I just snagged one of these it’s on the way does anyone else have one that they have restored ? Mine is missing the model tag on the front but I’m 90% sure that is the model.
I have one on my test bench and I have a copy of the manual. I do use it sometimes when working on project that have tubes like restoring old radios.
@kb6dx-jim very good. I might ask you some questions when it gets here.
I have restored the HP400H. Mine is missing the identification label too ;-). There is a youtube video from Gary Ramsey on his restoration of his HP400D. At the beginning, he is showing the HP400D and HP400H side by side. The latter having a larger meter window and a parallax correction mirror. Internally, however they are the same, and he is discussing the restoration. On my HP400H, I did not replace the selenium rectifier, but you may want to check the capacitors C18-C19, C23-C24 and C27-C28 and also the cathode decoupling electrolytics. You will find some additional info on radiomuseum.org.