The Minimalist Superhet Radio project.

[Geordie McBoyne]

6J7 and 6SJ7GT as an anode bend detector.
Information from the No6 Brimar valve book. With an anode voltage of 100V. Anode load resistor 0.25Meg. Screen series resistor 2.5Meg. Cathode bias resistor 10,000ohms. RMS input 1.6 volts. Peak outpt 17 volts.

With an anode voltage of 250V Anode load resistor 0.5Meg. Series screen feed resistor 4.7Meg. Cathode bias resistor 10,000 ohms. RMS input 1.4 volts. Peak output 17 volts.

It's the type of frequency changer valve I have to decide on. Octal types triode-hexode 6K8 or heptode 6A8?

Geordie McBoyne.

[Murphyv310]

Hi.
The EF91 works well as an Anode bend detector in my set. Bags of drive to the EL95 I am using.
Only disadvantage I see with the anode bend detector is it won't detect below a certain threshold and some weak stations don't come through.

[Geordie McBoyne]

News Flash! The detector valve in this set is in fact a 6SH7GT. The chassis is out of the cabinet and I discovered that the cathode bias components go to pin 3. On a 6SJ7GT pin 3 is the suppressor grid and pin 5 the cathode. In the 6SH7GT the cathode and suppressor grid are connected internally the connection goes to pins 3 and 5. The 6SH7 is an RF pentode, gm is a modest 4.9mA/V. Was also used as a video amplifier in some American TV receivers.
Successor valve is the 6AU6, B7G base.
It has been determined that the detector in the set is an anode bend type. Very high value cathode bias resistor, 22Kohms. Screen volts supplied from a potential divider of 1Megohm and 100Kohms, therefore 1/11th of the HT voltage.
From the Radiomuseum: http://www.radiomuseum.org/tubes/tube_6sh7.html

Geordie McBoyne.

[pwdrive]

Not superhet but you can use ECH types for direct conversion:

http://www.epanorama.net/sff/Radio/Commu...rt%201.pdf

Lawrence.

[Crackle]

Hi
This topic sounds familiar.
The tuning cap in the TRF set looks a bit bent, how easy will that be to straighten out.

Mike

[Murphyv310]

Hi Mike.
Are you referring to the cylindrical finned device on the right hand side of the chassis? If you are then I'm sure it isn't a cap but the HT rectifier.

[Terry]

My initial reaction was the same as Mike's - until I looked a bit more carefully.

The tuning gang is half meshed and sideways on in that shot so there is no way of telling whether the vanes are bent or straight!

[Crackle]

Should have looked closer like Terry

Mike

[Geordie McBoyne]

It's the bashed up SenTerCel finned HT rectifier. It's useless and I'm planning to replace it with a 6X5GT valve rectifier. I'm sure the heater transformer is up to the task of delivering the extra 0.6amp heater current.
The two gang tuning capacitor is in excellent condition. I've found almost all the fragments of the tuning scale so it might possible to have it scanned and copied on to transparent film.

Geordie McBoyne.

[Geordie McBoyne]

Circuit diagram of the superhet receiver I constructed some time ago.

Geordie McBoyne.