22-10-2023, 04:06 PM
(This post was last modified: 22-10-2023, 04:16 PM by Mike Watterson.)
No-one has made rod pentodes since 1991. Valves are still made. Transistors & ICs more so. No-one will ever make rod pentodes again. The USSR continued with them out of a mix of inertia and inability for a long time to make silicon transistors. I remember repairing mad "newish" USSR TVs and radios in late 1970s. All Germanium.
Also you are very limited in power. The sorts of things rod pentodes can do at audio can be done better by ICs. The rod pentodes main advantage is outperforming B7G battery valves and US subminiature wire ended valves in battery applications. Using them in mains gear is even more a curiosity than battery applications. Fine for a bit of fun.
They are quite microphonic, also work to over 100 MHz. USSR actually mounted them on alumina thickfilm substrates with SMD parts. Only earliest applications used point to point wiring.
Pros:
High to very high efficiency on filament except "radar/fuze" O/P application devices.
Can work at low HT (The 1j42a ONLY works at very low HT, 6V to 12V, 9V is good).
Very tolerant of filament volts, because designed for NiCd and silver rechargeable cells.
Sharp cut off.
Pentode like characteristic
Lower noise than regular pentodes.
Works well as Pentode mixer with direct drive / bias to g2 (20V (off) to 45V (full on) approx )
Lower electrode capacitance than any common battery valve.
Ideal for replacing 2V or 1.4V battery valves (I've done KK32, KLL32, DK91, DK92, DK96, DF97, 1T4, DAF96, DL9x. planing a "no re-tune" IL6 replacement)
Cons:
The g2 needs an HT rail or potential divider. The current changes too much to set voltage with a series resistor.
For RF / IF AGC you need to control gain via g2, not g1.
Very sensitive to magnetic fields
Sensitive to vibration
Gain very sensitive to voltage on g2
Filament needs small ballast resistor for NiMH and larger ballast resistor for Alkaline. Better suited to NiMH than Alkaline.
Needs electrostatic shield. Almost no built in shield.
Can be triodised, but unlike real pentodes the g3 should be at about f- or f+ voltage, never tied to anode.
No tetrode simulation.
RF devices to over 100 MHz, so care on audio.
As awkward on mains equipment as traditional 1.4V B7G valves.
Also you are very limited in power. The sorts of things rod pentodes can do at audio can be done better by ICs. The rod pentodes main advantage is outperforming B7G battery valves and US subminiature wire ended valves in battery applications. Using them in mains gear is even more a curiosity than battery applications. Fine for a bit of fun.
They are quite microphonic, also work to over 100 MHz. USSR actually mounted them on alumina thickfilm substrates with SMD parts. Only earliest applications used point to point wiring.
Pros:
High to very high efficiency on filament except "radar/fuze" O/P application devices.
Can work at low HT (The 1j42a ONLY works at very low HT, 6V to 12V, 9V is good).
Very tolerant of filament volts, because designed for NiCd and silver rechargeable cells.
Sharp cut off.
Pentode like characteristic
Lower noise than regular pentodes.
Works well as Pentode mixer with direct drive / bias to g2 (20V (off) to 45V (full on) approx )
Lower electrode capacitance than any common battery valve.
Ideal for replacing 2V or 1.4V battery valves (I've done KK32, KLL32, DK91, DK92, DK96, DF97, 1T4, DAF96, DL9x. planing a "no re-tune" IL6 replacement)
Cons:
The g2 needs an HT rail or potential divider. The current changes too much to set voltage with a series resistor.
For RF / IF AGC you need to control gain via g2, not g1.
Very sensitive to magnetic fields
Sensitive to vibration
Gain very sensitive to voltage on g2
Filament needs small ballast resistor for NiMH and larger ballast resistor for Alkaline. Better suited to NiMH than Alkaline.
Needs electrostatic shield. Almost no built in shield.
Can be triodised, but unlike real pentodes the g3 should be at about f- or f+ voltage, never tied to anode.
No tetrode simulation.
RF devices to over 100 MHz, so care on audio.
As awkward on mains equipment as traditional 1.4V B7G valves.
