Dog -- Thanks for the kind comments! If I may, it would seem that you are caught between wanting to do the modifications and not wanting to make any physical changes to the unit to implement them -- ergo, the answer to use an umbilical set up. I would suggest that from a long term and practical standpoint, that approach has a number of concerns:
1. While you may want to maintain the pristine element of your unit by not physically modifying it to accommodate the transformer, nothing screams "modification" more than a unit that now has to have an umbilical attachment to a separate chassis or device to make it operate.
2. Over time, I have found (from my own such efforts long ago) that umbilical modifications come off as clumsy and less than professional: This equipment is already heavy, so any attached umbilical devices make it more awkward to carry or maneuver about.
3. On the practical side, the center speaker terminal strip has only two connection posts, while the secondary of the transformer has three leads that connect into the circuit. Also, if the power to the external transformer ever becomes accidentally unplugged from the rear auxiliary receptacle, then all bias is lost on the output tubes (causing all of them to immediately red plate). This could also happen if the side of the AC power switch that services the rear receptacles fails, while the side powering the amplifier did not. On the other hand, if you accidentally plug the transformer into a receptacle that is powered all the time, then the preamp tubes will have their heaters lit 24/7, but without any current flowing between the cathode and plate elements. This will eventually poison the cathodes causing the tubes to rapidly wear out much faster than they normally would -- even if they were running properly 24/7.
Against this, mounting the transformer on the unit eliminates all of these concerns, at the expense of drilling four holes in the chassis. Yes, it's a permanent change to the chassis. But as a corollary to #1 above, nothing screams "professional" like a modification that is well executed, which mounting the transformer neatly on the chassis produces.
Remember too that the backdrop of all of this is the results that the modifications themselves produce -- which in this case is nothing short of outstanding. Consider that:
1. Power output is greatly increased, while distortion at the increased power level is greatly reduced from that which the stock unit produces at its lower power output capabilities at all frequencies.
2. Output tube quiescent current is greatly reduced over that of the original design, adding significantly to output tube life expectancy.
3. With less quiescent current draw through the output tubes and power supply, the unit runs notably cooler.
And, it warms up more quickly now, is easier on the small signal tube heaters, and the list goes on. And these are only the benefits from adding the small power supply and the EFB(tm) circuits. The rest of the modifications add significantly to the operating capabilities of the unit as well.
The point being that there are modifications, and then there are modifications. Many of us have seen modifications that were a "modification in search of an improvement" (meaning that the results produced are purely subjective or even questionable at best), or modifications that were so poorly thought out or executed as to actually detract from the performance of the original device. Audmod01 is desperately trying to undo that very type of effort on the unit he has now -- before he can even begin the modifications themselves.
But the modifications presented here are nothing like that. The wide spread improvements achieved from this set of modifications far more than outweigh the small penalty of the slight physical modifications required. And each portion of the modification adds its own factual enhancement to the operation of this unit in today's audio environment. That it can all be had within the same space of the original footprint is just another part of the attractiveness of the overall modification package in the first place.
Don may (or may not) have more to say on this. He has lived with his modified unit now for over a year, having good experience then with it in modified form, as well as before all the modifications were performed.
Ultimately, how you approach the modifications is your decision, with no judgement from me as to how you choose to approach them. I just wanted to give you some points to consider as you start putting your thoughts together towards that end.
I hope this helps!
Dave
