Today I replaced the socket for the 6M5 final amp valve on my Philips Radioplayer. When I reseated valves and powered up, all valves appeared to heat, but no tuned signal came through. After about 10 seconds, there was a ping and a flash from V2, the 6N8 IF amplifier valve.

I have a couple of spares so I took a risk and swapped in another 6N8 in case it was just a valve age problem. The replacement valve also pinged and flashed after warming up.

I haven't found any shorts. Any suggestions on where to look? What would cause the IF amp valve to blow?

Maven

First thing I would do is a visual inspection, followed by removing the valves and checking the output voltages on the transformer. If all is well there then I would insert the rectifier valve, power up again and check the high tension voltage.

You could also have a shorted coil, condenser, etc. Check the electrical condition of nearby components. Most valve types are pretty hardy. They'll go bang when something is horribly wrong though.

Today I replaced the socket for the 6M5 final amp valve

On the basis of what was last fixed often causes the next fault ... If the set was operating before that change, I would be looking for an error in rewiring the socket, or stray solder blobs causing shorts.

A suggestion here. Make a copy of the circuit diagram and mark in with a pencil the valve socket pin numbers. If you take a valve and look at it upside down the pin numbers will go from 1 to 9 clockwise. Unfortunately Philips don't mark the pin numbers on their circuit diagrams. I've included some addresses with the valve pin outs for your radio. Read these pin outs the same as you would looking at a valve upside down.
http://frank.pocnet.net/short/054/3/330.pdf see page 780 for ECH80 (6AN7) pin out.
http://frank.pocnet.net/short/054/3/303.pdf see page 686 for EBF80 (6N8) pin out.
http://frank.pocnet.net/short/054/2/215.pdf see page 429 for EL80 (6M5) pin out.
And remember the heater pins are 4 & 5.

Thanks for the wisdom. I've collected the referenced data. I also found online a Miniwatt 6M5 datasheet that listed "Basing connections" with pins numbered clockwise. I rechecked my wiring against that and I'm fairly sure I got the 6M5 socket wiring correct, UNLESS I'm still getting the pin numbers upside down.

I was a bit alarmed to see that the heater circuit uses common chassis ground - so pin 3 from the grid 3 ties to pin 4 from the heater. The other valves are wired the same, so I guess it is normal. I don't claim to understand coils and capacitances very well, so I'm working with mysteries here.

A couple of possible dry joints to re-do, but no stray solder blobs discovered.

Still trying to infer how too much current is getting to the IF 6N8. I don't have a valve tester, so I'll try to check capacitances from the data sheets with a multimeter, checking also against a presumed good 6N8.

If I find the same fault in two popped valves, that might point to where the current is flowing.

Maven

Pin 3 on the 6M5 is the Cathode (& Suppressor grid) and on the Philips 123 it is grounded. The same applies to the 2 6N8's & 6AN7.

It would be an idea to tell us what was done prior to the incident. viz. was it working before you attacked that socket, for whatever reason?

The valve socket is read clockwise, looking at the base or wiring side. What exactly is it I have a 132L?

You may have cut of the plate supply to the tubes. Pentodes are not very happy if the screen suddenly becomes the plate.

Make sure HT intended for pin 1 is not on 9 AWA say NC but the drawing shows it in such a manner that it just might be attached to the heater pin 5

Check the wiring ..... you may have B+ on a cathode and the generalisation is not more than 20V between them & heaters, or they will flash over.

Marc

Done all suggested checks and reflowed some dry-ish solder joints. Some previous re-wiring had been done with a 25-watt iron and joints looked suspect. I'm now using a 40-watt iron with much better results (see thread about irons in the Tools forum). Only problem is the iron has a tip-retaining screw that sticks out 5mm from the barrel, so care needed around meltable components.

Put in yet another 6N8 from dwindling stock, took a deep breath, and switched on. 8 seconds, then ..... music!!

