HP400 MILLIVOLT METERS

If you are going to calibrate and setup ANY tape recorder or analogue audio equipment, you will need an analogue millivolt meter. This is an essential piece of equipment with which you measure / set exact levels at various frequencies in the input / output, playback and record chains. It is an AC voltmeter that has a flat frequency response from about 10 Hz to 500 Khz or more. It usually measures over the range of 0.2mv to 100V and hence the term “milli” in its name. It has very specific accurately calibrated ranges and usually two different scales of measurement. Internally it’s not a simple AC voltmeter movement and attenuator for the ranges but rather a low distortion amplifier and rectification stage with a very flat frequency response driving an accurate DC meter movement. So there is a fair bit more to and inside them than their humble name suggests. .  It has a very high impedance and so does not load the signal you are measuring at all. Indeed, often you will add a known terminator to it so that the ‘loading’ is known and fixed. Also important, is that it is linear from very low to very high frequencies.

I recommend an old fashioned  analogue millivoltmeter and not a digital one. Why?  Simply because it is easier to take a reading and visually see what the trend is as you adjust. A digital meter measures ‘too precisely’ and you can’t easily visualize a peak or hump. The display is constantly updating so it’s also confusing.  There are good 2nd hand analogue units available on line and also new available from China – but  … dare I say a little cheap and nasty.  You can’t go wrong with one of these makes, which were industry leaders in their day

· Hewlett Packard 400 series. I highly recommend.

· Leader LMV 181, 185 & 186 series

· Rhode and Schwarz,  AWA, Kenwood, Grundig etc

I recommend that you consider a recap of any millivolt meter older than 20 years. Nagravox sometimes has reconditioned / recapped / calibrated units for sale as well as recap kits for HP400 series and Leader.  Nagravox also make available a set of calibration references with their China made signal generator  (available in 2022) which can be used to calibrate most millivolt meters.

AF millivolt meters tended to have banana type sockets and RF types shielded RF rated connectors – usually BNC. Various adapters and converters adapt BNC to XLR Cannon and RCA are also essential.  Banana type connectors can easily be converted to BNC, which I prefer to minimise hum and noise.

 The HP400 is an ideal millivolt meter to set up audio equipment. Robust, well made, easy scales to read, long lived and easily updated / recapped / calibrated. Nagravox buys batches of these from time to time specifically with the intention offering them to our customers who want to embark on the final journey of setting up and calibrating their tape machines. 

HP produced a lot of different models of precision AC voltmeters for almost 65 years. Starting with vacuum tube models through to digital. The HP400 was introduced mid 60’s and were available into the 80's in a number of different versions /   guises.

The 400 series is a solid-state (transistors) AC Voltmeter for measuring AC voltages on voltage and Db scales covering a flat frequency range from 20 Hz to 4 MHz or 10 hz to 10 Mhz and 0.5 - 4% accuracy depending on model and range. The input impedance is 10 Mohm, One of the main advantages of this millivolt meter is the taut band technology and superb robust workmanship of its meter movement.

 Dual Scales either log or lin can be in:

• Db 12 Db log or linear decade scale in 14 ranges from –72 Dbm to +52Dbm.
• Volts 100 divisions in log or lin decade scale in 14 ranges 100 uVs to 300V.

The meter can indicate both voltage and dB in a variety of linear or log configurations depending on model. Type EL, FL and GL have the Db scale linear and the voltage scale logarithmic. Type E and F versions have the voltage scale linear and the Db scale logarithmic. Generally we use the Db scale in setting up a tape recorder and there are advantages and disadvantages to having the Db scale linear or logarithmic (see picture in gallery for reasoning).

 The build quality is excellent in these meters as are the precision components used.

Some of the tantalum and electrolytic capacitors are starting to get a bit long in the tooth at 30+ years and should be replaced. Nagravox offers recap kits for these meters and a calibration reference with its digital signal generators should you wish to check or set the calibration. The recap kit includes extra BNC sockets and a switch so you can add a switched dual channel capability which is useful and relevant to setting up stereo tape machines.

The 5 different models are:

HP400E     10 hz - 10 Mhz logarithmic Db scale -10 to +2Db

HP400EL   10 hz - 10 Mhz linear Db scale -10 to +2Db

HP400 F     20 hz - 4 Mhz logarithmic Db scale -10 to +2Db

HP400 FL   20 hz - 4 Mhz linear Db scale -10 to +2Db

HP400GL   20 hz - 4 Mhz linear Db scale -20 to +0Db

 The different models are offered in 3 variations:

• 2^nd hand meter tested and working complete with a diy recap kit.
• Fully refurbished, recapped and calibrated as a single channel instrument
• Fully refurbished, recapped and calibrated as a switched dual channel instrument

Please note that we do not supply a mains lead as each country has a different plug. You will need to get an inexpensive widely available mains lead  (IEC C13) used for most computers, kettles and other appliances and available in different lengths. On some models a proprietary HP mains input socket is fitted that is difficult to get plugs or leads for. On these, the more common modern IEC 320 mains socket and mounting kit is supplied at no extra charge which makes the instrument IEC C13 compliant /  compatible.

