Topics

HP Meter refurbishment


Michael O'Beirne
 

Gents
 
After a long delay I am restarting on the repair of an old HP 411A RF millivoltmeter.  Sadly / stupidly it spent far too long in my basement storage, which is a little damp at times.  Thankfully there is no rust anywhere.
 
It has the same knobs and case style of the old 606B signal generator – late 1960s build??
 
The circuit is causing me grief – it seems to be some form of optical chopper, but I will deal with that later.
 
I want to start with the big meter.  It is 5.5 inches wide with a 1mA movement and a mirror scale.  The white scale face is discoloured, like an old newspaper.  Is there any smart of way of removing the discolouration without damaging the lettering? 
 
As a matter of interest, who made these series of meters for HP?  They are so easy to read.
 
73s
Michael
G8MOB
 
 


Hawkeye
 

Hello Michael,

 

Do you have an original copy of the HP manual?

 

If not, you can find one at www.hparchive.com 

Under quick links, select “equipment manuals” and  HP411A.

 

Normally, lettering is applied by screen printing, so any mechanical (abrasive) or dipping (bleach)

action will likely destroy the lettering.

The only way I know is bleaching with ozon, but that requires a spark gap and a more or less gastight enclosure;

This method is only based on my chemical knowledge; I have never tried it myself, but if all else fails, this may be worth

a trial on a non-visible spot of the scale.

 

I have a couple of old HP VTVM’s ; I will check if I can find any info on the manufacturer.

 

Good luck with your refurbishment.

 

73,

 

Cees Bekkers

 

 

Van: wireless-set-no19@groups.io <wireless-set-no19@groups.io> Namens Michael O'Beirne via groups.io
Verzonden: vrijdag 11 september 2020 14:32
Aan: wireless-set-no19@groups.io
Onderwerp: [wireless-set-no19] HP Meter refurbishment

 

Gents

<snipped a bit by moderator>

I want to start with the big meter.  It is 5.5 inches wide with a 1mA movement and a mirror scale.  The white scale face is discoloured, like an old newspaper.  Is there any smart of way of removing the discolouration without damaging the lettering? 

 

As a matter of interest, who made these series of meters for HP?  They are so easy to read.

 

73s

Michael

G8MOB

 


Michael O'Beirne
 

Cees
 
Thanks for your email.  I am pretty sure I have the manual otherwise I’d not know about the optical chopper.
 
TBH I am not entirely sure why I am spending time on this mV meter as I already have a decent newer Racal-Dana one but it is beautifully constructed and I’m loathe to bin it.
 
73s
Michael
G8MOB
 
 
 

From: Hawkeye via groups.io
Sent: Friday, September 11, 2020 3:32 PM
To: wireless-set-no19@groups.io
Subject: Re: [wireless-set-no19] HP Meter refurbishment
 

Hello Michael,

 

Do you have an original copy of the HP manual?

 

If not, you can find one at www.hparchive.com 

Under quick links, select “equipment manuals” and  HP411A.

 

Normally, lettering is applied by screen printing, so any mechanical (abrasive) or dipping (bleach)

action will likely destroy the lettering.

The only way I know is bleaching with ozon, but that requires a spark gap and a more or less gastight enclosure;

This method is only based on my chemical knowledge; I have never tried it myself, but if all else fails, this may be worth

a trial on a non-visible spot of the scale.

 

I have a couple of old HP VTVM’s ; I will check if I can find any info on the manufacturer.

 

Good luck with your refurbishment.

 

73,

 

Cees Bekkers

 

 

 


AllanIsaacs
 

I looked at a similar meter Michael, the HP431C.

http://www.radiomuseum.co.uk/hp431c.html

The scale paint was incredibly fragile and peeling off. I had to use a scalpel to remove the worst so the needle would move freely.

I recall after another couple of years I again had to dismantle it to remove yet more peeling paint as the needle had stuck once again.

I think I used a moistened cotton bud to remove discolouration, either spit or very dilute Fairy Liquid as anything stronger may ruin the paint. Spit has enzymes that with silver paper is great for removing rust.

Note my pet hate… the use of “M” instead of “m”. The HP guys couldn’t even decide which to use on the 431C so they used both!

73 Allan G3PIY

 

 

re

Gents

 

After a long delay I am restarting on the repair of an old HP 411A RF millivoltmeter.  Sadly / stupidly it spent far too long in my basement storage, which is a little damp at times.  Thankfully there is no rust anywhere.

 

It has the same knobs and case style of the old 606B signal generator – late 1960s build??

 

The circuit is causing me grief – it seems to be some form of optical chopper, but I will deal with that later.

 

I want to start with the big meter.  It is 5.5 inches wide with a 1mA movement and a mirror scale.  The white scale face is discoloured, like an old newspaper.  Is there any smart of way of removing the discolouration without damaging the lettering? 

 

As a matter of interest, who made these series of meters for HP?  They are so easy to read.

 

73s

Michael

G8MOB

 


Hawkeye
 

Michael,

 

I quickly checked  my HP400D and HP410B, but both have an 4,5 inch wide meter without mirror scale.

and looking inside gave no info on the meter manufacturer, but my meters look a lot like Simpson and in

a Simpson stack panel meters catalogue (bulletin no. 2065) there is a 6 ’’ (type 1150-1) meter with mirror scale.

 

Good luck.

 

73s,

 

Cees

 

Van: wireless-set-no19@groups.io <wireless-set-no19@groups.io> Namens Michael O'Beirne via groups.io
Verzonden: vrijdag 11 september 2020 17:35
Aan: wireless-set-no19@groups.io
Onderwerp: Re: [wireless-set-no19] HP Meter refurbishment

 

Cees

 

Thanks for your email.  I am pretty sure I have the manual otherwise I’d not know about the optical chopper.

