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Tunnel Diode Replacement and Modification: Difference between revisions
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Tunnel Diode Replacement and Modification (view source)
Revision as of 10:20, 9 February 2022
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Vintage dave (talk | contribs) (schematic is in the manual; two S/N ranges) |
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== Sweep Trigger TD Substitution == | == Sweep Trigger TD Substitution == | ||
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Step by Step Modification Instructions: | Step by Step Modification Instructions: | ||
# Replace the bad 10 mA Tunnel Diode (D245) with a new 4.7 mA Tunnel Diode (e.g. [[1N3717]] or [[Russian tunnel diodes]]). | # Replace the bad 10 mA Tunnel Diode (D245) with a new 4.7 mA Tunnel Diode (e.g. [[1N3717]] or [[Russian tunnel diodes]]). | ||
# Replace transistors Q234 and Q244 with silicon transistors having | # Replace transistors Q234 and Q244 with silicon transistors having f<sub>t</sub> around 200 MHz and Beta around 100, such as 2N4248. | ||
# Replace resistor R236 (30.1 kΩ) with a 47 kΩ | # Replace resistor R236 (30.1 kΩ) with a 47 kΩ, 1 W resistor. | ||
# Add new 30K 1 watt resistors in series with R247 and R248, which are each 15 kΩ | # Add new 30K 1 watt resistors in series with R247 and R248, which are each 15 kΩ, 2 W. (Total resistance is now 45 kΩ each). | ||
# Because the | # Because the tunnel diode must be biased below its trigger point, there is less adjustment margin with a 4.7 mA Diode than with the original 10 mA Diode. This means that the values of R247 and R248 can be quite picky. Because of the variations between individual tunnel diodes, it may be necessary to use slightly smaller or larger resistances. | ||
Morris points out that the B Sweep Trigger circuit is identical to the A Sweep Trigger. This modification should therefore be equally applicable for that circuit. | Morris points out that the B Sweep Trigger circuit is identical to the A Sweep Trigger. This modification should therefore be equally applicable for that circuit. | ||
Dave Wise believes that for S/N 6740-up, you would modify R236, R233, and R246. The goal is same node voltages with <4. | Dave Wise believes that for S/N 6740-up, you would modify R236, R233, and R246. The goal is same node voltages with <4.7 mA through the diode instead of <10 mA. | ||
[[Category:Repair issues]] | [[Category:Repair issues]] | ||