#68: HP-400D video 2: Investigating the components

[@Philipp..]

Your voice and your way of explaining is very pleasing.

[@Andrewausfa]

I love these old equipments, still useful to this day. Looking forward to the next installment.

[@jameslucas6589]

Looking forward to the next video.

[@radiophysicsandelectronics6923]

Am outlining next video now and am slowly making progress on the capacitors etc. Spent a lot of time on pondering the selenium rectifier bridge.

[@jameslucas6589]

Sure sounds like a beagle👍🏻 Great video as always. Love VTVM restores. The more the better.

[@radiophysicsandelectronics6923]

Close: Foxhound!

[@johnhannon4330]

My 400D is also missing the .75pF cap (C6) and the grounded terminal is clean, indicating it was never installed. Serial #25364

[@curtislucka9954]

Very interesting. Great cap testing. Would like to see how this turns out!

[@materialsguy2002]

Very informative, thanks.

[@robertcalkjr.8325]

Thanks. Are you going to leave the Allan Bradley resistors in it? I would as long as they are in good shape.

[@radiophysicsandelectronics6923]

I usually spot check several resistors so that I have something that feels like a reasonable sampling. If those are all within tolerance, then I assume the rest are likely to be as well. Given the initial look, I'll leave the Allan Bradley resistors alone, as they seem to have aged well. The capacitors, of course, are another story.

[@robertcalkjr.8325]

Yep, caps are a different story. From most people I have watched, those resistors age well and are usually in specs. Hopefully I'll get to restore some older equipment soon.

[@PapasDino]

Thanks for sharing...is that a selenium rectifier next to the transformer? Reason I ask is the schematic you used as closest to your model still appeared to have a tube rectifier. Just curious. 73 - Dino KL0S

[@radiophysicsandelectronics6923]

On the schematic there is a silicon full wave bridge rectifier (SR1) and a tube rectifier (V6), and both appear in the unit. I also thought that the alleged silicon bridge looked like selenium, but I believe that it is early silicon. We will investigate more closely as the project goes on!

[@alfredneumann4692]

In the first video, we saw, that you found a 4A Fuse in the fuseholder. Have you searched for the reason of this? Have you checked the powertransformer and the following rectifiers and so on? Or have i something missed in your video? Best regards from Germany.

[@oldblokeh]

0.75pF isn't very much. Perhaps there was enough stray capacitance between the tags to do the job?

[@radiophysicsandelectronics6923]

I thought about that after posting the video, and given the picture of the unit in the thread posted on the Antique Radio Forum (link provided above), I suspect you're right.

[@ViniciusMiguel1988]

Use Mr. Carlson's leak tester and you will see the leak