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Philips G17T320

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crustytv
(@crustytv)
Posts: 11869
Vrat Founder Admin
 

Apologies if you already know this.

The original cap was rated at 1500VDC. If the replacement cap is listed as 700VAC then the rule of thumb is roughly 3 x VAC rate, for VDC rate. So in this case the 700VAC will be fine at 2100VDC more than adequate for your needs.

Not sure if that answers your query.

 

e.g. I replaced a Dubilier 0.47 1500VDC with a poly 0.47 500VAC on a PYE 697, perfectly acceptable.

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Posted : 03/05/2018 10:43 am
sideband
(@sideband)
Posts: 4216
Famed Member Moderator
 

Seems reasonable. I think you actually multiply the 700Vac by 2.8 if I remember what Philips said (so 3 is near enough...and easier to work out)! That would give 1960 volts DC which is still way over the original rating so no problems with your replacement.

 
Posted : 03/05/2018 1:32 pm
Cathovisor
(@cathovisor)
Posts: 6391
Famed Member Registered
 
Posted by: sideband

Seems reasonable. I think you actually multiply the 700Vac by 2.8

Correct; 2 times the square root of 2.

 
Posted : 03/05/2018 4:12 pm
6.3volts
(@6-3volts)
Posts: 214
Reputable Member Registered
Topic starter
 

Thanks for your replies. My question was asked because I wasn't sure about the relationship between AC rating  and pulse voltage. I am familiar with the ac and dc ratings of caps but not the dynamics of pulses. You all have a much deeper knowledge than myself.

Jonathan

 
Posted : 04/05/2018 7:07 am
Nuvistor
(@nuvistor)
Posts: 4594
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A range of capacitors for AC and pulse circuits, mainly polypropylene for your info.

 

https://www.vishay.com/capacitors/film/ac-pulse/tab/products/

 

Frank

 
Posted : 04/05/2018 7:13 am
6.3volts
(@6-3volts)
Posts: 214
Reputable Member Registered
Topic starter
 

Final,(I hope) update on this set. After being very distracted I have finally fitted a correct type of harmonic tuning cap to the line o/p circuit.

I had only ever run this set with a temporary ceramic cap and concluded after much searching that the high voltage and scan problems were due to a replacement LOPT having been fitted from an earlier set. These transformers required a 2.7nf cap instead of this model's 2.2nf. Adding extra ceramic capacity brought everything into spec and I thought the issue was sorted.

Just before I fitted the new cap I had watched a Youtube video about ceramic caps and as a result I first tried the original value of 2.2nf - to be rewarded by a set operating perfectly and with loads of width to spare.

Several of you had suggested that I should not run the set on ceramics and you were right! The concept of caps changing their values drastically with applied voltages is new to me and in case it's of interest to anyone else take a look (link below)

Another lesson learned on my journey.

Jonathan.

 

 

 

 
Posted : 01/07/2018 3:42 pm
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