29-07-2020, 08:40 AM
(This post was last modified: 29-07-2020, 08:41 AM by Mike Watterson.)
I've discovered that a jumbo "chrome" effect paper clip makes good pins as it's got a steel core, stiffer than zinc plated garden wire and solders easily. Most importantly it's almost a perfect diameter. The garden wire I found is too fat and my tinned copper wire I used before only works on "perfect" sockets as it's a little skinny.
I've found a load of pin protectors that have eight holes, wide at one side and pin sized at the other end, so they sort of work as straighteners too. They have two bands, really fine grooves, on the side thus the bottom 1/3rd can be cut off. Most are some sort of thermoset plastic or Bakelite. A few seem to be softer stuff.
So I set a slice on an uncut one, poke in straightened paper clip and cut off about 1.5mm above the surface and then bend over outwards pressing with the flat of a screwdriver, then pliers. Solder blob goes into the wider gap at the top of the cut disc. Finally prise out the new plug when all seven pins are done.
Photos next time. I'm making up two, one triodised for the oscillator and one where the oscillator is a Pentode with the g2 going to the Heptode or Octode final screen grid (variously numbered) that takes HT.
The two g3 wires, two screen wires and two f- wires all bend gently to 180° and solder to the piece of coffee tin shield bent to hold both rod tubes. That then has a single heavier wire to the B7G f- pin. The two f+ wires are sleeved and also bent up to connect to 2 x 10Ω resistors to drop 0.2V maximum. The version for 50mA series or 25 mA (nominal) will have one of two values of resistor from pin 1 to pin 7, as the total current of both Rod tubes is about 21mA to 24mA. That might need adjusted on test; I maybe should measure all my 1j24b tubes to see what the variation of current is at the same supply voltage. The current is increased by the mixer HT current and the oscillator HT current.
Another aspect to look at is that on 67V and 45V designs the screen grid HT might be connected direct but on 90V it's via a decoupled resistor. Thus oscillator g2 would need a pull down resistor for the 50V (a 90V HT). The triodised version of the oscillator has no HT for a screen grid and the mixer g2 in all configurations is biased by the oscillator tube's anode voltage as you want about 35V with 20 to 50 swing for maximum conversion, ie about 30V AC, though even 5V drive does convert the input RF.
So though I know the circuit worked to replace a DK96, I didn't make any measurements. I'll also want an RF probe that doesn't load a shortwave LO.
I've found a load of pin protectors that have eight holes, wide at one side and pin sized at the other end, so they sort of work as straighteners too. They have two bands, really fine grooves, on the side thus the bottom 1/3rd can be cut off. Most are some sort of thermoset plastic or Bakelite. A few seem to be softer stuff.
So I set a slice on an uncut one, poke in straightened paper clip and cut off about 1.5mm above the surface and then bend over outwards pressing with the flat of a screwdriver, then pliers. Solder blob goes into the wider gap at the top of the cut disc. Finally prise out the new plug when all seven pins are done.
Photos next time. I'm making up two, one triodised for the oscillator and one where the oscillator is a Pentode with the g2 going to the Heptode or Octode final screen grid (variously numbered) that takes HT.
The two g3 wires, two screen wires and two f- wires all bend gently to 180° and solder to the piece of coffee tin shield bent to hold both rod tubes. That then has a single heavier wire to the B7G f- pin. The two f+ wires are sleeved and also bent up to connect to 2 x 10Ω resistors to drop 0.2V maximum. The version for 50mA series or 25 mA (nominal) will have one of two values of resistor from pin 1 to pin 7, as the total current of both Rod tubes is about 21mA to 24mA. That might need adjusted on test; I maybe should measure all my 1j24b tubes to see what the variation of current is at the same supply voltage. The current is increased by the mixer HT current and the oscillator HT current.
Another aspect to look at is that on 67V and 45V designs the screen grid HT might be connected direct but on 90V it's via a decoupled resistor. Thus oscillator g2 would need a pull down resistor for the 50V (a 90V HT). The triodised version of the oscillator has no HT for a screen grid and the mixer g2 in all configurations is biased by the oscillator tube's anode voltage as you want about 35V with 20 to 50 swing for maximum conversion, ie about 30V AC, though even 5V drive does convert the input RF.
So though I know the circuit worked to replace a DK96, I didn't make any measurements. I'll also want an RF probe that doesn't load a shortwave LO.
