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

Philco vtvom 7001 line caps?
#1

While checking out the vtvom I found it had 62v ac. between the chassis and earth ground. Did not matter which way it was plugged in.
It has 2 -.25 line bypass caps from the primary of transformer to chassis.
 Put an 1000 ohm resistor between the chassis and earth ground and measured across it and have 12 volts. So I cut the ground side of the .25 caps and jumpered in 2-.01 Y-type disc safety caps. It now reads 51v ac chassis to earth ground and.05v ac across the resistor.
 Two questions I need help with.
 Is the 51v with the new caps a phantom voltage?
Can I use the .01 safety caps to replace the .25 caps or should I order the larger value safety caps?
 Any help greatly appreciated.
#2

Quote:Can I use the .01 safety caps to replace the .25 caps or should I order the larger value safety caps?


Yes, the .01mf is sufficient bypass without having an excessive AC line current pass-through. A higher value of .03mf could, with other equipment on the same GFI branch circuit, cause a nuisance tripping of the circuit breaker.  The OEM value of .25mf is extreme by todays standards. Such a value even with NEW "Y" capacitors would give an uncomfortable tickle and under certain conditions a disturbing shock, if accidentally combined with another device in use the shock could be very hazardous. For the VTVOM it could make low level AC voltage measurements impossible.

I do not know the instrument being repaired, if it has a power transformer, the windings can be leaking to the core. That would be a problem, an open style transformer can be disassembled and the core more effectively insulated to reduce the shock. However the primary could be leaking to the secondary and often that is in direct reference to the chassis. If so, then the transformer would have to be replaced.

YMMV

Chas

Pliny the younger
“nihil novum nihil varium nihil quod non semel spectasse sufficiat”
#3

Thanks Chas. Went ahead and put the .01 safety caps in it. The tester does have a transformer so I'll check it for possible primary to secondary leakage.




Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
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
5U4 vs 5Z4 tubes
5U4 and 5Z4 almost identical. I think nothing happened if you left 5U4 instedad 5Z4 long time. Just heater current 5U4 ...Vlad95 — 11:02 PM
Philco 42-345 Restoration/Repair
Hello Vlad95 , Very Funny ! Sincerely Richardradiorich — 11:01 PM

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

>