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This was quite surprising... I picked up a pair of the Rat Shack
70V PA system transformers. I'm using the Nickel pinstripe version
instead of the pure nickel type. $2.95/ea.I'm using the 1.25W tap (alleged load of 4100 ohms) with a 4uF
paper/oil parafeed capacitor.. Output load is 8 ohms. Took 10
minutes to cliplead these guys in. ;)The nickel is definitely more detailed than than 1628SE, which is
still in the circuit, but is serving the role of plate load choke..Subtle details on a particular recording have now been revealed
where they werent heard before... Things like the creek of the
piano bench, movement of people behind the stage, and distant
voices off in the audience.There is some robbing of Paul to pay Peter... LF response isnt
as nice as I'd expect, theres something missing down around 20-40
Hz for sure.A fun and cheap $6.00 adventure. These might make another
fun and inexpensive project. Maybe an actively loaded DHT parafed
into one of these lovely Nickel wonders for a cheap project.
How about a low power A2 811A parafed ? :) Should be pretty and
sound nice too. Nothing like burning 100W to get a good clean 2W. ;)
Follow Ups:
Sounds like these might be great with a pair of 100+ horns and a good bi-amped sub. Nice work Jim! What operating point?
Vince
Jim,Would the RS iron also work as parafeed line-out trannies for a pre-amp? I'm looking for low-buck iron to do a CCS / parafeed on my 6sn7 based preamp. Any thoughts?
Pete (ParaPhrase) S
If nature loathes a vacuum then why do vac. tubes sound so natural???
Sure, why not. Edcor's offer good possibilities as well, albeit
not nickel core.Attached is an URL to some measurements I took.
I was going to post a more fullerer report on this, but I was
contacted by someone who claimed to hold patent on my test
circuit. I sat on the whole idea and data until recently when
someone I spoke to led me to question the claim of the alleged
patent holder.In any case, no more fear... Here's the data. The transformers
have some potential. The most useful being the 10K:150 (8:1 stepdown)
with a low Rp, low gain tubes... The ringing modes are shifted
way up spectrum, in comparison to the 10K:10K which ring like mad
and need to be tuned. For the 10K:150, you get some fairly good
flatness in the Bode plot from maybe 20Hz up to 40kHz.Use the trannies. As far as the driver circuit, its up to you to
find out if its patented. It just seemed to me to be a good ckt
for testing the trannies. Parafeed oughtta work too, and that
aint patented! :)-- Jim
nice work jim!(jd) Parafeed oughtta work too, and that aint patented! :)
sure it is :-) 1,448,550
Hi Pete,I know a couple of inmates have done parafeed preamps using some inexpensive Edcor transformers. I think they are $7 or $8 ea. If you do a search on the Bottlehead Forum, you can probably find the posts. Good luck and let us know if it turns out well.
As one of my to do projects, I am going to build a cheap parafeed active loaded 6DN7 amp (a la Dave Dintenfass and VALVE). I discussed the topic on the Bottlehead Forum and with Paul Joppa in detail (he knows *a lot* about budget iron, witness his column in VALVE), and arrived at the following list of possibilities for cheap iron:Radio Shack 32-1031A (peak 82H, leakage 60mH)
MCM 50-130 (peak 80H, leakage 40mH)
SPECO T-7010 (peak 106H, leakage 36mH)
Calrad 45-723L (peak 105H, leakage 47mH)I was going to go with the SPECO unit; it goes for $8 or so...
Thanks Eric, this is exactly the sort of info I've been looking for. I'm thinking I'd try just parafeed iron first, then add CCS.Pete (make mine parafeed) S
If nature loathes a vacuum then why do vac. tubes sound so natural???
Isn't it great goofing off and trying fun stuff like this?I'm not surprised that your are missing the very bottom. I built an amp using these as parafeed output transformers for a CCS loaded 12B4 SE amp. The sound is way better than it has any right to be. Quite magical actually.
When doing the power vs frequency response tests it was found that the little 10 watt 70 volt transformers would pass 1 clean watt at 20Hz and not an ounce more. By 30Hz you could get a whopping 1.5 watts. They are great little transformers if you keep in mind the limitations at low frequency.
does it really have a nickel core?how big is it?
do you have a catalog page.
Catalogue Number 32-1031BMarked as $6.99 but sold to me for $2.95/ea as the manager said
they are discontinued. Get 'em while they are still around.I have three. One of the three has a smaller core compared to
the others. The laminations are a brilliant shiny white.The other two, are slightly different. I call this "pinstrips".
It has a slightly larger core. Two different materials in the
lams, stacked in groups of three like a layer cake. On of the metals
is a dull grey colour, the other has a strange pinkish hue to it.I have no experience with mu-metal just M6, there is no oxidation
on these yet.The sample with the shiny bright white metal, I'm pretty certain
is nickel. It's heavy too, and Ni is fairly dense, so ....I unfortunately, no longer have access to a lab nor an AA to test it.
6 months ago and it would have been a fun Saturday morning project
in the lab to analyze the metal content.
physically how big are they?
Hi Jim,Welcome to Parafeed! Believe me good parafeed has much better bass then a standard SE OPT so you just need to get some better iron.
...is a better plate choke. Mike L. points out that good bass response is limited by the interaction of the plate choke and the parafeed OPT in parallel. If both are not up to the job the low freqs. will suffer.This is not to say a $6 OPT will be fabulous, but since you're es'perimentin' anyway, see if someone will loan you a righteous plate choke...you never know!
(I speak from trying a Tango U808 SEOPT as a plate choke for parafeed, then having my buddy loan me his 70H purpose-wound plate chokes. Big improvement in bass response, everything else being equal.)
The heat isn't wasted.
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