¿ªÔÆÌåÓý

  1. HP-Agilent-Keysight-Equipment
  2. Topics

HP 651B Oscillator restoration and an OOPS!!

[email protected]
 

651B 1975 edition.

Replaced all of the electrolytics and tantalums, quite a chore to get the exactly correct values
Several caps were replaced with two or three in parallel. Same or better tolerance and voltage.

BEWARE. I bought what were advertised as Spragues from Mouser, they came with 30-50 YEARS of oxidation on the leads. Severe oxidation which indicates either very old stock or storage in an aggressive atmosphere. The caps in the unit had much less oxidation.

Anyway, went most of the way through alignment, the unit is close enough in 2020 with easy availability of an external freq counter, that adjusting resistor values wasnt necessary. Didnt want to risk damaging the switch wafers. Back in the day, counters etc werent as cheaply available. Now they are and its not necessary to tweak this unit right on frequency, especially that its a mechanical VFO.

Points:

* replace ALL electrolytics. No old stock, get new fresh stock from Digi Key only. They religiously track stock and age. This is (or was) high end test equipment, not an old stereo.
* Ranges dead- cleaned switch segments with Q Tip and isopropyl alcohol. DELICATE WORK.
This fixed the 'dead range' problem. There was a LOT of black oxide residue. Spraying cleaner is NOT enough, because that doesnt clean the inside surfaces of the switch fingers that ride on the wafer segments.
* Used a Beckman DMM to monitor TP2, no 1K resistor needed. 10 Mohm input.
* used an AWG and good analog scope in place of distortion meter (its just a sine wave...)
Fed reference signal at 1Kc into one scope channel and the HP gen output into the other, then synchronized the frequencies and matched amplitude, then did an ADD and SUBTRACT on the scope channels. The trace was dead flat- no distortion
* when checking levels and tracking, FIRST check for spurious oscillation. If there is any, REDUCE the value of A2C21, 12 pF. Its very touchy, I used 10 pF leaving a very small amount of oscillation. Avoid changing the resistor value, it reduces output voltage.

Even after 30 years experience on the bench, I did something very bad..,.

Id shorted A1C11 with a pencil lead attempting to mark the stator plate with power on and destroyed A1Q9 and A1CR9 in the Monitor circuit. Yes, its a very sensitive circuit. Well, it **was** a very sensitive circuit...

Anyone have parts? (yes I just put an ad up...)

Am considering replacing the Monitor circuit and meter with a voltmeter unit. Thoughts?

73 Dave

 

David Campbell wrote on 3/6/2020 10:14 AM:

651B 1975 edition.

Replaced all of the electrolytics and tantalums, quite a chore to get the exactly correct values
Several caps were replaced with two or three in parallel. Same or better tolerance and voltage.

BEWARE. I bought what were advertised as Spragues from Mouser, they came with 30-50 YEARS of oxidation on the leads. Severe oxidation which indicates either very old stock or storage in an aggressive atmosphere. The caps in the unit had much less oxidation.
<snip>

Hello, Dave--

Were there any date codes on the Sprague caps? Thirty years ago might
register as, for example, 2690 (i.e., the 26th week of 1990).? Codes vary
among manufacturers, but IIRC Sprague used <two-digit week> <two-digit year>
format.

If there are no date codes present, the caps could be counterfeit.

I'm very surprised to learn that Mouser could be selling such old
stock-- you might consider writing them a letter of complaint.

73--

Brad? AA1IP

73--

Brad? AA1IP
Dale H. Cook
 

On 3/6/2020 10:14 AM, David Campbell wrote:

Replaced all of the electrolytics and tantalums, quite a chore to get the exactly correct values
Why? How did you determine that the electrolytics needed to be replaced? I have many HP instruments of that vintage that still meet spec and have never needed to have any of their caps replaced, including my 651B which was last used yesterday.

You cannot buy new caps that are anywhere near as good as the originals used by HP.

