Parallel connection of Plate Transformers

[linearone]

If you hook up two transformers out of phase you get 0v when you turn them on . Its then a simple matter to swap leads, and then label them. Alternatively, just rectify both transformers separately and combine the dc.

 

[nomadradio]

If you hook up two transformers out of phase you get 0v

In series, only. Connected in opposite phase, the voltage from each winding cancels the other winding's voltage. Like the man said, zero Volts.

If you put them in parallel, but in opposite phase, you get a dead short. Always best to test this hookup with a current limit like an incandescent bulb in series, or turning up a variac slowly with a low-current breaker in line.

73

 

[linearone]

In series, only. Connected in opposite phase, the voltage from each winding cancels the other winding's voltage. Like the man said, zero Volts.

If you put them in parallel, but in opposite phase, you get a dead short. Always best to test this hookup with a current limit like an incandescent bulb in series, or turning up a variac slowly with a low-current breaker in line.

73

tbh, i never realized it was actually a dead short. I just always noticed it showed 0v. I always did it with a meter and a power strip with a nice on/off switch. quick flip, nothing, reverse leads, try again.

 

[Naysayer]

'dead short yeah' yeah I saw that lol. All ok as I used reduced/isolated test connects at first. When I finally got it working on full power I still used Temporary connections (wires strewn across the floor) --it worked really good though.
Yesterday I began to making wiring permanent where both Plate xfrmr Primaries powered from Soft Start. New 12awg from AC input through SS module. Adding panel mount 2 pin jack for external Primary so amp will continue to work with only 1 plate transformer. I put the Ext lines together so there's only 1 cord btwn amp & external xfrmer (proper HV wire of course.

Now I'm trying to determine what size fuse to place in Hot line (btwn SS module and panel-mount Primary power jack) to Ext xfrmr (only). My temp test hookup required a 7A fuse just to energize the Ext xfrmr (w/out soft start).

Online calculators require the VA rating of xfrmr which I suspect I didn't understand because the math derives a nonsensical number for VA. Xfrmr rated 1800v @ 400mA w/ 115 Primary so how to determine proper Primary fuse?

 

[nomadradio]

1800 Volts time 4/10 of an Amp is 720 Watts. Divided by 120 Volts is 6 Amps. There will be additional power drain for filaments, 24 Watts for each 811A, and a fan. Let's just round off to 900 Watts. Divided by 120 Volts gets us a max current draw 7.5 Amps. A fuse should not be operated above 80 percent of its rating. This gets us a rating of 1.25 times 7.5 Amps for a recommended fuse size of (round up to) 10 Amps.

Power-on surge might be a factor if your filter caps are really big, and there's no surge limit between the rectifier and filter. Sure wouldn't want to go beyond a 12 Amp fuse.

73

 

[Naysayer]

Thank you. I should have known how to do that given what I'm doing and it's embarrassing I did not.
My transformers are all fed separately from the SS module which is powered from the Mains fuse at 16A. I'll start with a 6A fuse for the Ext transformer and if it holds that should do it.

 

[nomadradio]

fed separately from the SS module

Good choice.

73

 

[Naysayer]

COR works Nomad! Have not tried SSB yet because I still need to locate the switch somewhere. Reluctant to drill more holes, running out of metal lol. Only tested AM at 5w (lowest PO on FT-891) but worked right away. Thank you.

 

[nomadradio]

Way cool! Always what I want to hear.

The sideband switch delays the engagement of the relay, not just its release time. More noticeable if you listen to the relay on AM. The difference in response time is more clear-cut and easier to hear. Does prevent chatter in sideband, but a tiny sliver of every syllable that closes the relay will fail to get amplified. I never recommend a COR for sideband, and suggest installing a relay (like the one I sell) in the radio to key an amplifier.

Kinda like built-in receiver preamps in a transmit amplifier. Technically it works, but with a minimum of sophistication. To achieve a true fast-attack, slow-release response just takes more parts.

73