 WHY BUY FROM NAGRAVOX? 

*  My kits are relevant.    * My support is genuine and I am the only Revox and Studer service person offering it. 

NAGRAVOX SERVICE UPGRADE KITS are formulated to include all the bits likely to need replacing that are commonly related. 

These target the most likely worn or age degraded parts.

SUPPORT and HELP.  We try to incorporate most of the “confusing” or difficult aspects one needs to look out for in our upgrade kits instructional notes which we call “Service Sheets”.  We also refer you to the official factory service manuals most of which are in the public domain courtesy of Studer / Revox. As our customer we are happy to either provide you with a manual or refer you to the appropriate download site.  Further, as an after sales service, we are happy to answer any questions or difficulties you have in your repair or upgrade . We wont always know the answers but will certainly try our best to help. In any event, if we don’t know the answer it is an ideal opportunity for us to increase our knowledge and experience base and so  welcome all problems. Indeed perhaps you might share some of your innovative solutions and experiences. After all we certainly don’t know everything and welcome advice, suggestions and constructive criticism. My philosophy is that in reality their are few problems only solutions waiting to be communicated or discovered. Why do we offer this level of support?  Well as I indicated before, I do this out of a passion and I think I am right in saying so do you in your anticipated endeavors restoring your treasured vintage gear. It is in this common spirit I am happy to share my knowledge and experience with you as a customer.

ABOUT NAGRAVOX     specialists in Revox, Studer and Nagra tape recorder overhaul and upgrade kits and parts. 

I definitely DON'T consider Nagravox as a typical beady eyed Ebay vendor trying to get the highest price  and hocking anything that will sell.  Indeed ALL my kits and parts are buy it now not auction for that very reason.  I love and work with Revox, Studer and Nagra vintage gear every day. Its great equipment and I love helping other enthusiasts restore their gear. I back up everything offered with a help desk via email, phone or Skype to make sure what you buy from me works and is installed and set up the way it should be. Confusion and problems always occur on old gear but I am there to help you through it.  I don’t just sell stuff to enthusiasts - I help with solutions and make things as easy as possible whilst still retaining the high quality and integrity of the original designers. I am the only vendor that does this. Others of course may copy me, as they have already done in the last 2 years (just look at the other vendors suddenly offering overhaul kits on Ebay - hmm .... some with dubious white washing machine capacitors and below spec suppression caps !!).  I also am now re-manufacturing parts specifically for Revox, Studer and Nagra usually using small specialist manufacturers in Europe, Australia and Taiwan to my design and specifications. Some of the more complex triple can high voltage capacitors for example I personally hand make for the F36 / G36 machines and old A40 amplifiers. One enthusiast restoring a F36 said to me about a year ago - surely you cant make much money on those considering the time and effort involved? He is right of course but the satisfaction of knowing every time I sell one of those kits, a F or G36 will be brought back into this wonderful analogue world of ours, frankly tickles me pink! Revox A77 VU meters now remanufactured and better quality that the original. Motor parts such as low friction washers, shims, brake felts, lubrication felts etc - all newly manufactured for Nagravox. Solutions that make problems go away - see our new NAB deluxe overhaul kits with reel spacer disks.  GOOD IDEA - you bet. Why hasn't anyone else thought of it - who knows - its not rocket science. Will people copy me - of course - that’s life. Am I worried - no not at all - ts all good for the analogue tape enthusiast who wins all the way.  Gee - I do ramble on a bit - don’t I! 

If you are interested in our other endeavours please look at Nagravox or Laudarra.  If you want to have a chat or chin wag - comms me at Nagravox - only a pleasure.  Nagravox has a workshop and store in Sydney Australia.   Of course.. if you are ever in the vicinity please visit me  - there is always a good cup of tea or coffee and the chance of a chin wag.

