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MV Rectifier Voltage Doubler
MV Rectifier Voltage Doubler
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Old 15th February 2020, 07:18 PM   #11
rmb is offline rmb  United States
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An old 50 kW am transmitter I had my hands in (and still a standby) used six 857B mercury rectifiers for the 15 kV supply for the finals (recall they were air cooled 5671's...) The reliable Gates and RCA 1 kw early vintage AM transmitters used four 833A tubes (2 for modulator, 2 for RF) and there were 866A's and 872A's in the LV and HV power supplies. The later vintage tubed am transmitters used four 4-400A tubes (2 for AB1 modulator, 2 for RF). Power supply had 8008 merc rectifiers. The 833 ran about 2500 volts on the plates at little over half an amp for the pair; the pair of 4-400's liked around 3100 volts and 460 mA for the pair to get a kilowatt of RF at the antenna. The modulators loafed since approximately 500 watts of audio was needed for 100% modulation of the RF. In the day, it was customary to modulate asymetrical to make the station loud, which put stress on the HV components...but the managers liked a loud station...fwiw

As far as noise is concerned, at high power levels the noise from the M-V rectifiers was insignificant...There was one AM transmitter built by RCA (BTA5H) that used six 5563 mercury thyratrons for the 5 kV plate supply...and the plate voltage could be adjusted from the front panel without a large lossy rheostat...Typically, all the tubed AM and FM transmitters above 1 kW required three phase AC power in the day...Even RCA's 1960's vintage FM transmitters (BTF10 series) used six 8008 merc rectifiers for the 4CX5000A RF final....Some of the RCA BTF series transmitters still are on the air...

For what it's worth, I recall the old Gotham disk cutting amplifier (PFB150WA) for the Grampian mono cutter head used 3B28 gas rectifiers...to keep the voltage constant for the 811A output tubes...

Last edited by rmb; 15th February 2020 at 07:26 PM.
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Old 18th February 2020, 12:16 PM   #12
Gungnir is offline Gungnir  United States
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I should have clarified a few things. I have used MV rectifiers before, and I get it that SS diodes are superior in every way. I am aware of the dangers of MV, I like the way they look and I have a lot of them in stock; I have 866,816,8008, and 83. I also like Xenon gas diodes, which I also have many of. I want to build a 6c33c/6s41s/6as7 amp. I have a nice 75v 3.5A transformer that would be perfect for doubler duty. I will probably go with 6D22s for this project.
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Old 18th February 2020, 12:27 PM   #13
Kay Pirinha is offline Kay Pirinha  Germany
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Location: Somewhere in Germany
Originally Posted by rmb View Post
Do not use mercury vapor rectifiers for voltage multipliers. They don't like capacitor input type loads. Full wave choke input is best for mercury vapor rectifiers.
I'm not advocating MV rectifiers at all, mostly due to their poor efficiency in comparison with SS diodes. But voltage doubling doesn't exclude choke input. Get a Delon doubler and insert the choke into one of the AC leads - bingo! It even should work with a Greinacher doubler.
Best regards!
"I spent a lot of money on booze, birds and fast cars. The rest I just squandered." (George Best)
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