|
Title: How best to run a pair of 115vac filament transformers across 240vac Post by: KK7UV on September 02, 2019, 09:57:16 PM Referring to the attached drawings:
1. Primaries in series, returning the "center" to neutral with a rheo. 2. Primaries each with a rheo, returned to neutral. 3. Primaries in series with end of leg connecting to L2 with a rheo. By the way this is same 240 line that will run the plate transformer. Thoughts? Steve, KK7UV Title: Re: How best to run a pair of 115vac filament transformers across 240vac Post by: AB2EZ on September 02, 2019, 10:21:22 PM Steve
I don’t think any of these will work, unless the loads across the two secondaries are identical. None of these configurations will cause the input voltage to split 50-50 across the two primaries (again, except when the two secondary loads are equal. Stu Title: Re: How best to run a pair of 115vac filament transformers across 240vac Post by: kb3ouk on September 03, 2019, 06:12:29 AM Just run both from L1, I've seen a lot of 240 stuff that all the 115 loads are on L1 and only the other side of the 240 is on L2.
Title: Re: How best to run a pair of 115vac filament transformers across 240vac Post by: KK7UV on September 03, 2019, 06:35:10 AM The loads on the filament transformers are the same (pairs of 813s).
Title: Re: How best to run a pair of 115vac filament transformers across 240vac Post by: Opcom on September 03, 2019, 10:04:05 AM The top right one lets you individually adjust the fil's. Will you individually meter them in that case?
But yes either side of the 240V, L1 or L2, to neutral would be 120V. Title: Re: How best to run a pair of 115vac filament transformers across 240vac Post by: AB2EZ on September 03, 2019, 03:15:55 PM I stand corrected. If you assume that the voltage between L1 and the neutral wire is
0.5 x (the voltage between L1 and L2), then the upper right design will work fine. Stu Title: Re: How best to run a pair of 115vac filament transformers across 240vac Post by: w4bfs on September 04, 2019, 09:01:38 PM I stand corrected. If you assume that the voltage between L1 and the neutral wire is 0.5 x (the voltage between L1 and L2), then the upper right design will work fine. Stu agreed if you will adjust the rheos separately .... you should also select 813's for equal current draw at same fil V ... the state of the vacuum will affect this ... I have found that about 30% of randomly selected 813's will be outside spec Title: Re: How best to run a pair of 115vac filament transformers across 240vac Post by: kb2vxa on September 25, 2019, 11:36:33 AM There you go thinking like electrical engineers analyzing it to death. Think like an electrician, with a neutral conductor the same diameter as the current carrying conductors it doesn't matter. The current imbalance is carried by the neutral, so with one on each side the neutral current is the difference between the two, very little to none when the loads are the same. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
Then if you follow the RCA Transmitting & Industrial Tubes manual you go back to thinking like an electrical engineer and over tax your brain with circuit design. The filament should be operated at 10V +/- 5% which in itself isn't a problem since mains voltage is +/- 8% maximum and with a 10:1 reduction the secondary easily remains well within +/- 5%. Unless you're in an old neighborhood with outside wiring that hasn't been updated since 1950 it remains fairly static. Here's where the fun begins, during standby periods in ICAS operation it is recommended that filament voltage be reduced to 80% of normal when periods are less than 15 minutes. For longer periods the filament should be turned off. Well, you can add a step start circuit to your PTT, add manual rheostats and switches that increase the uh oh factor, use Eimac tubes instead of RCA, (;->) or best yet use tubes that aren't so fussy. |