Some blurb about me and why I do this.  Some people think I am a nutter!  Sometimes I might just agree!  My name is Peter Mony. I am according to the government "a senior citizen" - indeed I get to ride on all the trains, busses and ferries around Sydney for $2.50 flat fee a day (a perk of being 'old' I am told). I live in a stunningly beautiful part of the world in the Northern Beaches on the outskirts of Sydney Australia and am a tertiary qualified engineer and scientist.  I have worked in a few countries around the world for various companies in many different roles including in later years a few of my own businesses.  I love vintage audio equipment and have over the last 45 years been involved in one way or another with it.  I started Nagravox  in 2010 after 3 years of “hard thinking” (my wife thought I was asleep on the couch). I reckoned that I would love to see more of the old Revox, Studer and Nagra tape machines restored to their former glory.  I didn't want to be just another Ebay vendor hocking parts at the best price I could get for them. In 2011 I sold my specialist electronic manufacturing business Powerform Controls which was and still is successfully involved in HVAC controllers and electric motor speed control. This allowed me to have time to do those things in life which don’t necessarily have to be about making lots of money but rather being led in an ambulatory manner by ones passions.  I love playing classical guitar, classic cars and restoring old electronic gear. My wife and lovely daughters think I am nuts but they love me anyway. In 2016 I moved to a dedicated workshop and premises not far form home on the stunning Northern Beaches of Sydney.  In my “man cave”, as my dearest wife calls it, I can indulge a hobby and passion reliving my youth in the 60’s and 70’s when I was a youngster working as a recording studio technician and building valve amplifiers for friends. 

Why did I start in kits? Over the years restoring Revox's, Studer's and Nagra's and inevitably running the gauntlet of finding information and spares, the engineer in me has often asked the question.  “Why cant I just get a professional upgrade kit with all the bits and pieces that are really needed”?  There is a high degree of frustration in sifting through the hype of vendors sales talk, doubt on individual components serviceability and age and the need to shop bit by bit with many of the “bits in between” not available. One inevitably makes compromises and sometimes quick fixes often leaving a niggle of doubt and sadly sometimes not the results one was expecting or indeed all the promo hype intimated.  Service manuals are obviously great but there is always those little nuances not fully explained, aspects seemingly missing and your particular fault symptoms not listed. Inevitably I have found that with old equipment replacing just the item that is obviously faulty or worn isn't always the end of the story or quick fix one had hoped for. So, on this basis and in a spirit of doing the job properly the first time, I have put together a series of what I call upgrade kits with all the necessary bits and pieces that are likely to be worn or old and need replacing. Each kit is designed to address an important functional aspect of ones restoration or repair eg a kit for the mechanical tape handling aspects which includes not just a new fresh Revox factory sourced pinch rollers but also the guide bearings made of stainless steel (not el cheepo skate board ones). If one of these needs replacing, you can be sure a lot of the associated componentry will be in a similar condition and also soon need replacing. Doing one without the other doesn't make sense! Why fault find a leaky capacitor and replace it when its likely all electrolytic and tantalum capacitors, some of which may be 40 years old, really should be replaced despite what they may test like under low voltage test conditions.  What a hassle to have to source 50 or so odd value capacitors and then worry about the quality of cheap and nasty 'old stock' components that have been sitting on a shelf for years or fake Chinese made components! My upgrade kits are thus formulated to include all the bits likely to need replacing that are commonly related. Most of the components that make up a Revox or Nagra tape machine were top quality in their day and a fair bit of the mechanical gear with a good clean up and lube will function fabulously for another 30 years. Yes, I do and can sell individual items but would prefer that you do the job properly and upgrade functionally related sections at a time. These are the ones that will likely be degrading your tape machines performance. My full kits have written explanations and guide notes with pictures to help you. I call these Service Sheets. The bits and pieces that go into the kits have been researched extensively, assessed carefully for suitability and tested in many restorations and projects. They are not just ordinary cheap replacements but something that will last and is of an appropriate quality and grade. Capacitors I researched extensively in my previous business when I needed a high grade electrolytic with low leakage current and long term stability for a particular timer application. I went through 22 different manufacturers before eventually accepting just 2 of those as being of a suitable compliance to specification, performance and quality for the application. One was Japanese and the other Taiwanese. I have used this invaluable experience to source and put together the full electrolytic / tantalum capacitor upgrade kits. Likewise for the lubricating oil for the robust Revox and Nagra capstan motors. Don’t be fooled by some of the Ebay and internet hype. For Revox there are specific oils you use depending on how old the motor is and you do not mix them nor convert from one to the other.  For example, the PDP65 oil made by Kluber in Germany for both Nagra and later Revox / Studer capstan motors is very expensive but is the ONLY oil you should ever use on particular  motors. And, yes, you DO definitely need to lubricate despite Revox manuals being somewhat vague about it (later bulletins and in particular Studer did update and document this need for service lubrication). OK, before I digress further …. 

 

All the best with your restoration and hobby. I hope our kits and parts can help you achieve your goal of a perfectly operating Studer or Revox machine ... running like the proverbial Swiss watch! May the analogue force be with you.    

Kind Regards,

Upbeat Pete at Nagravox Australia.