Vertical Deflection PAs
Posted 24th December 2014 at 10:51 PM by Miles Prower
TV developed from B&W viewed on small electrostatically deflected CRTs, like o'scope CRTs. Screen size wasn't over 7".
Next came electromagnetic deflection, and bigger screens. At first, small signal triodes like the 6SN7 were up to the task of driving vertical deflection coils. Bigger screens and wider deflection angles meant for more demanding vertical deflection duties. This led to a hardened 6SN7GTB with grid radiator wings, a higher plate dissipation rating, and the characteristic extended into Vgk > 0 territory.
Low-u power triodes eventually gave way to power pentodes for vertical deflection duty. Some of these types look like good audio finals. Unlike the HD types, these can use impedance match ratios more like audio finals, so stock OPTs can be used.
10JA5
This is a singleton power pentode with some excellent loadlines. It also doesn't have the top cap connection of most of the HD types, and some designers find this desirable for end user safety. You keep all the high voltage under the chassis, and out of reach.
This one can make more than enough power for the home listener, and does so with very low distortion. It isn't a hard load for the driver either. The load of 5K44 (P-2-P) is very close to a stock value, so no custom designed OPT is needed here.
21LR8
The usual choices for a vertical deflection system is either a blocking oscillator, or a combination plate coupled astable multivibrator/vertical deflection power amp. The 21LR8 was intended for this service. It includes a small signal triode and a power pentode in the same glass. The triode is a high gain device with good looking characteristics.
This is convenient in that the triode can be used as a cathode follower grid driver. Since the linearity is good, you could also implement your LTP with the triode section and couple to the pents. That's one less hole to knock in the chassis.
Another good looking loadline. The 1K56/phase load impedance is likewise very close to stock OPT values: 6K24 (P-2-P). You could use a 6K (P-2-P) OPT, or a 6K6 (P-2-P) OPT here for somewhat lower output.
That's very good indeed.
Another advantage to these types is the availability of the types in odd heater voltages, as it was intended to "daisy chain" all the heaters across the AC mains, and use a PTX-less DC supply. even if the 6.3V types become rare and/or expensive, the odd heater types should remain available.
Next came electromagnetic deflection, and bigger screens. At first, small signal triodes like the 6SN7 were up to the task of driving vertical deflection coils. Bigger screens and wider deflection angles meant for more demanding vertical deflection duties. This led to a hardened 6SN7GTB with grid radiator wings, a higher plate dissipation rating, and the characteristic extended into Vgk > 0 territory.
Low-u power triodes eventually gave way to power pentodes for vertical deflection duty. Some of these types look like good audio finals. Unlike the HD types, these can use impedance match ratios more like audio finals, so stock OPTs can be used.
10JA5
This is a singleton power pentode with some excellent loadlines. It also doesn't have the top cap connection of most of the HD types, and some designers find this desirable for end user safety. You keep all the high voltage under the chassis, and out of reach.
This one can make more than enough power for the home listener, and does so with very low distortion. It isn't a hard load for the driver either. The load of 5K44 (P-2-P) is very close to a stock value, so no custom designed OPT is needed here.
21LR8
The usual choices for a vertical deflection system is either a blocking oscillator, or a combination plate coupled astable multivibrator/vertical deflection power amp. The 21LR8 was intended for this service. It includes a small signal triode and a power pentode in the same glass. The triode is a high gain device with good looking characteristics.
This is convenient in that the triode can be used as a cathode follower grid driver. Since the linearity is good, you could also implement your LTP with the triode section and couple to the pents. That's one less hole to knock in the chassis.
Another good looking loadline. The 1K56/phase load impedance is likewise very close to stock OPT values: 6K24 (P-2-P). You could use a 6K (P-2-P) OPT, or a 6K6 (P-2-P) OPT here for somewhat lower output.
That's very good indeed.
Another advantage to these types is the availability of the types in odd heater voltages, as it was intended to "daisy chain" all the heaters across the AC mains, and use a PTX-less DC supply. even if the 6.3V types become rare and/or expensive, the odd heater types should remain available.
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