Pye B16T.

[Murphyv310]

Hi.
The new smoothing caps arrived today. Unfortunately the diameter is too big for restuffing into the old cans. I've fitted them anyway and retested the HT and it now has risen to 300v within a few minutes with a 1k series resistor from 375vdc. That's correct owing to a few potential dividers in the set. I've also remade the EHT bleeder as it was O/C, I've also potted the series resistor/smoothing/bleeder network and replaced the damaged EHT lead with a modern red lead for safety. An X2 filter cap from mains to chassis has been fitted instead of the old waxy. Now just waiting on the rewound transformer from Ed. Should be here mid week and then a full test.

[ppppenguin]

Possibly silly question. If there is no more than 375V HT why did you need to get 500V capacitors?

[Freya]

Hi Trevor,

With regard to the safety capacitor, if an X class capacitor is fitted and it went short, would it make the chassis live ?, would a Y class not be recommended in this instance. (only ask as i can`t decide)

[attachment=19726]

Stephen

[Murphyv310]

Possibly silly question. If there is no more than 375V HT why did you need to get 500V capacitors?

Hi Jeffery.

Good question indeed. I have found in the past that any set with an EL38 will have the HT at full potential before the valve conducts, also if say the HT choke was to go O/C the voltage can rise on the reservoir. This could mean that the "surge" could be 400+ volts. As the set is not a local repair I would rather go down the belt and braces route than taking chances.
Also as yet I'm not using the sets own PSU so again the HT could be over 375v anyway.

[Murphyv310]

Hi Trevor,

With regard to the safety capacitor, if an X class capacitor is fitted and it went short, would it make the chassis live ?, would a Y class not be recommended in this instance. (only ask as i can`t decide)



Stephen

Hi Stephen.
Yes technically a Y type is the best for this position. In reality the leg of the transformer is at mains neutral where the cap is connected to chassis. The one I fitted is actually a universal type that conforms to both X1 and Y2 specs, my mistake for only quoting the X type.
In any case even an X type will be far far safer than a 600vdc wax capacitor.

[ppppenguin]

It must be a Y cap. No guarantee that mains polarity will be correct. Especially as you say the set will be out of your control.

[Murphyv310]

It must be a Y cap. No guarantee that mains polarity will be correct. Especially as you say the set will be out of your control.

Are you saying that the X1 Y2 type are no good. Never had a failure ever with these types.

These are the ones I use https://www.justradios.com/X1Y2capacitors.html

[ppppenguin]

The dual X1/Y2 types are fine. They are Y rated. But in an earlier post you said "Yes technically a Y type is the best for this position. ". It's not that Y type is merely best, it's absolutely essential where failure could cause a shock hazard.

[Murphyv310]

While I realise the Y type have the spec required for the position they are used in, I'm surprised that you forget how bad the paper capacitors were in that position, they were deadly.
In fact an X rated capacitor is as much likely to fail in that position as someone can switch the sun off!
Look at the circuit, the cap is between neutral and chassis, if the chassis is earthed and the plug is wired correctly it will lead a life of retirement virtually doing nothing, if it between live and earth if it was to fail it would blow the fuse or trip the RCD.
If the chassis was not earthed again it has an easy life especially if between mains neutral and the floating chassis. If the mains is not wired correctly or plug and the capacitor is between live and chassis then on the very slim chance it should fail then yes it could be an issue but let's put this into reality the wax original is 10,000 times more dangerous than an X type in that position, fact not fiction!

The only X type I've had a failure with is Rifa types which I would never ever use in any position.

[Murphyv310]

Hi.
The set will be returned with a three cored mains lead for a belt and braces approach in any case. On any job I do that has a double wound mains transformer I always fit a three core lead for safety.