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Old 2nd Mar 2018, 5:31 pm   #1
vinrads
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Default Supersonic Heterodyne radio 1920's.

I decided to have another go at this one. It is an early superhet "Raie Studio nine valve" using fixed iron core I.F transformers.
There appears to something missing at the front end.

There is only one coil unit, a Bowyer Lowe Oscillator Coupler model 3, 250/550 the I.F frequency is around 140 kc/s.

The strange thing is it works in a fashion by feeding a strong sig to the control grid of the first valve, and is tuned by the frame tuning capacitor, the osc tuning capacitor does nothing.

It may have modified in the past, I don't know !
Any help would be appreciated. Mick.
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Old 2nd Mar 2018, 11:48 pm   #2
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Default Re: Supersonic Heterodyne radio 1920's.

Does this set employ a Bi-grid mixer valve? This type of valve is unlike an RF tetrode, instead one grid accepts the radio signal and the other output from the local oscillator. At 140Kc/s your set has a surprisingly high intermediate frequency for an early superheterodyne receiver. Some 1920s superhets had an IF of 50Kc/s.
An example of a Bi-grid valve: http://www.r-type.org/exhib/aaj0031.htm

Also: http://www.r-type.org/articles/art-094.htm

DFWB.
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Old 3rd Mar 2018, 11:07 am   #3
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Default Re: Supersonic Heterodyne radio 1920's.

Thanks for that some interesting reading there , I was wondering about the coil pack , would this be the aerial coil and osc coil combined ,there are two separate coils not connected internally.
I will double check the IF freq there is no reference to the freq on the cans.

It's possible that it once had one of those mixer valves as all the bases are four pin except the output .comments please. Mick.
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Old 3rd Mar 2018, 2:04 pm   #4
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Default Re: Supersonic Heterodyne radio 1920's.

Hi Mick

You have a nice piece of vintage radio gear there, it would be of interest perhaps to see the circuit of the power supply you powered the set up with. Keep at it, well done.

Ken
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Old 3rd Mar 2018, 7:04 pm   #5
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Default Re: Supersonic Heterodyne radio 1920's.

Hi Ken all the power supply cct is in my head , I don't know if I should show you this ,but here goes , The two volt supply is via a LM317 . Grid bias is via a small tx and a nine volt reg and two preset pots ,to set the individual biasing , The HT and LT is from a OTT tx giving 150 volt ,this feeds a series of six 20 volt zener diodes , thus feeding different HT voltages to all stages of the set.
I think you could call it a bread board lash up , but it works , I could build a case around it with vents off course , having loads of fun with this one but I still don't understand why it works so well with no oscillator running , oh just checked the IF's are non adjustable at 140 kc/s Mick.
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Old 3rd Mar 2018, 10:14 pm   #6
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Default Re: Supersonic Heterodyne radio 1920's.

Seems strange that the frame aerial tuning capacitor tunes in stations and yet the oscillator tuning does nothing. However, the receiver might not employ a separate oscillator valve. The attachment shows the circuit of a self oscillating mixer which employs the Mullard bi-grid valve type PM1DG.

DFWB.
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Old 4th Mar 2018, 3:02 am   #7
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Default Re: Supersonic Heterodyne radio 1920's.

Update on the Raie Studio nine valve set . I decided to scope around the first two valves rf end what do you know a nice healthy sine wave , so something is oscillating ,decided to disconnect the osc tuning capacitor and try it in different points around the front end , no damage was done ,it's only a capacitor .
At one point on the what looks like the first IF can ,but when cleaned I see it is marked filter, it tuned , so it is now connected to the junction of the plug in coil pack and the filter tx it now tunes the osc freq .
At one stage I had it working fine, but something happened further work req It is now 2 am time for bed me thinks . Mick.

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Old 4th Mar 2018, 1:17 pm   #8
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Default Re: Supersonic Heterodyne radio 1920's.

Back in the workshop this morning , switched the set on , audio stages ok all voltages correct ,then I happened to touch one of the rf valves ,after a few crackles we have stations again, what had happened the valve had actually climbed out of it's socket ,

A bit of doctoring to the pins cured the problem .I am now experimenting with some aerial coils ,more pictures to follow , I need to retrieve the cabinet from the loft . Mick.
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Old 6th Mar 2018, 10:37 am   #9
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Default Re: Supersonic Heterodyne radio 1920's.

