quality of transformers

[otto]

Speaking about quality of components ...
How much is quality of transformers important in the sound of a tube amp? Given a required voltage is the difference between transformers hearable? Any experience? Is there any sound sample?

[MWJB]

OTs or PTs?

"Given a required voltage is the difference between transformers hearable?", suggests you are asking about PTs. A beefier PT, at the same B+, will ideally provide a more consistent voltage when demands are made of it, improving dynamics. So I don't necessarily feel that the final voltage produced is the whole story. In reality, however, finding 2 PTs of the same spec, that actually deliver the same voltage is another matter, so it can be a task & half to A/B products.

[otto]

I mean both PT and OT ...
the PT must have a 'reserve' of current when needed, for the dynamic, how is this indicated in the specs? Higher nominal voltage?
thx

[MWJB]

B+ secondary current rating.

[otto]

I report here a piace of consideration in tone-lizard site, only a piece as example, if you want to read more:
http://www.tone-lizard.com/Electronic_Parts.htm

"... More iron increases the low frequency response and the transformer core will saturate a little less. Some transformers were advertised as having a nickel core that offered less distortion! Primary impedance influences power output and frequency response. Higher impedances yield narrower bandwidth, less distortion, and less output. ..."

I understand that specs are not enough to describe the 'sound' of a transformer. Any experience with transformers substitution and sound changes?

[Old Tele man]

...from my TGP posting on the same subject

...there's an equation in the old vacuum tube engineering books showing low-frequency response being proportional to OT primary inductance.

...from Section 15-31 in Henney (Ed.), RADIO ENGINEERING HANDBOOK, 5th Ed (1959), McGraw-Hill:

L(pri) = Zpri / 2*pi*F(low)

...for example, if Zpri is to be 10K ohms (6V6?) and F(low) = 20Hz, then:

L(pri) = 10K / 2*pi*20Hz = 80 Henry!

...the three most important OT characteristics are:

1) Turns-Ratio (TR) = establishes the impedance transfer ratio from output into input.
2) L(pri) = establishes the low-frequency cutoff.
3) L(leakage) = establishes the high-frequency cutoff.