18 watt PT question

[rockybottom16]

I found the Dreamtone mA calculator the other day, it tells me that my recently built (cobbed together) 18 watt Lite amp should draw around 80mA in it's current configuration. I used a Weber 100mA Princeton tranny that I had on hand, and it seems to work fine. (I'm using diodes for rectification.) It gets warm, but so far it hasn't gotten so hot that I can't leave my hand on it for several seconds before it becomes uncomfortable. But I always read that 120mA is the minimum recommended for this amp. Should I upgrade?

Interesting to note is the fact that the calculator also says my recent Proluxe built will draw well over 150mA; yet the tranny recommended on the Weber layout is the standard 150mA tweed deluxe unit. (I'm using GZ34 glass in this amp.) It also gets a little warm but works like a charm. So, how much credibility should I assign to the Dreamtone calculator? How paranoid should I be? I'm also guessing that those old tweed deluxe's must have run pretty hot!

[g1]

Make sure all the numbers are for total input current, sometimes people will refer to the HT winding current.

[rockybottom16]

I guess I don't understand what you mean. There is no field to enter any current numbers, just PT voltage and tube type and number of tubes. Anyway, I'm gonna upgrade both the trannies. I left them running for about an hour and a half this afternoon with a small signal going through them at low volume, and they both got so hot that I could only hold them in my hand for about 3 seconds before some real pain. I have a 150mA tranny that will work nicely in the 18 watter. I'm not sure yet what to put in the Proluxe. I'm gonna shoot for around 200mA for that one.

I think the 150 would work in the Proluxe if I got some 6L6 or 6L6GB's. But the 6L6GC's draw too much current for that configuration. Weber's layout specifies 6L6GT's. I'm not sure what they are, but I bet they're a lower current version than the GC's.

[g1]

What I meant was that the calculator was telling you the current required for the whole amp (heaters, high voltage, etc.).
But sometimes people discussing an amp will mention the current capability of only the high voltage winding (HT), which will be lower than the total current number that the calculator gives. So it is important to know which current is being discussed.

[Chuck H]

At first glance I couldn't figure out why a power transformer good for a pair of 6V6's wouldn't be suitable for a pair of EL84's.?. But then I realized that you have the Princeton transformer intended for the single 6V6 class A Princeton. 100mA is very generous for that model but not really up to an 18W. Especially since the 18W amps are often cranked up loud. I think an upgrade is a good idea. I'm using a Hammond 270EX which has a 144mA HV secondary in my 2xEL84 amp. It barely gets warm cranking it for an hour. I would have thought a 100mA secondary would be alright with the possibility of a little power supply sag, but not overheating. If yours is too hot there's no options though.