Yeah GTC I was as a kid always interested in electrical & electronics...anything scientific really.

With books I was very much like that...actually I have oodles of EA ETI Elektor Wireless World etc here sadly boxed and so cant get to them like I use to ...actually I haven't looked at them in 20 years or so...God knows what state there in ..probably ready for the tip I suppose.

It did become my hobby and latter I worked as Tech for a few places ..I never thought of my self as much of a tech actually but seems I did know a fair bit...

One job I went for I was hired partly cause I could ID a circuit as switch mode psu ...that kinda worried me about the quality of techs he must have had through the door before me for the job??? switchers were becoming the in thing and they are everywhere now...dangerous little beasties...no guru, thought I've fixed a few.

I haven't done anything electronics wise really in 10 years or more & yeah I do find my self second guessing myself a lot atm (very cloudy memory)....with Radio well I haven't looked at anything along those lines since the late 70's I guess..chips did just about everything by then so I was more into computers....thought I still have my Playmaster Mosfet Amp circa 80's that Carl from ACE radio one said your lucky, yours actually worked LOL

I did some formal training for the E&C (at the time) but never finished it ...they change the courses around and it all when pear shaped. (would have had to run between tafes...)

Valves thought as I said were still quite used in the early 70's but it was really there last hoo ra lest as far as domestic stuff was concerned..unless your a muso.

So I really never bothered to learn much about them...sadly...and now it would be good to know...

Marc
Yeah I really hear you on Carer and Back pain, thought mine wouldn't be were yours is at...its not nice to have at all...and you really know about it when you make the wrong move..

On roads and stuff yeah sadly not to be nasty but people are pigs these days to put it bluntly... there really isn't much curtsy in fact quite the opposite...sad really.

Thanks for the explanation on time and I use to be quite active in a few other forums but time now I dont have much of with the real world demands...here I feel I really dont have much to contribute except from a more basics level...thought I probably over stress that point of my noobness.

Maven
Glad you "bit the bullet" but sure I feel your pockets pain...anyway its one less thing you'll have to worry about with the circuit...and if quality and up to the task should last a while.

It's one thing with Electros you should spend a bit of time knowing whats the better spec wise device to use in a circuit.

Case in point using crappy eletro in a VRM of a computer mother board is just asking for it to come back much sooner then later...they really cop a beating in those circuits...will work but definitely will fail in shorter time. (Due to lousy ESR)

(Also too you can actually by putting in a better spec device get a worse result as sometimes the circuits been designed around the original Caps characteristics...I guess that dont really apply so much to valve tech but it can with SMPSU's...just one of those little gotcha's that. can arise from time to time and lead you a merry chase)

I have been wondering thought weather its worth while building a few SS rectifies to mimic tube behaviour but with a bit of extra current protection like sacrificial resistors or fuses, lamps whatever for valve sets & amps...just I think its a better idea to pop one of them then a rec valve...esp if you have an intermittent failure problem and an expensive hard to find Rec Valve
(not that the valve you have is hard to find but well it costs a little more to replace it)

Anyway keep us posted on how you go.

Its is off topic but classic ignorance: Monday (2 funerals in the one day) Hearse on its own (no cortege) Priest & undertaker at the front sides, at least 400 witnesses.

Ignorance barges past the hearse as it is attempting to get onto the road, goes around a corner & parks? Everyone was disgusted with that effort.

Sorry to hear that Marc
Yeah sounds typical of these days....was in a line with others and lights on to indicate it was a funeral procession they just barged in breaking the line

Then today a lift, helping someone that can't walk properly two shoot past us but seen us heading for the lift didnt bother holding it...just pressed the close door button

The "ME" Generation mate

Not a bad topic to discuss. Let's shift it here though.

Worth noting that in some states it is a serious offence to break up the passage of a funeral.

Back on topic....

Lets say that while waiting for replacement valve and caps, I want to provide a temporary B+ to keep testing other components.

A 400v bridge rectifier puts out too much voltage. I put 330ohm in series with the DC+ but this seemed to overheat the transformer even without attaching to the B+ circuit.

How can I limit bridge rectifier output to about 215vdc with suitable current limit?

