Will,
I have often replaced such a fuse in my meters, when I did not have one
close, with a fine single strand of wire from a stranded wire. Just
place it in the fuse clip with the bad fuse to hold it in. Usually a
piece of wire of approximately the right size is somewhere in the junk heap.
73
Gary K4FMX
Will Matney wrote:
> Joe,
>
> I wonder why the 260 showed that or was it just set on the wrong ohms scale?
> I have about 3 of those 260's here and absolutely swear by them. They have to
> be the toughest analog VOM and most accurate I've ever used. Matter of fact,
> it was the only meter I ever bought new. The one I did buy new I've had since
> 1987. Heh, I did burn it out once, really frying it. I had my radio-TV shop
> then and had a Maco 750 11 meter amp there converting it over to 6 meters for
> a friend. It was bad when he got it. Well, before I started work, I had been
> servicing a TV set and had blew the fuse in the 260. So, I couldn't find a
> fuse and really couldn't leave the shop to get one. Stupid me went and took
> some aluminum foil out of a Marlboro pack and wrapped the old fuse as a
> temporary fix. Sure enough, I set down and started to work on the amp.
> Needless to say, I forgot to switch the 260 from ohms to volts and stuck the
> hot lead into +900 Vdc. I took it to my local electronics supply and it was
st
> ill under warranty. Believe it or not, Simpson put in a new main pc board at
> no cost, just the shipping. Plus, did a new calibration on it. I've stuck
> with that company ever since.
>
> If you want a good little small bench meter, Simpson made a model 467 and a
> lot was sold to the US government. They come in a small attache case
> including a lead kit, a 5 kV high voltage probe, and an ammeter shunt. I use
> it to check plate voltages all the time with a very good accuracy. You can
> pick these up surplus off eBay for about $25-$45 at any time. If anyone would
> want a good small digital meter, I'd sure suggest this one.
>
> Just the other day, Simpson sent me a complete manual on a model 713
> frequency counter, schematic and parts list included. This cost me $0.00, and
> is why I think Simpson is at the top of the heap on product and service.
>
> On the amp, you should get a normal reading for a NPN transistor when you
> lift the base and collector up off the pads. There's too much circuitry to
> read them attached to any benefit unless it's a voltage reading.
>
>
> Best,
>
> Will
>
> ----- Original Message -----
> From: "Joe Isabella" <n3ji@yahoo.com>
> To: "Will Matney" <craxd@engineer.com>
> Subject: Re: ALS-500 Problem (was Mobile amps)
> Date: Sun, 24 Jul 2005 07:26:46 -0700 (PDT)
>
>
>>Hi Will,
>>I just found out that the VOM (a Simson 260!!) was lying to me
>>about resistance. I lifted the base of the 2879 and it showed
>>open, but I was still measuring a direct short on its pad. I
>>lifted the 6.8 ohm resistor and it was measuring a dead short, so I
>>checked a ~1k I had in the junk box and it also showed short!!
>>Anyway, the base is now showing ~19 ohms to ground, and is not
>>shorted to the emitter (whew!!). So, now I'm back to square one.
>>I'll put the amp back in and see what's REALLY going on...
>>
>>Joe
>>
>>
>>Will Matney <craxd@engineer.com> wrote:
>>Joe,
>>
>>I'd have to look over the schematic on it to see what they've done.
>>I have seen relays cause this by restricting the RF into the amp
>>but you'd have a high SWR between the amp and transceiver. Without
>>knowing what their bias circuit is, I couldn't say on the base to
>>ground short. You have to remember that usually there are 10 ohm
>>resistors to ground anyhow. They should be soldered right on the
>>base lead to the foil ground. You figure one off each transistor,
>>that's 5 ohms to ground. Also, if it's a double sided pc board,
>>suspect a solder joint where it goes through the board to the other
>>sides circuit. Really the proper way to check those transistors is
>>to lift the base and collector legs from the board and test them.
>>If I can find the schematic, I'll look it over to see how it ticks.
>>
>>Best,
>>
>>Will
>>
>>
>>
>>
>>----- Original Message -----
>>From: "Joe Isabella"
>>To: "Will Matney"
>>Subject: Re: [Amps] Mobile amps
>>Date: Fri, 22 Jul 2005 08:45:24 -0700 (PDT)
>>
>>
>>>Will,
>>>eMailing you off-list... Do you know anything about the ALS-500
>>>by Ameritron? I just started having a strange problem and I
>>>thought I'd ask around for some advice. Since you brought up this
>>>subject, I hope you don't mind me bothering you.
