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Use 5KV transformer as output transformer?
Use 5KV transformer as output transformer?
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Old 14th March 2006, 06:42 AM   #1
vax, 9000 is offline vax, 9000  United States
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Default Use 5KV transformer as output transformer?

I got a 120V-5KV, 5KVA huge transformer. May I use it as tube output transformer? 5KV:120V = 40:1, roughly 1.6KOhm : 4Ohm. Is it good for single ended amplifier? I assume since it is huge, it might not be to easy to saturate? Any thought?
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Old 14th March 2006, 07:01 AM   #2
Tweeker is offline Tweeker  United States
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Is it center tapped, PP subwoofer amp maybe? I wouldnt expect very good HF responce.
Be sure your foil hat has a good low impedance ground.
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Old 14th March 2006, 09:39 AM   #3
lndm is offline lndm  Australia
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Sounds like a microwave oven transformer. The answer is maybe.

To work, the opt primary winding (5kv) has to have enough inductance to meet the proposed reflected impedance at 20Hz.

A large power xfmr winding will probably have large interwinding capacitance making it no good above a certain frequency.

I sweep all the power transformers I collect, measuring impedance with frequency, and note the impedance at 20Hz and the turnover resonance (highest useful frequency) and almost all are no good, even if you are not fussy, most are horrible.

Usually, larger xfmrs have very low inductances, I have found a few small (20va and smaller) that can be used as plate/grid chokes for pre stages.
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Old 14th March 2006, 10:39 AM   #4
Geek is offline Geek
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The advantage is MO transformers are usually large enough the typical DC for an average SE wont saturate it, despite the lack of gap.
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Old 14th March 2006, 05:01 PM   #5
kevinkr is offline kevinkr  United States
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Use 5KV transformer as output transformer?
Impedance transformation ratio of a 40:1 transformer is the square of the turns ratio so in this case it's 1600:1 or 1.6K to 1 ohm or 3.2K to 2 ohms, 6.4K:4 ohms, 12.8K:8 ohms, etc. It is doubtful it has anywhere near enough primary inductance for use at low frequencies, and unless there is a lot of interleaved primaries and secondaries leakage inductance is going to s*ck so there isn't going to be much high end response either... (Not done in 5KV power transformers as you want isolation.)

I would expect dcr on the 120V primary (used as a secondary) to be several ohms or greater which is not good for damping factor either.

It is very unlikely that this transformer would any good as an opt.
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Old 14th March 2006, 05:18 PM   #6
richwalters is offline richwalters
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Te leakage inductance is probably way over for isolation perhaps separete bobbin for sec....a square wave would become a sine at prob 5Khz and lower. Don't expect fantastic sound quality.
only ,my reasoning.p
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Old 14th March 2006, 05:22 PM   #7
bob_v5 is offline bob_v5  England
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i know a guy who uses sometimes mains tranformers for output on guitar amps. They sound pretty nice for thay job. Then again he always plays with vast amounts of distortion.......
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Old 14th March 2006, 05:51 PM   #8
Tubelab_com is offline Tubelab_com  United States
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In the original post the writer says that he has a 5KVA transformer. That my friends is large by huge by immense. If is works at all it would be strictly a low frequency item. Possibly for a subwoofer. I would think that the losses through this thing would be great.

Mains transformers for OPT's in a guitar amp. I did that too back in high school, when I didn't have any money for real transformers. Old dead TV sets were free at the local trash dump. I can't remember the sound exactly, but it does work to a degree. Definitely does not qualify for HiFi.

I have had some success using mains toroids for OPT's, but there can be no DC flowing through them.
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