Schematic wanted and Info Astor M3B

[RetiredHal]

Hi I am restoring a cream Bakelite Astor Mickey 4 valve radio. Model M3B.
The valve line up is 6X4, (6), Transformer Can, 6AD8, Transformer Can, 6BE6
The writing on the (6) is likely to be 6A?? as I can just see outline of 6/ making me think of 6A?? . (output valve?) (7 pin valve b7g base)

I am assuming that the other valves are correct.
I have surfed the internet for a couple of days but cannot find any schematic for a 1953- 1954 3 valve superhet plus 6x4 powervalve.

Astor was an Australian brand that made a lot of small bakelite sets.

Can someone give me some idea what the valve would be and if possible supply a schematic of a 4 valve radio preferably with those valves. Getting the correct cct diagram would be terrific but I would settle for any cct that would appear to use these valves .

Cheers John

NB I can supply pics of set, chassis etc if that will help
I have asked the same question on an Australian Vintage Radio Site

[HP3400A]

Hello,

If it's a 7-pin output valve, in a set with 6BE6, 6X4, etc, then it is possibly a 6AQ5. [6AQ5 = miniature equivalent of a 6V6]

cheers
Martin

[RetiredHal]

Hi, Martin,thank you for your suggestion, I am reasonably convinced that the 6AQ5 is the misssing valve.
I am still interested in a circuit diagram for a three valve radio and a power tube. (superhet is 6BE6,6AD8,6AQ5) and 6X4 is power tube.
I enclose two pictures.
Cheers John

[paulsherwin]

As a general rule, Australian radios of the 1950s are much closer to American than European practice. The valve lineup of this set is quite common in the US but very rare here (I can't think of a single radio offhand which uses these valves).

It's just a 4V+rect superhet though, and any 1950s circuit will probably be some help, though European sets normally use triode/heptodes as frequency changers rather than pentagrid heptodes like the 6BE6. This Murphy A168 from 1951 is likely to be broadly similar: http://www.******************************/A168M.jpg

Paul

[arjoll]

I see there's an old NZVRS bulletin with something about the Astor (scroll down to 07-2). I've only recently beccome a member so haven't got a copy, but 'audiomm' here may be able to help, or you can drop an email to the NZVRS librarian.

[paulsherwin]

Sorry Hal, I've reread your posts *properly* and I now appreciate that your radio is what is sometimes known as a 'short superhet' with only 3 active valves.

First, you should read this article on how the standard 4 valve superhet evolved: http://www.r-type.org/static/add034.htm

Your radio dispenses with the double-diode triode of the standard superhet design and puts the detector and rectifier diodes in the IF amplifier. This design is relatively rare here but the Pye P43 uses it - Pye were great fans of the short superhet in the 40s and 50s and got suprisingly good results, but most of their designs put the diodes in the output valve (an EBL31 usually). The valve types will be different than those in your radio but they are functionally the same.

You can order a set of manufacturers' service data for the P43 from Paul Stenning for GBP1.99: http://www.service-data.com/email/list/pye.htm Paul has also written up the restoration of the AC/DC version of the set, the P43U, here: http://www.vintage-radio.com/recent-.../pye-p43u.html

My avatar shows me holding a P43 which I restored

Good luck, Paul

[HP3400A]

Hi John,

Thanks for the pics.

- Sets using just 3 radio valves were unusual in UK, so finding a similar set may be problematical.

- Some sets with just three valves omitted the IF stage [some cheap merican sets intended for use within a city had no IF stage]. The picture of the chassis of you set seems to show two IF transformers, so it probably _does_ have an IF amplifier stage.

- Other sets with just three radio valves omitted the audio amplifier stage. But the 6AQ5 is not a specially sensitive output valve - it needs a large voltage to drive it (around 24 volts pk-pk, from memory), so it seems unlikely it would be driven directly from the diode demodulator.

This leads me to surmise that your radio is a reflex set. If it is, it maybe uses the 6AD8 as both IF amplifier and audio amplifier - maybe using the screen grid of the 6AD8 as the anode of the audio stage. If so, you will probably find a capacitor running from the screen grid of the 6AD8 to either the volume control or directly to the control grid of the 6AQ5.

I think that the 6AD8 is not a common valve in UK nor in USA.

Have you considered biting the bullet and tracing the circuit diagram from the
set? It's tedious to do but you will be quite familiar with its circuit once it's done.

cheers
Martin

[RetiredHal]

Hi, Arjoll, thank you for your suggestion , I will contact the NZVRS librarian. I have bumped into that site quite a few times over the last couple of days, but did not see the bulletin you referred to.
Paul, the term "short superhet" was unknown to me but searching with that term reveals that the set may have poor selectivity. This would be quite ok as this model and its many variants were usually the "kitchen" set tuned to the local station and left on all day in the background. Because of the distances in Aus, I dont think this (selectivity) would have been a problem. At this very time (2008) I can only pick up 2 or 3 clear stations on my modern kitchen set FM/AM/DVD Sanyo ( I live in the country) and I doubt that Arjoll in Invercargill will pick up more than 2 or 3 clear stations.

I am amazed however that there does not seem to any schematics available (on the internet) for a short superhet, using this valve combination, as the "Astor Bakelite Mickey" was an Australian icon.

Cheers John

[paulsherwin]

Originally Posted by RetiredHal

Paul, the term "short superhet" was unknown to me but searching with that term reveals that the set may have poor selectivity.

