1957 HP 400H Vacuum Tube RMS Voltmeter / DB Meter, HP112-66, Model 1051

Description

For sale is a 1957 vintage Hewlett Packard vacuum tube RMS voltmeter / DB meter, Model HP 400H, HP 112-66, Weston mirrored meter model 1051.   It was left behind in the electronics equipment left behind by my late father.   He was an active and avid HAM radio operator for over 70 years, and was an electronics serviceman for much of his life.   This meter must have been part of his "tools of the trade."
I really have no knowledge of testing Dad's electronic equipment, so I will have to sell this unit as is, as found and as photographed.   I have had good feedback from other equipment I have sold, but I can give no guarantees.   Please purchase this meter with the intent to refurbish it, and then be delighted if you don't have to!!
This is information from the tags:
R.M.S. volts  1-10
Decibles   -10 to +2
IMW   600 ohms
The sticker on the front says that it was last calibrated 11-8-71.   I'm guessing that my dad purchased this second hand,  either from work, or the Army Surplus Store near our home.
The RadioMuseum tells us that it was made in 1957, has 8 tubes, is 7.5" x 11" x 12", and the AC is 115/230V.   It also adds:
Model 400H has a 5" indicating meter with mirror scale and measures voltages from 0.1 mv to 300 volts. The high input resistance of 10 megohms effectively minimizes loading to circuits under test. A highly stabilized amplifier with 56 db feedback provides exceptional long term stability; even line voltage changes of *lo% cause negligible variations. Readings are direct in volts or db. Operation is extremely simple; input voltages up to 600 volts peak will not damage the instrument. The instrument is of highest quality construction throughout, and is available either in the lightweight, rugged -hp- portable cabinet or for rack mounting. Stabi 5651, 12 Messbereiche 1mV-300V, -72dB bis +52dB, 10Hz-4MHz.
I also found more information on a blog:
I previously repaired several HP-400 models, including the
HP-400
A
,
the
HP-400
C
,
and the
HP-400
D
.
The
HP-400H
has the largest meter of that group with a 5 inch mirrored scale. All of the 400 series are related. The 400H is essentially a slightly improved 400D. The schematic of the 400H is nearly the same as later serial numbers of the 400D. The specifications are the same for the two although for the 50Hz to 500 KHz range, the 400H is rated at plus/minus 1% of scale accuracy. The 400D does not have a separate specification for that range so the assumption is that its accuracy is 2% for the same range.
The HP-400H is a wide-band RMS Vacuum Tube VoltMeter with separate terminals for cathode-follower output of its amplifier. It is capable of reading AC from 1 millivolt full scale to 300 volts full scale. The wideband response is from below 10 Hertz to a specified working accuracy limit of 4 Megahertz. The cathode follower output for monitoring, regardless of input switch setting, is specified at 0.15 volts at 50 ohms impedance. Input impedance is 10 MegOhms.
Repairs
A copy of a Hewlett-Packard military manual that applies to both the HP-400D and the HP-400H can be found on BAMA under HP-400D.
https://people.ohio.edu/postr/bapix/HP400H.htm
I hope this helps you decide if this is the meter for you!
Thanks for looking here!!
(Radio shelves)