All valve receiver modification

Hi Ivan and Vulkan,

I use 230V AC transformers as speaker transformers, connected backwards.

I have found that if you dismantle the transformer, then re-assemble with ALL the "E"-formers from one side and all the "I"-formers at the other side, a bit of 0.1mm paper can be put between them, making the transformer suitable to have a DC bias current through it without saturation.

I think I described this on one valve project on the homepages.

BR Harry

Yes, this power transformer is good. It lacks a heater winding for the rectifier tube, but you probably intend using a diode bridge instead.
AF output transformers are often matched to a specific pentode type and schematic. It may be the best way to salvage a complete AF PA circuitry from an old tube radio (TV, tape recorder etc.) and connect it to the volume potentiometer.
Notice the tapping of the primary (anode) winding in the original schematic. This is not everywhere. And do not forget the proper air gap in the core, needed to prevent core saturation by the DC component of anode current.

BR from Ivan

This transformer also has a 6.3v - 5A output.
I prefer that the transformer be oversized, in case it can also be used in the transmitter.
As for the AF transformer, I have not looked for it yet. Should it be 4000 ohm - 8 ohm 5w?

Hi,
I expect you had the PSU transformer in mind. 170 VAC should yield 240 VDC with a two way rectifier. 130 mA looks rather like an overkill, but you can use it of course. What about heater winding(s)?
The AF output transformer primary may present a problem. Do you have some data about it?

BR from Ivan

Good Morning.
I have located a 170v-130mA AC output transformer
Is that transformer suitable?

Thanks for answering.
Like the F.I. it is 5mhz, the BFO I think should be 5,0015mhz and the capacitors 330pf
Must try.
Thank you

Hi Vulkan,
replace the variable capacitor and coil in the grid circuit of V2b by a suitable crystal with parralel grid leak resistor. Adjust values of the capacitor divider if necessary.
As for the frequency of the crystal, please look here.

BR from Ivan

Good afternoon.
My name is: Manolo
I have seen all valve receiver and would like to modify it to receive only 7mhz LSB.
I am sending you the modification of the F.I. and I would like you to indicate the modification to put an XTAL in BFO.
Thank you

Buenas tardes.
Mi nombre es manolo
He visto todos los receptores de válvula y me gustaría modificarlo para recibir solo 7 mhz LSB.
Le estoy enviando la modificación de la FI y me gustaría que indique la modificación para poner un XTAL en BFO.
Gracias