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Tuesday 5 June 2012

More shack test equipment

Well just taking a bit of time away from a project am working on some test kit I was given by brother of a G-QRP member when I visited the RSGB AGM A B4A Signal Generator. Was not supposed to be operational and it didn't turn on initially.

I lashed up a mains fed to it as did not have the appropriate plug. Fitted shrink wrap over the exposed plugs, I'll repair that later. The main transformer had an open secondary, it was a simple 230V:250V with a centre tap output, and I had been keeping one with 6.3V windings for a valve project but this looked suitable and right size so swapped it out. The old one I'll rewind the secondary and reuse.

I simply love the mains input choke.

PL1 was duff so replaced with a screw in 6V MES bicycle bulb.

Checked connectivity on the circuits. Insides (photos to follow) very clean.
Initially with the 6X5GT  removed turned it on and checked the heaters were all fine. Then put the 6X5GT back in and with the other valves removed tested the HT (301V) and other valve socket pins for the appropriate voltages. Seemed to loose the HT some where so thought maybe this was similar to the HRO problem so a quick once over with the home brew ESR meter and some of the bypass Dublier caps were proven to be open circuit. So rummage in the Dayton ham-fest brown bag of goodies and replaced three 350V paper tube 0.01uF and turned it on again. All seemed fine so turned off plugged in the three valves and turned on again waiting until heaters been on for a bit and then twiddled with the controls... The calibration is slightly off but I'll fix that. Nice rim dial control, must have slipped a bit.

Circuit and manual from a Google search...

Fed the signal into a oscilloscope and seems like nice clean output, across the various scales.... I now have a nice signal generator for the bench. I like the attenuation options dropping down to 1uV from 100mV

I do not have the RF/AF output leads so I might swap these (apologies all purists out there) for BNC or N type chassis connectors. And I have a spare digital frequency counter so might add that too after adding a pre-scaler as the generator will go from 100KHz to 80MHz.

Looks like this one (will put better photos up):

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