JAN CHS 811, VT-217, Transmitter tubes, Sylvania, NOS.
Joint Army Navy 811 VT-217 Power triodes, made by Sylvania. Made in the USA. Tested on TV7, priced each.
4 en stock
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These tubes appear to be unused, both in gm tests and their appearance.
The JAN 811 have 4 ridges on each side of the anode. This increases the mechanical stability of the plate somewhat. These tubes do not use the welded on U channels found on some 811 tubes (see reference below).
These tubes were tested on a TV7D/U and all read between 62 and 68, with a minimum specification of36. Price is per tube.
This from CTR Engineering:
"The thin 811/812 anode was improved by welding a series of U channels to the anode, normally three channels on each anode side. These U channels were welded to the anode. The U channels thicken the anode under each channel, and bridge the anode from side-to-side. The extra channels increase thermal mass in the area where electrons strike the anode, extending the thermal averaging time. The thermal averaging time of the anode tripled from the non-finned original anode.
"U-channels on the anodes of 811A and 812A tubes are expensive. To be effective the U-channel must be very flat and the U-channel has to be welded to the basic anode core. This is a costly process.
"When 811A tubes appeared from offshore, they had a modified anode. The original USA 811A tubes were perfectly flat at the high-temperature high-current anode area with welded U-channels to increase thermal lag and dissipation. The import tubes eliminated the channels, and folded the anode up. The fold provides about the same infrared radiation area as the original 811A, and the import tube has the same 65-watt long-term dissipation.
"Unfortunately, the new import anode greatly reduces shorter term dissipation capability. Instead of requiring 60-100 seconds of 200-watt dissipation to go beyond thermal limit like the USA finned anode "A" version, the import "A" version's folded anode thermal limits at hot spots in about 15-20 seconds at 200-watts dissipation."
The entire article is available here.