On Jul 17, 5:17*pm, flipper wrote:
On Wed, 16 Jul 2008 14:51:15 -0700 (PDT), bigwig
wrote:
trim
Hello,
* Your site is great!. I like the trick with a 7805.
I presume you mean the heater voltage bump on the PC Speaker Hybrid
amp.?
Years ago I used
to work in a TV repair shop owned by an ex RAF RADAR guy. He taught me
that little trick, you must be careful not to push it too far though
otherwise you end up with quite a good saw tooth oscillator. I saw a
design from an Indonesian guy that used this to make a linear supply
at low inputs that switched to a switcher at higher inputs. It was
quite ingenious.
* I checked out Edcors site, they have an extensive range!. I think I
will wind these trannys and then for my friends buy some. By the time
I purchased c-cores, wire insulation etc. plus the laour intensive
task of winding them it will work out about twice the price of a pre-
wound set. Mind you I will probably get the bug of winding them and
after the initial outlay I guess it gets cheaper. Also at least I will
get exactly what I want (providing my maths are OK).
Yeah. Btw, where do you get your c-cores?
I keep thinking that 'one of these days' I might try winding some
myself.
* Your use of TV tubes is good, they are plentifull and cheap. I have
seen a lot of people put these type of tubes down but they must be
using them wrong.
Hard to tell where attitudes come from and I doubt most critics
actually built anything with them. More likely passing on 'what they
heard', from someone passing on what they heard.
The 13FD7 is a 13EM7 in a similar sized bottle but with a 9 pin base
instead of octal and there's plenty of 13(6)EM7 amps out there. Octal
pin spacing might be better for flybacks but I'm only running 250V B+
and 9 pin is plenty good enough for that, plus the advantage it fits
the hole punch I've got 
That and I picked up a handful of them for
75 cents.
The reason I chose 5B255M (apart from the fact I had
some) is because they are very cheap, plentifull
Where you are I guess. They be 'rare foreign' stuff over here.
and as far as I can
tell a later ruggedised version of the 807.
* Have you thought about using mains trannys? I know it sounds crap,
but they are cheap and could be worth playing with. Steve Bench used a
couple on an amp he built, check out his web sitehttp://members,aol.com/sbench101/.
Yes, I saw his work on those but when I checked prices they were more
than Edcors.
I did use a power transformer for OPT on the 6CW5 guitar amp, though,
where there's no need to pretend a 20kHz top end and I didn't need
gobs of NFB with low output impedance because speaker 'color' is part
of the 'sound'. Even with pentodes I only wrapped 11dB around it and
they all love it.
*As for my power supply Im going to use an industrial control
transformer in reverse (415-230V). I experimented with this with a SS
bridge and I was getting almost 600V! plus a massive switch on surge.
If I was to use this I would be mad, I would have to go for AB2 I
guess.
More like B (or B2). Can't get much A at that voltage.
I looked at the same thing because I have a whole box of similar
control transformers, except 'US' 230/460-115 and I, too, operate them
'backwards' for my 300V B+ supplies, parallel winding (230VAC), but
can get 600V if I use the windings in series.
All the 'wallwart' powered jobs use reverse 115/230-12 (or 10) VAC
transformers too and you may have noticed the note I made about the
voltage being lower, in reverse, by the 'regulation' factor (twice the
number, actually).. That's because the winding ratio is 'bumped up' to
compensate for full load losses but in revere that translates to a
bump 'down', and then you still have the winding losses on top of that
at full load.
The ones I use are typically 18% load reg so using 10VAC on 12VAC is
just about right to get back the 'bump down' but there's still the
winding losses so it's still 18% less than one would guess from just
looking at the label thinking they'll get '230' from the primaries.
The B+ tranny in the 13FD7 amp is running backwards too, because it's
really a 115-115/230 isolation transformer, but it's also only 11
bucks.
Speaking of which, I just did a marathon session and got the right
channel done. Hopefully the left channel will go a little quicker but
it's dern tight in there and that makes for slow going.
Had me worried there for a sec or two when I rushed to put audio
through it and.... well, LTPs don't work real well when you forget to
connect the tail. hehe
I think this is going to turn out to be a nifty little amp and now I'm
beginning to wonder if I really want to give it way.
What I plan is to play with a half solid state half vacuum
rectifier bridge and a regulator. Any suggestions? perhaps a full
vacuum bridge with damper diodes would drop it a bit.
Well, you're going to burn a lot of power doing it by brute force and
my first thought, if the goal is to keep the control transformer, was
to add a 115 (store bought) in series with the 300V wiring. Or do the
Class B 600V/300V version.
Mine are 100VA so the 11 buck 50VA, at half the voltage, is a proper
match and at 115 out it can operate forward. Or backward if B+ needs
to be nudged down. Kinda kludgey but it would work.
* * * * * * Matt.- Hide quoted text -
- Show quoted text -
Sorry I have not responded earlier, been busy, work, kids you know the
drill.
I got my c-cores from ebay, I know it was silly but they dont seem
bad. The guy I got them from dissapeared from ebay. He or they seem to
be back now as JLW tools. The cores arrived from China in five days to
the UK!!. Be carefull though if you want some they seem a bit
optimistic with the specs. I went for the next size up from what I
needed and Im glad I did. I know you dont need as much iron with c-
cores but the ones I have seem to be about the same size/weight as the
core of a 150VA torroid so im thinking they should be fine. They are
their "core 40" size. They came with bobbin tubes which I will use
with added side cheeks. The cast ally (if you can call it that) base
they supply is very poor. It could be cleaned up but I think it is too
rough to be worth the effort. The cores on the other hand seem OK.
I agree about the control tranny. I just have a few lying about as
Im an industrial electrician by trade. I might wind my own on torroids
after reading a few posts on winding them. Your use of variouse
trannys to get the correct voltage/power is a good way to get what you
need at a reasonable cost. I have been thinking of building a line
stage(eek) to drive some long cables. It will need plus and minus 100V
or so and 4 10VA 0-18-0-18V transformers work out perfect.
Mat