Hickok 288x - Printable Version

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+--- Thread: Hickok 288x (/showthread.php?tid=25312)

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RE: Hickok 288x - daveone23 - 10-17-2024

I pulled all the tubes except the 6x5 and the B+ on both c31 caps is nothing (.5v).

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RE: Hickok 288x - daveone23 - 10-22-2024

new transformer and B+ but the machine is still dead. C20 and c26 are new and fine. 6c4 is good. I noticed the var audio freq knob and fins are frozen but i dont think it makes a difference, its just for audio. Probes still spark but my good machine does too. Where should i start looking?

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RE: Hickok 288x - MrFixr55 - 10-22-2024

Does your B+ still drop to near zero V when set warms up? You need to fix that before going anywhere else. If this is happening with only the rectifier installed, then troubleshoot by disconnecting all loads then adding them one at a time. Sounds like a cap shorts when things heat up. Check C18, a 100pF mica cap for shorts. Check the output and band switches as B+ may go to these switches.

Hope this helps.

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RE: Hickok 288x - daveone23 - 10-23-2024

The B+ stays steady at 277vdc will all the tubes in.

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RE: Hickok 288x - daveone23 - 10-23-2024

I put the scope on pin 8 of the 6sn7 and read something but i had to crank the scope WAY down to 10m volts and 10ms time. Read the same on the probe. Volts on tube plates are hit and miss.
6c4 = -.6vdc
6sn7 v2 = 243vdc
6sn7 v3 = 195vdc
6sj7 = 260vdc
6sg7 = 11vdc
Why does the pic of the 6sn7s look different?
Whats next to check?

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