like a Deluxe and so on. This is almost certainly the best
route but I've never been able to do it this way. Like you I'd like to build
one amp that can start small and grow big, so I don't have to buy the
same common parts over and over again. The main problem with this
approach are the transformers for which it's hard to come up with a chassis
that could receive different ones without heavy surgery (if you're prepared
to buy several transformers that is).

So, as Enzo would say, just do it, whatever "it" is. You'll learn from the
experience and if you don't come up with something useable the first time
you probably will the next time around.

As far as your Hammond 125ESE transformer goes, I don't see how it could
be used for push-pull as it doesn't have a center tap in its primary winding.

I'm using an Allen Amps TP40D power transformer which can power up to
two 6L6's in push-pull.

Good luck with your endeavor.

Paul P

[Bruce / Mission Amps]

My questions are:

1. Will these transformers sound good in a Champ/Princeton circuit?

2. Will the 125ESE transformer (designed for single-ended operation) sound OK in a push-pull dual 6V6 or dual EL-84 circuit?

Part of the problem is I live in Australia, where these transformers aren't $50 each! They're $150 to $300 each. So I'd like to buy a single set and have max tweakability!

!

You are getting the 125E and the 125ESE OTs mixed up.
You want to look at this series of OTs:
http://www.hammondmfg.com/125a.htm

You want a 125E... which by the way will barely work "fair" with a pair of 6L6s in PP.
A pair of 6V6s or EL84s in PP will have it close to maxed out at full power.

[Axeplyr]

Welcome John. I'm a newbie like yourself and have gone through just about the same thought process. I'm building an amp that will hopefully give me the flexibility in configuration you're talking about.

However, I'd say it's far from certain that this will work well. I've read the
opinion that an overpowered amp will sound sterile, much like using metal film
resistors is supposed to do. I'm going to prove this to myself by maybe
building the most sterile amp in existence. But then I'm going to change
things bit by bit until it sounds good (even if I have to rebuild the whole
thing, which isn't impossible given I'm going with a non-standard chassis
layout). At least by then I'll know what works and what doesn't. There's
too much information on the net to be able to come to a conclusion before
building something.

I believe conventional wisdom is to start small and then grow to bigger things
as your experience deepens. Start by building a Champ and then go on
to something like a Deluxe and so on. This is almost certainly the best
route but I've never been able to do it this way. Like you I'd like to build
one amp that can start small and grow big, so I don't have to buy the
same common parts over and over again. The main problem with this
approach are the transformers for which it's hard to come up with a chassis
that could receive different ones without heavy surgery (if you're prepared
to buy several transformers that is).

So, as Enzo would say, just do it, whatever "it" is. You'll learn from the
experience and if you don't come up with something useable the first time
you probably will the next time around.

As far as your Hammond 125ESE transformer goes, I don't see how it could
be used for push-pull as it doesn't have a center tap in its primary winding.

I'm using an Allen Amps TP40D power transformer which can power up to
two 6L6's in push-pull.

Good luck with your endeavor.

Paul P

Thanks, Paul. This just goes to show how little I know! I didn't realize that the single-ended ESE didn't have the required center tap.

You are getting the 125E and the 125ESE OTs mixed up.
You want to look at this series of OTs:
http://www.hammondmfg.com/125a.htm

You want a 125E... which by the way will barely work "fair" with a pair of 6L6s in PP.
A pair of 6V6s or EL84s in PP will have it close to maxed out at full power.

Thanks, Bruce. So if I get a 125E, I can use it in 6V6/EL84 push-pull, but you don't recommend? Will it sound bad, or just run close at its limit?