Re: odd ball PT question

On Fri, 18 Dec 2009 09:43:39 -0500, "Phil_S"
<psymondsnospam@xxxxxxxxxxx> wrote:

"RS" <RS@xxxxxxxxxxxxxxx> wrote in message
news:p57mi5h6tkc4cjmq6i9rv0df11ig4sqvsr@xxxxxxxxxx
On Thu, 17 Dec 2009 19:59:33 -0500, "RichL" <rpleavitt@xxxxxxxxx>
wrote:

Phil_S <psymondsnospam@xxxxxxxxxxx> wrote:

So, the nagging question...that single wire that goes nowhere? Just
a frame ground?

Did you try checking continuity between the wire and the frame?

When you have a friend who's working on his car and has a pile of
parts next to the engine, it's good to sneak over and throw an
odd-sized bolt into the pile.

Same thing with the wire, maybe.

Good one! LOL!

After thinking on this...I am pretty sure I'll be going forward with a 2x
6L6 project, but not in the chassis this PT arrived in. That chassis is
just too small. It would be good for a simplified Deluxe or similar. I am
between using this one that I know has the mA for a pair of 6L6 and one that
came from an old Magnavox driving a quad of 6V6.

Thinking out loud...please tell me if I'm not getting it. The Mag is marked
by the seller as 135mA but I keep thinking that's got to be below it's real
capacity.

Probably conservatively rated, but I wouldn't count on that. Can you
find a spec on the transformer?

The primary DCR is about 3.5 ohms suggesting a VA rating of about
150 or so and the physical size of it is substantial. In addition to the
HT, there are 2x 6.3V and a 5V winding. Allowing (guessing) 5A for the 6.3V
windings together and 2A for the 5V winding, that's 42VA, leaving over 108VA
for the B+. At 620V, that means the B+ is good for 175mA
(.175A*620V=108.5VA). Diode rectified, 620VAC will give about 415-425V.
Tube rectified with a 5Y3, it will be in the range of 340-360VDC. I'm
thinking that the diode rectification frees some of the VA rating for the B+
winding but I am not totally clear if the higher B+ voltage will really
depress current draw.

Not sure what you mean by "depress current draw". You mean require
colder bias? Or do you mean that drawing x amount of current is going
to be tougher on the transformer?

A pair of 6L6 operating in the low 400's will
typically draw how much current at that voltage? ~175mA for typical
operation and something a bit over 200 at maximum load?

You already know how much the output tubes are drawing, so you're
probably referring to the whole amp here. The preamp tubes are going
to draw very little.

Maybe I'm at the edge of capacity for the Magnavox PT? I keep thinking that
a quad of 6V6 (what the Mag was supplying) is roughly equivalent to a pair
of 6L6. Is this thinking not right?

Thanks.

Four 6V6's will usually draw more than two 6L6's, and the filament
current should balance out. I think you're good.
.

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