* used an AWG and good analog scope in place of distortion meter (its just a sine wave...)
That's fine if you just need test equipment, but your 651B is no longer an instrument if you don't know its specifications.
--
Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA
David Campbell
 

Being an EE with manufacturing, parts buying and engineering experience, these caps didn't even make it past check-in against the invoice on Receiving
they were that badly oxidised- so badly I could see it thru the packaging. Hand soldering, an inconvenience perhaps. Manufacturing? Possibly a real problem
if there are solderability issues. the oxidation was so bad I had to scrape it off with a hardened steel ruler to photograph it. Drawing the leads thru a cloth had no effect.

I contacted Vishay who said they bought and re-opened the old Sprague plant and were producing (something-whatever) and thats why they were advertised "Vishay-Sprague"
by Mouser, ALTHOUGH... no info on "Sprague" parts appeared on the Vishay site. Vishay said the date codes were 2018.

The Rep also said that this level of oxidation is not consistent with the date codes, which admits fraud. I dont know for a fact that fraud is ocurring, BUT
counterfeit goods from China is a plague these days. Its an absolute plague in the nuclear industry, so bad that DoE issued a inch-plus thick advisory
text for the Hanford site warning Engineers and Purchasing to carefully inspect goods.

I suppose its possible that old stock 'cans' (drawn cups/leads) were used in modern production- i have no way of knowing.
The date code is not necessarily reliable. Its printed on a heat shrink tubular sleeve. It can be forged easily. Maybe they
had old-stock caps and printed a? new label?

A 3 cent label, or throwing away a 50 cent old cap? Again, not saying Vishay did so, but it would be easy to do and to hide.

I do know from a LONG time riding a test and high volume repair bench to never trust an old electrolytic. Ive seen too many short, leak and explode and do circuit damage
especially in older gear with pass-transistor regulated supplies. One cap exploded and ended up buried in the false ceiling 10 foot up.
Used to see 'lytics that shorted destroy power transformers to fill the shop with smoke.

Power transformer / pass transistors, 200$ plus or not available. New caps? 50-ish?.

Mouser denied it six ways from Sunday but refunded my money. Vishay admitted the leads werent right. Both denied counterfeiting.
Vishay said Mouser didnt have counterfeit parts. How would they know?

I bought all new caps from DK for half the cost. Just more hand-tuning by testing and assembling combinations of the correct values/tolerance.
Trading time for $.

interesting trivia point- the 1100 uF NP cap in the '651 was an 'aerospace grade' part, rated at 200,000 feet operation by an old Sprague document.
It was odd that the end-plug was very thick with a hard plastic cover, and the 'anode-end crimp' was extra deep and wide... and only a 10V unit.
David Campbell
 

A. My comment is not about your claimed experience.
B. It might not work if you do it, but when I, with 30 plus years of experience and NIST traceable gear do it, its dead accurate

Its an instrument when I do it.


Your comments are not constructive. They are flaming. Not accepted.
Dale H. Cook
 

On 3/6/2020 12:46 PM, David Campbell wrote:

... they were that badly oxidised
That sounds like the parts were long stored in a very poor environment. I have never seen that in the original caps in any of my 16 HP instruments of that vintage (13 working and 3 parts junkers). Mine, however, were almost all purchased from individuals whom I know, or at meets, and in all of those cases I was able to have a look inside to evaluate condition. It is common for the HP caps of that vintage to look somewhat poor due to deterioration of the plastic sleeves but to measure fine at rated voltage for both C and D on a GR bridge.
--
Dale H. Cook, Member, NEHGS, AGS, MA Soc. of Mayflower Descendants;
Plymouth Co. MA Coordinator for the USGenWeb Project
Administrator of

Dale H. Cook
 

On 3/6/2020 12:47 PM, David Campbell wrote:

Your comments are not constructive. They are flaming. Not accepted.
You have not tried to ascertain my professional experience, which exceeds yours by more than a decade, so I consider that reply flaming and shall block your posts.
--
Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA
 

Aren't these children a bit excessive - maybe we should block both of them.

