I have a couple pairs of output transformers suitable for 4X 6550/KT88, so I have decided to build a pair of monoblocks from scratch. Never done that before, but I have built , modified and repaired many tube amps. Trying to narrow down which Hammond power transformer to use. I want a bias winding for fixed bias so that narrows it down to the 300 series. Would like to run around 500 volt B+, so I'm thinking the 370 MX transformer? Hammond Mfg. - Universal Primary - "Classic" Power Transformers
http://www.hammondmfg.com/pdf/EDB370MX.pdf
http://www.hammondmfg.com/pdf/EDB370MX.pdf
Looks good.
You might want to use a full-wave-bridge on the 550 V red-red secondary instead of the usual center tap, and then go for a so-called "choke loaded" filter section. This way you'll get closer (or at) your 475-to–525 volt B+ ideal.
There's plenty of horsepower in that transformer. Remember tho: it'll get HOT if you are running it close to limit-specification. Make sure the chassis has ventilation holes around the transformer to allow some airflow upward/convection style.
Also… you might want to use series B+ regulation (either with, or in lieu-of, the choke-loaded filtering). It is hugely effective, and you will give up very little in order to secure a SOLID (line voltage independent) B+. Indeed, using MOSFET series B+ regulation and a stack of Zeners (and some cute high-Ω resistors and mid-value capacitors), you can quite easily also simulate a slow-turn-on vacuum-tube rectification, whilst still using silicon rectifiers for all their volt-saving (and maintenance) glory.
Just recall, always, that the design goal of a HiFi power supply is to produce solid, low impedance, very, very low ripple DC output. The method (vacuum or sand) is actually pretty darn agnostic. Get 'er done, and get 'er well filtered.
Nuff said.
GoatGuy
You might want to use a full-wave-bridge on the 550 V red-red secondary instead of the usual center tap, and then go for a so-called "choke loaded" filter section. This way you'll get closer (or at) your 475-to–525 volt B+ ideal.
There's plenty of horsepower in that transformer. Remember tho: it'll get HOT if you are running it close to limit-specification. Make sure the chassis has ventilation holes around the transformer to allow some airflow upward/convection style.
Also… you might want to use series B+ regulation (either with, or in lieu-of, the choke-loaded filtering). It is hugely effective, and you will give up very little in order to secure a SOLID (line voltage independent) B+. Indeed, using MOSFET series B+ regulation and a stack of Zeners (and some cute high-Ω resistors and mid-value capacitors), you can quite easily also simulate a slow-turn-on vacuum-tube rectification, whilst still using silicon rectifiers for all their volt-saving (and maintenance) glory.
Just recall, always, that the design goal of a HiFi power supply is to produce solid, low impedance, very, very low ripple DC output. The method (vacuum or sand) is actually pretty darn agnostic. Get 'er done, and get 'er well filtered.
Nuff said.
GoatGuy
... to be honest, I kind of thought you'd be using a hat full of SMPS switching supplies! ... Just joking, LOL. But... you might! GoatGuy
I bought the Hammond 370MX , made a bridge rectifier from 8-HER108 diodes, , filtering is L-C-L-C, used Hammond 159V chokes, each followed by 200uf. Spot on 500VDC, with 350mA load, only .8mV ripple, and the ripple is nice clean 120Hz sine wave. Only issue I hadn't anticipated is I cant use the bias tap, because I'm not using the center tap, but I found a couple 60 volt. .4 amp transformers for $7/ea. So now to build the rest!
Top shelf.
Way to go.
High fives.
Knock e'm out of the park.
Cliché after cliché!
GoatGuy
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.