A short superhet without an IF amplifier will have poor selectivity, but I *think* yours has an IF amp but lacks an AF preamp. This means that the volume will need to be turned up for weaker stations and AGC operation may not be too good. Selectivity should be OK though.

There seem to have been two completely different types of listeners in Australia in the 50s - city dwellers with a very strong signal from the local station, and rural dwellers living hundreds of miles from the nearest transmitter. A short superhet is a poor choice for this latter group though a longwire external aerial may help.

The 6DA8 appears to be similar to the noval EBF80 and EBF89 used in short superhets in Europe: http://www.nj7p.org/Tube4.php?tube=6AD8

Paul

[RetiredHal]

HP3400A, Hi Martin

Have you considered biting the bullet and tracing the circuit diagram from the
set? It's tedious to do but you will be quite familiar with its circuit once it's done.

cheers
Martin

Yes, I am in the process of doing this, but it is not easy, the thing is all over the place.

I will have a cct in a few days and I will post it

It has been many years since I worked with valves (late 60's radar) and whilst I can recognise most of a 5 valve set this short superhet thing is a mystery to me.

Cheers John

[arjoll]

Originally Posted by RetiredHal

I doubt that Arjoll in Invercargill will pick up more than 2 or 3 clear stations.

After replacing all the caps in the Antone Cadet I'm working on (just have to finish the case and sort out a rattly speaker) it can pick up all 8 local AM stations and in the evenings can just pull in two Dunedin ones (Rhema 621 and RNZ National 810). That's with a modest aerial - just a couple of metres of hookup wire.

Its certainly not super-sensitive though, but changing the electrolytics helped significantly - it was pretty much deaf above 900 or so.

[paulsherwin]

I'm no expert on Australian geography or broadcasting but I reckon Hal will have problems picking up anything using a short superhet during the day. Melbourne is too far away. Even Ballarat and Geelong are a fair distance and I don't know if they have AM stations anyway.

Maybe it's time to invest in an AM microtransmitter, which will allow you to broadcast a satellite feed or FM station to an AM radio. These have been discussed widely on this forum - search for 'microtransmitter' and you'll find lots of threads.

Paul

[petervk2mlg]

This should help, although my M3B schematic specifies 12 volt valves.

Peter

[RetiredHal]

Arjoll, in Western Victoria there are some local stations about 100-150 ks apart plus some ABC repeaters. I am amazed that there are 8 local stations in Invercargill. You are very lucky here in Warrnambool there is one (I am talking AM) . Most likely if I use an aerial I'll pull in more stations but even the modern car radio with aerial has slim pickings in rural Victoria.
Petervk2mlg thank you for he schematic, it has similarities. Hopefully I will have finished the schematic in a day or two and I will upload it for comment as I still have a lot of trouble understanding the circuit,

Cheers John

[petervk2mlg]

The circuit looks pretty conventional. I guess the use of a solid state diode as detector and for the AGC is a little unusual. A typical Astor feature of this period is the use of negative feedback from the speaker voice coil and the resulting tapping on the volume control. If you need to replace the volume control, finding a replacement will not be easy. Also is you need to replace the speaker transformer at all make sure the replacement maintains the correct phasing or the negative feedback will become positive!
I'm supposing your radio will use the following tubes: 6AN7, 6AU6, 6Au6, 6AQ5, 6X4
My book of circuits does not list the M3B as using the 6 volt series, but I'm guessing it is an undocumented variation.

Peter

[petervk2mlg]

I've just gone back over your posts and it's obvious that the M3B schematic I have sent is not at all like your set - are you sure M3B is stamped onto the chassis of your radio? I wasn't paying close attention to the detail and got fixated on the model number.
Your set looks much more like a model PK - 4 tubes and permeability tuning.
Here is the PK schematic I hope it helps
Peter

[arjoll]

Originally Posted by RetiredHal

I am amazed that there are 8 local stations in Invercargill.

I worded that wrong - there are 8 local transmitters in Invercargill. I'll PM you the details to avoid taking the thread OT!

[RetiredHal]

Hi, petervk2mlg, That is the cct for he set (pk) thank you very much,
As I said the thing is all over the place and I notice now that someone has made some changes to the cct. and clears up some other things as well.

The reason I thought it was a m3b is this
look at http://www.bestradios.info/Book3sp.html

If you look you will see my radio left page bottom right marked as m3b (1953)

Cheers John

[RetiredHal]

Hi Peter, after changing some things so the wiring is in accordance with your cct diagram I now have a radio with reception. The sound is pretty awful. "Burbling" .
I will order caps to replace the wax ones and also replace about 6-8 resistors that have drifted way out eg 47K showing 62K. The tuning ferrite rods were loose so I think I may need to do an alignment. I notice in the Altronic catalogue you can buy 455khz resonators. can you use these? for alignment. I can easily make a near 50% dutycycle 455Khz square wave using a 555 chip. I really do not want the expense of buying a signal generator if I do not have to.

Thank you very much for the cct.

Did you look at that Just Astor link ?

Cheers John

[petervk2mlg]

Hi John

I use a Philips sig gen for alignment. Not sure about the resonators.
Yes I did look at the Astor book link -I have the author's three books. All I can say about them is that they are a rough guide only. They are riddled with errors and inaccuracies. It may be that Astor used the same cabinet for several different models.
Get in touch with Steve Milliken in your neck of the woods - he can help with a sig gen and alignment.

Peter