A mate dropped this on my bench to track down some hum & serious crackling so I went hunting for a circuit & found what I needed on Kevin Chants site...brilliant heap of info for this unit on there.. Thanks Kevin.

But the output valve is listed as type 30A5 and my Philips book shows nothing for that type of tube and from the 30 bit I am thinking it is a 30V filament which lines up with the circuit where it is dangled across the 110 & 140V mains transformer tapping on the Primary side of that transformer.
Bit nasty that as should the power cord be reversed one side of the filament has 240V on it so need to be VERY wary when poking about. One would hope that the Filament to Cathode insulation is very good as the Cathode in this unit is earthed and with a 3 pin cord fitted that would put the full mains voltage those 2 components of the valve.

I will be making absolutely certain that the mains cord is correctly wired before I start any work on it as the noise is there with the Vol control fully off so its between the pre-amp valve and the output stage.

In case I need another 30A5 anyone know of a source as the Evatco site does not list that valve at all.

Lindsay

Yes the 30A5 was a Hitachi special, aimed at the local radio market in Japan where the mains voltage is 100v and the heater voltage sums didn't add up.

The 35C5 is generally a drop-in replacement. Same pinout, same heater current. You can get it here:

https://tubedepot.com/products?utf8=%E2%9C%93&keywords=35C5

As usual, frank.pocnet.net is a valuable resource.

The schematic on Radiomuseum for that model shows a mains transformer with multiple taps on the primary for a range of inputs from 115V to 250V and the heaters for V1 and V2 paralleled across a 6.3V tap on the secondary. Why on earth they used a 30 volt valve beats me as there is no series chain involved.

Ian,

Not sure what you mean by heater sums not adding up but I am guessing you are adding the 2 x 6.3V valves plus the 30V heater type valve to suit a AC/DC style of operation. Not up to 100V??
This thing has a mains tranny and the 30A5 is fed from auto transformer winding on that tranny and the circuit I have sourced from Kevin Chants site shows 2 versions of the beast.
Up to Serial No 9203 they use one circuit and above that they use another config for the transformer all to do with how the 30A5 heater is fed. In the early versions the heater connection points were buried in the centre of the primary windings so the max volts ever to ground on that heater would only be around 110V when hooked to a 240V supply.
The later version which I am dealing with has the filament section at one end, what should be the Neutral end when correctly wired on the plug, but reverse the plug connections and its got 240V from the heater to the frame and the cathode which is tied to earth/frame.

Will check out the info re 35C5 type tube from Tube Depot.

Glad that I managed to get both circuits so I can see exactly what I am dealing with.

Lindsay

That is rather a weird way of doing things. It's not exactly an auto transformer. Its actually part shielded transformer and the primary more of a Ballast. Quite a few European Radios use what I call, just a tapped ballast (no secondary)

One needs to keep an eye out for them as they can be as intrinsically unsafe as the American transformer-less sets, when working on them. In many of those sets the heaters were in a series string, sometimes with series resistors: The sum total of the voltages had to add up to mains supply & all heaters usually drew the same current.

Reason for strange heater arrangement was probably so they could use a more commonly available (at that time and place) valve. Maybe they had excess stock to use up??

Heater voltages adding up? Mass-market radios at the time in Japan would have been based on US "AA5" practice. Valves were:

12BE6
12BA6
12AV6
35C5
45Z3 (or other rectifier with a 45 volt heater)

In a series heater string. That's 116 volts, close to nominal mains voltage in the US.
Problem is, nominal mains voltage in Japan is 100V so for the local market they needed to drop some heater voltages a bit. Hence the 30A5.

QUOTE: can be as intrinsically unsafe as the American transformer-less sets

The isolation between the heater and cathode of the 30A5 isn't good enough to pass "Hi-pot" tests (where the insulation needs to take 1.4KVDC). Thus this machine wouldn't pass our UL safety tests, and it would not get the UL seal of approval.

I sometimes wonder as to how some stuff here actually gets into the country? I have actually modified several transformer types where there is no earth and a non line cap to a metal cabinet.

C19 (sg-11) (double) goes one, from active, one from neutral, the middle to an un-grounded chassis,, metal case and Heathkit IT-4 is another with a single one to ground and metal body. These are two, of many, that I consider intrinsically unsafe, as there is a risk of active being on the metal case, should the cap fail.

I would also note that the SG-11 seems to be made in different factories. I have one here which had oil filled caps: Not any more. These from my experience are as bad as wax paper types. Test equipment has the same caps as radios & are just as reliable (not); That will impinge on the way they work.

Standards marks are meaningless these days, in my opinion. The manufactures apply these marks to their products and often there is no independent testing to ensure that products meet any standards at all. There is also a misguided belief that because something does actually meet an appropriate standard that it is a safe product to use under all circumstances. It would be wrong to assume that no shock hazard exists just because something meets standards. A knife into a toaster is a classic example.
Appliances sold in Australia have at least one of four different tags to show compliance. These include the C-Tick, showing electro-magnetic compliance; the A-Tick, showing telecommunications network compliance; a state electrical safety approval number which is a string of numerals preceded by the letter N for New South Wales, V for Victoria, etc.; and/or a simple sentence stating that the product meets a specific Australian Standard. Some products have more than one of these marks. Recently, C-Tick and A-Tick were merged and compliance requirements are represented under one Regulatory Compliance Mark which looks similar to the former A-Tick.
As far as RFI/EMC interference is concerned, most products do appear to emit and excess of this interference and I seriously doubt most of it would meet Australian requirements under any circumstance.

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A valve a day keeps the transistor away...

From Standards Australia website: "We do not enforce, regulate or certify compliance with standards. We publish voluntary standards. However, State and Commonwealth governments often refer to standards in their legislation. When this happens, these standards can become mandatory."

Standards that are not enforced are treated with contempt by manufacturers. These days it seems that the only time such standards would come to the fore would be in a prosecution, and I could see a manufacturer prosecuted for RFI emissions arguing in his defence that he is being singled out from a group that generally takes no notice of the standards.

Hi Lindsay, if you still require that 30A5 valve let me know as I have one that you can have for the cost of the postage. Mike from Maleny Qld

Michael,

That would be great. Thanks for the offer. If you can unhide your email or even email me I can give you my postage details to get this happening.

Looks like the weird noises ARE coming from the 30A5 as with the grid grounded the noise is still there. Maybe the heater cathode insulation has given out.
Interesting that the thing tests OK in a valve tester but not having any data for this valve to set the sensitivity correctly I am only guessing.

Whenever I get my hands on new valves I test them and note the relative Sensitivity setting that shows as GOOD in a book for future reference.

Lindsay