Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: fossilshark on February 07, 2023, 07:27:02 pm
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I am having a hard time sourcing a 50VA, 110v primary, 250v secondary, 6.3v center tapped toroidal transformer. I found a few models with a 240v secondary but no 6.3v center tap winding.
I think it has to be toroidal because I am cramming it into a 1U rackmount chassis for a preamp. Does anyone have any suggestions?
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Hi FS
Not sure exactly what your application is (ie max tubes) but I have used 2 Toroids to achieve Preamp power supplies in 1Ru.
In the "leanest form" a 240V:12V AC 15VA Toroid for Heater and feed to second Tx and a reversed 240V:12V AC 5VA for HT in a 2 Tube 12A*7 Preamp. Very successful. As I'm in Australia, the HT was easy ie 12:240V gave me a nice 320V DC with SS Bridge Rect + suitable Caps.
You would need to use a Doubler for your HT (having 110 AC as your raw AC)
Anyway, my thoughts, it works well esp in 1RU but requires a little more real estate and parts.
Regards
Mirek
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i have this bookmarked for builds i first used a cheapo record player toroidal power transformer from ebay in that is no longer available: https://www.antekinc.com/as-05t240-50va-240v-transformer/
i'll send ya the two 100r resistors for the artificial center tap if ya need em ;-)
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Hi FS
Not sure exactly what your application is (ie max tubes) but I have used 2 Toroids to achieve Preamp power supplies in 1Ru.
In the "leanest form" a 240V:12V AC 15VA Toroid for Heater and feed to second Tx and a reversed 240V:12V AC 5VA for HT in a 2 Tube 12A*7 Preamp. Very successful. As I'm in Australia, the HT was easy ie 12:240V gave me a nice 320V DC with SS Bridge Rect + suitable Caps.
You would need to use a Doubler for your HT (having 110 AC as your raw AC)
Anyway, my thoughts, it works well esp in 1RU but requires a little more real estate and parts.
Regards
Mirek
I am about to start looking into having a xfrmr custom wound to avoid having 2 trannies in the chassis. It is a high gain guitar preamp I plan on doing point to point so the extra real estate isnt really an option.
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I used to get Custom Torodal Tx's made esp for Mesa B's here in Aussie (Cheaper and more reliable than Randies tx's :laugh:) But about 4 years ago the owner fell ill and the business faded along with Covid. They were world class, very cost effective and very reliable, made to order.
So I am a fan of custom made toroids at cost effective prices.
I don't know your location but here is a US manufacturer ISO Certified (with an extra winding):
https://toroid.com/tube-amplifier-transformers/ (https://toroid.com/tube-amplifier-transformers/)
Eg: Pre-Amp Power Transformer P/N 205.5076 (54VA)
Regards
Mirek
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80VA _ Meh! Wind your own!
https://toroid.com/sku/401.008/
--Pete
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I don't know your location but here is a US manufacturer ISO Certified (with an extra winding):
https://toroid.com/tube-amplifier-transformers/ (https://toroid.com/tube-amplifier-transformers/)
Eg: Pre-Amp Power Transformer P/N 205.5076 (54VA)
Regards
Mirek
I may ask them for a quote for a custom jobby.
80VA _ Meh! Wind your own!
https://toroid.com/sku/401.008/
--Pete
This is also not a terrible idea that I need to research. I imagine it would also be the most cost effective route.
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https://www.antekinc.com/as-05t240-50va-240v-transformer/ (https://www.antekinc.com/as-05t240-50va-240v-transformer/)
i'll send ya the two 100r resistors for the artificial center tap if ya need em ;-)
I just used the same one linked above in a 6G15 Reverb unit. Built in a Bassman chassis, the same height as a 1U rack. 100 Ohm Artificial CT on the board.
just fit...
no heater noise..