Thread: Old Valve Radio Identification

Originally Posted by PenTurner

Third, The electros are rated 600vdc, the max I have are rated 450vdc, opinion on whether that should do??

Why take a risk?
Using 2x 450V capacitors in series will double the overall rating to 900V, but halve the capacitance, so you'll need to double the value. ie, 2x 100uF, 16V caps in series will be rated at 50uF, 32V. It may also be an idea to include large value resistors in parallel with each cap to create a voltage divider that ensures the mid-point stays at half the overall voltage. You don't want one cap failing, and having the entire 600V appearing across the other cap.

What is the B+ voltage?

Hi Amos
Firstly, I recommend that you replace the white twin AC power cable with three core cable and make a good earth connection to the metal chassis, and to the radio earth. Use a “through chassis” grommet as well. Replace that other piece of “figure eight” also.

The power transformer connection plate seems to be stamped 285 V CT 285V for the HT DC, and if this is correct, then 450 volt electros will be probably OK. Jaycar stocks these. Confirm that the loudspeaker has a permanent magnet, and not a wound core type? This may tell us whether the DC supply voltage at the rectifier output is 450 or 350 volts. The DC HT rail volts for the valves probably will be 250 – 300 volts DC or so.

If the speaker has a field winding instead of a permanent magnet at the speaker rear, then the voltage rating of the DC supply capacitors needs to be higher at 600 V.

As another forum member has asked also, you could measure the DC voltage across the presently fitted electros, and report back.

I would leave that unknown (ceramic?) capacitor until last and replace only if necessary, as it probably is OK anyway. If you cannot identify it in any other way, and if it is in the RF section, (I cannot see it on the big chassis photo) try 100 pfd 250 volt ceramic as a starter. It is just possible that this cap is across a coil or RF/IF transformer, and if so, its capacitance value will be critical, and you will have to identify it on a circuit, or else resolve the capacitance value markings on the body. These small caps can be crudely tested for leakage to a degree with a DVM on resistance, if you lift one end. They very rarely change capacitance value, they just go leaky ie develop some resistance, sometimes intermittently, which is the techos curse.

Replace that 25 MFD 40 Volt cathode bypass capacitor in the audio, as these always lose capacitance.

What we need here is for someone to recognise the radio, and provide you with a circuit, although in most cases you can replace components with a “like for like” approach quite successfully, whilst observing polarities.

I am intrigued with the Siemens device. It is the white squarish thing with a blue lined border and big letter “S” going through a letter “H” (Siemens-Halske). This looks suspiciously "modern" in a relative sense, and maybe being used as a substitute half wave rectifier for HT or bias.
I see another modern polyester cap also.

It is a bit hit and miss without a circuit.
And beware of previous modifications, which may complicate your replacements.
We haven't talked yet about replacing audio coupling capacitors, and AGC bypass capacitors, which is always a good idea.

Caution - You may require a licenced electrician, or someone with a Limited Electrical Licence (Communications Work) to do some of this work.

Good luck!
cheerio, mike

Mike, Cliff and SJM, thanks for that input, I am a qualified Electronics Technician and run my own repair shop, started on Valves and progressed right through and now back on valves; I will probably go safety with the Voltage of the electros, and use two in series as suggested. I have now replaced all paper capacitors with high quality modern capacitors,(those orange things), That Siemens device looks like TWO Electros in the one can!? I will try for a close up of it tomorrow.
I will also Measure the B+ and report on that. The set originally came on and the after 3 minutes drifted right off, giving me concerns that the RF section components needed replacing, I have to replace the electros on top of what is already done, then try it again. I am looking for a resistor that may have gone high or goes high after warm up. Either way, I will report back my findings, would have been good if the previous "restorer" had left the Manufacturer markings on it, a circuit would be of great value. Amos

The language that you fellas are speaking is it eh English? I don't know if the Forum owners are aware of the strange way you are speaking.....do you wear grass skirts and put a bone through your nose???

I know when I took the components for a 240-415v 3 phase converter project, to another Forumite, I asked him the same question.

Oh its the Electronics Section of the Forum. Your secrets will be safe with me. I read all of the above threads and didn't really understand much at all.

As has been said before this Forum has people who will answer questions on any subject. THAT'S WHY I LOVE IT!!!!!!!

I threw all my Rad School text books (TIDS) away last century, wish I hadn't now.

I have several valve amps in my collection.
Mostly guitar amps but there is one hybrid PA system in there too.

