SLOW DRIVE 84 PSU problem

[TIMBO]

Hi guys. Doing some tests as i'm doing this build and i thought that this could be a problem and it might be. I'm using a second tranny for the heaters and SS stuff.The tranny has 0,6,12 and 15v taps, so the 0 and 6v tap with artificial CT got me 3.1v per leg for the heaters, great and the 0 and 12v tap through voltage reg. got me the desired voltage for the SS circuit but when rechecking the heater legs it throws the heater legs out of balance to 4v on the 0 side and 2v on the 6v side. I kinda thought that this might happen, would putting a Diode on one of the legs help ?

While got you here, the tranny is rated @ 30VA, 2A and when calculated the load of heaters and SS stuff could be a bit higher in total than the 2A mention or is the Amp rating calculated at each of the taps 

eg. Heaters :-
If the tranny is rated @ 30VA @ the 15v tap is 2A, is the rating @ the 6v tap 5A 

And the 12v tap of 2.5A
OR
When all loads are added together regardless of what taps they are connected too make up the amount of amps the transformer needs to be able to handle  Thanks 

[sluckey]

You need a PT with separate secondaries, rather than one secondary with several voltage taps.

[PRR]

> tranny has 0,6,12 and 15v taps

Re-label the taps like this:

0 --- 6 --- 12 --- 15
12 -- 3 --  0 ---  3
DC -- H -- gnd -- H

The plan shown has only little solid-state loads, 10mA max. The 12V arm to a half-wave rectifier and 1000uFd 25V cap will give plenty of +17V to regulate (or simple-filter).

[TIMBO]

Thanks guy's, I was not sure at first what you had in mind PRR so i tinkered with the PT and nutted it out. I was not aware that you were able to shift the 0v to make a CT. I did not mention that the transformer also had a 9v tap as well and when connected the way you had it, it read 3v one leg and 6v the other. So measuring the 9v tap gave me the other 3v leg. This is a simple fix and and great bit of info. Also, i was going to connect the new CT to the power tubes cathode to elevate the heaters will this also help with any buzz that is sometime caused by these regulating circuits? 

[tubenit]

I am very intrigued by your design and build here!  Can't wait to hear you give it a review.  Thanks for sharing your work.

with respect, Tubenit

[PRR]

> i was going to connect the new CT to the power tubes cathode to elevate the heaters

NO!! You can't extract DC for the chips AND raise the heaters on the same winding!

Or probably you could get something like that, but there is such a thing as "too-too tricky".

[DummyLoad]

> tranny has 0,6,12 and 15v taps

Re-label the taps like this:

0 --- 6 --- 12 --- 15
12 -- 3 --  0 ---  3
DC -- H -- gnd -- H

The plan shown has only little solid-state loads, 10mA max. The 12V arm to a half-wave rectifier and 1000uFd 25V cap will give plenty of +17V to regulate (or simple-filter).

why not forgo grounding the 6V tap and just pull FWB off the ends (0V & 15V) - let the filaments float?

--DL 

[PRR]

That gives large UN-balanced AC voltages, also rectifier glitches, on the heater wires.  

You can do a guitar amp good with BALanced AC heat. And tolerable with one side grounded. But not with this mixed AC/DC scheme. IMHO.

At this point, perhaps best to K.I.S.S. and derive one or more DC voltages for all purposes. The 15VAC wil give 20V DC. Can this tube-set be wired for something near 20V? Or if the regulated only has to be 12V, take the 12VAC tap for 17V DC and wire heaters for 12V. DC heat is not the same as elevated heaters, it is better; but you can also put your more-sensitive stages at the top of the stack and elevate them to turn-back cathode leakage.

[TIMBO]

Thanks for the feedback guys, I've redrawn the schem and i'll try it this way and see how it goes. Thanks