Maven

It sounds like you connected something up wrong. You can replace the valve rectifier with a pair of silicon diodes (1N4006 or 1N4008) as long as you have a series resistor in the HT line AFTER the rectifier to drop the voltage back to the correct level.

If you look at the circuit, the two diode anodes are pin 1 and 7 of V5. This is where you connect the silicon diode anodes. Both the cathodes then connect together and connect to your 330 ohm resistor. The other end of the 330 ohm resistor then connects to pin 3 of the V5 socket.

If the transformer still gets hot, something is very wrong somewhere. Are you using an incandescent lamp in series with the transformer primary for load limiting / safe testing? This will prevent the transformer being damaged by shorts or overloads while you're poking around. It will also supply a slightly reduced voltage which will be useful for testing purposes. There is no protection for the transformer as built by the factory as there are no fuses!

I did some more reading ("if all else fails, read the instructions") and realised that I should not put a BRIDGE rectifier across the two poles of a centre-tapped transformer, because it shorts the load via the DC negative. Lucky I didn't try too many tests..

I then made a diode rectifier as TVC describes, but perhaps too low specs. I used 1N4004 diodes and a 100ohm wire-wound resister. This time, the transformer stayed cool, but the resister got hot to the point of smoking so I cut the power again.

I'll make up an incandescent bulb resistor for safety's sake, and try again with 330ohm and 1N4008s.

I've been doing this with all valve sockets empty, so minimum B+ load. Will that affect socket voltage measurements that I am trying to check?

Maven

With no valves the voltages will be considerably higher. If the resistor is getting hot with no valves installed it sounds like you have a short somewhere in the B+. With no valves the current draw would be minimal, maybe a few mA through electro's and possibly a bleed resistor but not enough to start smoking things!

I have already lost a mains transformer to a 6CA4 which was shorted internally, and nearly another. A friend had the same problem in another radiogram. The whole radiogram (Kriesler 11-102 ) could have burned down along with the house if really unlucky, so now I have put in line fuses in, and would suggest anyone using an appliance with this valve does the same.

The whole radiogram (Kriesler 11-102 ) could have burned down along with the house

This is not the first time I've heard or seen of 1960's Kriesler radiograms almost catching on fire due to a cooking power transformer. The question is are these meltdowns due to the transformer itself or associated components such as the filter caps or rectifier. Even a recent thread was about a concern for a hot transformer in a 11-81.

The two radiograms I've seen that nearly caught fire was a 11-97 & a 11-98. A later version of the 11-98 (11-133) has a solid state full bridge rectifier in place of the 6V4, thus the HT not having a centre tap. The 11-97 & 11-102 both use a 6CA4 rectifier.

It appears that overheating power transformers in Kriesler radiograms are not isolated incidents and that anyone owning or restoring one should be concerned.

Something is not reading right here. You do not use a bridge rectifier on a centre tapped valve transformer. You leave the CT where it is and put a 1N4007 or similar in what was the plate leads.

However, it is fairly clear the the filter caps & paper caps in there, or if rubber wire is involved something is shorted. Fix it before powering again.

Marc

You do not use a bridge rectifier on a centre tapped valve transformer

Yes, I understand that. I think my post was misread. What I meant to say is that the power transformer HT section in the 11-133 doesn't have a centre tap and a full bridge rectifier is used.

In my case anyway (11-102) the fault was traced to the 6CA4 . I had another power supply unit ( they were seperate from main chassis in this model) I replaced it but put the same valve in . The transformer immediately began to hiss, luckily I was in a position to switch off before any damage was done. Replacing the valve remedied the situation.

The 6CA4 has a comparatively high heater current and DC output current capability for its small 9-pin package. Driven to its limit, it would not surprise me if it was a very hot valve in operation.

I didn't want to risk burning out a transformer or valves, so I went ahead with full re-cap (except micas)
and checked all connections to ground. Meantime the EZ81 arrived by post from Germany. All running sweetly now.

The EZ81 does run quite hot - glowing at base, middle and top. Radio draws about 58watts running warm. Cabinet is quite tight. Ventilation slots on both sides, with warm air rising through the gaps around the spring-mounted turntable and a long slot at the back - so unit should only be operated with speakers open for good ventilation.

Maven