A couple of the dry joints were in the HT area. One was on the ground side of the biggest capacitor. I'm now guessing that one of these joints was sparking as it warmed up and maybe putting a damaging surge onto V2. Or the plate supply was intermittent, as Marcc suggested.

I've learned a few things from this. Thanks all!

Maven

One of the most critical factors with minature tube sockets in particular, is lead dress and neatness.

Some of those sockets are a bit ratty & the pins wobble The idea is to get the least amount of solder on a joint that is possible with out compromising it's effectivness.

Stranded wire can be a curse as bits can stick out & get involved with something it should not be involved with. Some of the insulation also suffers "melt back" & makes a gooey mess.

Often you need solder wick to clear the terminal of all remnants of previous parts as thes can Bulk up a joint, making it look crappy & increases the risk of flashover to an adjacent pin.

Never be afraid to put heat proof spagetti, or shrink tube on a wire or lead that has the potential to short to an adjacent part.

I can apreciate that screw issue. One of my biggest (Chasses) soldering irons sports that "screw feature, and it is treacherous.

Marc

Marc: "Some of those sockets are a bit ratty & the pins wobble"

When I replaced the V4 noval socket I noticed that it was the only original one in the chassis. It fell to bits when I drilled out the chassis rivets. 3 other 9-pin sockets had been replaced during the past 60 years. I also noticed how flimsy the connection to each pin was. No tube at all to grip the pin, just the edges of a thin metal sheet sandwiched between two insulation sheets. No wonder they could become unreliable with a bit of twisting or abrasion.

I've replaced socket V4 with a ceramic that seems to have at least some tube length for more secure pin contact, and I have three more ceramics that I will install in due course (i.e. when I am completely bored or have future reason to suspect poor socket contacts).

I used pop-rivets to fix the new socket. I considered machine bolts, but thought the speaker vibration might loosen the nuts over time. Is that standard for socket replacement?

Maven

I used pop-rivets to fix the new socket. I considered machine bolts, but thought the speaker vibration might loosen the nuts over time. Is that standard for socket replacement?

Personally, I hate pop rivets and use machine bolts for sockets, etc, on chassis. I don't have any concerns about them coming loose, but if I did I'd use star washers under the nuts.

I don't have issues with pop rivets in chasses, other than using them before era. Under stress they are known to gradually work loose. They have been holding the sign on my gate for over 40 years. Using Aluminium in Iron will cause the Aluminium to get eaten where there is moisture (electrolysis)

That crumbling issue is not confined to minatures. I find a lot of rectifier & output tube sockets with heat damage. If these need replacing I try to use Ceramic.

Noval pins & sockets are notorious for connection issues.

Marc

Are the 6N8s that had the flash toast? Now that you fixed the problem, those tubes *might* still be in working condition. If you have a tube tester, check for shorts, and if none are found, see if the emission or transconductance measures right. If they pass that, try them in a junker radio.

If the flash was between the cathode and heater, because the cathode ended up being at a high voltage, in normal use the issue may not reappear. As the cathode and heater are only a few volts away from each other in Aussie radios (the ones with power transformers).

Good catch, Wa2ise!

I don't have a tube tester, but I do have more courage than sense, so just before tossing them I did rotate the flashed 6N8s through the repaired radio. One worked, one didn't. So the fault has only cost me one 6N8, I think.

I had checked all tube pin combinations for shorts with a DMM, but couldn't get resistance readings of any kind. are there techniques for valve testing with a multimeter or oscilloscope?

Maven

Why not use a grubscrew to hold the tip in?

If you have $100 to spend, the Hakko No. 921 is the best iron I have used. It is 55/110 watt and rivals my Weller station.

Don't use aluminium riverts on zinc plated steel or your chassis will rust away. These two metals have a different number of free electrons.

A little silastic on the thread before or after you tighten the screw will work. Besides, the vibration from a speaker is slow and they are usually held in with screws.