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69.71.1.1
General Radio designed a toroid audio transformer that was a test bed transformer for audio amplifier design. It has been written that a toroid AC tranny with dual primary 2x 120 and two 12 volt secondaries will have good frequency response when used as an output transformer like for the Lynn Olsen RAVEN output stage using 5687 in push pull. Anyone here had similar experience? Another possibility for single ended 5687 is 70v loudspeaker transformers that have 4,8,16 ohm secondaries. Grounding the 4 ohm tap as a CT would allow balanced output. If I cascade each side of the 5687 in parallel which primary tap should I use for the single ended 5687. They are rated in wattage not impedance. I don't have a bridge for measuring impedance. This is for a preamp feeding power amps. Thanks, Ray
"The gift of imagination is a gift of the Gods imparted to a few who receive innumerable kicks in the a$$ their entire life." Le Corbusier (Charles-Édouard Jeanneret)
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nt
"The gift of imagination is a gift of the Gods imparted to a few who receive innumerable kicks in the a$$ their entire life." Le Corbusier (Charles-Édouard Jeanneret)
I routinely use toroids as output transformers in my PP tube amplifiers.
They work fine provided that there is no uncompensated DC bias current.
This is a serious limitation in SE projects.
Best Regards
Luca
ecc230
What do I look for? Can you give me some manufacturers type numbers for possibility to use push pull with a 5687 and 600 ohm balanced output for preamp service? Thanks, Ray
"The gift of imagination is a gift of the Gods imparted to a few who receive innumerable kicks in the a$$ their entire life." Le Corbusier (Charles-Édouard Jeanneret)
I would rather recommend a 2X115V - 2X9V tranny like this
http://it.rs-online.com/web/p/trasformatori-di-toroide/6719075/
The 2X12V output model I think is good too (but an higher plate resistance should also get a lower distortion).
You might wish a 50VA model as an alternative to the 30 VA model, but I do not think there will be any practical difference with the intended (5687) tube.
The extra 9V output winding can be used for NFB or wired in parallel.
Best Regards
Luca
ecc230
I have used 50VA units before as SE output transformers either parallel feed or using a secondary fed with a high impedence to offset DC in the primary . 230:6+6 can be used with secondaries in series in place of a 3k TX in parafeed or 230:9+9 can be used as a 5K unit if a secondary is used as offset winding . What limits the useability is the primary inductance and saturation , so best to use low Ra valves and use for low power applications . 50VA units have a good 25H in the primary , it is unlikely that 70/100V matching transformers will exhibit anything like this (or have top end as extended as toroids)
Al
Al,Have you measured any matching transformers, or done an A/B comparison with a toroid of the same turns ratio?
I think wer're, obviously, talking parafeed here...
Edits: 07/02/12
I only have some 1w/5w matching transformers . The 5W tap works out approx 2k with 2H primary inductance (no DC) . These are small , the top end is nice and extended although these do fall apart under 100Hz .
Al
Ideally I would like to replicate the Raven output stage using 5687 as per Lynn Olsen. Or applying B+ to the CT of the primary so it has to tolerate Dc in the primary. The Sowter tranny is just kind of expensive, but I may have to use it. Thanks, Ray
"The gift of imagination is a gift of the Gods imparted to a few who receive innumerable kicks in the a$$ their entire life." Le Corbusier (Charles-Édouard Jeanneret)
You can get speaker matching transformers online
from companies like Atlas Sound.Radio Shack also has
one for 10 bucks but it's online only.I would not
spend too much money at first because you want to
make sure the transformer will work for what you
want it to do.If the results are good then you can
spend more money for a higher quality transformer.
Regards,
Swanson
I think the problem that you are going to have
if you try to use a speaker matching transformer
as a single ended output transformer is core saturation
due to the DC flowing through the windings.I have a few
of these transformers in my collection including a
massive Triad rated at 30 watts.It clearly says on the
box label "NO DC".Now wether or not this type of
transformer can take some DC or how much DC and still have good frequency response and low distortion is something you will have to find about yourself.Those transformers will probably work much better in
push pull or obviously parafeed.
Regards,
Swanson
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