Peter,
The 8640B is the one I more of less am going to get and the reason being the
frequency is on a spinner knob, no dial switches or keypads. Keypads are
notorious to wear out and so are the dial switches if flipped through enough.
Finding replacements is a nightmare. I think the equipment of today which most
all use keypad input because of cost is their downfall. Plus as you mention,
there's a good bit of junkers around for parts. The use of modules is another
plus for me. When the manufacturers in the TV industry quit modular sets, it
made serviving an expensive thing to do unless you just replaced the entire
chassis. In this case it is now so costly that nobody will repair a set and buy
new. In fact, it put many repair shops out of business, I was one of them. Then
too, the Wal-Marts and the Lowes sprang up all over and could sell new sets for
what they cost a small shop. At the time, I sold for N.A.P. as a authorized
Philco and Quasar shop. The Philco was the same set as the Sylvania and
Magnavox (and still is), but Lowes and Wal-Mart had the Sylvania and Magnacox
lines tied up and sold them for my cost. When that happened, and the modular
sets stopped, I shut the doors on the shop like all the others. Back during the
module days, you could repair a set generally within 15-30 minutes. You turned
the old module in at a supply house to get a "dud" fee and got a new module
back to put in your caddy. Back then, Quasar had the "works in the drawer", I
never will forget, all the modules were on each side of the drawer. The N.A.P.
sets had an upright chassis with all the modules in full view. Two others had
similar which was RCA and Zenith. I will have to say though that the old Zenith
sets were the toughest and the easiest fix. GE sets, every repairman ran from
because they used cheap PC boards that warped. Bad solder joints plauged them.
Fix one and in 30 days it was back for the same thing, just in a different
spot. The best money came from rejuvenating picture tubes. I still have my B&K
467, and can still get new sockets for it. Anyhow, I've rambled on enough about
my old TV service days. It just seems a lot of the time, the older equipment
and electronic products was just built tougher and easier to service than
todays stuff coming out. Now they have surface mount which I highly despise and
is another story.
Best,
Will
----- Original Message -----
From: Peter <peter@wires.ndo.co.uk>
To: "Karl-Arne Markström" <sm0aom@telia.com>
Subject: Re: [Amps] Signal Generators
Date: Tue, 05 Jul 2005 03:06:13 +0100
>
> I would agree the 8640B is much the superior generator of the pair.
> The close in phase noise and ultimate noise floor performance make
> it suitable for demanding adjacent channel (interferer), out of
> band blocking tests and LO substitution. The 3001 is still
> perfectly satisfactory for in channel (wanted signal) testing. The
> suggestion that the 8640 is low noise by current standards is, I
> feel, an accolade too far, but that is not the input Will requested.
>
> For me the continuously variable carrier tuning of the 8640B has to
> be the clincher on an HF amateur bench when compared with the dial
> up selection of the 3001. (The 3001 1kHz step resolution is also
> something of a limitation.) To be fair the primary application of
> the 3001, along with similar synths of that era, was testing
> channelised receivers and transmitters. Frequency dial up is an
> operating advantage in that application.
>
> Whilst it is correct that the 8640 series are loaded with long
> obsolete HP special devices I would offer a different view on
> maintenance. The 8640B probably holds the record for the longest
> ever sig gen production run and there are many thousands of these
> generators in the world. (The US military probably purchased as
> many as the rest of the world combined and they are still flooding
> out of DMRO) The second user market has also passed the point at
> which most were bought for commercial use. They are now common
> place at hamfests and bootsales. Junkers, depending on your
> location, are plentiful and relatively cheap. Repair by module
> substitution from a junker is now a perfectly feasible approach.
> (The simple 8640 rf oscillator/divider chain is also easier to
> trouble shoot than the multi loop 3001.)
>
> What to look for?
> Choose a plain 8640B. By far the most common build configuration,
> also has the frequency counter and freq lock capability which the
> earlier "A" variant lacks.
> Avoid opt 02 internal doubler 512-1024MHz. ( Spares availability;
> much rarer option. The output and driver hybrids are different to
> those fitted to a plain 512MHz model.) Opt 02 also degrades the o/p
> level accuracy and VSWR (= attendant mismatch uncertainty) below
> 512MHz. If you must have coverage to 1024MHz use an external Mini
> circuits doubler and high pass filter when you need it. A simple
> cludged diode doubler is OK. That's all HP did!
> Also avoid Opt 003 RPP (Reverse Power Protection) for the same
> reasons on level spec and donor spares from a junker. An external
> 20-30db pwr attenuator is a better bet if you are forgetful near
> transceivers.
> Opt 001 (internal variable audio osc) Nice in place of the 400/1000
> standard fixed tones but not essential; also a little fiddly to
> operate. Metered external mod inputs will take virtually any bench
> audio source. Only takes 10 mins and screwdriver to retrofit if one
> is available.
> Opt 004 Avionics. Really a different variant. "Option" is
> something of a misnomer. Steer clear... Similarly with the 8640M
> mil version.
>
> What to watch for?
> Two pattern faults on 8640 series. HP used a "degradable" nylon on
> the toothed wheels of the Vt pot driven from the main tuning and
> also the bandswitch assy. These frequently suffer fatigue splits.
> Not an easy repair but possible with shop facilities and patience.
> Easy to spot by removing top & bottom covers; two screws. Second
> fault is the mechanical limit device on the main tuning. Over
> enthusiastic pressure by tech gorillas attempting to tune beyond
> the cavity band limits deforms the plastic tabs. Tuning then feels
> lumpy in mid range when the tabs jump out of sync in severe
> cases.(Risk of cavity osc damage) Can usually be "reformed".
> Finally if you have the opportunity to lift the covers check the
> condition of the semi rigid cable SMC connectors and the presence,
> or otherwise, of the connector service spanner clipped to the side
> of the o/p attenuator. Lack of spanner and messed up connectors
> might indicate less than careful service.........!
>
> 73/
>
> Peter
> G3YYN
> Remove the obvious to reply
>
>
> Karl-Arne Markström wrote:
> > In my opinion the HP8640 is a superior signal generator.
> > Its phase noise performance is hard to match even by today's
> > signal generators, and it is still in the same class as the best
> > HF receivers around.
> >
> > On the down side, some of the components used in the HP8640 are
> > very exotic today,
> > so i.a. a burned-out output amplifier can be difficult and
> > expensive to replace.
> >
> snip
--
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