I think I have just destroyed my portable radio.

Had all of my battery holders and batteries ready and attached to the fly leads, only one lead had "polarity" which I figured must be the 90 volt B battery, which I accordingly connected to the longer lead, red to positive and black to negative, then wired up the 7.5 volt and turned it on only for the 90 volt connector to start fizzing!

Upon looking at the map inside the radio (which I should have done first) it appears I have connected the wrong connectors to each battery...

When I plugged in the AC the radio no longer works, just stays silent and only the 6X4 valve appears to light up?

Arghhhhh!!!

Does this mean the radio is ruined or maybe just the valves filaments?

Oops
Most likely blown all the filaments.

ben

Best way to confirm is to test continuity on all the valve filaments and go from there.

The fact that the rectifier still works is something to go on. It wouldn't be in use on battery power.

Yep, you've probably killed all the battery bottles. But because they are in series, if you are lucky, you may not have killed all 4.

Pull each one out and measure resistance between pins 1 and 7. O/C = dead.

I have a set of valves - 1R5, 1T4, 1S5, 3V4 - for your radio if it helps.

Don't be too sad - those AC / DC radios usually contain a set of low emission valves because of the amount of use they got running on AC. So a new set of bottles should improve performance greatly.

Ok thanks, I feel a little silly for assuming that the black and red wires went to the HT... One look at the diagram would have saved it, just my eager enthusiasm, a lesson learned. Thank you for the offer of valves, much appreciated, however I have managed to find them all on Ebay (for a small fortune), but worth it I guess, if they are indeed NOS! I'll wait and see and hopefully it'll work again!

Another issue I had is when running it on AC for several hours, after re-capping, I noticed the two 3 watt resistors were getting very hot, the black one, closer to the rear of the case, in particular, showing evidence of previous overheating. After about 4 hrs the radio was quiet t only one third of it's previous volume and after turning off to allow things to cool, it was only half the volume it had before, so I think these resistors may be dicky, I ordered 5 watt versions (cement) as replacements. One is 1.1 and the other 1.2k. I'm having trouble reading the schematic as all power goes through the switch, which is pictures as a circular bunch of arrows! What goes to where and when is nearly impossible to fathom, but with new valves hopefully the issue may disappear? Can only wait and see at the moment.

Hi Jamie

Rather than Ebay, the ones I have would be free to you, just cover the postage. Some are NOS, some are tested-good 2nd hand. I won't be using them, they are free to a good home!

Those resistors are supposed to get hot. They drop the HT voltage from the 6X4 down to the 7.5 volts for the valve filament series string. It was done this way because it was difficult with the contemporary technology to get a smooth, low voltage, high current source to substitute for the A battery. Easier to drop 120v DC down to 7.5v 50mA with a hefty resistor.

It was normal for the black cement on these resistors to disintegrate, it doesn't affect the performance of the resistors. There is no real need to replace them, even if you could still get the right values. And that's important.

Your change in volume issue lies elsewhere. Once you get the new valves I'd start by measuring the AGC - see how much it changes when you tune a strong station.. This will tell you if the low gain is before or after the volume control. Once you know this, you'll know (I'll tell you?) where to measure.

Always measure first before changing anything.

I'm having trouble reading the schematic as all power goes through the switch, which is pictures as a circular bunch of arrows! What goes to where and when is nearly impossible to fathom

With the diagram at hand, look look at the back of the switch as you operate the rotary switch though its stops. You'll notice the contact bridging different contact lugs in each position. The diagram ought to match that operation.

If the wires to the switch have coloured insulation, then note those colours on the schematic.

Unfortunately I have seen many cases where exuberance has been the cause of many a disaster. Whilst that may bee seen as a good thing for those like me, who repair, it is fact quite destructive and can in some case ruin any chance of a repair.

This is why I say time and again, never power up until it has been established that it is safe to do so. There was a colour code, often loosely applied, as to what power & polarity & function was applied.

This is not the first set of battery filaments to be destroyed this way and in reality a fuse is unlikely to prevent a similar accident. It is just a case now of ensuring that incompatible plugs are used, or the filament battery holder is hard wired.

Often it is only the filaments that are switched although I have seen DPST used. If the filaments are cold you do not need a HV switch unless there is something that can conduct between B+ & B-: More commonly there is.

Normally for filaments I use two "D" Cells in parallel in a holder/s.

Luckily your valves (1R5, 1T4, 1S5, 3V4) are quite common ones. I've never had to replace valves in battery receivers except for the 1R5 which seems less reliable than the others.

Well luckily all valves have continuity, except the 3V4, which has it seems failed and saved the others thus. Ian I thank you very much for offering your valves. I am happy to pay you to post them as I am acquiring another battery radio next week from a friend who bought it in Adelaide for me for $10! Not sure if it uses the same valves, but this radio is my first priority s the case (leather) is immaculate and with some dubbin, looks like new! In any case, spares are a good thing to have. I can pay you via paypal through your email if you like or COD, whatever works best for you, with paypal I can at least buy you a beer or 3 for your kindness!

Thank you too for the information on those resistors, good to know.
When I re-capped it, there is large electrolytic can, which is a 2 in one, one side is HT mains smoothing at 40μF, the other is lov voltage at around 8μF, from memory. I snipped the mains 40μF wires and put a new 40μF (actually 4x10μF in parallel) in place of, but left the low voltage side connected. I might re-visit and replace that also, it wouldn't do any harm! But yes GTC, what you said about physically visually inspecting the switch should help me make heads or tails of it, thank you for demystifying the diagram! I should be able to figure it out now!.

Hi Jamie

Good to hear that it was just the 3V4 that failed. Good luck with the Battery Portables. As I stated before in the other post I am a collector of them. They are great to get away with and still be able to listen to. When the wife kids and I go away often and take one to listen to.

Do your self a favour and don't use the stacked 9v batteries. I know I got shouted down in the other forum as not knowing anything, but if you use the eliminator then it has current limiting so this accident shouldn't happen again. In the long run it is also cheaper to run.

But then I expect to be shouted down again. What would I know.... I am only a Electronics tech. by day who repairs radios in my spare time.

Hi Flakes. Your advice is welcome, as I know practically nothing about these things, it's all a learning curve for me and all accidents short of being electrocuted are lessons and learning from the lessons of others is definitely preferable to having incidents, accidents and unfortunate occurrences, given your experience, I would feel a fool if I didn't get my hands at least on one of these eliminators and make my own comparison. My overwhelming thought or question is basically how can a mere half dozen little AA Batteries pack the same electrical punch for the HT requirements as a beefy stack of juicy 9V batteries equaling the full 90V, whilst running it's own internal circuit and have any longevity? Given the low cost of AA's I suppose it doesn't matter as much, so long as I'm not forever changing them during an evenings listening, but I best suppose I try it and see!
Cheers. Jamie.
I see you are a fellow Adelaidean! (I'm in Clare) But yes I have the same wish, to have a nice portable set to take on outings with the wife, fishing, camping etc.!

Just sent you an email.

Have a good read it should help clear things up for you.

Jamie Lee I would like a Wife that likes camping and fishing lol let alone the radio.