Cummon guys - GROW UP


Quoting "Dale H. Cook" <bridgewaterma@...>:

On 3/6/2020 12:46 PM, David Campbell wrote:

... they were that badly oxidised
That sounds like the parts were long stored in a very poor environment. I have never seen that in the original caps in any of my 16 HP instruments of that vintage (13 working and 3 parts junkers). Mine, however, were almost all purchased from individuals whom I know, or at meets, and in all of those cases I was able to have a look inside to evaluate condition. It is common for the HP caps of that vintage to look somewhat poor due to deterioration of the plastic sleeves but to measure fine at rated voltage for both C and D on a GR bridge.
--
Dale H. Cook, Member, NEHGS, AGS, MA Soc. of Mayflower Descendants;
Plymouth Co. MA Coordinator for the USGenWeb Project
Administrator of

 

It is possible that someone ordered from them, ther returned existing stock that wasn't properly inspected. I was involved in Sprague shutting down their plant near Oralando, 30 years ago. That one wasn't reopened, because the machines and tools were ether shipped to other plants, or in some cases, sold as scrap metal.. Ithink that I still have a damaged spool of 'comonent lead', and a roll of metalized film that I kept from being sent out as scrap. Neither were full reels or rolls.

On Fri, Mar 6, 2020 at 12:46 PM David Campbell <k_8_b_y_p@...> wrote:
Being an EE with manufacturing, parts buying and engineering experience, these caps didn't even make it past check-in against the invoice on Receiving
they were that badly oxidised- so badly I could see it thru the packaging. Hand soldering, an inconvenience perhaps. Manufacturing? Possibly a real problem
if there are solderability issues. the oxidation was so bad I had to scrape it off with a hardened steel ruler to photograph it. Drawing the leads thru a cloth had no effect.

I contacted Vishay who said they bought and re-opened the old Sprague plant and were producing (something-whatever) and thats why they were advertised "Vishay-Sprague"
by Mouser, ALTHOUGH... no info on "Sprague" parts appeared on the Vishay site. Vishay said the date codes were 2018.

The Rep also said that this level of oxidation is not consistent with the date codes, which admits fraud. I dont know for a fact that fraud is ocurring, BUT
counterfeit goods from China is a plague these days. Its an absolute plague in the nuclear industry, so bad that DoE issued a inch-plus thick advisory
text for the Hanford site warning Engineers and Purchasing to carefully inspect goods.

I suppose its possible that old stock 'cans' (drawn cups/leads) were used in modern production- i have no way of knowing.
The date code is not necessarily reliable. Its printed on a heat shrink tubular sleeve. It can be forged easily. Maybe they
had old-stock caps and printed a? new label?

A 3 cent label, or throwing away a 50 cent old cap? Again, not saying Vishay did so, but it would be easy to do and to hide.

I do know from a LONG time riding a test and high volume repair bench to never trust an old electrolytic. Ive seen too many short, leak and explode and do circuit damage
especially in older gear with pass-transistor regulated supplies. One cap exploded and ended up buried in the false ceiling 10 foot up.
Used to see 'lytics that shorted destroy power transformers to fill the shop with smoke.

Power transformer / pass transistors, 200$ plus or not available. New caps? 50-ish?.

Mouser denied it six ways from Sunday but refunded my money. Vishay admitted the leads werent right. Both denied counterfeiting.
Vishay said Mouser didnt have counterfeit parts. How would they know?

I bought all new caps from DK for half the cost. Just more hand-tuning by testing and assembling combinations of the correct values/tolerance.
Trading time for $.

interesting trivia point- the 1100 uF NP cap in the '651 was an 'aerospace grade' part, rated at 200,000 feet operation by an old Sprague document.
It was odd that the end-plug was very thick with a hard plastic cover, and the 'anode-end crimp' was extra deep and wide... and only a 10V unit.

 

If it's just normal oxidation rather than poor storage I wouldn't worry about it. I'd far rather have 'new old stock' from decent manufacturers that's 40 years old than something brand new from some unknown manufacturer in China. But it's hard to say without a photograph. Can you not post one?

1 - 10 of 10