>>>
>>>The amp was working one day until I stopped using it, then I
>>>attempted to run it later and could get no replies. When I looked
>>>at the current meter on the front of it, it was no longer drawing
>>>much current. It is showing a little current draw, though (less
>>>than 5A or so, which only shows up with RF drive). It has the
>>>2879s, and there is no collector short to ground, but I'm seeing
>>>what appears to be a direct short on the base. I haven't had a
>>>lot of time to troubleshoot it, but does that mean there's a
>>>base-emitter short?? Is that a common failure mode? I had planned
>>>to isolate the transistors and re-check them, but I just haven't
>>>gotten to it yet.
>>>
>>>Any thoughts?
>>>
>>>Joe, N3JI
>>>
>>>Will Matney wrote:
>>>Dan,
>>>
>>>Yes, they are really the same wide-banded amps that have been
>>>around for years and the same as in the Motorola app notes. Most
>>>use the 2SC2879 transistors. The only thing is for them to be
>>>linear, and clean, they have to be converted to class AB1 or AB,
>>>an output filter should be used, and a bandswitching network
>>>added to the input to level the SWR across the bandspread.
>>>Generally these are made by the one doing the conversion as
>>>there's too many differences in amps to make a one-size-fits-all
>>>type of circuit. They generally make them using switchable pi net
>>>circuts switched in with relays from a rotary switch on the front
>>>of the amp. Henry did this on their mobile amps and is the upper
>>>board over the main one. These 11 meter amps dont have this. What
>>>I'm making is a good RF keyer, and the bias circuit to set the
>>>transistors to class AB, or AB1. The keying circuit they've been
>>>using on a bunch of different models just tie the parts together
>>>in mid air, and look like a rats ne
>>>st. Terrible construction, but the rest of the amp is usable.
>>>Another thing that will have to be used is an attenuated input as
>>>5-20 watts will open up a set of 2SC2879's to their rated output.
>>>That is if the transceiver can't be cut back. However an
>>>attenuator is easy to build. You can buy these amps second hand
>>>off eBay for a good bit less than new. I may even build some new
>>>ones but that's a good bit in the future. For homebrewers, I can
>>>get the cabinets, and heatsink along with other parts they may
>>>need. There is also pre-punched PC boards but not etched. The
>>>punched holes are for the transistors. These holes can be made
>>>though by drilling the board first, and then cleaning up the rest
>>>using a spiral bit in a mini-router, or a Dremel tool with a
>>>router base added. The best drill to use is one of those cone
>>>bits. The way they've been building them is by dead bug
>>>construction. I prefer to use an etched board myself, but do use
>>>surface mount with through hole components by
>>>bending the leads. Those amps are too hard to repair without the
>>>parts mounted on the top, and unsoldered from the top. Those
>>>traces can be routed too if you have a steady enough hand. Hope
>>>this helps.
>>>
>>>Best,
>>>
>>>Will
>>>
>>>
>>>----- Original Message -----
>>>From: "Dan Sawyer"
>>>To: "Will Matney"
>>>Subject: Re: [Amps] Mobile amps
>>>Date: Fri, 22 Jul 2005 06:59:46 -0700
>>>
>>>
>>>>Will,
>>>>
>>>>Is it practical to adapt these to work on 80 through 10 meters?
>>>>
>>>>Thanks,
>>>>Dan
>>>>
>>>>Will Matney wrote:
>>>>
>>>>
>>>>>All,
>>>>>
>>>>>Some have been buying those 11 meter mobile amps and
>>>>
>>>converting > > them over for amateur use. The ones which use
>>>un-etched PC > > boards, etc. The RF keying in these are
>>>generally rats nests and > > pretty weak circuit wise. Most dont
>>>last very long and are for > > use only with about 5 watts max
>>>input and have no SSB > > capabilities. I am now offering
>>>retrofit kits for RF keying, and > > bias control. Most are made
>>>class C only and the ones with any > > bias are not adjustable
>>>only using a diode clamp. I can do > these > on tie strips or on
>>>small PC boards made to mount upright > on > edge. The tie strips
>>>take up the less room. If any are > interested > in these, give
>>>me an e-mail. I'll be glad to help in > converting > these in any
>>>way possible.
>>>
>>>>>Best,
>>>>>
>>>>>Will
>>>>>
>>>>>Amateur Transformer & Supply
>>>>>
>>>>>
>>>>>
>>>>
>>>
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