Just a quick question.

The Electro. Caps. Used in this radio are rated at 500v. I cant find 8μF at 500v caps anywhere. the closest I come to is a 10μF 450v (DC).

What should I expect the HT of a radio like this to be? I figured it would be no more than about 300v.

Could I use to 450v cap or would its working voltage be exceeded?

I think the next rating up from 450 is 630 and this is definitely recommended. If you use a 450v cap on a 500v supply it'll most likely blow up, literally, and the foil could short out other components causing further damage. At best it will have a very short service life.

The Electrolytic filter caps in it look like the standard 525V Ducons.

Normally depending on the HT these units will surge to a PIV of around 450V prior to the bulk of the tubes going into conduction. 5Y3 being a filament valve, with low thermal inertia filament. It gets mobile fairly quickly and that is what causes the surge.

Try EVATCO as they have Sprague Atoms which go to 500V
To keep the inventry down it is of little practical advantage to buy caps to replace the paper ones in Valve radio's under 630V.

Going back to an original question 250VDC HT the bias on a 6F6 is -16.5V (in respect to Cathode) 7K load. 6V6 -12.5V, 5K load

If the set is not back biased (CT of transformer floating) then a Cathode resistor of 410 Ohm for 6F6 and around 265 Ohm for a 6V6 would be likely.

If you need a new 5Y3 (still made) and you wish to reduce the surge, consider a Sovtek 5Y3, which is built completely differently and has a high thermal inertia heater.

The 5Z4 is as I thought but will not handle the PIV of a 5Y3.

Marc

Hi Marc

My set uses a 5Y3 as the Rect. Valve. Its stamped onto the chassis. (Visible in red on the back of the chassis in above picture)

I already have 10μF 450v caps and I WAS just going to use these.

There is NO cathode resistor on the 6F6. It is grounded straight to chassis.

The power supply stage and output are as shown in the cct with my red pen all over it.

The CCT diagram isn’t exactly what I have but my red pen amendments show what I am playing with. (Except the rect valve, I hadn’t changed the text at time of scanning in my rough working diagrams)

So...

Back to my question, Will I be able to use the 450v caps or will they blow. I intend this radio to be used on a daily basis.

What caps are you using that are 630v? I replace with values close but always just a bit high than the ones that were in there originally. e.g. a 0.01μF 200v Paper will be replaced with a 0.01μF 400v "Orange Drop", a 0.05μF 400v paper will be replaced with a 0.05μF 400v "Orange Drop". The only time I will use a 630v CAP or higher is if the original part was rated that high.

630V Caps are expensive in comparison to the 400v and if the voltage isn’t near that high why use them?

Hi Marc

My set uses a 5Y3 as the Rect. Valve. Its stamped onto the chassis. (Visible in red on the back of the chassis in above picture)

I already have 10μF 450v caps and I WAS just going to use these.

There is NO cathode resistor on the 6F6. It is grounded straight to chassis.

The power supply stage and output are as shown in the cct with my red pen all over it.

The CCT diagram isn’t exactly what I have but my red pen amendments show what I am playing with. (Except the rect valve, I hadn’t changed the text at time of scanning in my rough working diagrams)

So...

Back to my question, Will I be able to use the 450v caps or will they blow. I intend this radio to be used on a daily basis.

What caps are you using that are 630v? I replace with values close but always just a bit high than the ones that were in there originally. e.g. a 0.01μF 200v Paper will be replaced with a 0.01μF 400v "Orange Drop", a 0.05μF 400v paper will be replaced with a 0.05μF 400v "Orange Drop". The only time I will use a 630v CAP or higher is if the original part was rated that high.

630V Caps are expensive in comparison to the 400v and if the voltage isn’t near that high why use them?

Many of the sets I repair do get to the 450 to 500V mark. When you put through radios in hundreds, one needs to watch the inventory. Eg I can easily go through 10+ caps of one value in one day especially if I get one like I have at the moment, with sixteen valves and a parts list that goes to C67. It only has papers to a max of 400V listed all of which have been previously replaced (message there).

Axial Metalised polyesters are of a better shape to replace the axial papers and are not expensive.

Whilst I occasionally use the Red greencaps and others of that style. The lead length of them is more often than not, an issue.

I would not dare use a 400V on the plate of the 6B6.or to replace the 0.1μF decoupler on the HT. That to me is getting to the upper limits of a 400V at Surge.Albeit if the 20000 Ohm screen divider is there, in your set, it will help drag down the surge.

The 450V issue is unfortunately like "how long is a piece of string" in order to gauge that one needs to know the HT of the radio. The AC voltage of the HT secondary may be a clue. eg 285 - 0 - 285. I would suspect that you will get away with it as the surge value of those caps will be higher.

The fact that the 6F6 has a grounded cathode is a clue that it is (like the 1051) back biased.

Keep plodding

Marc

Hmmm.....

I figured that the ht voltage would be like the value in my Astor GN set that you helped me with before (Similar valve line up). Its HT voltage was stated as being 285v before the choke and 245V after .(1000ohm/volt meter) In real with my fluke digital I got somewhere over 300V ish. I put 450v caps in that set for the electros.

Should I have made these a higher value?

Update!

I have finished working on this radio. It got a complete overhaul. The caps were in a very bad way! A few resistors and a lot of dodgy repairs made in the past.

I have worked out it is the cct listed in an above post. The 1st valve is a 6A8GA not the EK2G. It does work in SW as well as BC.

The sound from the old electrodynamic speaker is clear but not as much Bass response as I am use to from a 8" speaker.

For the Caps I have ended up using 500V types in the electros. Most of the other caps are 400V. there is a few 600v ones as well like the one across the O/P for the speaker.

Other things I have noticed are it will pick up the strong stations around me (Canberra) without an antenna attached.

Well its another one done......

Looking for more!!!

Uploading of images will be great Brad, we all greatly appreciate what you do for this forum.