 

TBH I am not entirely sure why I am spending time on this mV meter as I already have a decent newer Racal-Dana one but it is beautifully constructed and I’m loathe to bin it.

 

73s

Michael

G8MOB

 

 

 


Michael O'Beirne
 

Allan
 
Your lengthy screed on the HP431C was very interesting and instructive.  I know the later 435B power meter and both have very delicate sensors which are a lot more expensive than the meter box and a lot easier to destroy.
 
The scale discolouration on mine is not too bad and nothing is peeling away, so perhaps better to leave it than attempt heroic surgery.
 
I am sure you are familiar with the German black-cased meters used on old R&S gear.  They were made by Gossen (who also made professional photographic light-meters) and I have heard from several sources that with the large precision ones the scales were hand calibrated.  I have never experienced any scale peeling with them.
 
As for MW and mW – there is a difference!!!  You would think that someone would have mentioned this to the meter people at HP!!  Perhaps they did because in the HP catalogue for 1986 the pic for the 435B shows mW and dBm.
 
Do you know who made the meters for HP, or were they built in-house.  They are so easy to read.
 
73s
Michael
G8MOB
 

From: AllanIsaacs
Sent: Friday, September 11, 2020 4:37 PM
To: wireless-set-no19@groups.io
Subject: Re: [wireless-set-no19] HP Meter refurbishment
 

I looked at a similar meter Michael, the HP431C.

http://www.radiomuseum.co.uk/hp431c.html

The scale paint was incredibly fragile and peeling off. I had to use a scalpel to remove the worst so the needle would move freely.

I recall after another couple of years I again had to dismantle it to remove yet more peeling paint as the needle had stuck once again.

I think I used a moistened cotton bud to remove discolouration, either spit or very dilute Fairy Liquid as anything stronger may ruin the paint. Spit has enzymes that with silver paper is great for removing rust.

Note my pet hate… the use of “M” instead of “m”. The HP guys couldn’t even decide which to use on the 431C so they used both!

73 Allan G3PIY

 

 


Paul_ZS2PG
 

I have had quite good success with the following procedure.
1. Remove the scale plate from the meter.
2. Scan it into your computer as an image using a high dpi value.
3. Using your favourite image processor, rebuild the scale to as much perfection as you wish.
4. Print it out again on to whatever paper suits you. Do this again and again until the size is right, and the look of it is what you want. 
5. If your scale plate is symmetrical then stick the new scale on the back side, then you still have the original in case you want it. Otherwise, you will have to lose the original.
This has worked well for me, in renewing and replacing meter scales.

Paul Galpin
ZS2PG




Sent from my Samsung Galaxy smartphone.


Michael O'Beirne
 

Cees
 
Thanks for the swift email. 
 
Had it been a Simpson meter (or by any other manufacturer) I would have thought their logo would be on the face.  They supplied meters to Heathkit and I can see their logo clearly.  Hence the thought that it was made in-house.
 
73s
Michael
G8MOB
 
 
 

From: Hawkeye via groups.io
Sent: Friday, September 11, 2020 5:07 PM
To: wireless-set-no19@groups.io
Subject: Re: [wireless-set-no19] HP Meter refurbishment
 

Michael,

 

I quickly checked  my HP400D and HP410B, but both have an 4,5 inch wide meter without mirror scale.

and looking inside gave no info on the meter manufacturer, but my meters look a lot like Simpson and in

a Simpson stack panel meters catalogue (bulletin no. 2065) there is a 6 ’’ (type 1150-1) meter with mirror scale.

 

Good luck.

 

73s,

 

Cees

 

 


vk2no
 

Hi All,

Some of the HP cataloges
had the meter scales in them.
I just photocopied them,
and glued them to the old meter face.

Regards
Ray

Allan

Your lengthy screed on the HP431C was very interesting and instructive. I
know the later 435B power meter and both have very delicate sensors which
are a lot more expensive than the meter box and a lot easier to destroy.

The scale discolouration on mine is not too bad and nothing is peeling
away, so perhaps better to leave it than attempt heroic surgery.

I am sure you are familiar with the German black-cased meters used on old
R&S gear. They were made by Gossen (who also made professional
photographic light-meters) and I have heard from several sources that with
the large precision ones the scales were hand calibrated. I have never
experienced any scale peeling with them.

As for MW and mW – there is a difference!!! You would think that
someone would have mentioned this to the meter people at HP!! Perhaps
they did because in the HP catalogue for 1986 the pic for the 435B shows
mW and dBm.

Do you know who made the meters for HP, or were they built in-house. They
are so easy to read.

73s
Michael
G8MOB

From: AllanIsaacs
Sent: Friday, September 11, 2020 4:37 PM
To: wireless-set-no19@groups.io
Subject: Re: [wireless-set-no19] HP Meter refurbishment

I looked at a similar meter Michael, the HP431C.

http://www.radiomuseum.co.uk/hp431c.html

The scale paint was incredibly fragile and peeling off. I had to use a
scalpel to remove the worst so the needle would move freely.

I recall after another couple of years I again had to dismantle it to
remove yet more peeling paint as the needle had stuck once again.

I think I used a moistened cotton bud to remove discolouration, either
spit or very dilute Fairy Liquid as anything stronger may ruin the paint.
Spit has enzymes that with silver paper is great for removing rust.

Note my pet hate… the use of “Mâ€&#65533; instead of “mâ€&#65533;. The HP guys
couldn’t even decide which to use on the 431C so they used both!

73 Allan G3PIY