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16th Mar 2018, 7:39 pm | #1 |
Hexode
Join Date: Aug 2010
Location: nr. Hannover, Germany
Posts: 372
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Output transformer question
Hi,
one of my current projects is building the signal tracer Smithy presented in the March 1970 edition of the much missed Radio Constructor. The output valve is a 6BW6 and an OPT of 45:1 for 3 Ohm LS was specified. As the output stage will normally not be running at any significant power and will have a low duty cycle, I am thinking of using a 100V PA system transformer with a primary impedance of ~ 4600 ohms into a 4 ohm LS. Will this be OK or are there any pitfalls to watch out for? As always many thanks for taking the time to read and reply..
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Eddie BVWS Member. Friend of the BVWTM |
16th Mar 2018, 7:51 pm | #2 |
Octode
Join Date: Aug 2006
Location: Stoke-on-Trent, Staffordshire, UK.
Posts: 1,082
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Re: Output transformer question
Core saturation the 100 volt line unit has interleaved E and I so it's likely to suffer from core saturation. Having said that I have used them with a fair result. You could always pull the laminations and then rebuild. I have also done this, but I did not think it was worth the effort.
Trev |
17th Mar 2018, 12:06 am | #3 |
Banned
Join Date: Jun 2015
Location: Mareeba, North Queensland, Australia
Posts: 2,704
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Re: Output transformer question
AS you state: the duty cycle is very low, you dont need hi-fi response, and you won't be using full power, so "any" small single ended transformer should work. If you do have real problems ( you shouldn't ) then I am sure somebody here can find such a transformer.
I have seen many projects using line transformers as output stages, so maybe a look at some of the guitar amp builder's sites would give you more accurate advice. Best of luck Joe |
17th Mar 2018, 10:05 am | #4 |
Moderator
Join Date: Dec 2010
Location: Exeter, Devon and Poole, Dorset UK.
Posts: 6,824
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Re: Output transformer question
As Quality isn't that important you could try a 6V mains transformer.
It will saturate and the HF response won't be that good but such transformers are cheap and plentiful might be worth an experiment to see if it's good enough in this use Cheers Mike T
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Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk |
21st Mar 2018, 4:01 pm | #5 |
Octode
Join Date: Aug 2003
Location: Welwyn Garden City, Herts. UK.
Posts: 1,906
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Re: Output transformer question
A 100v line transformer will be too low an impedance.
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21st Mar 2018, 9:36 pm | #6 |
Octode
Join Date: Aug 2006
Location: Stoke-on-Trent, Staffordshire, UK.
Posts: 1,082
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Re: Output transformer question
Not quite true some 100 volt line units can be anything from 10 k down to 1k the main problem with them is core saturation
ren |