Strange readings on the rf amp valve on my beloved supersonic , there is only about two volts on the anode ,this is due to it being connected via the filter tx to the heater cct .

The valve is amplifying in fact there is loads of gain , I need to use an attenuate the input on strong stations. Has anyone come across the type of thing before. Mick.
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Old 8th Mar 2018, 10:50 pm   #10
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Default Strange low volts on rf amp on a two volt battery set

I thought I would try again to see if anyone has any thoughts , the thing is there is only two volts on the anode of the first rf amp valve , according to the layout there is no way it can get anything like HT , it gets the two volts via a filter tx , by the way this is on the early superhet the nine valve RAIE supersonic heterodyne I am working on ,the strange thing is the valve in question works and amplifies very well . any thoughts welcome , Mick.
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Old 9th Mar 2018, 6:27 am   #11
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Default Re: Strange low volts on rf amp on a two volt battery set

Try removing the valve and see what is on the pin then in case there is a defect in the valve or holder.

Ed
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Old 9th Mar 2018, 7:24 am   #12
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Default Re: Strange low volts on rf amp on a two volt battery set

What type of volt meter are you using?

Mike
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Old 9th Mar 2018, 9:38 am   #13
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Default Re: Strange low volts on rf amp on a two volt battery set

Thank's for the replies, tried different valves , just the same with no valve I can trace the origin of the two volts ,it gets it via a what they call a filter tx it looks like the other IF TX's but is stamped filter , so one end of this filter goes to a heater pin the other goes to the anode of the first valve , this is not the oscillator valve that is the second valve in the chain. connecting a capacitor from grid to anode pins with valve removed produces a signal but very weak .

I thought I had a bad connection with the probe on my Fluke meter which sometimes happens, but no there is only two volts . Mick.
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Old 9th Mar 2018, 9:56 am   #14
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Default Re: Strange low volts on rf amp on a two volt battery set

Some pictures of the front end of the set the third pic is the coil pack there are two basket woven coils , not connected internally ,the second pic shows the socket from the left there is a coil connected across the first two pins and another coil across the other two.
I am not to bothered about it, the set works very well , just curious regarding the anode volts. Mick.
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Old 9th Mar 2018, 11:54 am   #15
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Default Re: Supersonic Heterodyne radio 1920's.

Quote:
Originally Posted by vinrads View Post
Strange readings on the rf amp valve on my beloved supersonic , there is only about two volts on the anode ,this is due to it being connected via the filter tx to the heater cct .

The valve is amplifying in fact there is loads of gain , I need to use an attenuate the input on strong stations. Has anyone come across the type of thing before. Mick.
I guess that there could be a design or wiring problem that's leaving the RF valve with only 2V on the anode. Maybe the manufacturer found, as you have, that it works well anyway, so didn't mess with it . Are you sure that it's the RF amp valve that's giving the gain, or is it coming from the later stages of the set?

Martin
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Old 9th Mar 2018, 2:02 pm   #16
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Default Re: Supersonic Heterodyne radio 1920's.

Hi Martin I think I need to draw the schematic out ,so people can see what's happening ,Mick.
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Old 15th Mar 2018, 11:43 am   #17
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Default Re: Supersonic Heterodyne radio 1920's.

Hi back to the Supersonic Heterodyne the question is how does it work ,and it works very well with -2 volts on the anode.Mick.
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Old 16th Mar 2018, 3:29 pm   #18
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Default Re: Supersonic Heterodyne radio 1920's.

Is it actually an RF amp or is it just being used as the first detector (mixer)?
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Old 16th Mar 2018, 4:55 pm   #19
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Default Re: Supersonic Heterodyne radio 1920's.

Now that's a good question Chris , I thought it may be some kind of buffer stage but it works, remove the valve no sig join the anode and grid with 1000pf cap very low signal , Mick.
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Old 16th Mar 2018, 10:41 pm   #20
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Default Re: Supersonic Heterodyne radio 1920's.

Even if it's only behaving as a diode it will work as a mixer- you only need a nonlinear response with a signal and LO contribution for this.
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