Same here Cliff, my case I gave them away to a young bloke, wish I had kept them! Amos

Originally Posted by PenTurner

Mike, Cliff and SJM, thanks for that input, I am a qualified Electronics Technician and run my own repair shop, started on Valves and progressed right through and now back on valves; I will probably go safety with the Voltage of the electros, and use two in series as suggested. I have now replaced all paper capacitors with high quality modern capacitors,(those orange things), That Siemens device looks like TWO Electros in the one can!? I will try for a close up of it tomorrow.
I will also Measure the B+ and report on that. The set originally came on and the after 3 minutes drifted right off, giving me concerns that the RF section components needed replacing, I have to replace the electros on top of what is already done, then try it again. I am looking for a resistor that may have gone high or goes high after warm up. Either way, I will report back my findings, would have been good if the previous "restorer" had left the Manufacturer markings on it, a circuit would be of great value. Amos

Hi Amos
Good - I can just sit and watch now.

I suspect that your set is Australian made as it has Technico and Chanex caps.
Possibly Airzone etc, and pre WW2 (based on valve lineup).
Suggest you post a piccie of the whole radio on a vintage radio website.
Someone will recognise it and give you a reference, then you can get the circuit.

Vintage Radio Restoration is not my forte per se, but I too trained on this stuff and I have fixed a few. My everyday radio is a HMV valve mantle set from the 60s, and I use it everyday for ABC Radio National (4QG if you are old enough) while I cook dinner!

The mystery cap looks like a small silver mica, but it is obscured.
As you know, green on components normally meant "5" in radio code, but it could mean anything in isolation.

If you websearch on your valve lineup, you will get approximate circuits, which are useful.
The component values in these radios are not critical, with just a few exceptions.
The old Body End Dot resistors for example were mostly 20%, and you can use components at +/- 500% for test replacements.

I dont understand why your radio has 285V a side AC for HT, when you probably have a field coil type speaker. Most trannies I have seen used 385V a side and 600V electros for radios with this speaker type.
Did I misread it?

rgds mike

Hello Mike thanks for the info I am a member of Radio Museum and will eventually post there, however I hope this can be informative to us here and it has been for me so far, and here is an update, thus far
The B+ is 232Volts DC(of course)
1.I have put in 3 electros and made them up in series for voltage rating.
2.I have replaced the power cord with a quality "iron" cloth power cord, and have put in an earth connection. As yet I may anchor the power lead internally.
3. Have replaced majority of old caps with new caps.
4. Have switched on and nothing blew up!!!
speaker 2 (Small).jpgprogression 1 (Small).jpgsiemens caps 1 (Small).jpgspeaker 1 (Small).jpg

Originally Posted by PenTurner

4. Have switched on and nothing blew up!!!

Always a good thing

That's a nice radio Amos, they don't make pieces of furniture like those anymore. I can't help with ID or the electronics, but the speaker might hold a clue if the details are still on the coil/magnet (if there were any there to start with of course)
I know that know speakers had manufacturers codes that tell the date etc, but I don't know when that started. Just a thought that might help.
It's interesting with the ARTS&P transfer still on it. Somewhere around here I still have a Receiving Licence, probably from one of the last years of issue.

By the way, is that a baked bean can over the speaker??

Yes John, a can over the speaker coil, not sure why? maybe they tried to keep out the dust.
The Latest update---it has been running over 1 hour and going very well; the speaker does pole if it is up too loud, but there is sufficient volume to give a beautiful sound with well rounded tones(love valves for their audio quality).
Someone suggested I put a rubber grommet in the chassis where the power cord enters, went to do that, BUT, it has a good well rounded brass grommet that came with the set, so I will leave off that modification.
Will put in a new dial lamp, a fridge globe of about 20watts should be sufficient and also run new cable to it. Then try putting it back together.
PS, at the moment I have to take the AM sets home as my shop area is a dead spot to AM; maybe will try a long run up to the roof and around it, see if that will help. Thanks for all suggestions and advice. Now to start looking out for circuits and Model?! Amos
So far, the closest Model is an Airzone Model 550 as far as circuit goes.!

Is it possible to mount the speaker turned 180°?
Maybe that will counter any sag in the cone & help with the poling problem.

Cliff I will give that a go, the radio ran 7 hours straight with no problems. I am thinking of making a small preamp and putting an "audio in" socket at the rear, that way the output from a modern FM/Digital could be fed into it!? Amos

Can you pick up digital stations on that thing


The 6U7G is a octal base valve , the other valves are 6 pin I think, so i'd say its from the late 1930's or early 40's

That would have cost 6 months of wages when it was new

Mike