Welcome Guest! Be sure you know and follow the Phorum Rules before posting. Thank you and Enjoy! (January 12) x

Thread Closed
Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5

B+ too high! Two different radios.
#15

Your B+ is running higher because of the 25 cycle pwr trans being used on 60 cycles mains. It would be best to replace the pwr trans if possible. Transformers do run hotter internally when applying 60 cycles into a 25 cycle because of the size of wires windings inside a 25hz type as compared to the 60hz types. If ac trans swap is out of the question, here are a couple things ( guaranteed) so you can bring down B+ voltage in your sets that have 25 cycle trans.

(1) find your power transformers center-tap wire that usually is soldered directly to chassis. Cut & lift it off chassis, install a 25 watt wirewound power resistor ( exact best ohms needed can be found by subbing in & out a few different values with jumper wires with alligator clips in "series" with trans CT back to chassis ground) while monitoring your B+ voltages, slow upping with your variac to modern line voltage. Ohms needed could be anywhere from 3-500 ohms in my guess. Monitoring your B+ while subbing in the resistors will yield you a good match.

or try this: ( may be easier)
(2) find the socket connection (wire) off your rectifier tube socket that feeds your radios 1st [ First] B+ filter cap according to schematic. Cut & lift the wire, add a 20 watt wirewound pwr resistor in "series" ( try subbing anywhere from 250- 350 ohms) using alligator clip jumpers while monitoring your B+ while slow upping your variac to work on modern line voltage. You will find a good match by subbing in various resistors until you get your B+ voltages near schematics ratings +/- 15%

* either of the above suggestions will drop your B+ voltage. Exact matching yield by experimental subbing the 20 watt w.w. resistors via 2 jumper wires with alligator clips on each ends.


*for those that say it is ok to run a 25hz power trans on 60hz mains needs to try this to be "convinced" sometimes via "audio"!
find a vintage German or Mexico 50 hz version of a vintage tape-deck. Plug it into 60hz mains & listen to it thru any amplifier. Distortion , lousy sound, are due to "higher B+" voltages courtesy of only 10hz difference upping the B+! Try it sometime, and the nay-sayers 25hz vs 60hz can be convinced easily "by ear"! Enjoy your vintage Radios!! Icon_wink


Messages In This Thread
B+ too high! Two different radios. - by davemc - 02-08-2009, 02:24 PM
Re: B+ too high! Two different radios. - by rickd - 02-08-2009, 02:34 PM
Re: B+ too high! Two different radios. - by AI2V - 02-08-2009, 10:08 PM
Re: B+ too high! Two different radios. - by exray - 02-09-2009, 07:37 AM
Re: B+ too high! Two different radios. - by AI2V - 02-09-2009, 10:48 AM
Re: B+ too high! Two different radios. - by Arran - 02-10-2009, 11:36 PM
Re: B+ too high! Two different radios. - by Texasrocker - 02-21-2009, 11:32 PM
Re: B+ too high! Two different radios. - by exray - 02-22-2009, 09:57 AM
Re: B+ too high! Two different radios. - by Arran - 02-23-2009, 12:29 AM
Re: B+ too high! Two different radios. - by Arran - 02-24-2009, 01:19 AM



Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
Philco 42-345 Restoration/Repair
Hi OSanders, Look carefully at the band switch. Turn it slowly and "wiggle" it around the desired band. ...MrFixr55 — 12:33 AM
5U4 vs 5Z4 tubes
I think that RCA and GE introduced metal tubes in the USA in 1936.  I don't know if they were being made by RCA, GE or b...MrFixr55 — 11:20 PM
Philco 42-345 Restoration/Repair
Vlad95, Thank you for the stringing guides and wow there are so manyosanders0311 — 06:01 PM
5U4 vs 5Z4 tubes
A pre war Hallicrafters, and an early one too, very nice! 1936 is pretty early for metal tubes too, which would explain ...Arran — 05:58 PM
Philco 42-345 Restoration/Repair
Thanks Rod, "When you hear the background hiss and no station it usually indicates that the oscillator quit" ...osanders0311 — 05:52 PM
Philco 42-345 Restoration/Repair
RodB :beerchug:Vlad95 — 10:22 AM
Philco 42-345 Restoration/Repair
Vlad, you nailed it. Swiss and German roots.RodB — 09:54 AM
5U4 vs 5Z4 tubes
Well this is a Hallicrafters SX/9 circa 1936. No real issues so far although I dodged a real bullet with a cap that was...bridkarl — 07:59 AM
5U4 vs 5Z4 tubes
The pinout is the same but the 5U4 has a 3 amp filament, verses 2 amps or less on the 5Z4. I think that the pinout of a ...Arran — 12:04 AM
Philco 42-345 Restoration/Repair
By the way. osanders0311 Take a look here: Dial cord stringing Guides May be here you can fount correct string settin...Vlad95 — 11:15 PM

[-]
Who's Online
There are currently no members online.

>