04-02-2021, 09:14 PM
Let me clarify so there won't be any confusion:
The HP 8657A has the capability of internal and external modulation, both AM and FM, and either 400Hz or 1 Khz. I always use internal AM at 400 Hz, and have aligned probably 50 radios with this sig gen. The 8657A has an inline 50Ω attenuator.
I also use a seperate gridcap for the det/osc. so the signal is fed directly into the grid of the tube.
Using an internal modulation of 400 Hz, I can inject that signal into the 6A7 grid, at ANY frequency from between 500 KHz and 1550 KHz. By tuning the var.cap to the frequency injected, I can adjust all 4 compenating condensers for maximum volume.
I can also adjust the LH and HF padders. AND, I can receive stations (however not too clear) all across the dial with an antenna.
What I CAN"T do is hear any audio when injecting the IF of 460 KHz. I can adjust the primary and secondary of both IF coils through their entire range, and still not hear any audio from the 460 KHz.
However, even though no schematics show it, the wire attached to pin 4 (grid 2) of the 6A7 from #42, a 32K resistor, first goes in and out of the osc. transformer, with a resistance of around 16 Ω (tickler maybe?). There are several variations of the 610, and several changes, but nothing makes any reference to this. You can tell by the untouched solder joints that this was factory installed, and I also found reference to it on another thread (someone else mentioned it).
All clear?
The HP 8657A has the capability of internal and external modulation, both AM and FM, and either 400Hz or 1 Khz. I always use internal AM at 400 Hz, and have aligned probably 50 radios with this sig gen. The 8657A has an inline 50Ω attenuator.
I also use a seperate gridcap for the det/osc. so the signal is fed directly into the grid of the tube.
Using an internal modulation of 400 Hz, I can inject that signal into the 6A7 grid, at ANY frequency from between 500 KHz and 1550 KHz. By tuning the var.cap to the frequency injected, I can adjust all 4 compenating condensers for maximum volume.
I can also adjust the LH and HF padders. AND, I can receive stations (however not too clear) all across the dial with an antenna.
What I CAN"T do is hear any audio when injecting the IF of 460 KHz. I can adjust the primary and secondary of both IF coils through their entire range, and still not hear any audio from the 460 KHz.
However, even though no schematics show it, the wire attached to pin 4 (grid 2) of the 6A7 from #42, a 32K resistor, first goes in and out of the osc. transformer, with a resistance of around 16 Ω (tickler maybe?). There are several variations of the 610, and several changes, but nothing makes any reference to this. You can tell by the untouched solder joints that this was factory installed, and I also found reference to it on another thread (someone else mentioned it).
All clear?
